JP2008066575A - Manufacturing method of epitaxial wafer for semiconductor device and epitaxial wafer for semiconductor device - Google Patents

Abstract

Epitaxial semiconductor device capable of producing LD with highly stable optical characteristics such as vertical radiation angle and less variation by enabling highly accurate structural design and accurate feedback to growth conditions A method for manufacturing a wafer is provided.
In a method for manufacturing an epitaxial wafer for a semiconductor device in which a plurality of epitaxial layers are grown on a substrate, a profile in the depth direction of the Al composition in the plurality of epitaxial layers prepared in advance is determined as a secondary ion mass. This is a method in which the Al composition is grown so that the Al composition has a predetermined profile in the depth direction based on the obtained Al composition depth direction profile data.
[Selection] Figure 2

Description

  The present invention relates to an epitaxial wafer for a semiconductor device, and more particularly to a method of manufacturing an epitaxial wafer for LD (semiconductor laser) used for reading information on an optical disk or recording information on an optical disk, and an epitaxial wafer for LD.

  Conventionally, when designing the structure of an LD epitaxial wafer and producing an epitaxial wafer for realizing the structure, it is first necessary to determine the growth conditions of the MOVPE (metal organic vapor phase epitaxy) method.

  For this reason, first, PL wavelengths of a p-type cladding layer, a guide layer, and an n-type cladding layer made of a quaternary layer such as AlGaInP or a ternary layer such as AlGaAs measured by a photoluminescence (PL) method are used. Specifically, a single-layer epi (single-layer epitaxial wafer) in which each epitaxial layer such as the above-described p-type cladding layer is formed on a substrate is used.

  These single-layer epis were measured by the PL method, and the result of calculating the Al composition with respect to Ga from the PL wavelength of each epitaxial layer was used. Further, a three-stage calculation is required in which the refractive index of each epitaxial layer is further calculated from the Al composition, and the optical structure is designed.

  Finally, the growth conditions of each epitaxial layer are calculated from this structural design in the reverse procedure, and based on the growth conditions, each epitaxial layer is grown on the substrate to produce an LD epitaxial wafer.

  On the other hand, as a method for directly measuring the Al composition with respect to Ga, there is a quantitative analysis method of elements such as EDX (energy dispersive X-ray spectroscopy).

  The prior art document information related to the invention of this application includes the following.

Japanese Patent Laid-Open No. 10-308530

  However, when calculating the Al composition with respect to Ga from the quaternary or ternary layer PL wavelength, there is a problem of measurement error during PL measurement. In particular, in an epitaxial wafer having a multilayer structure, the PL emission intensity of the p-type cladding layer is often weak, and there has been a serious problem in measurement accuracy. When the Al composition for Ga exceeds 0.7, the emission intensity may be so weak that almost no peak wavelength can be read.

  As a matter of course, it is a problem to perform the calculation by using the measurement result having such a low accuracy and to design the structure because the optical characteristics of the obtained LD become unstable and there are many variations.

  On the other hand, the elemental quantitative analysis method that directly measures the Al composition with respect to Ga can only analyze the surface of the crystal. The multilayer structure such as an epitaxial wafer is measured at once, and the Al composition in the multilayer structure is measured. Measurements that quantify compositional differences and correlations are not possible.

  Therefore, the object of the present invention is to solve these problems and to enable highly accurate structural design and accurate feedback to the growth conditions, so that the optical characteristics such as the vertical radiation angle are very stable. Another object of the present invention is to provide an epitaxial wafer for a semiconductor device and an epitaxial wafer for a semiconductor device capable of producing an LD with less product variation.

The present invention was devised to achieve the above object, and the invention of claim 1 is a method for producing an epitaxial wafer for a semiconductor device, wherein a plurality of epitaxial layers are grown on a substrate.
A depth direction profile of the Al composition in the plurality of epitaxial layers prepared in advance is obtained directly by secondary ion mass spectrometry, and the Al composition is in the depth direction based on the obtained depth direction profile data of the Al composition. In this method, a plurality of epitaxial layers are grown so as to have a predetermined profile.

