JP6901995B2 - Film thickness measurement method, method for manufacturing nitride semiconductor laminates, and nitride semiconductor laminates - Google Patents

Description

The present invention relates to a film thickness measuring method, a method for producing a nitride semiconductor laminate, and a nitride semiconductor laminate.

Fourier transform infrared spectroscopy (FT-IR method) is known as a method for measuring the film thickness of a semiconductor crystal thin film homoepitaxially grown on a substrate in a non-contact and non-destructive manner (for example, Patent Documents). 1).

Japanese Unexamined Patent Publication No. 4-120404

However, crystals of group III nitride semiconductors represented by gallium nitride (GaN) have been largely affected by dislocation scattering, especially in the infrared region (IR) at low carrier concentrations of ^{1 × 10 17} cm ^{-3 or less.} Since there was no difference in absorption coefficient, it is difficult to measure the film thickness in principle in the case of a homoepitaxial film composed of crystals having the same composition as the substrate.

The present invention relates to a homoepitaxial film of a group III nitride semiconductor crystal, for example, 1 × 1.
A film thickness measurement method that enables film thickness measurement using the FT-IR method or the like, a method for producing a nitride semiconductor laminate, and nitridement even in the case of a low carrier concentration of 0 ¹⁷ cm- ^{3 or less.} It is an object of the present invention to provide a product semiconductor laminate.

According to one aspect of the invention
A film thickness measuring method for measuring the film thickness of a thin film in a nitride semiconductor laminate obtained by homoepitaxially growing a thin film on a substrate composed of crystals of a group III nitride semiconductor.
As the substrate, a substrate having a dependency between the carrier concentration in the substrate and the absorption coefficient in the infrared region is used.
A film thickness measuring method for measuring the thickness of the thin film by using Fourier transform infrared spectroscopy or infrared spectroscopic ellipsometry is provided.

According to the present invention, for a homoepitaxial film of a group III nitride semiconductor crystal, the IR absorption coefficient differs depending on the carrier concentration even in the case of a low carrier concentration of ^{, for example, 1 × 10 17} cm ^{-3 or less.} , And the film thickness can be measured by using the FT-IR method or the like.

It is sectional drawing which shows typically the schematic structure example of the nitride semiconductor laminate 1 which concerns on one Embodiment of this invention. It is a figure which shows the structural example of the substrate 10 in the nitride semiconductor laminate which concerns on one Embodiment of this invention, (a) is a schematic plan view, (b) is a schematic sectional view. It is a figure which shows the displacement law of Wien. It is a figure which shows the free electron concentration dependence of the absorption coefficient measured at room temperature (27 ° C.) in the GaN crystal produced by the production method which concerns on one Embodiment of this invention. It is a figure which shows the intrinsic carrier concentration with respect to the temperature of a GaN crystal. (A) is a diagram showing the relationship of the absorption coefficient at a wavelength of 2 μm with respect to the free electron concentration in the GaN crystal produced by the production method according to the embodiment of the present invention, and (b) is a diagram showing the relationship between the wavelength with respect to the free electron concentration. It is a figure which compares the relationship of the absorption coefficient at 2 μm. It is a flow chart which shows the schematic procedure of the manufacturing method of the nitride semiconductor laminate 1 which concerns on one Embodiment of this invention. It is a schematic block diagram of a vapor phase growth apparatus 200. (A) is a diagram showing a state in which the GaN crystal film 6 is thickly grown on the seed crystal substrate 5, and (b) is a plurality of nitride crystals by slicing the thickly grown GaN crystal film 6. It is a figure which shows the state which acquired the substrate 10. (A) is a schematic top view showing a holding member 300 on which the nitride crystal substrate 10 or the semiconductor laminate 1 is placed, and (b) is a schematic top view on which the nitride crystal substrate 10 or the semiconductor laminate 1 is placed. It is a schematic front view which shows the holding member 300. It is a flow chart which shows an example of the procedure of the film thickness measurement method which concerns on one Embodiment of this invention. (A) is a schematic diagram showing an example of an optical model of a multilayer film, and (b) is a schematic diagram showing an example of an optical model simplified from (a). It is explanatory drawing which shows a specific example of the calculation result about the refractive index n and the extinction coefficient k by the Drude model, (a) is the figure which shows the calculation result about an epi layer, (b) is the figure which shows the calculation result about a substrate. It is a figure which shows. It is explanatory drawing which shows a specific example of the calculation result about the refractive index n and the extinction coefficient k by the Lorenz-Drude model, (a) is the figure which shows the calculation result about an epi layer, and (b) is the calculation about a substrate. It is a figure which shows the result. It is explanatory drawing which shows a specific example of the calculation result about the reflection spectrum in the case of vertical incidence (θi = 0 °), (a) is a figure which shows the reflection spectrum about the Drude model, (b) is about the Lorenz-Drude model. It is a figure which shows the reflection spectrum. It is explanatory drawing which shows a specific example of the calculation result about the reflection spectrum in the case of non-vertical incident (θi = 30 °), (a) is the figure which shows the reflection spectrum about the Drude model, (b) is the Lorenz-Drude model. It is a figure which shows the reflection spectrum with respect to. It is a schematic block diagram of the FT-IR measuring apparatus 50.

<One Embodiment of the present invention>
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

(1) Configuration of Nitride Semiconductor Laminate 1 First, a configuration example of the nitride semiconductor laminate 1 according to the present embodiment will be described.

The nitride semiconductor laminate 1 described by way of example in the present embodiment is, for example, a substrate-like structure used as a substrate when manufacturing a semiconductor device as a Schottky barrier diode (SBD). Since it is used as a substrate for a semiconductor device, the nitride semiconductor laminate 1 may be referred to as an "intermediate" or an "intermediate precursor" below.

As shown in FIG. 1, the nitride semiconductor laminate (intermediate) 1 according to the present embodiment includes at least a substrate 10 and a semiconductor layer 20 which is a thin film formed on the substrate 10. Has been done.

(1-i) Detailed Configuration of Substrate 10 Next, the substrate 10 constituting the nitride semiconductor laminate (intermediate) 1 will be described in detail. In the following, the main surface of the substrate or the like mainly refers to the upper main surface of the substrate or the like, and may be the surface of the substrate or the like. The back surface of the substrate or the like refers to the lower main surface of the substrate or the like.

As shown in FIG. 2, the substrate 10 is formed in a disk shape, and is made of a single crystal of a group III nitride semiconductor, specifically, for example, a single crystal of gallium nitride (GaN).

The plane orientation of the main plane of the substrate 10 is, for example, the (0001) plane (+ c plane, Ga polar plane).
However, for example, it may be 000-1 plane (−c plane, N polar plane).
The GaN crystal constituting the substrate 10 may have a predetermined off-angle with respect to the main surface of the substrate 10. The off-angle refers to the angle formed by the normal direction of the main surface of the substrate 10 and the main axis (c-axis) of the GaN crystal constituting the substrate 10. Specifically, the off angle of the substrate 10 is, for example, 0 ° or more and 1.2 ° or less. It is also conceivable that it is larger than this and is 2 ° or more and 4 ° or less. Further, for example, it may be a so-called double off having an off angle in each of the a direction and the m direction.

The dislocation density on the main surface of the substrate 10 is, for example, 5 × 10 ⁶ pieces / cm ² or less. If the dislocation density on the main surface of the substrate 10 is more than 5 × 10 ⁶ pieces / cm ² , there is a possibility that the local withstand voltage of the semiconductor layer 20 to be described later formed on the substrate 10 will be lowered. On the other hand, as in the present embodiment, the dislocation density on the main surface of the substrate 10 is 5 × 10 ⁶ pieces / c.
By setting the value to m ² or less, it is possible to suppress a local decrease in withstand voltage in the semiconductor layer 20 formed on the substrate 10.

The main surface of the substrate 10 is an epiready surface, and the surface roughness (arithmetic mean roughness Ra) of the main surface of the substrate 10 is, for example, 10 nm or less, preferably 5 nm or less.

The diameter D of the substrate 10 is not particularly limited, but is, for example, 25 mm or more. If the diameter D of the substrate 10 is less than 25 mm, the productivity when manufacturing a semiconductor device using the substrate 10 tends to decrease. Therefore, the diameter D of the substrate 10 is preferably 25 mm or more. The thickness T of the substrate 10 is, for example, 150 μm or more and 2 mm or less. If the thickness T of the substrate 10 is less than 150 μm, the mechanical strength of the substrate 10 may decrease and it may be difficult to maintain the self-supporting state. Therefore, the thickness T of the substrate 10 is preferably 150 μm or more. Here, for example, the diameter D of the substrate 10 is 2 inches, and the substrate 10
The thickness T of the above is 400 μm.

Further, the substrate 10 contains, for example, an n-type impurity (donor). Examples of the n-type impurities contained in the substrate 10 include silicon (Si) and germanium (Ge). In addition to Si and Ge, examples of n-type impurities include oxygen (O), O and Si, O and Ge, O and Si and Ge. By doping the substrate 10 with n-type impurities, free electrons having a predetermined concentration are generated in the substrate 10.

(About absorption coefficient, etc.)
In the present embodiment, the substrate 10 satisfies a predetermined requirement for the absorption coefficient in the infrared region. As a result, the substrate 10 has a dependency between the carrier concentration in the substrate 10 and the absorption coefficient in the infrared region, as will be described in detail later.
The details will be described below.

When manufacturing the nitride semiconductor laminate 1 or when manufacturing a semiconductor device using the nitride semiconductor laminate 1, for example, as described later, a step of epitaxially growing the semiconductor layer 20 on the substrate 10 or the like. A step of heating the substrate 10 may be performed, such as a step of activating impurities in the semiconductor layer 20. For example, when the substrate 10 is irradiated with infrared rays to heat the substrate 10, it is important to set the heating conditions based on the absorption coefficient of the substrate 10.

Here, FIG. 3 is a diagram showing Wien's displacement law. In FIG. 3, the horizontal axis is the blackbody temperature (
° C.), and the vertical axis represents the peak wavelength (μm) of blackbody radiation. According to Wien's displacement law shown in FIG. 3, the peak wavelength of blackbody radiation is inversely proportional to the blackbody temperature. Peak wavelength λ
(Μm), when the temperature is T (° C.), it has a relationship with λ = 2896 / (T + 273). Assuming that the radiation from a predetermined heating source in the step of heating the substrate 10 is blackbody radiation, infrared rays having a peak wavelength corresponding to the heating temperature will be emitted from the heating source to the substrate 10. .. For example, when the temperature is about 1200 ° C, the infrared peak wavelength λ is 2μ.
When the temperature is about 600 ° C., the peak wavelength λ of infrared rays is 3.3 μm.

When the substrate 10 is irradiated with infrared rays having such a wavelength, absorption by free electrons (free carrier absorption) occurs in the substrate 10, which causes the substrate 10 to be heated.

Therefore, in the present embodiment, the absorption coefficient in the infrared region of the substrate 10 satisfies the following predetermined requirements based on the free carrier absorption of the substrate 10.

FIG. 4 shows room temperature (27) in the GaN crystal produced by the production method according to the present embodiment.
It is a figure which shows the free electron concentration dependence of the absorption coefficient measured at (° C.). Note that FIG. 4 shows the measurement results of a substrate made of GaN crystals produced by doping Si with a production method described later. In FIG. 4, the horizontal axis represents the wavelength (nm), and the vertical axis represents the absorption coefficient α (c) of the GaN crystal.
It ^{shows m -1} ). Further, the free electron concentration in the GaN crystal as N _e, plots the α absorption coefficient of GaN crystal for each predetermined free electron concentration N _e. As shown in FIG. 4, in the GaN crystal produced by the production method described later, the absorption coefficient of the GaN crystal increases toward a longer wavelength due to free carrier absorption in a wavelength range of at least 1 μm or more and 3.3 μm or less. It shows a tendency for α to increase (monotonically increase). Further, according to the free electron concentration N _e in the GaN crystal increases, a tendency to free carrier absorption in the GaN crystal increases.

Since the substrate 10 of the present embodiment is made of a GaN crystal produced by the production method described later, the crystal strain is small, and impurities other than oxygen (O) and n-type impurities (for example, n-type impurities are compensated for). It is in a state where it contains almost no impurities (such as impurities). As a result, the free electron concentration dependence of the absorption coefficient as shown in FIG. 4 is shown. As a result, the substrate 10 of the present embodiment
Then, the absorption coefficient in the infrared region can be approximated as a function of free carrier concentration and wavelength as follows.

Specifically, the wavelength is λ (μm), and the absorption coefficient of the substrate 10 at 27 ° C. is α (cm ^-1 ).
The free electron concentration in the substrate ^{_{10 N e (cm -3),}} K and a a when the respective constants, the substrate 10 of the present embodiment, at least 1μm or 3.3μm or less (preferably 1μ
The absorption coefficient α in the wavelength range (m or more and 2.5 μm or less) is approximated by the following equation (1).
^{_{α = N e Kλ a ··· (}} 1)
(However, 1.5 × 10 ^-19 ≦ K ≦ 6.0 × 10 ^-19 , a = 3)

The phrase "the absorption coefficient α is approximated by the equation (1)" means that the absorption coefficient α is approximated by the equation (1) by the method of least squares. That is, the above provision includes not only the case where the absorption coefficient completely matches the equation (1) (satisfies the equation (1)) but also the case where the equation (1) is satisfied within a predetermined error range. The predetermined error is, for example, within ± 0.1α, preferably within ± 0.01α at a wavelength of 2 μm.

