JP2008162888A - Substrate for electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a large surface area substrate which has characteristics equal to those of a bulk single crystal wafer of a nitride such as AlN, GaN or InN and can be applied for manufacturing electronic devices. <P>SOLUTION: The substrate for electronic devices is composed of a nitride thin film including a nitride crystal containing, as main components, N and at least one kind selected from Al, Ga and In, and having a wurtzite type crystal structure. In the substrate, the (0001) plane of the nitride crystal is singly oriented to be parallel to the surface of the nitride thin film and has an area of ≥10 cm<SP>2</SP>. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electronic device substrate applied to a light emitting diode, a laser diode, and the like, and a method for manufacturing the same, and more particularly, to a substrate applied to a nitride semiconductor device including a nitrogen-containing group III-V compound semiconductor layer and the like. It relates to a manufacturing method.

  III-V nitride semiconductors such as gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN), aluminum nitride gallium (AlGaN), or mixed crystals thereof are field effect transistors, LEDs (light emitting). Diodes) and laser diodes are used as constituent materials for nitride semiconductor devices. Particularly recently, for example, Nikkei Electronics no. 674, p. 79 (1996), attention has been paid to an LED that has such a laminated structure of nitride semiconductors and emits short-wavelength light such as blue and green.

  In a semiconductor device using a GaN thin film, sapphire is generally used as a substrate material for forming the thin film. However, since sapphire has a lattice constant and thermal expansion coefficient that are significantly different from GaN, dislocations are introduced from the interface between the substrate and the GaN thin film to the GaN thin film side, or the GaN crystal is deformed by stress, resulting in a good quality crystal. There is a problem that it cannot be obtained. Further, the sapphire substrate has a problem that it is difficult to break a cleaved surface, and it is difficult to form an end face when manufacturing a laser diode. In addition, the sapphire substrate is more expensive than a semiconductor substrate such as Si and has problems such as poor surface flatness.

  The most suitable substrate for the nitride semiconductor device has the same crystal structure and lattice constant as those of the nitride crystal thin film formed thereon, and has the same thermal expansion coefficient. For example, when a semiconductor element is fabricated using an epitaxial thin film made of GaN, a high-quality semiconductor device can be obtained because a high-quality GaN epitaxial thin film can be grown by using a GaN single crystal substrate. In this case, the surface of the GaN single crystal substrate needs to be a (0001) plane.

However, only bulk cubic crystals of nitride such as AlN, GaN, and InN have been obtained. That is, it is impossible to manufacture a wafer having an area of 10 cm ² or more that can replace the sapphire substrate with the nitride bulk single crystal.

  On the other hand, the use of Si, which is cheaper than sapphire, as a substrate for a GaN-based semiconductor element has also been studied. However, since Si and GaN have large differences in lattice constant, thermal expansion coefficient, and lattice structure, it is still difficult to form a good quality GaN thin film on a Si single crystal substrate.

  As a proposal for improving the crystallinity of a nitride semiconductor layer such as GaN, for example, Japanese Patent Application Laid-Open No. 9-45960 describes providing an InGaAlN layer on a Si substrate via a ZnO buffer layer. In this publication, a ZnO buffer layer is directly formed on a Si substrate by sputtering or the like. However, in the experiments by the present inventors, it is substantially impossible to form a ZnO buffer layer as a single crystal film (epitaxial film in the present specification) on a Si substrate, and the crystallinity and surface properties are excellent. It turned out that it cannot be made into a film. For this reason, a nitride semiconductor layer having good crystallinity cannot be formed on such a ZnO buffer layer.

JP-A-8-264894 discloses a Ca _x Mg _1-x F ₂ (0 ≦ x ≦ 1) layer and a Mg _t Ca _3−t N ₂ (0 ≦ t ≦ 3) on a Si or SiC substrate. ) Layer is formed, and a Ga _y In _z Al _1-yz N (0 ≦ y, z ≦ 1) layer is formed thereon. In this publication, Si, SiC, or the like having a high surface flatness can be used, and a good quality GaInAlN layer can be formed. However, according to the experiments by the present inventors, the Ca _x Mg _1-x F ₂ layer and the Mg _t Ca _3-t N ₂ layer formed on the Si substrate have insufficient crystallinity and surface properties. I understood. Therefore, a nitride semiconductor layer having good crystallinity cannot be formed on these layers.

  It is also known that when a GaN layer is formed on a Si substrate, an AlN layer or a SiC layer is used as a buffer layer [J. Cryst. Growth 128, 391 (1993) and J. Cryst. Growth 115, 634 (1991). )]. However, according to experiments by the present inventors, it has been found that the AlN layer and the SiC layer directly formed on the Si substrate have insufficient crystallinity and surface properties. Therefore, a nitride semiconductor layer having good crystallinity cannot be formed on these layers.

  On the other hand, the present inventors have proposed a method for obtaining a high-quality nitride epitaxial film on a Si substrate in Japanese Patent Application No. 8-264894.