  The invention according to claim 2 is the semiconductor device according to claim 1, wherein the Al composition is obtained by determining the Al atom concentration and the Ga atom concentration by secondary ion mass spectrometry, and calculating the obtained atomic concentration and formula (1) It is a manufacturing method of an epitaxial wafer.

  According to a third aspect of the present invention, the growth conditions of the respective epitaxial layers are determined by using the amount of Ga raw material, the amount of Al raw material used in the manufacture of the plurality of epitaxial layers prepared in advance, and the Al composition obtained by the formula (1). The method for producing an epitaxial wafer for a semiconductor device according to claim 2 to be obtained.

  In the invention of claim 4, the growth conditions of the respective epitaxial layers are determined by the previous Ga raw material amount, the previous Al raw material amount used in the manufacture of the plurality of epitaxial layers produced previously, and the previous time obtained by the formula (1). 4. The semiconductor according to claim 2, wherein the Al composition is determined by Formula (2) and Formula (3) using the Al composition determined by Formula (1) required for a plurality of epitaxial layers to be fabricated this time. It is a manufacturing method of the epitaxial wafer for devices.

  According to a fifth aspect of the present invention, the plurality of epitaxial layers include a quaternary layer made of Al, Ga, In, or P, or a ternary layer made of Al, Ga, As. It is the manufacturing method of the epitaxial wafer for semiconductor devices.

  The invention of claim 6 is the method for producing an epitaxial wafer for a semiconductor device according to any one of claims 1 to 5, wherein the plurality of epitaxial layers include at least a p-type cladding layer, an active layer, and an n-type cladding layer. .

  According to the seventh aspect of the present invention, when the plurality of epitaxial layers are prepared in advance, a dummy active layer having a thickness larger than a normal thickness of the active layer is prepared, and the active activity is determined based on data of the dummy active layer. The method for producing an epitaxial wafer for a semiconductor device according to claim 6, wherein the layer is produced with a normal thickness.

  The invention of claim 8 is an epitaxial wafer for semiconductor devices produced by using the method for producing an epitaxial wafer for semiconductor devices according to any one of claims 1 to 7.

  ADVANTAGE OF THE INVENTION According to this invention, the epitaxial wafer for semiconductor devices which can produce LD with a very stable optical characteristic and few product variations is realizable.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.

  First, an example of an epitaxial wafer for a semiconductor device manufactured using the method for manufacturing an epitaxial wafer for a semiconductor device according to this embodiment will be described with reference to FIG.

  As shown in FIG. 1, an epitaxial wafer (epiwafer) 1 for a semiconductor device according to this embodiment is for a double heterostructure LD in which a plurality of epitaxial layers 3 are formed on a substrate 2 such as an n-type GaAs substrate. It is an epitaxial wafer.

  Each layer of the plurality of epitaxial layers 3 is composed of a quaternary layer made of Al, Ga, In, and P, or a ternary epitaxial layer made of Al, Ga, and As. The epitaxial wafer 1 including the quaternary layer is used when manufacturing an LD that emits high-output red light, and the epitaxial wafer 1 including the ternary layer is used when manufacturing an LD that emits high-power infrared light. Used. The LD obtained from the epitaxial wafer 1 is used, for example, for writing or reading a DVD or CD.

  The plurality of epitaxial layers 3 include a first n-type cladding layer 4, a second n-type cladding layer 5, an n-type active layer 6, a first p-type cladding layer 7, an etching stop layer 8, a second p-type cladding layer 9, and a contact layer 10. Are sequentially epitaxially grown from the substrate 2 side by the MOVPE method.

  The active layer 6 has an Al mixed crystal ratio necessary for the desired emission wavelength of the LD. The Al mixed crystal ratio is also referred to as an Al composition with respect to Ga contained in each layer of the plurality of epitaxial layers 3, or simply an Al composition, or an Al composition ratio.

  Each of the cladding layers 4, 5, 7, 9 is a layer that prevents backflow of electrons and becomes a window that is transparent to light generated in the active layer 6. For example, Zn is used as the p-type impurity, and Si is used as the n-type impurity.