The absorption coefficient α in the above wavelength range may be considered to satisfy the following equation (1)'.
1.5 × 10 ^-19 N _e λ ³ ≦ α ≦ 6.0 × 10 ^-19 N _e λ ³・ ・ ・ (1)'

Further, among the substrates 10 satisfying the above specifications, in the substrate having extremely small crystal strain and extremely high purity (that is, low impurity concentration), the absorption coefficient α in the above wavelength range is expressed by the following equation (
1) Approximate by'' (satisfies equation (1)'').
_{^{α = 2.2 × 10 -19 N e}} λ 3 ··· (1) ''

The provision that "the absorption coefficient α is approximated by the equation (1)'" satisfies the same as the above-mentioned provision that the absorption coefficient completely matches the equation (1)'(the equation (1)' is satisfied. ) Not only the case but also the case where the equation (1)'is satisfied within a predetermined error range. The predetermined error is, for example,
It is within ± 0.1α, preferably within ± 0.01α at a wavelength of 2 μm.

In FIG. 4 described above, the measured value of the absorption coefficient α in the GaN crystal produced by the production method described later is shown by a thin line. Specifically, the free electron concentration _Ne is 1.0 × 10 ¹⁷ cm ^-3.
The measured value of the absorption coefficient α at the time of is shown by a thin solid line, and the free electron concentration _Ne is 1.2 × 10 ¹⁸ c.
The measured value of the absorption coefficient α when m ^-3 is shown by a thin dotted line, and the free electron concentration _Ne is 2.0 × 10.
^{The measured value of the absorption coefficient α at 18} cm ^-3 is shown by a thin alternate long and short dash line. On the other hand, in FIG. 4 described above, the function of the above equation (1) is shown by a thick line. Specifically, the free electron concentration _Ne is 1.
.. The function of equation (1) when 0 × 10 ¹⁷ cm ^-3 is shown by a thick solid line, and the function of equation (1) when the free electron concentration _Ne is 1.2 × 10 ¹⁸ cm ^-3 is shown by a thick dotted line. Shown, free electron concentration _Ne
The function of equation (1) when is 2.0 × 10 ¹⁸ cm ^-3 is shown by a thick alternate long and short dash line. Figure 4
As shown in the above, the measured value of the absorption coefficient α in the GaN crystal produced by the production method described later can be accurately fitted by the function of the equation (1). In the case of FIG. 4 (in the case of Si doping), the absorption coefficient α is accurately approximated to the equation (1) when ^{K = 2.2 × 10-19.}

Thus, by the absorption coefficient of the substrate 10 is approximated by the equation (1), the absorption coefficient of the substrate 10, can be accurately designed based on the free electron density N _e in the substrate 10.

Further, in the present embodiment, for example, in the wavelength range of at least 1 μm or more and 3.3 μm or less, the absorption coefficient α of the substrate 10 satisfies the following equation (2).
0.15λ ³ ≤ α ≤ 6λ ³ ... (2)

When α <0.15λ ³ , the substrate 10 cannot sufficiently absorb infrared rays, and the heating of the substrate 10 may become unstable. On the other hand, by setting 0.15λ ³ ≦ α, infrared rays can be sufficiently absorbed by the substrate 10 and the substrate 10 can be heated stably. On the other hand, when 6λ ³ <α, it corresponds to the concentration of n-type impurities in the substrate 10 ^{exceeding a predetermined value (1 × 10 19} at · cm ^{-3 or} more) as described later, and the substrate 10
Crystallinity may decrease. On the other hand, ^{by setting α ≦ 6λ 3} , the substrate 10
This corresponds to the concentration of the n-type impurities in the substrate being equal to or less than a predetermined value, and good crystallinity of the substrate 10 can be ensured.

The absorption coefficient α of the substrate 10 preferably satisfies the following formula (2)'or (2)'.
^{0.15λ 3 ≦ α ≦ 3λ 3 ···} (2) '
0.15λ ³ ≤ α ≤ 1.2λ ³ ... (2)''
This makes it possible to stably heat the substrate 10 while ensuring better crystallinity of the substrate 10.

Further, in the present embodiment, for example, in the wavelength range of at least 1 μm or more and 3.3 μm or less, the difference between the maximum value and the minimum value of the absorption coefficient α in the main surface of the substrate 10 (the minimum value is subtracted from the maximum value). Difference. Hereinafter, when Δα is defined as “difference in in-plane absorption coefficient of substrate 10”), Δα (cm)
^-1 ) satisfies the equation (3).
Δα ≦ 1.0 ・ ・ ・ (3)
When Δα> 1.0, the heating efficiency due to infrared irradiation may become non-uniform in the main surface of the substrate 10. On the other hand, by setting Δα ≦ 1.0, the heating efficiency due to the irradiation of infrared rays can be made uniform in the main surface of the substrate 10.

It is preferable that Δα satisfies the equation (3)'.
Δα ≦ 0.5 ・ ・ ・ (3)'
By setting Δα ≦ 0.5, the heating efficiency due to infrared irradiation can be stably made uniform in the main surface of the substrate 10.

The provisions of equations (2) and (3) regarding the absorption coefficients α and Δα are, for example, a wavelength of 2μ.
It can be replaced with the regulation in m.

That is, in the present embodiment, for example, the absorption coefficient of the substrate 10 at a wavelength of 2 μm is 1.
.. 2cm is ^-1 or more 48cm ^-1 or less. The absorption coefficient of the substrate 10 at a wavelength of 2 μm ^{is preferably 1.2 cm -1} or more and 24 cm ^-1 or less, and ^{more preferably 1.2 cm -1} or more and 9.6 cm ^-1 or less.

Further, in the present embodiment, for example, the difference between the maximum value and the minimum value of the absorption coefficient at a wavelength of 2 μm in the main surface of the substrate 10 is ^{within 1.0 cm -1} , preferably within ^{0.5 cm -1.} is there.

Although the upper limit value of the in-plane absorption coefficient difference of the substrate 10 has been described, the lower limit value of the in-plane absorption coefficient difference of the substrate 10 is preferably zero because the smaller it is, the better. Even if the in-plane absorption coefficient difference of the substrate 10 is 0.01 cm- ¹ , the effect of the present embodiment can be sufficiently obtained.

Here, the wavelength 2 μm corresponding to the peak wavelength of infrared rays when the temperature is about 1200 ° C.
The requirements for the absorption coefficient of the substrate 10 are specified in. However, the effect of satisfying the above requirements for the absorption coefficient of the substrate 10 is not limited to when the temperature is about 1200 ° C. Because the spectrum of infrared rays emitted from the heating source is Stefan-
It has a predetermined wavelength width according to Boltzmann's law, and has a component having a wavelength of 2 μm even if the temperature is other than 1200 ° C. Therefore, if the absorption coefficient of the substrate 10 satisfies the above requirements at a wavelength of 2 μm corresponding to a temperature of 1200 ° C., the absorption coefficient of the substrate 10 and the inside of the main surface of the substrate 10 can be obtained even at a wavelength other than 1200 ° C. The difference between the maximum value and the minimum value of the absorption coefficient in is within a predetermined range. As a result, even if the temperature is other than 1200 ° C.
The substrate 10 can be stably heated, and the heating efficiency with respect to the substrate 10 can be made uniform in the main surface.

By the way, FIG. 4 above is the result of measuring the absorption coefficient of the GaN crystal at room temperature (27 ° C.). Therefore, when considering the absorption coefficient of the substrate 10 under a predetermined temperature condition in the step of heating the substrate 10, the free carrier absorption of the GaN crystal under the predetermined temperature condition is the GaN crystal under the temperature condition of room temperature. It is necessary to consider how it changes with respect to the free carrier absorption of.

FIG. 5 is a diagram showing the intrinsic carrier concentration with respect to the temperature of the GaN crystal. As shown in FIG. 5, in the GaN crystal forming the substrate 10, as the temperature increases, the concentration of the intrinsic carrier concentration N _i which is thermally excited at (between the valence band and the conduction band) between the band becomes higher .. However, even if the temperature of the GaN crystal becomes around 1300 ° C., the concentration of the intrinsic carrier concentration _{N i} which is thermally excited across the band of the GaN crystal is less than 7 × ¹⁰ 15 ^{cm -3,} n-type impurity Concentration of free carriers produced in the GaN crystal by doping with (eg 1x)
It is sufficiently lower than ^{10 17} cm ^-3). That is, the free carrier concentration of the GaN crystal is G.
It can be said that the free carrier concentration is determined by doping the n-type impurity under the temperature condition that the temperature of the aN crystal is less than 1300 ° C., which is within the so-called exogenous region.

That is, in the present embodiment, the substrate 1 is at least under the temperature conditions (room temperature (27 ° C.) or more and 1250 ° C. or less) in the manufacturing process of the semiconductor laminate 1 and the semiconductor device 2 described later.
The concentration of intrinsic carriers thermally excited between the 0 bands is lower than the concentration of free electrons generated in the substrate 10 by doping n-type impurities under temperature conditions at room temperature (for example, 1/10).
Less than double). As a result, it can be considered that the free carrier concentration of the substrate 10 under a predetermined temperature condition in the step of heating the substrate 10 is substantially equal to the free carrier concentration of the substrate 10 under a temperature condition of room temperature. Free carrier absorption under temperature conditions can be considered to be approximately equal to free carrier absorption at room temperature. That is, as described above, at room temperature, the substrate 10
When the absorption coefficient in the infrared region in the above satisfies the above-mentioned predetermined requirement, it can be considered that the absorption coefficient in the infrared region in the substrate 10 substantially maintains the above-mentioned predetermined requirement even under a predetermined temperature condition.

Further, in the substrate 10 of the present embodiment, the absorption coefficient α in the wavelength range of at least 1 μm or more and 3.3 μm or less is approximated by the equation (1). Therefore, at a predetermined wavelength λ, the absorption coefficient α of the substrate 10 is determined. It has substantially proportional relationship with the free electron concentration N _e.

FIG. 6A is a diagram showing the relationship between the absorption coefficient at a wavelength of 2 μm and the free electron concentration in the GaN crystal produced by the production method according to the present embodiment. In FIG. 6A, the lower solid line (α = 1.2 × ^10-18 n) is K = 1.5 × ^10-19 and λ =
It is a function in which 2.0 is substituted into equation (1), and the upper solid line (α = 4.8 × ^10-18 n) is
It is a function in which K = 6.0 × ^10-19 and λ = 2.0 are substituted into the equation (1). In addition, FIG.
In (a), not only Si-doped GaN crystals but also Ge-doped GaN crystals are shown. Moreover, the result of measuring the absorption coefficient by the transmission measurement and the result of measuring the absorption coefficient by the spectroscopic ellipsometry method are shown. As shown in FIG. 6A, the wavelength λ is set to 2.0 μ.
when the m, alpha absorption coefficient of GaN crystal produced by a production method described later, it has a relationship substantially proportional to the free electron concentration N _e. Further, the measured value of the absorption coefficient α in the GaN crystal produced by the production method described later is 1.5 × 10 ^-19 ≦ K ≦ 6.0 × 10.
^{Within the range of -19} , it can be fitted accurately by the function of equation (1).
The GaN crystal produced by the production method described later has high purity (that is, low impurity concentration).
Moreover, since the thermal and electrical characteristics are good, the measured value of the absorption coefficient α is K = 2.2.
In many cases, the fitting can be performed accurately by ^{the function of the equation (1) when × 10-19} is set, that is, α = 1.8 × ^{10-18 n.}

In the present embodiment, based on the absorption coefficient of the substrate 10 as described above α is proportional to the free electron concentration N _e, the free electron density N _e in the substrate 10, satisfies the following predetermined condition.

In the present embodiment, for example, the free electron density _{N e} in the substrate 10, 1.0 × ^{10 18}
cm ^-3 or more 1.0 × 10 ¹⁹ cm ^-3 or less. As a result, from the equation (1), the substrate 1
The absorption coefficient at a wavelength of 2 μm at 0 ^{can be 1.2 cm -1} or more and 48 cm ^-1 or less. Incidentally, the free electron density _{N e} in the substrate 10 is preferably 1.0 × ¹⁰ 18 ^{cm -3} or more 5.0 × ¹⁰ 18 ^{cm -3} or less, 1.0 × ¹⁰ 18 ^{cm -3} or more 2
.. More preferably, it is 0 × 10 ¹⁸ cm ^{-3 or less.} As a result, the absorption coefficient of the substrate 10 at a wavelength of 2 μm can be preferably 1.2 cm ^-1 or more and 24 cm ^-1 or less, and more preferably 1.2 cm ^-1 or more and 9.6 cm ^-1 or less.

Further, as described above, the difference between the maximum value and the minimum value of the absorption coefficient α in the main surface of the substrate 10 is Δ.
and alpha, the difference between the maximum value and the minimum value of the free electron concentration N _e in the main surface of the substrate 10 and .DELTA.N _e, when 2.0μm wavelength lambda, by differentiating the equation (1), the following Equation (4) is obtained.
Δα = 8KΔN _e ... (4)

In the present embodiment, for example, the difference .DELTA.N _e between the maximum value and the minimum value of the free electron concentration _{N e} in the main surface of the substrate 10, 8.3 × ¹⁰ 17 ^{cm -3,} preferably within 4.2 × 10 ¹⁷ cm ^-
It is within ^3. As a result, from the equation (4), the difference Δα between the maximum value and the minimum value of the absorption coefficient at a wavelength of 2 μm can be set to 1.0 cm ^{-1 or} less, preferably 0.5 cm ^{-1 or} less.