  However, in any method using a sapphire substrate or a Si single crystal substrate, there is a lattice constant difference or a difference in thermal expansion coefficient between the substrate and the nitride semiconductor thin film grown on the substrate. Even if the buffer layer is sandwiched between the nitride semiconductor thin film, stress is generated in the nitride semiconductor thin film. This stress hinders the epitaxial growth of the nitride semiconductor thin film and also causes the electrical characteristics of the nitride semiconductor thin film to become unstable.

  As described above, in a nitride semiconductor device having a nitride semiconductor thin film such as GaN on a substrate and applied to an LED or a laser diode, the most ideal substrate is a nitride single crystal such as AlN, GaN, or InN. It is a wafer. In addition, since nitride bulk single crystal wafers are characterized by excellent properties such as piezoelectricity and high thermal conductivity, a substrate for SAW (surface acoustic wave) element, a heat sink for ICs are utilized by utilizing the characteristics. It is also suitable for a substrate. At present, however, nitride bulk single crystals cannot be increased in area, and thus have not been put to practical use as substrates for these electronic devices.

  The present invention has been made under such circumstances. An object of the present invention is to provide a large-area substrate having characteristics equivalent to those of a nitride bulk single crystal wafer such as AlN, GaN, and InN and applicable to the manufacture of electronic devices.

Such an object is achieved by any one of the following (1) to (12).
(1) A nitride thin film having a nitride crystal having a wurtzite structure, the main component being at least one selected from Al, Ga and In, and N, wherein the (0001) plane of the nitride crystal is A substrate for electronic devices which is single-oriented so as to be parallel to the surface of the nitride thin film and has an area of 10 cm ² or more.
(2) Electrons in which a buffer layer, which is an epitaxial film composed of an oxide of rare earth elements (including Sc and Y) and / or zirconium oxide, is present on one surface side of the electronic device substrate of (1) above. Device substrate.
(3) An electronic device substrate in which a support member made of Si is present on a part of one surface of the electronic device substrate of (1) or (2).
(4) An electronic device substrate in which a reinforcing plate is attached to one surface of the electronic device substrate of (1) or (2).
(5) An electronic device substrate in which a reinforcing film for reinforcing the self-supporting property of the nitride thin film is formed on one surface of the electronic device substrate of (1) or (2).
(6) The electronic device substrate according to (5), wherein the reinforcing film is mainly composed of at least one selected from Al, Ga and In and N, and is polycrystalline or amorphous.
(7) The electronic device substrate according to any one of (1) to (6), wherein the nitride thin film is an epitaxial film.
(8) A method for producing an electronic device substrate according to any one of (1) to (7) above, wherein a rare earth element oxide and / or a surface of a support substrate whose surface is made of a Si single crystal. After forming a buffer layer, which is an epitaxial film composed of zirconium oxide, and growing the nitride thin film on the surface of the buffer layer, at least a part of the support substrate or at least a part of the support substrate and the buffer layer is removed. The manufacturing method of the board | substrate for electronic devices which has a process to do.
(9) The method for manufacturing a substrate for an electronic device according to (8), wherein the support substrate has a Si (100) surface on the surface, and the buffer layer has a (111) orientation.
(10) The method for manufacturing a substrate for an electronic device according to (8), wherein the support substrate has a Si (111) surface on the surface and the buffer layer has a (111) orientation.
(11) The electronic device substrate according to any one of (8) to (10), wherein polishing or etching is used when removing at least a part of the support substrate or at least a part of the support substrate and the buffer layer. Production method.
(12) The method for manufacturing a substrate for electronic devices according to any one of (8) to (11), wherein the nitride thin film is grown by a sputtering method.

  In the present invention, a thin film having high crystallinity and excellent surface flatness (an R-Zr-based oxide thin film described later) can be formed on a Si substrate, and the crystal structure and lattice constant of the thin film can be formed. Focusing on a nitride thin film, first, the thin film is formed on a support substrate whose surface is made of Si single crystal, and this is used as a buffer layer to form a nitride thin film thereon. The nitride thin film thus obtained has high crystallinity and good surface flatness.

  Next, the support substrate is removed, or the support substrate and the buffer layer are removed to obtain a nitride thin film or a laminated film of this and the buffer layer, which is used as an electronic device substrate.

  The substrate for an electronic device manufactured in this way exhibits an effect equivalent to that of a nitride bulk single crystal substrate when a nitride semiconductor thin film is epitaxially grown thereon. In addition, this electronic device substrate exhibits electrical characteristics and thermal conductivity equivalent to those of a nitride bulk single crystal substrate. Moreover, as described above, a nitride single crystal bulk body having a large area cannot be obtained, but in the present invention, a nitride single crystal substrate having a large area equivalent to that of a Si single crystal wafer used as a support substrate can be obtained. In addition, since the Si single crystal used as the support substrate is the cheapest among the single crystals, the present invention can provide a high-performance electronic device at a low cost.

  The electronic device substrate of the present invention exhibits ideal characteristics as a substrate for nitride semiconductor elements such as high-quality LEDs and lasers. Moreover, not only for nitride semiconductor elements, but also for electronic devices utilizing characteristic properties of nitrides such as AlN, GaN, InN, such as piezoelectricity and high thermal conductivity, for example, substrates for SAW elements, It is also suitable for a heat sink substrate for IC.

  Hereinafter, embodiments of the present invention will be described in detail.