  Although not shown in FIG. 1, in order to obtain a high quality active layer 6, the upper and lower layers of the second n-type cladding layer 5 and the active layer 6, the active layer 6 and the first p-type cladding layer 7, or A guide layer may be formed in the active layer 6 as a buffer layer that alleviates lattice mismatch.

  Now, a method for manufacturing an epitaxial wafer according to the present embodiment will be described.

  Conventionally, the secondary ion mass (SIMS) analysis method has been considered not to be able to analyze the composition such as the profile in the depth direction of the Al composition with respect to Ga. As a result, it has become possible to measure with considerable accuracy.

  Therefore, the present inventor makes use of the feature of the SIMS analysis method that the profile in the depth direction of the multilayer structure can be measured, and the measurement result is used to calculate the structure design of the epitaxial wafer for semiconductor device to be manufactured and the growth conditions at the time of manufacturing. The present invention has been invented for feedback.

  In the manufacturing method of the semiconductor device epitaxial wafer 1 according to the present embodiment, a depth direction profile of Al composition with respect to Ga in a plurality of epitaxial layers prepared in advance by the MOVPE method (for example, a profile X described later in FIG. 2) The MOVPE method is used so that the Al composition becomes a predetermined profile in the depth direction (for example, profile Y described later in FIG. 2) based on the obtained Al profile depth direction profile data. In this method, a plurality of epitaxial layers 3 are grown on the substrate 2.

  Here, the plurality of epitaxial layers prepared in advance refers to a sample prepared prior to manufacturing or a plurality of epitaxial layers prepared on site according to customer requirements.

In the SIMS analysis method, ions such as O ²⁺ and Cs ⁺ are irradiated on the sample surface, and secondary ions ionized in the sputtered atoms are subjected to mass analysis, thereby analyzing the components and impurities of the substance. How to do it. Since the sample surface is sputtered by ions, an element distribution in the depth direction from the sample surface can also be obtained.

Examples of the raw material for the multiple epitaxial layers 3 include TMG (trimethylgallium) as a Ga raw material, TMA (trimethylaluminum) as an Al raw material, TMI (trimethylindium) as an In raw material, AsH ₃ (arsine) and P as an As raw material. PH ₃ (phosphine) is used as a raw material, Si ₂ H ₆ (disilane) is used as a Si raw material, and DMZ (dimethyl zinc) is used as a Zn raw material that is a p-type impurity.

  The Al composition is obtained from the obtained atomic concentration and formula (1) by obtaining the Al atom concentration and the Ga atom concentration by SIMS analysis.

  The growth conditions of each epitaxial layer 4 to 10 are as follows: the amount of Ga raw material, the amount of Al raw material used in the production of a plurality of epitaxial layers prepared in advance, and the Al composition obtained by the formula (1) are used. It asks so that it may become a composition ratio.

  For example, an epitaxial wafer manufactured in-situ in accordance with customer requirements (optical characteristics such as the vertical emission angle of LD) X is 1X, and the multiple epitaxial layers are the previously prepared multiple epitaxial layers 3X. Thereafter, the customer's request X is changed to the request Y, and an epitaxial wafer manufactured in response to the request Y is defined as 1Y, and the plurality of epitaxial layers are defined as an epitaxial layer 3Y fabricated this time.

  In this case, the growth conditions of the respective epitaxial layers 4 to 10 are as follows: in the plurality of epitaxial layers 3X, the previous amount of Ga raw material used in the production of each layer, the previous amount of Al raw material, and the previous Al amount obtained by the equation (1) In the multiple epitaxial layer 3Y produced this time, using the present Al composition obtained by the formula (1) required for each of the layers 4 to 10, the formula (2), so as to obtain a desired Al composition ratio, Obtained by equation (3).

  In addition, when preparing a plurality of epitaxial layers in advance, a dummy active layer having a thickness larger than the normal thickness of the active layer (for example, 100 nm or more) is prepared, and based on the data of the dummy active layer, the active layer 6 may be produced with a normal thickness.