Although described for the upper limit of .DELTA.N _e, the lower limit of .DELTA.N _e, because the smaller the better, it is preferable that the zero. Even if ΔN _e is 8.3 × 10 ¹⁵ cm ^-3 , the effect of this embodiment can be sufficiently obtained.

In the present embodiment, the free electron concentration _Ne in the substrate 10 is equal to the concentration of the n-type impurities in the substrate 10, and the concentration of the n-type impurities in the substrate 10 satisfies the following predetermined requirements. There is.

In the present embodiment, for example, the concentration of n-type impurities in the substrate 10 is 1.0 × 10 ¹⁸
At · cm ^-3 or more 1.0 × 10 ¹⁹ at · cm ^-3 or less. As a result, the substrate 10
The free electron concentration _{N e} in the middle, 1.0 × ¹⁰ 18 ^{cm -3} or more 1.0 × ¹⁰ 19 cm ^-
It can be ^{3 or less.} The concentration of n-type impurities in the substrate 10 is 1.0 × 1.
0 ¹⁸ at · cm ^-3 or more and 5.0 × 10 ¹⁸ at · cm ^-3 or less is preferable.
More preferably, it is 1.0 × 10 ¹⁸ at · cm ^-3 or more and 2.0 × 10 ¹⁸ at · cm ^{-3 or less.} Thus, the free electron density _{N e} in the substrate 10, preferably 1.0
× 10 ¹⁸ cm ^-3 or more 5.0 × 10 ¹⁸ cm ^-3 or less, more preferably 1.0 × 1
It can be 0 ¹⁸ cm ^-3 or more and 2.0 × 10 ¹⁸ cm ^-3 or less.

Further, in the present embodiment, for example, the difference between the maximum value and the minimum value of the concentration of n-type impurities in the main surface of the substrate 10 (hereinafter, also referred to as the in-plane concentration difference of n-type impurities) is 8.3 ×. 10 ¹⁷ at ・
It ^{is within cm -3} , preferably within 4.2 × 10 ¹⁷ at · cm ^-3 . _{As a result, the difference ΔN e} between the maximum value and the minimum value _{of the free electron concentration N e} in the main surface of the substrate 10 is equal to the in-plane concentration difference of the n-type impurities, and is within 8.3 × 10 ¹⁷ cm ^-3 . Preferably 4.2 × 10 ¹⁷ c
It can be within m ^-3.

Although the upper limit of the in-plane concentration difference of n-type impurities has been described, the lower limit of the in-plane concentration difference of n-type impurities is preferably zero because the smaller it is, the better. Even if the in-plane concentration difference of the n-type impurities is 8.3 × 10 ¹⁵ at · cm ^-3 , the effect of the present embodiment can be sufficiently obtained.

Further, in the present embodiment, the concentration of each element in the substrate 10 satisfies the following predetermined requirements.

In the present embodiment, among Si, Ge and O used as n-type impurities, the concentration of O, whose addition amount is relatively difficult to control, is extremely low, and the concentration of n-type impurities in the substrate 10 is added. The amount is determined by the total concentration of Si and Ge, which is relatively easy to control.

That is, the concentration of O in the substrate 10 is negligibly low with respect to the total concentration of Si and Ge in the substrate 10, for example, 1/10 or less. Specifically, for example, 10 in the substrate
The concentration of O in is ^{less than 1 × 10 17} at · cm ^-3 , while the total concentration of Si and Ge in the substrate 10 is 1 × 10 ¹⁸ at · cm ^-3 or more and 1.0 × 10 ¹⁹ at. -Cm- ³ or less. Thereby, the concentration of the n-type impurity in the substrate 10 can be controlled by the total concentration of Si and Ge, which are relatively easy to control the addition amount. As a result, the free electron concentration _Ne in the substrate 10 can be accurately controlled to be equal to the total concentration of Si and Ge in the substrate 10, and the maximum concentration of free electrons in the main surface of the substrate 10 can be controlled. the difference .DELTA.N _e between the value and the minimum value, it is possible to accurately control so as to meet the predetermined requirements.

Further, in the present embodiment, the concentration of impurities other than the n-type impurities in the substrate 10 is negligibly low with respect to the concentration of the n-type impurities in the substrate 10 (that is, the total concentration of Si and Ge), for example. It is 1/10 or less. Specifically, for example, the concentration of impurities other than the n-type impurities in the substrate is less than ^{1 × 10 17} at · cm ^-3. This makes it possible to reduce the factors that hinder the generation of free electrons from n-type impurities. As a result, the free electron concentration _Ne in the substrate 10 can be accurately controlled to be equal to the concentration of n-type impurities in the substrate 10, and becomes the maximum value of the free electron concentration in the main surface of the substrate 10. the difference .DELTA.N _e between the minimum value, it is possible to accurately control so as to meet the predetermined requirements.

The present inventors have confirmed that the concentration of each element in the substrate 10 can be stably controlled so as to satisfy the above requirements by adopting the manufacturing method described later.

According to the manufacturing method described later, the concentrations of O and carbon (C) in the substrate 10 are set to 5 × 10 ¹⁵ a.
It can be reduced to less than t · cm ^-3 , and the concentration of iron (Fe), chromium (Cr), boron (B), etc. in the substrate 10 can be reduced to less than 1 × 10 ¹⁵ at · cm ^-3. It is known that it can be reduced. Further, according to this method, secondary ion mass spectrometry (SIMS: Secondary Ion Mass S) is also used for elements other than these.
It is known that it is possible to reduce the concentration to less than the lower limit of detection in the measurement by spectrumry).

Further, in the substrate 10 manufactured by the manufacturing method described later in the present embodiment, the absorption coefficient due to free carrier absorption is smaller than the absorption coefficient of the conventional substrate. Therefore, the substrate 10 of the present embodiment has a higher absorption coefficient than the conventional substrate. , It is estimated that the mobility (μ) is high. As a result, even when the free electron concentration in the substrate 10 of the present embodiment is equal to the free electron concentration in the conventional substrate, the resistivity (ρ = 1 / eN _e μ) of the substrate 10 of the present embodiment is increased. , It is lower than the resistivity of the conventional substrate. Specifically, the free electron density _{N e} in the substrate 10 is 1.0
When it is × 10 ¹⁸ cm ^-3 or more and 1.0 × 10 ¹⁹ cm ^-3 or less, the resistivity of the substrate 10 is, for example, 2.2 mΩ · cm or more and 17.4 mΩ · cm or less.

(1-ii) Detailed Configuration of Semiconductor Layer 20 Next, the semiconductor layer 20 constituting the nitride semiconductor laminate (intermediate) 1 will be described in detail.

The semiconductor layer 20 is formed by epitaxially growing on the main surface of the substrate 10. The semiconductor layer 20 is made of a single crystal of a group III nitride semiconductor, specifically, like the substrate 10, for example, a single crystal of GaN. Further, since the semiconductor layer 20 is epitaxially grown on the substrate 10, its plane orientation is, for example, (00), as in the substrate 10.
01) Plane (+ c plane, Ga polar plane) or 000-1 plane (−c plane, N polar plane).
The off-angle of the GaN crystal constituting the semiconductor layer 20 is the same as that of the substrate 10.

In the present embodiment, the surface (main surface) of the semiconductor layer 20 satisfies a predetermined requirement for reflectance in the infrared region. Specifically, the reflectance of the surface of the semiconductor layer 20 is at least 1 μm or more 3
.. It is 5% or more and 30% or less in the wavelength range of 3 μm or less. As a result, the substrate 10 (
In the step of heating the semiconductor laminate 1), infrared rays can be sufficiently delivered to the substrate 10. As a result, the substrate 10 can be heated stably.

The surface roughness (arithmetic mean roughness Ra) of the surface of the semiconductor layer 20 is, for example, 1 nm or more and 3
It is 0 nm or less. Thereby, the reflectance of the surface of the semiconductor layer 20 can be set to 5% or more and 30% or less in a wavelength range of at least 1 μm or more and 3.3 μm or less.

Next, a specific configuration of the semiconductor layer 20 of the present embodiment will be described.

As shown in FIG. 1, the semiconductor layer 20 includes, for example, the base n-type semiconductor layer 21 and the drift layer 2.
It is configured to have 2.

(Base n-type semiconductor layer)
The base n-type semiconductor layer 21 is provided so as to be in contact with the main surface of the substrate 10 as a buffer layer that inherits the crystallinity of the substrate 10 and stably epitaxially grows the drift layer 22. Further, the base n-type semiconductor layer 12 is configured as an n-type GaN layer containing n-type impurities. The n-type impurities contained in the base n-type semiconductor layer 12 include, for example, as in the substrate 10.
Examples include Si and Ge. The concentration of n-type impurities in the base n-type semiconductor layer 12 is determined by the substrate 10.
Approximately equal to, for example, 1.0 × 10 ¹⁸ at · cm ^-3 or more 1.0 × 10 ¹⁹ at · c
It is m ^-3 or less.

The thickness of the base n-type semiconductor layer 21 is thinner than the thickness of the drift layer 22, for example, 0.1 μ.
It is m or more and 3 μm or less.

(Drift layer)
The drift layer 22 is provided on the base n-type semiconductor layer 21 and contains n-type impurities having a low concentration.
It is configured as a type GaN layer. Examples of the n-type impurities in the drift layer 22 include Si and Ge, as in the case of the n-type impurities in the underlying n-type semiconductor layer 21.

The n-type impurity concentration in the drift layer 22 is lower than the n-type impurity concentration of each of the substrate 10 and the underlying n-type semiconductor layer 21, for example, 1.0 × 10 ¹⁵ at · cm ^-3 or more 5.0 ×.
It is 10 ¹⁶ at · cm ^-3 or less. The n-type impurity concentration of the drift layer 22 is 1.0 × 10 ^{1
By setting the value to 5} at · cm ^-3 or more, the on-resistance of the semiconductor device can be reduced. On the other hand, by setting the concentration of n-type impurities in the drift layer 22 to 5.0 × 10 ¹⁶ at · cm ^-3 or less, a predetermined withstand voltage of the semiconductor device can be secured.

In order to improve the withstand voltage of the semiconductor device, the drift layer 22 is, for example, the base n-type semiconductor layer 2
It is provided thicker than 1. Specifically, the thickness of the drift layer 22 is, for example, 3 μm or more and 40 μm or less. By setting the thickness of the drift layer 22 to 3 μm or more, a predetermined withstand voltage of the semiconductor device can be secured. On the other hand, by setting the thickness of the drift layer 22 to 40 μm or less, the on-resistance of the semiconductor device can be reduced.

(1-iii) Structural Features of Nitride Semiconductor Laminate 1 Next, the structural features of the nitride semiconductor laminate 1 in which the semiconductor layer 20 is formed on the substrate 10 will be described.

As described above, both the substrate 10 and the semiconductor layer 20 constituting the nitride semiconductor laminate 1 are made of a group III nitride semiconductor crystal (specifically, for example, a GaN single crystal). That is, a semiconductor layer 20 which is a thin film composed of crystals having the same composition as that of the substrate 1 is formed on the substrate 10 by epitaxial growth. Therefore, the nitride semiconductor laminate 1 corresponds to a semiconductor layer 20 homoepitaxially grown on the substrate 10.

Further, the substrate 10 constituting the nitride semiconductor laminate 1 satisfies a predetermined requirement for the absorption coefficient in the infrared region, and thereby between the free electron concentration (carrier concentration) in the substrate 10 and the absorption coefficient in the infrared region. It has a dependency on. Having a dependency here means that there is a special correlation (necessity) between two or more events. For example, when an event occurs, a specific event depends on it. It must appear.
Specifically, as already described, the absorption coefficient in the infrared region can be approximated as a function of free carrier concentration and wavelength. More particularly, dependent on the substrate 10, the wavelength lambda ([mu] m), the absorption coefficient alpha ^{(cm -1)} of the substrate 10 at 27 ° C., the free electron concentration in the substrate 10 (carrier concentration) _N e (cm ^-3 ) When K and a are constants, the absorption coefficient α in the wavelength range of at least 1 μm or more and 3.3 μm or less is approximated by the above-mentioned equation (1). Equation (1) is as follows when reprinted.
^{_{α = N e Kλ a ··· (}} 1)
(However, 1.5 × 10 ^-19 ≦ K ≦ 6.0 × 10 ^-19 , a = 3)

The dependence on the substrate 10 is not limited to the above-mentioned example, and may include a case where there is a certain correlation such that the absorption coefficient decreases depending on the decrease in the carrier concentration.

By the way, for the nitride semiconductor laminate 1 in which the semiconductor layer 20 is formed on the substrate 10, it is very important to control the film thickness of the semiconductor layer 20 which is homoepitaxially grown. For that purpose, a method capable of measuring the film thickness of the semiconductor layer 20 in a non-contact and non-destructive manner is required. For example, the FT-IR method is known as a method for measuring a thin film obtained by homoepitaxial growth in a non-contact and non-destructive manner.