  The substrate for an electronic device according to the present invention is formed by forming a buffer layer on the surface of a support substrate having at least a surface of Si single crystal, and forming a nitride thin film on the buffer layer. It is manufactured by removing.

  An R-Zr-based oxide thin film, which will be described later, is used for the buffer layer for forming the nitride thin film.

When two layers of thin films are continuously formed, such as a buffer layer and a nitride thin film in the present invention, a lattice between a thin film (underlying thin film) serving as a base and a thin film (growing thin film) grown thereon The degree of inconsistency is represented by the degree of mismatch. For example, if the lattice constant of the bulk body of the underlying thin film constituent material is d _sub and the lattice constant of the bulk body of the grown thin film constituent material is d _epi , the mismatch degree δ (unit:%) is
δ (%) = [(d _epi −d _sub ) / d _sub ] × 100
It is represented by If the lattice constant of the grown thin film is larger than that of the underlying thin film, δ is a positive value. On the other hand, when δ is negative, it means that the lattice constant of the underlying thin film is larger than that of the grown thin film. When δ = 0, it means that the lattices of the base thin film and the grown thin film are matched, that is, the lattices are matched. Regardless of the sign of δ, the larger the value of δ, the greater the degree of lattice mismatch, which is not preferable because distortion, defects, and the like due to lattice mismatch are easily introduced into the crystal.

Conventionally, as described above, a sapphire substrate is generally used as a substrate for forming a GaInAlN nitride thin film such as a GaN thin film. However, when (0001) -oriented GaN grows on the sapphire c-plane, the relationship between the two crystals during epitaxial growth is sapphire [0001] / GaN [0001] and sapphire [1000] / GaN [-1010], Since the lattice constant in the sapphire c plane (a-axis lattice constant) is 0.476 nm and the lattice constant in the GaN (0001) plane (a-axis lattice constant) is 0.316 nm, the mismatch degree δ is (3 ^{1 / 2} × 0.316) /0.476-1,
That is, it increases to + 15.0%.

In contrast, in the present invention, the constituent material of the R—Zr-based oxide thin film in contact with the nitride thin film, for example, the stabilized zirconia (YSZ) crystal in which Y is added to ZrO ₂ is a cubic crystal having an a-axis lattice. Since the constant is 0.5204 nm, the lattice constant in the (111) plane is 0.3680 nm as shown in FIG. This lattice matches the lattice in the GaN (0001) plane, and δ at that time is −14.1%, which improves the degree of mismatch compared to the case where a sapphire substrate is used. If Yb ₂ O ₃ , Lu ₂ O ₃ , or Sc ₂ O ₃ is used instead of YSZ, the lattice constants in the (111) plane are 0.3679 nm, 0.3674 nm, and 0.3481 nm, respectively, and GaN (0001 ) Matching with the surface is even better.

  As described above, in the present invention, the degree of lattice mismatch becomes small as compared with a combination with a conventionally used sapphire substrate, and thus a nitride thin film with high crystallinity can be obtained.

  Next, each thin film will be described.

R-Zr-based oxide thin film The R-Zr-based oxide thin film used as a buffer layer in the present invention is an epitaxial film mainly composed of oxides of rare earth elements (including Sc and Y) and / or zirconium oxide. .

Oxides of rare earth elements are Yb ₂ O ₃ , Tm ₂ O ₃ , Er ₂ O ₃ , Y ₂ O ₃ , Ho ₂ O ₃ , Gd ₂ O ₃ , Dy ₂ O ₃ , Tb ₂ O ₃ , Pr ₂ O. ₃ , Nd ₂ O ₃ , CeO ₂ , Eu ₂ O ₃ , Sm ₂ O ₃ , La ₂ O ₃ , Sc ₂ O ₃ and Lu ₂ O ₃ , or a solid solution containing two or more of these Among these, Yb ₂ O ₃ , Tm ₂ O ₃ , Er ₂ O ₃ , Y ₂ O ₃ , Ho ₂ O ₃ , Tb ₂ O ₃ , Sc ₂ O ₃ and Lu ₂ are preferred. It is preferably composed of one kind of O ₃ or a solid solution containing two or more kinds of these. When two or more rare earth elements are contained, the ratio is arbitrary. Note that these oxides may deviate from the stoichiometric composition.

Zirconium oxide is preferably substantially ZrO ₂ in composition, but may be deviated from the stoichiometric composition.

When the R—Zr-based oxide thin film is a solid solution of a rare earth element oxide and zirconium oxide, the solid solution ratio is arbitrary. However, in order to improve the surface flatness, it is preferable that the R—Zr-based oxide thin film is substantially composed of a rare earth element oxide or substantially composed of zirconium oxide. In addition, when zirconium oxide is the main component, the higher the purity of zirconium oxide, the higher the insulation resistance and the smaller the leakage current, which is preferable when insulation characteristics are required. When zirconium oxide is the main component, the ratio of Zr in the constituent elements excluding oxygen in the thin film is preferably more than 93 mol%, more preferably 95 mol% or more, further preferably 98 mol% or more, and most preferably 99 mol%. More than 5 mol%. In the high-purity zirconium oxide thin film, the constituent elements excluding oxygen and Zr are usually rare earth elements and P. The upper limit of the Zr ratio is currently about 99.99 mol%. Further, since the difficult separation of ZrO ₂ and HfO ₂ with the current high purification technique, the purity of ZrO ₂ it is usually refers to purity with Zr + Hf. Accordingly, the purity of ZrO ₂ in the present specification is a value calculated by regarding Hf and Zr as the same element, but HfO ₂ is exactly the same as ZrO ₂ in the R—Zr-based oxide thin film of the present invention. Because it works, there is no problem.