  In general, the active layer 6 is often formed with a film thickness of several tens of μm. In this case, even if an attempt is made to obtain a depth profile of the Al composition of the active layer prepared in advance by SIMS analysis, the resolution is low. This is because it is low and cannot be measured accurately.

  When each of the layers 4 to 10 is epitaxially grown on the substrate 2 using the MOVPE apparatus under the obtained growth conditions to form a plurality of epitaxial layers 3, for example, an epitaxial wafer 1 as shown in FIG. 1 is obtained. . When this epitaxial wafer 1 is made into chips and electrodes are formed, an LD as a light emitting element is obtained.

  The operation of this embodiment will be described.

  In the method for manufacturing an epitaxial wafer for a semiconductor device according to the present embodiment, first, an Al composition depth direction profile in a plurality of epitaxial layers prepared in advance by the MOVPE method is obtained by direct measurement using SIMS analysis.

  Then, feedback is performed so that the Al composition has a predetermined profile in the depth direction based on the depth profile data of the Al composition obtained from the measurement result.

  The feedback here means that in each layer constituting a plurality of epitaxial layers prepared in advance, when the amount of Ga raw material and / or Al raw material is larger than the design value or theoretical value, the equations (1) to (3) When the amount of the Ga raw material and / or Al raw material obtained in (1) is reduced and the amount of the Ga raw material and / or Al raw material is small, the amount of the Ga raw material and / or Al raw material obtained by the formulas (1) to (3) To increase the amount.

  Thereby, the deviation of the Al composition and the film thickness from the design value and the theoretical value generated in each layer constituting the plurality of epitaxial layers prepared in advance is corrected, and the plurality of epitaxial layers 3 are grown on the substrate 2. Let

  That is, based on the measurement data, the Al composition is changed from the measurement data according to the characteristics required for each of the layers 4 to 10 of the multiple epitaxial layers 3 (for example, optical characteristics such as the vertical emission angle of the LD). The Al composition after the change (in the case of optical characteristics, for example, the refractive index of the active layer 6 and each cladding layer is obtained, and the Al composition is determined so as to obtain the obtained refractive index).

  Subsequently, based on the determined Al composition, the growth conditions of the respective layers 4 to 10 of the epitaxial wafer 1 produced by the MOVPE method are obtained, and the respective layers 4 to 10 are epitaxially grown on the substrate 2 under the obtained growth conditions. A plurality of epitaxial layers 3 are formed.

  That is, according to the manufacturing method according to the present embodiment, by using a method of directly measuring the Al composition with respect to Ga of a plurality of epitaxial layers prepared in advance by SIMS analysis, each layer in the epitaxial wafer structure prepared in advance is used. The correlation between the Al composition, its depth profile, and the Al composition between the layers can be measured with high accuracy.

  By using this measurement result for the structural design of epi-wafer 1 and the calculation of growth conditions, it is possible to provide highly accurate structural design and accurate feedback to the growth conditions, and when calculating the Al composition from the conventional PL wavelength. The measurement error that was a problem can be eliminated.

  As a result, according to the manufacturing method according to the present embodiment, there is very little variation in products including optical characteristics such as the vertical radiation angle characteristics of laser caused by the conventional method, and the optical characteristics are very stable for LD. An epitaxial wafer 1 is obtained.

  Here, the operational effects of the method for manufacturing an epitaxial wafer for a semiconductor device according to the present embodiment will be described in more detail.

  The feature of the present invention is to determine the growth conditions of the layers 4 to 10 constituting the LD using SIMS measurement for high quality LD design.

i) Conventional Method and Problems As described above, conventionally, the growth condition of the composition of each layer constituting a plurality of epitaxial layers has been determined using a PL measurement method. However, for example, an epitaxial layer (semiconductor layer) such as a p-type cladding layer has an indirect transition in the band gap. Therefore, even if it is attempted to observe PL emission from the p-type cladding layer by irradiating laser light during PL measurement. There is a problem that the intensity is too weak, the peak wavelength is not properly detected, and the measurement accuracy is deteriorated.

  If the PL measurement accuracy deteriorates, the composition of each layer deviates from the design value, and a desired LD spot diameter cannot be obtained and cannot be used as a writing / reading LD.