However, the nitride semiconductor laminate 1 in the present embodiment is a so-called GaN-on-GaN substrate in which a semiconductor layer 20 also made of a GaN crystal is homoepitaxially grown on a substrate 10 made of a GaN crystal. As for the crystals of group III nitride semiconductors represented by GaN crystals, the influence of dislocation scattering has been large so far, and there is no difference in the absorption coefficient in the infrared region ^{especially at a low carrier concentration of 1 × 10 17} cm ^{-3 or less.} Therefore, in the case of a GaN-on-GaN substrate in which the substrate 10 and the semiconductor layer 20 are made of GaN crystals having the same composition, in principle, FT-
It is a conventional common sense that it is difficult to measure the film thickness by the IR method. More specifically, for example, even if an attempt is made to measure using light in the far infrared ^{region with a wave number of 500 cm -1 or less, the wave number is 100.}
0 cm ^-1 or more (in particular, a wave number 1500 cm ^-1 or more) for light in the infrared region, the amount of absorption is very small, because the difference in absorption coefficient is hardly actualized, films using light of such infrared region The conventional wisdom is that it is difficult to measure the thickness.

However, in the present embodiment, as described above, the dislocation density on the main surface of the substrate 10 constituting the nitride semiconductor laminate 1 is ^{low, for example, 5 × 10 6} pieces / cm ² or less. It has become something like that. Moreover, the substrate 10 constituting the nitride semiconductor laminate 1 satisfies a predetermined requirement for the absorption coefficient in the infrared region, and thus has a dependency between the carrier concentration in the substrate 10 and the absorption coefficient in the infrared region. It has become a thing. Then, in the present embodiment, such a substrate 10 is used, and the semiconductor layer 20 is homoepitaxially grown on the substrate 10 to form the nitride semiconductor laminate 1. By homoepitaxially growing, the GaN crystal constituting the semiconductor layer 20 becomes similar to the GaN crystal constituting the substrate 10 on which the semiconductor layer 20 is formed. That is, even if there is a difference in carrier concentration between the semiconductor layer 20 and the substrate 10, the semiconductor layer 20 has low dislocations and has a dependency between the carrier concentration and the absorption coefficient in the infrared region, as in the substrate 10. Will have.

Therefore, in the case of the nitride semiconductor laminate 1 of the present embodiment, for example, 1 × 10 ¹⁷ cm ^{−.
Even if the carrier concentration is as low as 3} or less, the absorption coefficient in the infrared region will differ depending on the difference in carrier concentration between the substrate 10 and the semiconductor layer 20, and as a result, the FT-IR method will be used. wave number 1000 cm ^-1 above using (especially, a wave number 1500 cm ^-1 or more) it is possible to perform film thickness measurement by the light of the infrared region. That is, the nitride semiconductor laminate 1 is GaN-on.
Even in the case of a −GaN substrate, the film thickness can be measured by the FT-IR method, overturning the above-mentioned conventional wisdom of technology.

More specifically, in the nitride semiconductor laminate 1 in the present embodiment, the substrate 10 has the formula (1).
Since the relationship approximated by the above is satisfied, the relationship between the carrier concentration _Ne and the absorption coefficient α is also established in the semiconductor layer 20 homoepitaxially grown on the substrate 10. Therefore, for example, ^{even with a low carrier concentration of 1 × 10 17} cm ^-3 or less, a wavelength range of at least 1 μm or more and 3.3 μm or less (that is, wave number 3030 cm ^-1 or more 10).
In the 000 following ranges), surely become a difference in absorption coefficient α depending on the carrier concentration N _e occurs, it becomes very suitable in performing thickness measurement using an FT-IR method ..

As described above, the FT of the nitride semiconductor laminate 1 which is a GaN-on-GaN substrate
The fact that the film thickness can be measured by the −IR method means that the nitride semiconductor laminate 1 is configured as described below.

As will be described in detail later, in the FT-IR method, the object to be analyzed is irradiated with infrared light to obtain a reflection spectrum. The reflection spectrum referred to here is the wavelength (the amount of light reflected when irradiating infrared light).
It is plotted against wave number). Then, in the FT-IR method, the film thickness of the object to be analyzed is measured by analyzing the fringe pattern in the obtained reflection spectrum. The fringe pattern referred to here is a pattern showing the existence of fringes (interference fringes) in which a portion having a large amount of light and a portion having a small amount of light are alternately generated due to the interference of light, and is according to the variation of the optical path length when obtaining the reflection spectrum. It is the pattern that occurs.

Therefore, the nitride semiconductor laminate 1 whose film thickness can be measured by the FT-IR method is included in the reflection spectrum obtained by irradiating the semiconductor layer 20 on the substrate 10 with infrared light. It will have a fringe pattern. If there is a fringe pattern in the reflection spectrum, it is possible to measure the film thickness of the semiconductor layer 20 by analyzing the fringe pattern, that is, to measure the film thickness using the FT-IR method. It becomes.

(2) Method for Producing Nitride Semiconductor Laminate 1 Next, a procedure for manufacturing the nitride semiconductor laminate 1 having the above-described configuration, including film thickness measurement by the FT-IR method, that is, nitriding according to the present embodiment. A method for manufacturing the material semiconductor laminate 1 will be described.

As shown in FIG. 7, the method for manufacturing the nitride semiconductor laminate 1 according to the present embodiment is at least a substrate preparation step (step 110, hereinafter the step is abbreviated as “S”) and a semiconductor layer growth step (S120). ) And a film thickness measuring step (S130).

(2-i) Substrate Preparation Step In the substrate preparation step (S110), the substrate 10 is manufactured. The substrate 10 is manufactured by using the hydride vapor phase deposition apparatus (HVPE apparatus) 200 shown below.

(Configuration of HVPE device)
Here, the configuration of the HVPE apparatus 200 used for manufacturing the substrate 10 will be described in detail with reference to FIG.

The HVPE apparatus 200 includes an airtight container 203 in which the film forming chamber 201 is configured inside. An inner cover 204 is provided in the film forming chamber 201, and a seed crystal substrate (hereinafter, also referred to as “seed substrate”) 5 is arranged as a base at a position surrounded by the inner cover 204. A susceptor 208 is provided. The susceptor 208 is connected to a rotation shaft 215 of the rotation mechanism 216, and is configured to be rotatable according to the drive of the rotation mechanism 216.

At one end of the airtight container 203, a gas supply pipe 232a for supplying hydrogen chloride (HCl) gas into the gas generator 233a, _{a gas supply pipe 232b for supplying ammonia (NH 3} ) gas into the inner cover 204, and an inner cover 204. Gas supply pipe 232c for supplying the doping gas described later, and gas supply for supplying a mixed gas (N ₂ / H ₂ gas) _{of nitrogen (N 2} ) gas and hydrogen (H _{2) gas as a purge gas into the inner cover 204.} Tube 232d and
Gas supply pipe 232e for supplying the _{N 2} gas as a purge gas into the deposition chamber 201 is connected. The gas supply pipes 232a to 232e are connected to the flow rate controllers 241a to 241a to 2 in order from the upstream side.
41e and valves 243a to 243e are provided, respectively. A gas generator 233a for accommodating a Ga melt as a raw material is provided downstream of the gas supply pipe 232a. In the gas generator 233a, gallium chloride (Ga) produced by the reaction of HCl gas and Ga melt is used.
Cl) Nozzle 249 that supplies gas toward the seed substrate 5 or the like arranged on the susceptor 208.
a is provided. On the downstream side of the gas supply pipes 232b and 232c, nozzles 249b and 249c for supplying various gases supplied from these gas supply pipes to the seed substrate 5 and the like arranged on the susceptor 208 are connected, respectively. .. The nozzles 249a to 249c are arranged so as to allow gas to flow in a direction intersecting the surface of the susceptor 208. Nozzle 249
The doping gas supplied from c is a mixed gas of a _{doping raw material gas and a carrier gas such as N 2} / H _{2 gas.} As for the doping gas, HCl gas may be flowed together for the purpose of suppressing thermal decomposition of the halide gas as the doping raw material. Examples of the doping raw material gas constituting the doping gas include dichlorosilane (SiH ₂ Cl ₂ ) gas or silane (SiH ₄ ) gas in the case of silicon (Si) doping, and germanium (Ge) doping in the case of germanium (Ge) doping. It is conceivable to use dichlorogerman (GeCl ₄ ) gas or germanium (GeH ₄ ) gas, respectively, but the present invention is not limited thereto.

At the other end of the airtight container 203, an exhaust pipe 230 for exhausting the inside of the film forming chamber 201 is provided. The exhaust pipe 230 is provided with a pump (or blower) 231. Airtight container 20
Zone heaters 207a and 207b for heating the inside of the gas generator 233a and the seed substrate 5 on the susceptor 208 to a desired temperature for each region are provided on the outer periphery of the third. In addition, the airtight container 20
A temperature sensor (but not shown) for measuring the temperature in the film forming chamber 201 is provided in 3.

The constituent members of the HVPE apparatus 200 described above, particularly each member for forming various gas flows, are described below, for example, in order to enable crystal growth having a low impurity concentration as described later. It is configured.

Specifically, as identifiable by the hatching type in FIG. 8, the airtight container 203 is heated to the crystal growth temperature (for example, 1000 ° C. or higher) by receiving radiation from the zone heaters 207a and 207b. It is preferable to use a member made of a quartz-free and boron-free material as a member that constitutes a high-temperature region that is a region in which the gas supplied to the seed substrate 5 comes into contact. Specifically, as the member constituting the high temperature region, for example, it is preferable to use a member made of silicon carbide (SiC) coated graphite. On the other hand, in a relatively low temperature region, it is preferable to construct the member using high-purity quartz. That is, in the high temperature region where the temperature becomes relatively high and comes into contact with HCl gas or the like, each member is composed of SiC coated graphite instead of high-purity quartz. Specifically, the inner cover 204, the susceptor 208, the rotating shaft 215, the gas generator 233a, the nozzles 249a to 249c, etc. are made of SiC.
Consists of coated graphite. Since the core tube constituting the airtight container 203 can only be made of quartz, an inner cover 204 that surrounds the susceptor 208, the gas generator 233a, and the like is provided in the film forming chamber 201. Walls at both ends of the airtight container 203 and the exhaust pipe 230
For example, a metal material such as stainless steel may be used.

For example, "Polyakov et al. J. Apple. Phys. 115,
According to "183706 (2014)", it is disclosed that growth of a GaN crystal having a low impurity concentration can be realized by growing at 950 ° C. However, such low-temperature growth causes deterioration of the obtained crystal quality, and good thermophysical properties, electrical characteristics, and the like cannot be obtained.

On the other hand, according to the above-described HVPE apparatus 200 of the present embodiment, the temperature becomes relatively high and H
In the high temperature region where it comes into contact with Cl gas or the like, each member is composed of SiC coated graphite. As a result, impurities such as Si, O, C, Fe, Cr, and Ni caused by quartz, stainless steel, and the like are supplied to the crystal growth portion even in a temperature range suitable for the growth of GaN crystals, for example, 1050 ° C. or higher. It can be blocked. As a result, it is possible to grow a GaN crystal having high purity and good thermal and electrical characteristics.

Each member of the HVPE device 200 is connected to a controller 280 configured as a computer, and is executed by a program executed on the controller 280.
It is configured to control the processing procedure and processing conditions described later.

(Substrate manufacturing procedure)
Subsequently, FIG. 8 refers to FIG. 8 for a series of processes from epitaxially growing a GaN single crystal on the seed substrate 5 using the above-mentioned HVPE apparatus 200 and then slicing the grown crystal to obtain the substrate 10. I will explain in detail. In the following description, the HVPE device 2
The operation of each part constituting 00 is controlled by the controller 280.

The procedure for producing the substrate 10 performed by using the HVPE apparatus 200 includes a carry-in step, a crystal growth step, a carry-out step, and a slice step.

(Bring-in step)
Specifically, first, the furnace opening of the reaction vessel 203 is opened, and the seed substrate 5 is placed on the susceptor 208. The seed substrate 5 placed on the susceptor 208 serves as a base (seed) for producing the substrate 10, and is a plate-like structure made of a single crystal of GaN, which is an example of a nitride semiconductor.

When placing the seed substrate 5 on the susceptor 208, the surface of the seed substrate 5 mounted on the susceptor 208, that is, the main surface (crystal growth surface, base surface) on the side facing the nozzles 249a to 249c. Is the (0001) plane of the GaN crystal, that is, the + C plane (Ga polar plane).

(Crystal growth step)
In this step, after the delivery of the seed substrate 5 into the reaction chamber 201 is completed, the furnace port is closed, and while heating and exhausting the inside of the reaction chamber 201, H ₂ gas or H 2 gas into the reaction chamber 201 or
Start supplying H ₂ gas and N _{2 gas.} Then, the desired processing temperature in the reaction chamber 201 is set.
When the processing pressure was reached and the atmosphere in the reaction chamber 201 became the desired atmosphere, the supply of HCl gas and NH ₃ gas from the gas supply pipes 232a and 232b was started, and the surface of the seed substrate 5 was supplied. supplying GaCl gas and NH ₃ gas, respectively.

As a result, as shown in the cross-sectional view in FIG. 9A, GaN on the surface of the seed substrate 5 in the c-axis direction.
The crystal grows epitaxially and the GaN crystal 6 is formed. At this time, _{by supplying SiH 2} Cl ₂ gas, Si as an n-type impurity can be added to the GaN crystal 6.

In this step, in order to prevent thermal decomposition of the GaN crystals constituting the seed substrate 5, NH _{3 enters the reaction chamber 201 when the temperature of the seed substrate 5 reaches 500 ° C. or before that.}
It is preferable to start supplying gas. Further, in order to improve the in-plane film thickness uniformity of the GaN crystal 6, it is preferable to carry out this step in a state where the susceptor 208 is rotated.