  An additive may be introduced into the R—Zr-based oxide thin film for improving the characteristics. For example, when an alkaline earth element such as Ca or Mg is doped, pinholes in the film are reduced and leakage can be suppressed. Al and Si have an effect of improving the resistivity of the film. Furthermore, transition elements such as Mn, Fe, Co, and Ni can form a level (trap level) due to impurities in the film, and the conductivity can be controlled by using this level. .

  The R—Zr-based oxide thin film plays a role of forming a highly crystalline nitride thin film by preferably matching the lattice constant with the nitride thin film formed thereon. Since the nitride thin film is composed of hexagonal crystals, the R-Zr-based oxide thin film is composed of an epitaxial film having a (111) orientation.

  The rare earth element oxide thin film has a (111) orientation regardless of whether it is formed on a Si (111) substrate or a Si (100) substrate. In this case, the support substrate has a (100) orientation. It may be. In contrast, a zirconium oxide thin film has a (111) orientation on a Si (111) substrate, but a (001) orientation on a Si (100) substrate. In this case, a (111) oriented support substrate is used. Use.

  In addition, the epitaxial film in this specification needs to be a single alignment film first. In the present specification, the single alignment film means that when measured by X-ray diffraction, the peak intensity of reflection of objects other than the target surface is 10% or less, preferably 5% of the maximum peak intensity of the target surface. It is the following film. For example, in the (111) single alignment film, the intensity of the reflection peak other than the (LLL) plane in 2θ-θX-ray diffraction of the film is 10% or less, preferably 5% or less of the maximum peak intensity of the (LLL) plane reflection. It is a film. In the present specification, (LLL) is a display that collectively refers to equivalent surfaces such as (111) and (222). Further, for example, in a (0001) single orientation film in a hexagonal crystal, that is, a c-plane single orientation film, the intensity of the reflection peak other than the (000L) plane is 10% of the maximum peak intensity of the (000L) plane reflection. Hereinafter, the film is preferably 5% or less. Note that (000L) is a generic name for equivalent surfaces such as (0001) and (0002).

  And the epitaxial film in this specification is the above-mentioned single alignment film, where the crystal plane is in the X-axis, Y-axis and Z-axis directions when the film plane is the XY plane and the film thickness direction is the Z-axis. Both are aligned together. Such orientation can be confirmed by showing a spot or streak pattern by RHEED evaluation. Note that RHEED is reflection high energy electron diffraction, and RHEED evaluation is an index of crystal axis orientation in the film plane.

  When the RHEED image is streaky and sharp, it means that the crystallinity and surface flatness of each layer are excellent.

In order to form a nitride thin film with high crystallinity, the R—Zr-based oxide thin film is preferably excellent in crystallinity and surface flatness. Specifically, the R-Zr-based oxide thin film or each of the thin films constituting the R-Zr-based oxide thin film has a crystallinity such that the full width at half maximum of the rocking curve of reflection on the (111) plane by X-ray diffraction is 1.50 ° or less. It is preferable to have. Further, when the surface property of the R—Zr-based oxide thin film is represented by a surface roughness Rz (ten-point average roughness, reference length 500 nm) measured by an AFM (atomic force microscope), Rz is preferably Is 2 nm or less, more preferably 0.60 nm or less. Such surface roughness is desirably realized in a region of preferably 80% or more, more preferably 90% or more, and further preferably 95% or more of the surface. The surface roughness is a value obtained by measuring at least 10 arbitrary points distributed in an average over a region having an area of 10 cm ² or more when each layer is formed over the entire surface of the substrate. In the present specification, for example, Rz is 2 nm or less at 80% or more of the thin film surface means that Rz is 2 nm or less at 80% or more of the positions when 10 or more are measured as described above. To do. The surface roughness Rz is defined in JIS B 0610.

  The rocking curve half-value width and the lower limit value of Rz in the R-Zr-based oxide thin film are not particularly limited and are preferably as small as possible. At present, the lower limit value of the rocking curve half-value width is generally about 0.7 °, particularly 0. About 4 °, and the lower limit of Rz is about 0.10 nm.

  The preferred thickness of the R—Zr-based oxide thin film is preferably 5 to 500 nm, more preferably 10 to 50 nm. The R—Zr-based oxide thin film is preferably thin enough not to impair its crystallinity, surface property, and insulation.

  The R—Zr-based oxide thin film may be a laminate of two or more thin films having different compositions, or may be an inclined structure film in which the composition gradually changes in the thickness direction.