  Moreover, in order to obtain | require carrier concentration and a growth rate, it was necessary to prepare the measurement sample according to the objective and to use the evaluation method suitable for it.

ii) Present Invention Therefore, in the present invention, first, a temporary LD epi structure is grown, and the composition, carrier concentration, and growth rate (film thickness) of each layer of the temporary LD epi structure are evaluated at once by SIMS measurement. There is an advantage that immediately after the next growth, those results are fed back to proceed to production of LD epi (actual LD epi and LD epi after changing customer requirements).

  That is, according to the present invention, the above-described problems of the conventional method are solved, and the following effects a) to d) are exhibited.

  a) Even in a semiconductor layer having a band gap of indirect transition such as a p-type cladding layer, the Al composition can be measured with high accuracy and fed back to actual manufacturing.

b) Further, in order to determine the growth conditions of the layers 4 to 10 constituting the LD, each layer is grown by single-layer epitaxy as in the prior art, and various evaluations are performed for various evaluations. Since it is no longer necessary to prepare a sample and evaluate it using various evaluation apparatuses, the production period of the epitaxial wafer 1 is shortened.
c) By eliminating the need for single-layer epi for the growth condition determination, raw material costs can be saved.

d) Since the single-layer epi for determining the growth conditions is no longer necessary, the epitaxial film thickness can be used for LD production, so that the number of production per production lot can be increased and the throughput can be improved. (In the conventional method, for each production lot, the flow of MOVPE apparatus maintenance-growth condition determination-production-MOVPE apparatus maintenance is performed, and an epi-growth limit per production lot (total epi-growth film thickness limit) )
For example, a specific example of d)
(D1) Number of epi wafers produced per production lot (3 inch product)
(Conventional) 300 sheets (Invention) 330 sheets (d2) Days required for one production lot (Conventional) 15 days → That is, 600 sheets per month (Invention) 13 days → That is, 761 sheets per month (+ 127%)
In the above embodiment, the example of the epitaxial wafer 1 having an n / p structure has been described. However, a plurality of epitaxial layers including a p-type cladding layer, a p-type active layer, an n-type cladding layer, and the like on a p-type substrate. Alternatively, an epitaxial wafer having a p / n structure may be used.

  In the above embodiment, an example of an LD epitaxial wafer as a light emitting element has been described as an example of an epitaxial wafer for a semiconductor device, but the present invention can also be applied to an epitaxial wafer for an LED (light emitting diode).

(Example 1)
FIG. 2 shows a depth profile of the Al composition by SIMS analysis of a red high-power LD epitaxial wafer for DVD writing produced in a certain MOVPE furnace (previous production). This is the curve X shown by the one-dot chain line in FIG. The left side of FIG. 2 is the epi surface side, and the right side is the substrate side. Of this curve X, 4X is the first cladding layer, 5X is the second cladding layer, 6X is the active layer, 7X is the first p-type cladding layer, 8X is the etch stop layer, 9X is the second p-type cladding layer, and 10X is the contact Corresponds to a layer.

  In the next production (current production), it is necessary to reduce the vertical radiation angle of the laser beam by 1 ° in the LD characteristics at the customer, so the Al composition of the four layers 4X, 5X, 7X, and 9X in FIG. Based on the calculated refractive index as a basis, the vertical radiation angle was calculated back to be reduced by 1 °, and it was found that the Al composition of the two layers of 4X and 5X should be lowered by 0.01. However, the refractive index was obtained from the relationship between the Al composition and the refractive index obtained in advance.

  Therefore, the growth conditions in which the Al composition of both layers 4X and 5X is 0.01 smaller than the previous time are calculated by the equations (1) to (3), and the epitaxial wafer 1 for semiconductor devices described in FIG. Produced.

  The profile in the depth direction of the Al composition by SIMS analysis of the epitaxial wafer 1 for semiconductor devices produced under the changed growth conditions is the curve Y indicated by the solid line in FIG. When the curve Y is seen, it can confirm that each layer 4Y-10Y of the epitaxial wafer 1 for semiconductor devices requested | required by this production has Al composition as a design.