In this step, the temperature of the zone heaters 207a and 207b is, for example, 700 to 900 ° C. for the heater 207a that heats the upstream portion in the reaction chamber 201 including the gas generator 233a.
The temperature of the heater 207b, which heats the downstream portion in the reaction chamber 201 including the susceptor 208, is preferably set to, for example, 1000 to 1200 ° C. This will
The susceptor 208 is adjusted to a predetermined temperature of 1000-1200 ° C. In this step, the internal heater (but not shown) may be used in the off state, but as long as the temperature of the susceptor 208 is in the above range of 1000 to 1200 ° C., the temperature control using the internal heater is performed. You may carry it out.

The following are examples of other processing conditions in this step.
Processing pressure: 0.5 to 2 atmospheres Partial pressure of GaCl gas: 0.1 to 20 kPa
Partial pressure of NH ₃ gas / Partial pressure of GaCl gas: 1 to 100
Partial pressures of / GaCl gas of the H ₂ gas: 0-100
Partial _{pressure of SiH 2} Cl ₂ gas: 2.5 × 10 ^{-5 to} 1.3 × 10 ^-3 kPa

Further, when supplying GaCl gas and the NH ₃ gas to the surface of the seed substrate 5, the respective gas supply pipes 232A～232b, the _{N 2} gas as a carrier gas may be added. N ₂ gas was added by adjusting the blow-out flow rate of the gas supplied from the nozzle 249A～249b, by appropriately controlling the distribution of the supply amount of the raw material gas at the surface of the seed substrate 5, uniformly over the over the entire surface A stable growth rate distribution can be realized. A rare gas such as Ar gas or He gas may be added instead of the N _{2 gas.}

(Delivery step)
After growing a GaN crystal 6 having a desired thickness on the seed substrate 5 _{, a gas generator is provided while supplying NH 3} gas and N ₂ gas into the reaction chamber 201 and exhausting the inside of the reaction chamber 201. 233a
The supply of HCl gas to the supply of the _{H 2} gas into the reaction chamber 201, zone heaters 207a, 20
The heating by 7b is stopped respectively. Then, when the temperature in the reaction chamber 201 drops to 500 ° C. or lower, _{the supply of NH 3} gas is stopped, the atmosphere in the reaction chamber 201 is _{replaced with N 2} gas, and the atmospheric pressure is restored. Then, in the reaction chamber 201, for example, a temperature of 200 ° C. or lower, that is, a temperature at which the GaN crystal ingot (seed substrate 5 on which the GaN crystal 6 is formed on the main surface) can be carried out from the reaction vessel 203. To lower the temperature. After that, the crystal ingot was placed in the reaction chamber 201.
Carry out from inside to outside.

(Slice step)
Then, by slicing the carried-out crystal ingot in a direction parallel to the growth plane of the GaN crystal 6, for example, one or more substrates 10 can be obtained as shown in FIG. 9B.
Since the various compositions and various physical properties of the substrate 10 are as described above, the description thereof will be omitted. This slicing process can be performed using, for example, a wire saw, an electric discharge machine, or the like. Board 10
The thickness of is 250 μm or more, for example, about 400 μm. After that, the surface (+ c surface) of the substrate 10 is subjected to a predetermined polishing process to make this surface an epiready mirror surface. The back surface (−c surface) of the substrate 10 is a lap surface or a mirror surface.

As described above, the substrate 10 of the present embodiment configured as shown in FIG. 2, that is, the substrate 10 having a dependency between the carrier concentration and the absorption coefficient in the infrared region is produced.

(2-ii) Semiconductor layer growth step After the substrate 10 is manufactured in the substrate preparation step (S110), the semiconductor layer growth step (S) is then followed.
120). In the semiconductor layer growth step (S120), a GaN crystal is homoepitaxially grown on the substrate 10 to form the semiconductor layer 20.

The formation of the semiconductor layer 20 is, for example, metalorganic vapor phase growth (MOVPE: Metal Org).
It is carried out by the anic Vapor Phase Epitaxy) method. The semiconductor layer 2
The MOVPE apparatus used for forming 0 may be a known one, and detailed description thereof will be omitted here.

In forming the semiconductor layer 20, for example, the substrate 10 is irradiated with at least infrared rays by the MOVPE method, and the GaN crystals constituting the semiconductor layer 20 are epitaxially grown on the substrate 10.
At this time, if the substrate 10 satisfies the above requirements for the absorption coefficient in the infrared region, the substrate 10 can be stably heated by irradiating the substrate 10 with infrared rays, and the temperature of the substrate 10 can be controlled accurately. Further, the heating efficiency due to the irradiation of infrared rays can be made uniform in the main surface of the substrate 10. As a result, the crystallinity, thickness, concentration of various impurities, and the like of the GaN crystal constituting the semiconductor layer 20 can be controlled with high accuracy, and can be made uniform in the main surface of the substrate 10.

Specifically, for example, the semiconductor layer 20 of the present embodiment is formed by the following procedure.

First, the substrate 10 is carried into the processing chamber of the MOVPE apparatus (not shown).

At this time, as shown in FIGS. 10A and 10B, the substrate 10 is placed on the holding member 300. The holding member 300 has, for example, three convex portions 300p, and the three convex portions 300.
It is configured to hold the substrate 10 by p. As a result, when the substrate 10 is heated, the substrate 10 can be heated mainly by irradiating the substrate 10 with infrared rays instead of transferring heat from the holding member 300 to the substrate 10. Here, when the substrate 10 is heated by heat transfer from a plate-shaped holding member (or when heat transfer is performed in combination), the substrate 10 is subjected to the surface state depending on the back surface state of the substrate 10 and the surface state of the holding member. It becomes difficult to heat uniformly over the entire area. Further, the substrate 10 may be warped as the substrate 10 is heated, and the contact condition between the substrate 10 and the holding member may gradually change. Therefore, the substrate 10
The heating conditions may be non-uniform over the entire in-plane area. On the other hand, in the present embodiment, such a problem is solved by using the holding member 300 as described above and heating the substrate 10 mainly by irradiating the substrate 10 with infrared rays. The substrate 10 can be heated stably and uniformly in the main surface.

In order to reduce the influence of heat transfer, the convex portion has a size such that the contact area between the convex portion 300p and the substrate 10 is 5% or less, preferably 3% or less of the supported surface of the substrate 10. 30
It is preferable to properly select the shape and dimensions of 0p.

After the substrate 10 is placed on the holding member 300, hydrogen gas and NH ₃ gas (further N ₂ gas) are supplied into the processing chamber of the MOVPE apparatus, and the substrate 10 is supplied from a predetermined heating source (for example, a lamp heater). The substrate 10 is heated by irradiating with infrared rays. When the temperature of the substrate 10 becomes a predetermined growth temperature (e.g., 1000 ° C. or higher 1100 ° C. or less), for example, trimethyl gallium (TMG) as a group III metal organic raw materials, and NH ₃ gas as group V source, on the substrate 10 Supply to. At the same time, for example, supplying a SiH ₄ gas to the substrate 10 as n-type impurity material. As a result, the base n-type semiconductor layer 2 as the n-type GaN layer is placed on the substrate 10.
1 is epitaxially grown.

Next, the drift layer 22 as an n-type GaN layer containing an n-type impurity having a lower concentration than that of the base n-type semiconductor layer 21 is epitaxially grown on the base n-type semiconductor layer 21.

When the growth of the drift layer 22 is completed, the supply of the group III organic metal raw material and the heating of the substrate 10 are stopped. Then, when the temperature of the substrate 10 becomes 500 ° C. or lower, the supply of the group V raw material is stopped. Thereafter, the atmosphere in the processing chamber of the MOVPE apparatus causes return to substituted to atmospheric pressure to N ₂ gas, after reducing the processing chamber to a substrate unloading temperature capable, the substrate after growth 10
Is taken out of the processing room.

As a result, the nitride semiconductor laminate 1 of the present embodiment configured as shown in FIG. 1 is manufactured.

Here, in the production of the nitride semiconductor laminate 1, the case where the substrate preparation step (S110) and the semiconductor layer growth step (S120) are performed is taken as an example, but in addition to each of these steps, for example, annealing is given. You may go through the process.

In the annealing step, for example, the substrate 10 is irradiated with at least infrared rays in an atmosphere of an inert gas by a predetermined heat treatment device (not shown) to anneal the nitride semiconductor laminate 1. Thereby, for example, activation of the semiconductor layer 20 constituting the nitride semiconductor laminate 1 and recovery of crystal damage can be performed.

At this time, if the substrate 10 satisfies the above requirements for the absorption coefficient in the infrared region, the substrate 10 can be stably heated by irradiating the substrate 10 with infrared rays, and the temperature of the substrate 10 can be controlled accurately. Further, the heating efficiency due to the irradiation of infrared rays can be made uniform in the main surface of the substrate 10. As a result, the degree of activation (activation rate, free hole concentration) of impurities in the semiconductor layer 20 can be controlled with high accuracy, and can be made uniform in the main surface of the substrate 10.

Further, at this time, if the holding member 300 shown in FIGS. 10A and 10B is used to heat the substrate 10, the heat is not transferred from the holding member 300 to the substrate 10, but mainly to the substrate 10. The substrate 10 can be heated by irradiating with infrared rays. As a result, the substrate 10
Can be heated stably and uniformly in the main surface.

(2-iii) Film Thickness Measurement Step After the nitride semiconductor laminate 1 is manufactured through the substrate preparation step (S110) and the semiconductor layer growth step (S120), the film thickness measurement step (S130) is then performed. Film thickness measurement step (S1
In 30), the film thickness of the semiconductor layer 20 constituting the nitride semiconductor laminate 1 is measured.

If the film thickness of the semiconductor layer 20 is measured in the film thickness measuring step (S130), the semiconductor layer 2 is measured.
It becomes possible to strictly control the film thickness with respect to 0. Specifically, for example, the semiconductor layer 20
The quality of the produced nitride semiconductor laminate 1 can be determined by measuring the film thickness of the product and comparing it with a predetermined reference value. Further, for example, it is conceivable to determine the suitability of various processing conditions when manufacturing the nitride semiconductor laminate 1 based on the measured value obtained in the film thickness measuring step (S130).

In the film thickness measurement step (S130) in the present embodiment, the film thickness of the semiconductor layer 20 is measured by using the FT-IR method, which is a method capable of measuring the film thickness in a non-contact and non-destructive manner.
The details of the film thickness measuring method by the FT-IR method will be described below.

(3) Film Thickness Measuring Method by FT-IR Method As shown in FIG. 11, the film thickness measuring method according to the present embodiment is at least a pretreatment step (S).
210), a measurement step (S220), a spectrum analysis step (S230), and a film thickness value identification and output step (S240) based on the analysis result. Pretreatment step (S210)
Has a process of specifying various data related to the substrate (S211), a process of specifying a baseline by calculation (S212), and a registration step (S213) as a reference. Further, the measurement step (S220) includes a measurement target setting step (S221) and an infrared light irradiation step (S2).
22) and a step of acquiring a reflection spectrum (S223). Hereinafter, each of these steps will be described in order.

(3-i) Pretreatment Step In the pretreatment step (S210), a treatment that needs to be performed in advance for film thickness measurement by the FT-IR method is performed as a pretreatment prior to the measurement step (S220). ..

(Modeling of dielectric function)
Here, first, modeling of the dielectric function of the measurement object (sample), which is a premise of the pretreatment step (S210), will be described. The dielectric function of the sample is required for data analysis, but if the dielectric function of the sample is unknown, it is necessary to model the dielectric function.

The object to be measured is an intermediate 1 constituting the Schottky barrier diode (SBD).
Specifically, it is a nitride semiconductor laminate 1 in which a semiconductor layer 20 is formed on a substrate 10.
The nitride semiconductor laminate 1 has a two-layer structure in which the semiconductor layer 20 is a base n-type semiconductor layer 21 and a drift layer 22. Regarding the nitride semiconductor laminate 1 having such a laminated structure, the relationship between light reflection and transmission is as shown in the optical model shown in FIG. 12 (a).
However, in the nitride semiconductor laminate 1 having such a laminated structure, for example, when light is incident on a material having a high refractive index to a material having a low refractive index, almost no reflection occurs at the interface of each layer. so that,
The nitride semiconductor laminate 1 to be measured can be simplified as shown in FIG. 12 (b) instead of the optical model shown in FIG. 12 (a).
Hereinafter, the nitride semiconductor laminate 1 to be measured will be considered as being approximated to an optical model composed of _{medium N 0} / epi layer N ₁ / substrate N _{2 as shown in FIG. 12 (b).}

In such an optical model, the amplitude reflection coefficient of the sample, the r ₀₁₂ in consideration of the multiple reflection in the epitaxial layer N _1. This amplitude reflectance coefficient r ₀₁₂ is calculated by the following equation (5) using the Fresnel equation.
) Can be obtained.

The phase change β in the equation (5) can be obtained by the following equation (6). In addition, it should be noted.
In the formula (6), θ ₁ and θ ₀ are both incident angles of light (see FIG. 12). Further, N ₁ is the complex refractive index of the epi layer.

As described above, for the nitride semiconductor laminate 1 to be measured, consider a simplified optical model as shown in FIG. 12B, and use a virtual substrate approximation that considers only the dielectric function of the uppermost layer. Therefore, the analysis can be performed relatively easily.
Here, although not detailed description, when the analysis, but also to primary reflection coefficient r ₀₂ from the primary reflection coefficient r ₀₁ and the substrate N ₂ in the absence of the epitaxial layer N ₁ from the surface of the epitaxial layer N ₁ , The calculation shall be performed using a known calculation formula.