Nitride thin film A nitride thin film is mainly composed of at least one selected from Al, Ga and In and N, and is preferably substantially Ga _x In _y Al _1-xy N (0 ≦ x ≦ 1, 0 ≦ x + y ≦ 1). The specific composition may be determined so as to match the required characteristics according to the applied electronic device. For example, by controlling the composition of the nitride thin film, it is possible to adjust the lattice constant and the coefficient of thermal expansion, so depending on the epitaxial film that needs to be grown on the nitride thin film in the applied electronic device, What is necessary is just to determine the composition of a physical thin film.

  The nitride thin film is preferably a (0001) single orientation film composed of a nitride having a wurtzite crystal structure, and more preferably an epitaxial film.

The nitride thin film can be used as an insulating substrate, and can also be used as an n-type or p-type semiconductor substrate. When used as a semiconductor substrate, a known doping element such as Si or Mg may be added in making Ga _x In _y Al _1-xy N into a semiconductor.

  The reason why the nitride thin film is formed through the buffer layer without being directly formed on the support substrate is that when the nitride thin film is formed directly on the support substrate surface, epitaxial growth does not occur.

The nitride thin film is preferably excellent in crystallinity and surface flatness. Specifically, the nitride thin film preferably has crystallinity such that the half-value width of the rocking curve of reflection on the (0001) plane by X-ray diffraction is 2.50 ° or less. Further, in order to form a nitride semiconductor thin film with high crystallinity on the nitride thin film, it is preferable that the surface flatness of the nitride thin film is good. When the surface flatness of the nitride thin film is expressed by a surface roughness Rz (ten-point average roughness, reference length 500 nm) measured by an AFM (atomic force microscope), Rz is preferably 20 nm or less. Preferably it is 10 nm or less. Such surface roughness is desirably realized in a region of preferably 80% or more, more preferably 90% or more, and further preferably 95% or more of the surface. The surface roughness is a value obtained by measuring at least 10 arbitrary points distributed in an average over a region having an area of 10 cm ² or more when each layer is formed over the entire surface of the substrate.

  There are no lower limit values for the rocking curve half-value width and Rz in the nitride thin film, and it is preferable that the lower limit is smaller. However, at present, the lower limit value for the rocking curve half-value width is generally about 0.9 °, and the lower limit value for Rz is 0 .About 10 nm.

  In addition, in order to improve surface flatness, you may grind | polish the surface of each thin film. For polishing, chemical polishing using an alkaline solution or the like as a polishing solution, mechanical polishing using colloidal silica, or the like, combined use of chemical polishing and mechanical polishing, or the like may be used.

  The thickness of the nitride thin film is preferably 0.1 to 300 μm, more preferably 1 to 100 μm. If the nitride thin film is too thin, handling after removing the support substrate becomes difficult, and it may not be a self-supporting film. On the other hand, if the nitride thin film is too thick, stress is likely to be generated, and the formation time is too long.

  When the nitride thin film is thin (for example, less than 10 μm), it is possible to improve handling properties, electrical characteristics, structural characteristics, etc. by attaching a reinforcing plate to the surface of the nitride thin film. . Reinforcing plates that do not cause stress in the nitride thin film, specifically, those having a thermal expansion coefficient equivalent to or close to that of the nitride thin film and having good surface flatness, such as a smooth glass plate Is preferably used. The method for fixing the nitride thin film to the reinforcing plate is not particularly limited as long as it does not cause stress in the nitride thin film. For example, an adhesive may be used for fixing, but if the surface property of the reinforcing plate is good, it is fixed in close contact with the reinforcing plate simply by placing a nitride thin film.

  In addition to a structure in which a reinforcing plate such as a glass plate is bonded, a film (hereinafter referred to as a reinforcing film) for reinforcing the self-supporting property of the nitride thin film may be formed on the nitride thin film. The reinforcing film is preferably made of nitride having the same or similar composition as the nitride thin film in consideration of matching of thermal expansion coefficients and the like in order to suppress the stress generation of the nitride thin film. However, since the reinforcing film is not required to have high crystallinity, it does not have to be a single crystal and may be a polycrystalline film or an amorphous film. Therefore, the reinforcing film can be formed near room temperature, and the film formation rate can be increased. The thickness of the reinforcing film may be appropriately determined so as to obtain a sufficient reinforcing effect, and the preferable range varies depending on the thickness of the nitride thin film, but is, for example, from 50 to 1000 μm, preferably from 100 to 500 μm. Just choose.

  The nitride thin film as the electronic device substrate may be a laminate of two or more thin films having different compositions, or may be a gradient structure film whose composition gradually changes in the thickness direction. For example, a thin film made of nitride having relatively good lattice matching to the support substrate and a thin film made of nitride having relatively good lattice matching to the nitride semiconductor thin film are laminated to form a two-layer nitriding A thin film may be used.

A support substrate having a Si single crystal on its surface is used. At least the surface of the support substrate is preferably composed of a (111) plane or a (100) plane of Si single crystal, and more preferably a (111) plane.

Thin Film Forming Method The method for forming the buffer layer is not particularly limited, but preferably, a vapor deposition method is used according to the method described in Japanese Patent Application Laid-Open No. 8-1090099 by the present applicant.