  When a red high output LD for DVD writing was produced by a customer using this epitaxial wafer 1 for semiconductor devices, the vertical emission angle of the laser beam was reduced by 1 ° as desired.

  In this series of operations, wavelength measurement data by the photoluminescence method used in the conventional method is not used at all.

(Example 2)
Considering the value of the Al composition of the guide layer included in the active layer 6 in FIG. 1 in addition to Example 1, the optical characteristics such as the vertical radiation angle characteristics of the LD are further improved, and the product variation is further increased. Can be reduced.

  However, since the guide layer usually has a film thickness of only several tens of nm, the Al composition depth profile by SIMS analysis has low resolution and cannot be measured accurately.

  Therefore, a dummy guide layer is formed by intentionally growing a thick guide layer (about 100 nm) only on an epitaxial wafer to be subjected to SIMS analysis, and its Al composition is also measured by SIMS analysis. The structural design of each layer 4Y to 10Y including this measurement data and calculation of growth conditions are performed by equations (1) to (3), and the thickness of the guide layer is returned to the normal value during actual production. Then, the respective layers 4Y to 10Y were grown to prepare the epitaxial wafer 1 for semiconductor devices of FIG.

  This Example 2 is particularly effective for the production of a red high-power LD epi of 300 mW class or higher with strict specifications of the vertical emission angle.

(Example 3)
An infrared LD epiwafer for CD writing was also produced in the same manner as the red LD epiwafer for DVD writing in Examples 1 and 2, and the same effect was confirmed.

It is sectional drawing which shows an example of the epitaxial wafer for semiconductor devices produced using the manufacturing method of the epitaxial wafer for semiconductor devices which is suitable embodiment of this invention. It is a figure which shows the depth direction profile of Al composition by the SIMS analysis in an Example.

Claims (8)

In a method for producing an epitaxial wafer for a semiconductor device, which is produced by growing a plurality of epitaxial layers on a substrate,
The Al composition depth profile in a plurality of epitaxial layers prepared in advance was directly obtained by secondary ion mass spectrometry, and the Al composition was determined in the depth direction based on the obtained Al profile depth profile data. A method of manufacturing an epitaxial wafer for a semiconductor device, wherein the epitaxial wafer is grown to have a predetermined profile. The said Al composition is the manufacturing method of the epitaxial wafer for semiconductor devices of Claim 1 which calculates | requires Al atom concentration and Ga atom concentration by secondary ion mass spectrometry, and calculates | requires by these calculated | required atomic concentration and Formula (1).

  3. The semiconductor according to claim 2, wherein the growth condition of each epitaxial layer is obtained by using the Ga raw material amount, the Al raw material amount used in the manufacture of the plurality of epitaxial layers prepared in advance, and the Al composition obtained by the formula (1). Manufacturing method of epitaxial wafer for device. The growth conditions for each of the epitaxial layers are the previous Ga raw material amount used in the manufacture of the plurality of epitaxial layers prepared last time, the previous Al raw material amount, the previous Al composition obtained by the equation (1), and the current production time. The manufacturing method of the epitaxial wafer for semiconductor devices of Claim 2 or 3 calculated | required by Formula (2) and Formula (3) using this Al composition calculated | required by Formula (1) requested | required of the multiple layers of epitaxial layer .

  5. The semiconductor device epitaxial wafer according to claim 1, wherein the plurality of epitaxial layers include a quaternary layer made of Al, Ga, In, and P, or a ternary layer made of Al, Ga, and As. Production method.   The method for producing an epitaxial wafer for a semiconductor device according to claim 1, wherein the plurality of epitaxial layers include at least a p-type cladding layer, an active layer, and an n-type cladding layer.   When preparing the plurality of epitaxial layers in advance, a dummy active layer having a thickness larger than the normal thickness of the active layer is prepared, and the active layer is formed at a normal thickness based on the data of the dummy active layer. The manufacturing method of the epitaxial wafer for semiconductor devices of Claim 6 produced.   An epitaxial wafer for a semiconductor device, which is produced by using the method for producing an epitaxial wafer for a semiconductor device according to claim 1.

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