By the way, the reflection of light is determined by the complex permittivity or the complex refractive index of a substance. Further, the light is classified into p-polarized light and s-polarized light according to the direction of the electric field of the light incident on the sample, and each exhibits different reflection.

Fresnel equation for the amplitude reflection coefficient r _p for p-polarized light component, the following equation (7).

Further, the Fresnel equation for the amplitude reflectance coefficient _s of the s polarization component is as shown in the following equation (8).

However, in equations (7) and (8), θ _i is the angle of incidence of light from the medium i. Further, N _ti is a complex refractive index of light incident on the medium t from the medium i, and is defined by the following equation (9). In equation (9), n is the real part of the complex refractive index, k is the extinction coefficient, and k> 0.
Is.

In addition, there is a close relationship between the permittivity and the refractive index of a substance, and the complex permittivity ε is calculated by the following equation (
It is defined in 10).

The square of the amplitude reflectance r obtained from the Fresnel equation as described above is the intensity reflectance R.
Specifically, for example, in the case of vertical incidence (θi = 0 °), the medium N ₀ is a vacuum (N = 1-i).
If it is 0), the interfacial reflectance R with the dielectric (N = n−ik) is as shown in the following equation (11).

On the other hand, for example, in the case of non-vertical incidence (θi ≠ 0 °), the amplitude reflectance coefficients r _{01, p} , r _{01, S} , r _{012, p} , r _{012 and S} are calculated for the p-polarized light component and the s-polarized light component, respectively. Then, the interfacial reflectance R with the dielectric (N = n-ik) becomes as shown in the following equation (12).

By the way, the complex permittivity ε is also defined by the following equation (13) in addition to the above equation (10).

Then, from the above two equations (9) and (13), the following equations (14) and (15)
It turns out that holds true.

Based on each of these equations, the complex refractive index N is given by the following equations (16) and (17) using the value of the complex permittivity.

Based on the relationships defined by the above equations, the dielectric function model that should be applied to the analysis of the optical model is examined. Since there is free carrier absorption, Drude (Dr.
It is conceivable to apply the ude) model or the Lorentz-Drude model.

The Drude model is a model that considers only free carrier absorption, and the permittivity ε can be obtained by the following equation (18).

On the other hand, the Lorenz-Drude model is a model that considers not only free carrier absorption but also coupling with LO phonons, and the permittivity ε can be obtained by the following equation (19).

In the above equation (18) or (19), ε _∞ is the high frequency permittivity. ω _p
, Ω _LO and ω _TO are plasma frequency, LO phonon frequency and TO phonon frequency, respectively. Both γ and Γ are damping constants. In Eq. (19), the attenuation constants of LO phonons and TO phonons are assumed to be _{Γ = Γ LO} = Γ _TO. The plasma frequency ω _p is given by the following equation (20), and the attenuation constant γ is given by the following equation (21).

In the above formula (20) or (21), m ^* represents the effective mass of the sample. Further, in the equation (21), μ is the drift mobility.

As described above, in the present embodiment, the measurement object (sample) is simplified as in the optical model shown in FIG. 12 (b), and then at least one of the Drude model and the Lorenz-Drude model as the dielectric function model. Decide to apply. Then, using at least one of the Drude model and the Lorenz-Drude model, the processing of each step described below is performed. It should be noted that which of the Drude model and the Lorenz-Drude model is applied, or whether both of them are applied is not particularly limited and may be appropriately determined.

(S211: Specific process of various data related to the substrate)
After specifying the dielectric function model as described above, first, various data required for performing arithmetic processing using the dielectric function model are specified. Specifically, various data required for arithmetic processing using the above equation (18) or (19) are specified.

The various data to be specified here correspond to, for example, physical property values (characteristic values) for each of _{the substrate N 2} and the epi layer N _{1 constituting the optical model shown in FIG. 12 (b).} However, the substrate N ₂ and the epi layer N ₁ are the substrate 10 and the drift layer 22 in the nitride semiconductor laminate 1.
Is a model of. Therefore, various data to be specified can be specified based on the physical property values (characteristic values) of the substrate 10 and the drift layer 22.

At this time, as described above, the substrate 10 has a low dislocation density.
Moreover, the absorption coefficient in the infrared region satisfies a predetermined requirement. That is, the substrate 1
0 is configured with high controllability of the free carrier concentration, which makes the reliability of various physical property values (characteristic values) high. The same can be said for the drift layer 22 epitaxially grown on the substrate 10. Therefore, the substrate 10
If various data required for arithmetic processing using the dielectric function model are specified based on the physical property values (characteristic values) of the drift layer 22 and the drift layer 22, the various data are real objects (that is, manufactured nitride semiconductors). It conforms to the laminate 1) and is extremely reliable.

Examples of various data specified here include the following specific examples when the substrate 10 and the semiconductor layer 20 are made of GaN crystals.
Specifically, for example, in the case of applying the Drude model, ε _∞ = 5.35, _{m e}
= 0.22, ω _{p_sub} = 390.4 cm ^-1 (μ = 320 cm ² V ^-1 s ^-1 ), ω
_{p_epi} = 23.1 cm ^-1 (μ = 1200 cm ² V ^-1 s ^-1 ), γ _sub = 132
.. There are things like ^{_{6cm -1, γ epi = 35.4cm -1}} .
Also, for example, when applying the Lorenz-Drude model, ε _∞ = 5.35.
_{, M e = 0.22, ω LO} = 746cm -1, ω TO = 560cm -1, ω p_sub =
390.4 cm ^-1 (μ = 320 cm ² V ^-1 s ^-1 ), ω _{p_epi} = 23.1 cm ^−
1 (μ = 1200 cm ² V ^-1 s ^-1 ), Γ = Γ _LO = Γ _TO = 1.27 cm ^-1 , γ _{s
There are ub} = 132.6 cm ^-1 and γ _epi = 35.4 cm ^-1 .
The various data given as specific examples here correspond to the physical property values peculiar to GaN or the values calculated based on the physical property values by the calculation using each of the above equations. That is, all the data are values that are uniquely determined if they are GaN crystals.
In the present embodiment, when the data is calculated by calculation, the carrier concentration of the epitaxial layer is obtained in advance by CV measurement, and the value is used as a constant (fixed) fitting parameter. .. Even in that case, for example, the free carrier concentration of the substrate 10 is ^{about 1.0 to 1.5 × 10 18} cm ^-3 , and the free carrier concentration of the semiconductor layer 20 which is a homoepitaxial layer is 2.0 × 10 ¹⁸ Considering that each is controlled very high, such as about cm- ^3, the various data obtained by the data calculation are very reliable.
As described above, in the present embodiment, after obtaining the expected carrier concentration, various data are specified, and then the film thickness is measured by the FT-IR method as described later. This is
For example, if the accuracy of the FT-IR measurement itself is improved in the future, it is suggested that the carrier concentration and the film thickness may be obtained by the measurement respectively.

(S212: Baseline identification process by calculation)
After specifying the various data as described above, the operation processing by the dielectric function model is subsequently performed using the specified various data.

In the arithmetic processing by the dielectric function model, first, the refractive index n and the extinction coefficient k for _{the substrate N 2} and the epi layer N _{1 are obtained.}

Specifically, for example, in the case of applying the Drude model, the arithmetic processing according to the above equation (18) is performed using the various data specified as described above to obtain the dielectric constant ε. Then, using the calculation result and the above equations (13) to (17), the substrate N ₂ and the epi layer N _{1 are used.}
The refractive index n and the extinction coefficient k are obtained for each of the above. The calculation result is, for example, as shown in FIGS. 13 (a) and 13 (b).

Further, for example, in the case of applying the Lorenz-Drude model, the arithmetic processing according to the above equation (19) is performed using various data specified as described above to obtain the dielectric constant ε. Then, using the calculation result and the above equations (13) to (17), the refractive index n and the extinction coefficient k are obtained for each of the _{substrate N 2} and the epi layer N _1. The calculation result is, for example, as shown in FIGS. 14A and 14B.

After obtaining the refractive index n and the extinction coefficient k, the reflectance R is calculated using the calculation result and the above equation (11) or (12), and the reflection spectrum specified from the calculation result is obtained. ..
For example, in the case of vertical incidence (θi = 0 °), the reflection spectrum is as shown in FIG. 15 (a) for the Drude model, and shown in FIG. 15 (b) for the Lorenz-Drude model. It will be something like.
Further, the reflection spectrum is as shown in FIG. 16A for the Drude model, for example, in the case of non-vertical incident (θi ≠ 0), more specifically in the case of θi = 30 °. The Lorenz-Drude model is as shown in FIG. 16 (b).

The reflection spectra as described above are for an _{optical model consisting of medium N 0} / epi layer N ₁ / substrate N ₂ based on the _{reflectance coefficient r 012} (see the solid lines in FIGS. 15 and 16) and the reflectance r. The one about the interface between the medium N ₀ and the epi layer N _{1 based on 01} (see the broken lines in FIGS. 15 and 16), and the medium N ₀ and the substrate based on the reflectance coefficient r _{02 in the absence of the epi layer N 1.} It can be determined for each of the interface with N ₂ (see the dotted line in FIGS. 15 and 16). Among these, those for the interface of the substrate N ₂ based on the reflection coefficient r ₀₂ is, will correspond to the baseline as a reference when analyzing the reflection spectrum by FT-IR method.

That is, in the present embodiment, _{the reflection spectrum when the substrate N 2} is a single substance is obtained by arithmetic processing such as simulation, and the reflection spectrum is specified as a baseline used for film thickness measurement by the FT-IR method.

As described above, such a baseline is specified based on the physical property value (characteristic value) of the substrate 10. The substrate 10 is configured to have high controllability of the free carrier concentration, whereby the reliability of various physical property values (characteristic values) is high. As described above, since various data used for specifying the baseline are highly reliable, in the present embodiment, the baseline can be reliably specified by using arithmetic processing such as simulation. is there.

In addition, in FIG. 16, the optical model to be analyzed is actually F for a laminate having the same configuration.
The reflection spectrum obtained by measuring by the T-IR method is also shown (see the arrow "FT-IR" in the figure). The reflection spectrum is shown in the medium N ₀ / epi layer N.
Compared with the reflection spectrum of the optical model consisting of _{1 /} substrate N ₂ (see the solid line in the figure), it can be seen that each is approximated (in particular, the Lorentz shown in FIG. 16 (b) - if the Drude model) .. From this, it can be seen that the reflection spectrum obtained by the arithmetic processing in the present embodiment is extremely reliable.

Incidentally, for the reflection spectrum described above, as is done in the film thickness measurement by FT-IR method, which by Fourier transform, it may be subjected to calculation of the film thickness of the epitaxial layer N ₁ is there. Specifically, the example of FIG. 15 or FIG. 16, when calculating the thickness of the epitaxial layer _{N 1,} the film thickness _d epi = 13.6 .mu.m next For Drude model, Lorentz - in the case of Drude model thickness _{d epi} = 12.87 μm. In this way, the difference in the calculation results between the models is due to the fact that the Drude model does not have the LO phonon term, so the refractive index n is larger and the film thickness is calculated thicker than in the Lorenz-Drude model. Inferred. Further, as a practical point to be noted, as is clear from FIG. 16A, in the case of the Drude model, the value fluctuates depending on the wave number range used for the film thickness calculation. With this tendency in mind, it may be decided whether to apply the Drude model or the Lorenz-Drude model, or both.

(S213: Registration process as a reference)
After specifying the baseline as described above, the data related to the specified baseline is then used as reference data (reference data) used in the film thickness measurement by the FT-IR method, and the reference data is registered.

The reference data may be registered by storing the reference data in a memory unit included in the FT-IR measuring device described later, or by storing the reference data in an external storage device accessible to the FT-IR measuring device.

When the registration of the reference data is completed, the preprocessing step (S210) is completed.

(3-ii) Measurement step After the pretreatment step (S210) is completed, the measurement step (S220) can be performed thereafter. In the measurement step (S220), the nitride semiconductor laminate 1 to be measured is subjected to a reflection spectrum acquisition process required for film thickness measurement by the FT-IR method. The reflection spectrum acquisition process is performed using an FT-IR measuring device.

(Overview of FT-IR measuring device)
Here, the outline of the FT-IR measuring device 50 will be briefly described.
As shown in FIG. 17, the FT-IR measuring device 50 includes a light source 51 that emits light in the infrared region (IR), a half mirror 52, a fixed mirror 53 that is fixedly arranged, and a movable movement that is arranged so as to be movable. It is configured to include a mirror 54, a reflection mirror 55, a detector 56 that receives and detects light, and an analysis control unit 57 including a computer device connected to the detector 56.

In the FT-IR measuring device 50 having such a configuration, the light from the light source 51 is the half mirror 52.
It is obliquely incident on the surface and is divided into two luminous fluxes, transmitted light and reflected light. The two luminous fluxes are reflected by the fixed mirror 53 and the moving mirror 54, respectively, return to the half mirror 52, and are combined again to generate an interference wave (interferogram). At this time, different interference waves can be obtained depending on the position (optical path difference) of the moving mirror 54. The obtained interference wave is the reflection mirror 5
The optical path is changed by 5, and the object to be measured (specifically, the nitride semiconductor laminate 1) is irradiated. Then, the reflected light (or transmitted light) generated by the object to be measured in response to the irradiation of the interference wave is
After the optical path is changed by the reflection mirror 55 again, the light is received by the detector 56 and detected. After that, the detection result of the detector 56 is analyzed by the analysis control unit 57. Specifically, as will be described in detail later, the analysis control unit 57 performs spectrum analysis using the Fourier transform.