  The method for forming the nitride thin film is not particularly limited, but it is preferable to use a sputtering method or a MOVPE (organometallic vapor phase epitaxy) method, and it is particularly preferable to use a sputtering method. In the MOVPE method, the substrate temperature needs to be as high as about 1000 ° C., but according to the experiments by the present inventors, it is possible to form a highly crystalline nitride thin film at a substrate temperature of about 600 ° C. by the sputtering method. In addition, in order to remove the support substrate and make the nitride thin film a self-supporting film, it is necessary to reduce the internal stress of the nitride thin film. Unlike the MOVPE method, the sputtering method has different conditions for the internal stress of the thin film. Since it can be freely controlled by, for example, gas pressure, substrate-target distance, input power, etc., it is easy to reduce internal stress.

In the present invention, an electronic device substrate having an area equivalent to that of the support substrate can be obtained. Therefore, by using a large-area Si single crystal wafer, for example, an Si single crystal wafer having an area of 10 cm ² or more as the support substrate, 10 cm ² or more. A large-area substrate for electronic devices can be produced. Since the Si single crystal is remarkably cheaper than sapphire, the manufacturing cost can be remarkably reduced as compared with the case of using a sapphire substrate. The current semiconductor manufacturing process mainly uses a 2 to 8 inch Si single crystal wafer, particularly a 6 inch type, but the present invention can cope with this. Note that a nitride thin film may be formed only on a part of the wafer using a mask or the like.

As a method of removing the support substrate, for example, a method of polishing the support substrate, a method of chemically wet etching, a method of dry etching in vacuum, a method using a combination of these methods, or the like is preferable. . For polishing, chemical polishing using an alkaline solution or the like as a polishing solution, mechanical polishing using colloidal silica, or the like, a method using a combination of chemical polishing and mechanical polishing, or the like may be used.

Note that selective etching for selectively removing a part of the support substrate is possible by forming a protective pattern made of a photoresist layer, a SiO ₂ layer, or the like during etching. Therefore, when the nitride thin film is relatively thin, it can be used as a structural reinforcing member while leaving a part of the support substrate. For example, an arbitrary substrate structure suitable for a target device can be obtained by selectively etching the support substrate or performing so-called micromachining. Note that the support substrate may be removed at any stage. For example, depending on the type of device, the support substrate may be removed after the element is formed on the nitride thin film.

  In the substrate for electronic devices obtained by removing the support substrate, the surface opposite to the support substrate is usually used as a surface on which a nitride semiconductor thin film or the like is epitaxially grown.

Nitride Semiconductor Device The specific use of the nitride semiconductor device using the electronic device substrate of the present invention is not particularly limited, and can be preferably applied to various uses utilizing the high crystallinity and flatness of the nitride semiconductor thin film. Specifically, for example, a Schottky electrode is formed on one nitride semiconductor thin film to form a Schottky diode, or a plurality of nitride semiconductor thin films are provided to form a pn junction, and a diode or transistor is formed. A light emitting diode can be formed by providing an active layer, or a laser diode can be formed as a resonant structure.

  Hereinafter, specific examples of the present invention will be shown to describe the present invention in more detail.

Example 1
First, a ZrO ₂ thin film was formed as a buffer layer on a support substrate. Formation of the ZrO ₂ thin film was carried out according to the following procedure in accordance with the method described in Japanese Patent Application Laid-Open No. Hei 8-109099 by the present applicant.

As the support substrate, a Si single crystal wafer (circular with a diameter of 2 inches, thickness of 300 μm) which was cut so as to have a (111) plane on the surface and mirror-polished was used. The polished surface was etched and cleaned with a 40% aqueous ammonium fluoride solution. Next, the vapor deposition apparatus 1 shown in FIG. 1 is used to support a substrate holder 3 having a rotating means 4 having a rotating shaft 4 and a motor 5 installed in the vacuum chamber 1a and a heating means having a heater 6. The substrate 2 was fixed, and the inside of the vacuum chamber was evacuated to 10 ⁻⁶ Torr with an oil diffusion pump. Next, in order to protect the cleaning surface of the support substrate 2 with Si oxide, first, the substrate is rotated at 20 rpm, and oxygen is supplied from the oxidizing gas supply nozzle 8 of the oxidizing gas supply device 7 in the vicinity of the surface of the support substrate 2. Was heated to 600 ° C. while being introduced at a rate of 25 cc / min. As a result, thermal oxidation occurred, and a Si oxide layer having a thickness of about 1 nm was formed on the surface of the support substrate 2.

Next, the support substrate was heated to 900 ° C., rotated at 20 rpm, and while introducing oxygen gas from the nozzle at a rate of 25 cc / min, the metal Zr was evaporated from the Zr evaporation section 9 and supplied to the substrate surface. Thereby, reduction of the Si oxide layer formed in the previous step and formation of a ZrO ₂ thin film (buffer layer) were performed. The thickness of this ZrO ₂ thin film was 10 nm.