Hereinafter, the measurement step (S220) performed by using the FT-IR measuring device 50 having such a configuration will be specifically described.

(S221: Setting process of measurement target)
In the measurement step (S220), first, the nitride semiconductor laminate 1 to be measured is subjected to.
It is set at the irradiated portion of the interference wave in the FT-IR measuring device 50. The method for setting the nitride semiconductor laminate 1 to the irradiated portion is not particularly limited as long as it conforms to the specifications of the FT-IR measuring device 50. That is, the nitride semiconductor laminate 1 which is the object to be measured depends on the specifications and configuration of the sample mounting table (not shown) in the FT-IR measuring device 50.
All you have to do is set.

(S222: Infrared light irradiation step)
After setting the nitride semiconductor laminate 1, the light source 51 subsequently emits light in the infrared region (IR), and the moving mirror 54 is appropriately moved to obtain an interference wave (interferogram).
Is generated, and the interference wave is applied to the nitride semiconductor laminate 1. As a result, the nitride semiconductor laminate 1 emits reflected light corresponding to the interference wave.

(S223: Reflection spectrum acquisition step)
After that, the detector 56 receives the reflected light emitted from the nitride semiconductor laminate 1 and detects it. That is, the film thickness is measured by the FT-IR method by observing the interference waveform (interferogram) of the reflected light from the nitride semiconductor laminate 1 as a function of space or time by receiving and detecting the light received by the detector 56. The reflection spectrum required for this is obtained from the nitride semiconductor laminate 1. The reflection spectrum referred to here is a plot of the amount of light reflected when the nitride semiconductor laminate 1 is irradiated with an interference wave with respect to a wavelength (wave number).

By the way, as described above, the nitride semiconductor laminate 1 which is the object to be measured is the substrate 10.
Has a low dislocation and has a dependency between the carrier concentration and the absorption coefficient in the infrared region. The same applies to the semiconductor layer 20 homoepitaxially grown on the substrate 10.

Therefore, in the case of the nitride semiconductor laminate 1 of the present embodiment, the reflection spectrum obtained by irradiating the interference wave reflects the influence of the interference wave. Specifically, the reflection spectrum has a fringe pattern, which is a pattern representing the existence of fringes (interference fringes) in which a portion having a large amount of light and a portion having a small amount of light alternately occur due to the interference of light.

If the acquired reflection spectrum has a fringe pattern, the film thickness of the nitride semiconductor laminate 1 which is the object to be measured can be measured by analyzing the fringe pattern, that is, the FT-IR method can be used. It is possible to measure the film thickness used.

In this way, when the reflection spectrum having the fringe pattern is acquired from the nitride semiconductor laminate 1 which is the measurement target, the measurement step (S220) is completed.

(3-iii) Spectrum analysis step After the measurement step (S220) is completed, the spectrum analysis step (S230) is then performed.
In the spectrum analysis step (S230), the reflection spectrum acquired in the measurement step (S220) is subjected to a Fourier transform using the reference data registered in the preprocessing step (S210) to mathematically convert the wavelength (wavenumber) component. Perform analysis (analysis) processing to separate.

Specifically, in the spectrum analysis step (S230), the following analysis processing is performed. First, the reflection spectrum acquired from the nitride semiconductor laminate 1 is used as a sample spectrum, and the baseline (reflection spectrum) specified by the reference data is used as a background spectrum. Then, Fourier transform is applied to each of the sample spectrum and the background spectrum to obtain each single beam spectrum (SB), and then the intensity of the sample spectrum is backgrounded based on, for example, the following equation (22). The reflection interference pattern is calculated by dividing by the intensity of the spectrum.

(Sample SB) / (Background SB) x 100 = Reflect interference pattern ...
(22)

Based on the reflection interference pattern calculated in this way, the semiconductor layer 20 (specifically, for example, the semiconductor layer) in the nitride semiconductor laminate 1 is determined from the fringe interval of the reflection interference pattern in the near infrared region. It is possible to estimate the film thickness of the drift layer 22) constituting 20.

(3-iv) Identification and Output Step of Film Thickness Value Based on Analysis Results After completion of the spectrum analysis step (S220), the film thickness value identification and output step (S240) based on the analysis result is then performed.

In the identification and output step (S240) of the film thickness value based on the analysis result, first, based on the reflection interference pattern obtained as the analysis result in the spectrum analysis step (S220), the semiconductor layer 20 (for example, the semiconductor layer 20) in the nitride semiconductor laminate 1 is used. , The thickness value of the drift layer 22) is specified. Specifically, in the reflection interference pattern calculated in the spectrum analysis step (S220), there are bursts that appear when light is strengthened by interference, and the distance between the bursts corresponds to the optical path difference of each reflected light component. Therefore, the film thickness value of the semiconductor layer 20 (for example, the drift layer 22) is specified by dividing the distance between the bursts by the value of the refractive index of the semiconductor layer 20.

Then, after the film thickness value of the semiconductor layer 20 is specified, the specified film thickness value is output thereafter. The film thickness value may be output by using, for example, a display unit (not shown) included in the FT-IR measuring device 50, a printer device (not shown) connected to the FT-IR measuring device 50, or the like.

By outputting the film thickness value in this way, the FT-IR measuring device 5 with reference to the output result
The user of 0 can recognize the measurement result of the film thickness of the semiconductor layer 20 in the nitride semiconductor laminate 1. That is, the film thickness of the semiconductor layer 20 of the nitride semiconductor laminate 1 can be measured by using the FT-IR method.

(4) Effects obtained by the present embodiment According to the present embodiment, one or more of the following effects can be obtained.

(A) In the present embodiment, a substrate 10 having a dependency between the carrier concentration and the absorption coefficient in the infrared region is used, and the semiconductor layer 20 is homoepitaxially grown on the substrate 10.
It constitutes the nitride semiconductor laminate 1. Therefore, for the nitride semiconductor laminate 1, the absorption coefficient in the infrared region differs depending on the difference in carrier concentration between the substrate 10 and the semiconductor layer 20, and the FT-IR method is used. It is possible to measure the film thickness.

More specifically, in the present embodiment, the dislocation density of the substrate 10 is, for example, 5 × 10 ⁶ pieces /
It ^{has low dislocations such as cm 2} or less, and the substrate 10 satisfies a predetermined requirement for the absorption coefficient in the infrared region, whereby there is a dependency between the carrier concentration in the substrate 10 and the absorption coefficient in the infrared region. It has become a thing. Further, the semiconductor layer 20 is also homoepitaxially grown on the substrate 10, so that the GaN crystals constituting the semiconductor layer 20 are similar to the GaN crystals constituting the substrate 10. That is, even if there is a difference in carrier concentration between the semiconductor layer 20 and the substrate 10, the semiconductor layer 20 has low dislocations and has a dependency between the carrier concentration and the absorption coefficient in the infrared region, as in the substrate 10. Will have.
Therefore, in the case of the nitride semiconductor laminate 1 of the present embodiment, for example, 1 × 10 ¹⁷ cm ^{−.
Even if the carrier concentration is as low as 3} or less, the absorption coefficient in the infrared region will differ depending on the difference in carrier concentration between the substrate 10 and the semiconductor layer 20, and as a result, the FT-IR method will be used. It is possible to measure the film thickness using.

As described above, according to the present embodiment, the semiconductor layer 20 which is a homoepitaxial film of the group III nitride semiconductor crystal has carriers even in the case of a low carrier concentration of ^{, for example, 1 × 10 17} cm ^{-3 or less.} The absorption coefficient of IR becomes different depending on the concentration, and FT
The film thickness can be measured non-contact and non-destructively using the -IR method. Therefore, it is very useful for controlling the film thickness of the semiconductor layer 20, and through the film thickness control, it contributes to the improvement of characteristics and reliability of the semiconductor device configured by using the nitride semiconductor laminate 1. Can be realized.

(B) In particular, as described in the present embodiment, the substrate 10 satisfies the relationship approximated by the above formula (1), that is, the dependence on the substrate 10 is defined by the above formula (1). _{If so, the relationship between the carrier concentration Ne} and the absorption coefficient α is surely established even in the semiconductor layer 20 homoepitaxially grown on the substrate 10. Therefore, even at low carrier concentration of, for example, 1 × ¹⁰ 17 ^{cm -3} or less, in a wavelength range of at least 1μm or 3.3 [mu] m, a difference in the absorption coefficient α occurs depending on reliably carrier density _{N e} As a result, it becomes very suitable for measuring the film thickness using the FT-IR method.

The reason why the substrate 10 satisfies the relationship approximated by the above formula (1) is that the substrate 10 has a small crystal strain and impurities other than O and n-type impurities (for example, impurities compensating for n-type impurities and the like). ) Is almost not included. Accordingly, the substrate 10 of the present embodiment, approximated by the absorption coefficient alpha in a wavelength range of at least 1μm or 3.3μm using a predetermined constant K and the constant a formula _{(1) (α = N e} Kλ a) can do.

For reference, in a GaN crystal produced by a conventional production method, it is difficult to accurately approximate the absorption coefficient α by using the above-defined constant K and constant a according to the above equation (1).

Here, FIG. 6B is a diagram comparing the relationship of the absorption coefficient at a wavelength of 2 μm with respect to the free electron concentration. FIG. 6B shows not only the absorption coefficient of the GaN crystal produced by the production method of the present embodiment, but also the absorption coefficient of the GaN crystal described in the papers (A) to (D).
Paper (A): A. S. Barker Physical Review B 7 (
1973) p743 Fig. 8
Paper (B): P.I. Perlin, Physics Review Letter
75 (1995) p296 Fig. Estimated from a curve of 1 0.3 GPa.
Paper (C): G.M. Bentoumi, Medical Science En
gineering B50 (1997) p142-147 Fig. 1
Paper (D): S.A. Pourowski, J. et al. Crystal Growth 18
9-190 (1998) p. 153-158 Fig. 3 However, T = 12K

As shown in FIG. 6B, the absorption coefficient α of the conventional GaN crystals described in the papers (A) to (D) is larger than the absorption coefficient α of the GaN crystal produced by the production method of the present embodiment. It was. Further, the slope of the absorption coefficient α in the conventional GaN crystal was different from the slope of the absorption coefficient α in the GaN crystal produced by the production method of the present embodiment. The treatises (A) and (
In C), it seems that the slope of the absorption coefficient α _{changes as the free electron concentration Ne increases.} Therefore, in the conventional GaN crystals described in the papers (A) to (D), it is difficult to accurately approximate the absorption coefficient α by the above equation (1) using the above-specified constants K and a. there were. Specifically, for example, there is a possibility that the constant K is higher than the above-specified range, or the constant a is a value other than 3.

This is considered to be due to the following reasons. It is considered that a large crystal strain was generated in the conventional GaN crystal due to the manufacturing method thereof. When crystal strain occurs in a GaN crystal, many dislocations occur in the GaN crystal. Therefore, in the conventional GaN crystal, dislocation scattering occurs, and it is considered that the absorption coefficient α becomes large or varies due to the dislocation scattering. Alternatively, it is considered that the concentration of O mixed unintentionally was high in the GaN crystal produced by the conventional production method. When O is mixed in a GaN crystal at a high concentration, Ga
The lattice constants a and c of the N crystal increase (Reference: Chris G. Van de W)
alle, Physical Review B vol. 68, 165209 (
2003)). Therefore, in the conventional GaN crystal, it is considered that a local lattice mismatch occurs between the portion contaminated by O and the portion having a relatively high purity, and crystal strain occurs in the GaN crystal. As a result, it is considered that the absorption coefficient α of the conventional GaN crystal is large or varies. Alternatively, it is considered that in the GaN crystal produced by the conventional production method, the p-type compensating impurity compensating for the n-type impurity was unintentionally mixed and the concentration of the compensating impurity was increased. When the concentration of compensating impurities is high, a high concentration of n-type impurities is required to obtain a predetermined free electron concentration. Therefore, it is considered that in the conventional GaN crystal, the total impurity concentration including the compensating impurity and the n-type impurity is high, and the crystal strain is large. As a result, it is considered that the absorption coefficient α of the conventional GaN crystal is large or varies. It has been confirmed that the GaN free-standing substrate actually containing O and having a distorted lattice has a higher absorption coefficient α (lower mobility) than the substrate 10 of the present embodiment having the same free electron concentration. ..

For this reason, in the conventional GaN crystal, it is difficult to accurately approximate the absorption coefficient α by using the above-mentioned constant K and the constant a by the above equation (1). In other words
In the conventional GaN crystal, it is difficult to accurately design based on absorption coefficient on the free electron density N _e. For this reason, in a conventional substrate made of GaN crystals, the heating efficiency tends to vary depending on the substrate in the process of irradiating the substrate with at least infrared rays to heat the substrate.
It was difficult to control the temperature of the substrate. As a result, the reproducibility of the temperature of each substrate may be low.