When X-ray diffraction was performed on this ZrO ₂ thin film, the (111) peak of ZrO ₂ was clearly observed, and it was found that the ZrO ₂ thin film was a single-oriented highly crystalline film. The full width at half maximum of this (111) reflection rocking curve was 0.7 ° (measured value including reflection from the support substrate), and it was confirmed that the orientation was excellent. Moreover, as a result of evaluating this ZrO ₂ thin film by RHEED, the diffraction pattern on the surface of this thin film was completely streaky. This completely streak pattern indicates that this ZrO ₂ thin film is an epitaxial film having excellent crystallinity and surface properties. In addition, ten points average roughness Rz (reference length L: 500 nm) according to JIS B 0610 was measured at 10 points on almost the entire surface of the thin film. The average was 0.80 nm, the maximum was 1.00 nm, and the minimum It was 0.08 nm and was confirmed to be flat at the molecular level.

In addition, when the rare earth element was evaporated from the rare earth element evaporation section 10 shown in FIG. 1 to form a rare earth element oxide thin film instead of the ZrO ₂ thin film, and the crystallinity and surface properties were evaluated in the same manner, ZrO ₂ The same result as the thin film was obtained. However, when a thin film made of a solid solution of ZrO ₂ and a rare earth element oxide was formed, the surface properties were slightly deteriorated. Further, as a result of measuring the resistivity of the ZrO ₂ thin film and the YSZ (Y stabilized zirconium) thin film, it was confirmed that the ZrO ₂ thin film had a resistance five times higher than that of the YSZ thin film and was excellent in insulation.

Next, an AlN thin film having a thickness of 20 μm was formed as a nitride thin film on the ZrO ₂ thin film. The AlN thin film was formed by RF magnetron sputtering in an N ₂ gas atmosphere. Al was used as the target, the substrate temperature was 600 ° C., the N ₂ gas pressure was 0.25 Pa, and the RF power was 300 W.

  When X-ray diffraction was performed on this AlN thin film, the (0002) peak of AlN was clearly observed, and it was found that the film was a unidirectionally oriented wurtzite type highly crystalline film. The half-value width of the rocking curve of this (0002) reflection was 1.9 °, and it was confirmed that the orientation was excellent. This AlN thin film was evaluated by RHEED. The diffraction pattern in RHEED was such that when the support substrate was rotated in the plane, the pattern of FIG. 2 and the pattern of FIG. 3 appeared alternately at every rotation angle of 30 °. From these patterns, it can be seen that the AlN thin film is an epitaxial film. The ten-point average roughness Rz (reference length L: 500 nm) according to JIS B 0610 was measured at almost ten locations on the surface of the thin film. The average was 2.5 nm, the maximum was 5 nm, and the minimum was 1.0 nm. And it was confirmed to be flat.

  Next, the support substrate was removed by wet etching. Specifically, after the surface of the AlN thin film was protected with a photoresist layer, the support substrate was dissolved and removed by putting it in a KOH solution. Thereby, the board | substrate for electronic devices which consists of a self-supporting AlN thin film was obtained.

Example 2
A support substrate (100) made of a Si single crystal (circular with a diameter of 2 inches, thickness of 300 μm) cut and mirror-polished so that the surface becomes a (100) plane, and cut so that the surface becomes a (111) plane, A support substrate (111) made of mirror-polished Si single crystal (diameter 2 inches, thickness 300 μm) was prepared, and the surfaces of these support substrates were etched and washed with a 40% ammonium fluoride aqueous solution. Using these support substrates,
1. Support substrate,
2. Buffer layer (Lu ₂ O ₃ thin film),
3. A film structure in which thin films were stacked in the order of nitride (GaN) thin film was produced by the following procedure.

First, a Si oxide layer was formed on the support substrate surface in the same manner as in Example 1, and then a Lu ₂ O ₃ thin film was formed in the same manner as in Example 1 except that Lu was used instead of Zr. The thickness of the Lu ₂ O ₃ thin film was 10 nm.

When X-ray diffraction was performed on the Lu ₂ O ₃ thin film, when the support substrate (100) was used, the (222) peak of the rare earth C-type structure of the Lu ₂ O ₃ thin film was clearly observed, and strongly oriented Lu It was confirmed that a ₂ O ₃ crystal film was obtained. Similarly, when the support substrate (111) is used, the (222) peak is clearly observed, and a Lu ₂ O ₃ crystal film strongly oriented in an orientation reflecting the crystal structure and symmetry of the support substrate is obtained. It was confirmed that

In addition, the Lu ₂ O ₃ thin film on each support substrate was evaluated by RHEED. As a result, the diffraction pattern was a sharp streak, and it was confirmed that these thin films were epitaxial films and the surfaces thereof were flat at the atomic level. In addition, when 10-point average roughness Rz (reference length L: 500 nm) according to JIS B 0610 was measured at 10 points on almost the entire Lu ₂ O ₃ thin film surface, Lu ₂ on the support substrate (100) was measured. In the O ₃ (111) thin film, the average is 0.70 nm, the maximum is 0.95 nm, and the minimum is 0.10 nm. In the Lu ₂ O ₃ (111) thin film on the support substrate (111), the average is 0.80 nm. The maximum was 1.00 nm and the minimum was 0.08 nm, both of which were flat at the molecular level.

Next, a (0001) GaN thin film was formed to a thickness of 100 μm on each Lu ₂ O ₃ (111) thin film. RF magnetron sputtering was used for the formation, nitrogen was used as the reactive gas, and Ga was used as the target. The substrate temperature was 600 ° C.

  When X-ray diffraction was performed on the GaN thin film formed on the support substrate (111), the (0002) peak of GaN was clearly observed, and it was found to be a unidirectionally oriented wurtzite-type highly crystalline film. It was. The half-value width of the rocking curve of this (0002) reflection was 1.3 °, and it was confirmed that the orientation was excellent. This GaN thin film was evaluated by RHEED. The diffraction pattern in RHEED was such that when the support substrate was rotated in the plane, the pattern of FIG. 4 and the pattern of FIG. 5 appeared alternately at every 30 ° rotation angle. From these patterns, it can be seen that this GaN thin film is an epitaxial film. The ten-point average roughness Rz (reference length L: 500 nm) according to JIS B 0610 was measured at almost 10 locations on the surface of the thin film. The average was 0.9 nm, the maximum was 1.5 nm, and the minimum was 0.00. It was 5 nm and was confirmed to be flat.

  Similar results were obtained for the GaN thin film formed on the support substrate (100) in the evaluation of X-ray diffraction, RHEED, and surface flatness.

Next, the support substrate is ground to a thickness of 20 μm by mechanical polishing using colloidal silica, and then the remaining portion of the support substrate and the Lu ₂ O ₃ thin film are removed by wet etching to form a self-supporting GaN thin film. An electronic device substrate was obtained.

Example 3
A film structure comprising a support substrate, a buffer layer and a nitride thin film was obtained in the same manner as in Example 2 except that the support substrate (111) was used and the thickness of the GaN thin film was changed to 400 nm.

A GaN film having a thickness of 200 μm was formed as a reinforcing film on the nitride thin film of this film structure. For the formation of the reinforcing film, RF magnetron sputtering was used as in the case of the nitride thin film. The sputtering conditions were selected so that no stress was generated in the reinforcing film. Specifically, the substrate (film structure) temperature was room temperature, the RF power was 1 kW, and the sputtering atmosphere was Ar + N ₂ (N ₂ : 20%). The obtained reinforcing film was a polycrystalline film in which the c-axis was oriented vertically in the plane.

Next, the support substrate was ground to a thickness of 20 μm in the same manner as in Example 2, and then the remaining portion of the support substrate was removed by wet etching. Further, the Lu ₂ O ₃ thin film was completely removed by Ar ion etching to obtain a self-supporting film composed of a laminate of a reinforcing film and a nitride thin film. When removing the Lu ₂ O ₃ thin film, the nitride thin film was also removed over a thickness of about 50 nm. When the reinforcing film was not formed, it was impossible to make the nitride thin film a self-supporting film.

It is a figure which shows an example of the vapor deposition apparatus used for manufacture of the board | substrate for electronic devices of this invention. A drawing-substitute photograph showing a crystal structure, Si (111) supporting the substrate / ZrO ₂ (111) is a RHEED pattern of AlN thin film formed on the thin film structure. A drawing-substitute photograph showing a crystal structure, Si (111) supporting the substrate / ZrO ₂ (111) is a RHEED pattern of AlN thin film formed on the thin film structure, the incident direction of the electron beam, in the support substrate surface Figure In the case of the direction rotated by 30 ° with respect to 2. A drawing-substitute photograph showing a crystal structure, Si (111) supporting board / Lu ₂ O ₃ (111) a RHEED pattern GaN thin film formed on the thin film structure. A drawing-substitute photograph showing a crystal structure, Si (111) supporting the substrate / Lu ₂ O ₃ (111) is a RHEED pattern of GaN thin film formed on the thin film structure, the incident direction of the electron beam, the supporting substrate plane In FIG. 4, the rotation direction is 30 ° with respect to FIG. It is a schematic diagram for demonstrating the lattice constant of a YSZ cubic crystal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vapor deposition apparatus 1a Vacuum chamber 2 Support substrate 3 Holder 4 Rotating shaft 5 Motor 6 Heater 7 Oxidizing gas supply device 8 Oxidizing gas supply nozzle 9 Zr evaporation part 10 Rare earth element evaporation part

Claims (7)

A nitride thin film having a nitride crystal having at least one selected from Al, Ga and In and N as a main component and having a wurtzite structure is formed, and the (0001) plane of the nitride crystal is the nitride A substrate for electronic devices that is single-oriented so as to be parallel to the surface of a thin film and has an area of 10 cm ² or more.   A substrate for electronic devices, wherein a buffer layer, which is an epitaxial film composed of an oxide of rare earth elements (including Sc and Y) and / or zirconium oxide, is present on one surface side of the substrate for electronic devices of claim 1.   An electronic device substrate in which a support member made of Si is present on a part of one surface of the electronic device substrate according to claim 1.   An electronic device substrate, comprising a reinforcing plate attached to one surface of the electronic device substrate according to claim 1.   An electronic device substrate comprising a reinforcing film for reinforcing the self-supporting property of the nitride thin film formed on one surface of the electronic device substrate according to claim 1.   6. The electronic device substrate according to claim 5, wherein the reinforcing film is mainly composed of at least one selected from Al, Ga and In and N, and is polycrystalline or amorphous. The electronic device substrate according to claim 1, wherein the nitride thin film is an epitaxial film.