On the other hand, the substrate 10 manufactured by the manufacturing method of the present embodiment has a small crystal strain and has a small crystal strain.
In addition, it is in a state of containing almost no impurities other than O and n-type impurities. The absorption coefficient of the substrate 10 of the present embodiment is less affected by scattering (dislocation scattering) caused by crystal strain, and is mainly dependent on ionized impurity scattering. As a result, the variation in the absorption coefficient α of the substrate 10 can be reduced, and the absorption coefficient α of the substrate 10 can be set to the above equation by using a predetermined constant K and a constant a.
It can be approximated by 1). By absorption coefficient of the substrate 10 alpha can be approximated by the equation (1), well absorption coefficient of the substrate 10, based on the free electron density N _e caused by doping n-type impurities into the substrate 10 precision Can be designed. By precisely designed based absorption coefficient of the substrate 10 to the free electron concentration N _e, at least in the step of heating the infrared rays irradiated substrate 10, it is possible to easily set the heating conditions for the substrate 10 , The temperature of the substrate 10 can be controlled with high accuracy. As a result, the temperature reproducibility of each substrate 10 can be improved. In this way, in the present embodiment, the substrate 10 can be heated with high accuracy and reproducibility.

(C) In the present embodiment, in the film thickness measurement using the FT-IR method, after specifying the dielectric function model for the substrate 10 satisfying the above formula (1), the substrate 10 is based on the specified dielectric function model. The reflection spectrum (baseline) when is a single unit is obtained by arithmetic processing, and the obtained reflection spectrum is used as reference data (reference data).
That is, the substrate 10 has low dislocations and is of high quality, and the carrier concentration N in the substrate 10 is N.
_e is high controllability of the relationship between the absorption coefficient α from (i.e., a high reliability of the carrier concentration N _e) that, the reflection spectrum as a base line can be obtained by the arithmetic processor (simulation). Therefore, when measuring the film thickness using the FT-IR method, the reflection spectrum is obtained from the dielectric function model and the carrier concentration and the calculated value is used as a reference. Therefore, for example, it is not necessary to actually measure the reflection spectrum as a reference from the substrate alone. , It is possible to improve the efficiency of the film thickness measurement.

(D) In the present embodiment, the crystal of the group III nitride semiconductor is a GaN crystal, so-called Ga.
The film thickness of the N-on-GaN substrate is measured by using the FT-IR method. That is, according to the present embodiment, GaN-on-, which was conventionally considered to be difficult to measure the film thickness in principle.
Even with a GaN substrate, it is possible to measure the film thickness using the FT-IR method.

(E) The nitride semiconductor laminate 1 in the present embodiment has a fringe pattern in the reflection spectrum obtained by irradiating the semiconductor layer 20 on the substrate 10 with infrared light by the FT-IR method. .. In this way, if there is a fringe pattern in the reflection spectrum, the film thickness of the semiconductor layer 20 can be measured by analyzing the fringe pattern, that is, the film thickness measurement using the FT-IR method can be performed. It becomes possible to do. Therefore, the nitride semiconductor laminate 1 in the present embodiment can measure the film thickness in a non-contact and non-destructive manner by using the FT-IR method, and the nitride semiconductor laminate 1 is nitrided through the film thickness control based on the measurement result. Material Semiconductor laminate 1
It is possible to contribute to the improvement of characteristics and reliability of the semiconductor device constructed by using the above.

<Other Embodiments>
The embodiments of the present invention have been specifically described above. However, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist thereof.

In the above-described embodiment, the case where the film thickness measurement using the FT-IR method is mainly performed has been described as an example, but the present invention is not limited thereto. For example, when the nitride semiconductor laminate 1 is constructed using the substrate 10 described in the above-described embodiment, the TO phonon (560c) is used.
Since the ^{extinction coefficient k becomes relatively large on the lower wavenumber side than m -1} ) due to free carrier absorption, the film thickness can be measured not only by the FT-IR method but also by the infrared spectroscopic ellipsometry method. It is possible. The infrared spectroscopic ellipsometry method is one of the optical measurement methods, and is a technique for measuring the film thickness or the like by measuring the change in the polarization state due to light reflection in the sample.

In the above-described embodiment, the case where the substrate 10 and the semiconductor layer 20 are each made of GaN has been described, but the substrate 10 and the semiconductor layer 20 are not limited to GaN but are made of crystals of other group III nitride semiconductors. It may be. As another group III nitride semiconductor,
For example, indium nitride (InN), indium gallium nitride (InGaN), and the like can be mentioned. Further, AlN, aluminum gallium nitride (AlGaN), indium gallium nitride (AlInGaN) and the like may be used. As described above, the group III nitride semiconductor includes Al _x In _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1).
) Is included. That is, in the present invention, not only the GaN-on-GaN substrate but also the AlN-o obtained by homoepitaxially growing the AlN layer on, for example, the AlN substrate.
It can be applied to the n-AlN substrate and to the homoepitaxial growth substrate made of other group III nitride semiconductors in exactly the same manner. For those containing Al composition, it is conceivable to measure the film thickness by the spectroscopic ellipsometry method.

In the above-described embodiment, the case where the substrate 10 is produced by using the seed substrate 5 made of a GaN single crystal in the substrate preparation step (S110) has been described, but the substrate 10 may be produced by the following method. For example, a GaN layer provided on a dissimilar substrate such as a sapphire substrate is used as a base layer, and a crystal ingot in which a GaN layer is thickly grown via a nanomask or the like is peeled from the dissimilar substrate, and a plurality of substrates 10 are peeled from the crystal ingot. May be cut out.

In the above-described embodiment, the case where the semiconductor layer 20 is formed by the MOVPE method in the semiconductor layer growth step (S120) has been described, but other vapor phase growth methods such as the HVPE method, the flux method, the amonothermal method, and the like have been described. The semiconductor layer 20 may be formed by the liquid phase growth method of.

In the above-described embodiment, the case where the semiconductor device configured by using the nitride semiconductor laminate 1 is SBD has been described, but if the semiconductor device uses the substrate 10 containing n-type impurities,
It may be configured as another device. For example, the semiconductor device may be a light emitting diode, a laser diode, a junction barrier Schottky diode (JBS), a bipolar transistor, or the like.

<Preferable Aspect of the Present Invention>
Hereinafter, preferred embodiments of the present invention will be added.

(Appendix 1)
According to one aspect of the invention
A film thickness measuring method for measuring the film thickness of a thin film in a nitride semiconductor laminate obtained by homoepitaxially growing a thin film on a substrate composed of crystals of a group III nitride semiconductor.
As the substrate, a substrate having a dependency between the carrier concentration in the substrate and the absorption coefficient in the infrared region is used.
A film thickness measuring method for measuring the thickness of the thin film by using Fourier transform infrared spectroscopy or infrared spectroscopic ellipsometry is provided.

(Appendix 2)
In the film thickness measuring method described in Appendix 1, preferably
The dependence on the substrate is that the wavelength is λ (μm), the absorption coefficient of the substrate at 27 ° C is α (cm ^-1 ), and the carrier concentration in the substrate is _Ne (cm ^-3 ), K and a. When each is a constant, the absorption coefficient α in a wavelength range of at least 1 μm or more and 3.3 μm or less is approximated by the following equation (1).
^{_{α = N e Kλ a ··· (}} 1)
(However, 2.0 × 10 ^-19 ≦ K ≦ 6.0 × 10 ^-19 , a = 3)

(Appendix 3)
In the film thickness measuring method described in Appendix 2, preferably
After specifying the dielectric function model for the substrate satisfying the equation (1), the reflection spectrum when the substrate is a single unit is obtained by arithmetic processing based on the specified dielectric function model.
The obtained reflection spectrum is used as a reference when measuring the film thickness by the Fourier transform infrared spectroscopy or the infrared spectroscopic ellipsometry method.

(Appendix 4)
In the film thickness measuring method according to any one of Appendix 1 to 3, preferably.
The crystal of the group III nitride semiconductor is a gallium nitride crystal.

(Appendix 5)
According to another aspect of the invention
A method for producing a nitride semiconductor laminate in which a thin film is homoepitaxially grown on a substrate made of group III nitride semiconductor crystals.
As the substrate, a substrate having a dependency between the carrier concentration in the substrate and the absorption coefficient in the infrared region is used, and a growth step of homoepitaxially growing the thin film on the substrate and a growth step.
A measurement step for measuring the film thickness of the thin film formed on the substrate, and
With
In the measuring step, there is provided a method for producing a nitride semiconductor laminate in which the thickness of the thin film is measured by using Fourier transform infrared spectroscopy or infrared spectroscopic ellipsometry.

(Appendix 6)
According to yet another aspect of the invention.
A substrate made of group III nitride semiconductor crystals and
A thin film homoepitaxially grown on the substrate,
With
Provided is a nitride semiconductor laminate having a fringe pattern in a reflection spectrum obtained by irradiating the thin film on the substrate with infrared light by Fourier transform infrared spectroscopy.

(Appendix 7)
In the nitride semiconductor laminate described in Appendix 6, preferably
The substrate has a dependency between the carrier concentration in the substrate and the absorption coefficient in the infrared region.

(Appendix 8)
In the nitride semiconductor laminate described in Appendix 7, preferably
The dependence on the substrate is that the wavelength is λ (μm), the absorption coefficient of the substrate at 27 ° C is α (cm ^-1 ), and the carrier concentration in the substrate is _Ne (cm ^-3 ), K and a. When each is a constant, the absorption coefficient α in a wavelength range of at least 1 μm or more and 3.3 μm or less is approximated by the following equation (1).
^{_{α = N e Kλ a ··· (}} 1)
(However, 2.0 × 10 ^-19 ≦ K ≦ 6.0 × 10 ^-19 , a = 3)

(Appendix 9)
In the nitride semiconductor laminate according to any one of Appendix 6 to 8, preferably.
The crystal of the group III nitride semiconductor is a gallium nitride crystal.

1 ... Nitride semiconductor laminate (intermediate), 10 ... Substrate, 20 ... Semiconductor layer, 21 ... Base n-type semiconductor layer, 22 ... Drift layer

Claims (6)

A film thickness measuring method for measuring the film thickness of a thin film in a nitride semiconductor laminate obtained by homoepitaxially growing a thin film on a substrate composed of crystals of a group III nitride semiconductor.
As the substrate
When the wavelength is λ (μm), the absorption coefficient of the substrate at 27 ° C is α (cm ^-1 ), the carrier concentration in the substrate is _Ne (cm ^-3 ), and K and a are constants, at least The absorption coefficient α in the wavelength range of 1 μm or more and 3.3 μm or less is approximated by the following equation (1) by the least squares method.
At a wavelength of 2 μm, the error of the measured absorption coefficient with respect to the absorption coefficient α obtained from the equation (1) is within ± 0.1α.
A film thickness measuring method for measuring the thickness of the thin film by using Fourier transform infrared spectroscopy or infrared spectroscopic ellipsometry.
^{_{α = N e Kλ a ··· (}} 1)
(However, 1.5 × 10 ^-19 ≦ K ≦ 6.0 × 10 ^-19 , a = 3) After specifying the dielectric function model for the substrate satisfying the equation (1), the reflection spectrum when the substrate is a single unit is obtained by arithmetic processing based on the specified dielectric function model.
The film thickness measuring method according to claim 1, wherein the obtained reflection spectrum is used as a reference when measuring the film thickness by the Fourier transform infrared spectroscopy or the infrared spectroscopic ellipsometry method. The film thickness measuring method according to claim 1 or 2, wherein the crystal of the group III nitride semiconductor is a crystal of gallium nitride. A method for producing a nitride semiconductor laminate in which a thin film is homoepitaxially grown on a substrate made of group III nitride semiconductor crystals.
A growth step of homoepitaxially growing the thin film on the substrate,
A measurement step for measuring the film thickness of the thin film formed on the substrate, and
With
In the growth step, as the substrate,
When the wavelength is λ (μm), the absorption coefficient of the substrate at 27 ° C is α (cm ^-1 ), the carrier concentration in the substrate is _Ne (cm ^-3 ), and K and a are constants, at least The absorption coefficient α in the wavelength range of 1 μm or more and 3.3 μm or less is approximated by the following equation (1) by the least squares method.
At a wavelength of 2 μm, the error of the measured absorption coefficient with respect to the absorption coefficient α obtained from the equation (1) is within ± 0.1α.
In the measurement step, a method for producing a nitride semiconductor laminate, in which the thickness of the thin film is measured by using Fourier transform infrared spectroscopy or infrared spectroscopic ellipsometry.
^{_{α = N e Kλ a ··· (}} 1)
(However, 1.5 × 10 ^-19 ≦ K ≦ 6.0 × 10 ^-19 , a = 3) A substrate made of group III nitride semiconductor crystals and
A semiconductor layer obtained by homoepitaxially growing one or more group III nitride semiconductor thin films having a carrier concentration different from that of the substrate on the substrate.
With
The substrate is
The absorption coefficient for infrared rays with a wavelength of 2 μm is 1.2 cm ^-1 or more and 48 cm ^-1 or less.
The in-plane variation of the absorption coefficient for infrared rays with a wavelength of 2 μm is within ^{1.0 cm-1.}
The substrate and the semiconductor layer have different absorption coefficients for infrared rays having a wavelength of 1 μm or more and 3.3 μm or less.
Have a fringe pattern in the reflected spectrum by Fourier transform infrared spectroscopy obtained by irradiating infrared light to the semiconductor layer on the substrate,
The surface of the semiconductor layer is a nitride semiconductor laminate having a reflectance of 5% or more and 30% or less with respect to infrared rays having a wavelength of 1 μm or more and 3.3 μm or less. Each concentration of oxygen and carbon in the substrate is less than ^{5 × 10 15} at · cm- ^3.
The nitride semiconductor laminate according to claim 5, wherein the concentrations of iron, chromium, and boron in the substrate are ^{less than 1 × 10 15} at · cm- ^3.

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