JP2012106907A - METHOD FOR PRODUCING GaN FILM - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a GaN film in which a GaN film having a large principal plane area and a small warp can be produced.SOLUTION: The method for producing a GaN film includes the steps of: preparing a composite substrate 10; and depositing a GaN film 20 on the principal plane 13m of a single crystal film 13 in the composite substrate 10. The composite substrate 10 includes: a supporting substrate 11 in which the coefficient of thermal expansion in the principal plane 11m is larger than 1.0 times and smaller than 1.2 times the coefficient of thermal expansion in the a-axis direction of a GaN crystal; and a single crystal film 13 arranged on the principal plane 11m side of the supporting substrate 11, wherein the single crystal film 13 is a SiC film with 3-fold symmetry about an axis perpendicular to the principal plane 13m of the single crystal film 13.

Description

  The present invention relates to a method for manufacturing a GaN-based film that provides a GaN-based film having a large principal surface area and small warpage.

  The GaN-based film is suitably used as a substrate and a semiconductor layer of a semiconductor device such as a light emitting device or an electronic device. As a substrate for producing such a GaN-based film, a GaN substrate is most excellent from the viewpoint of matching or approaching the lattice constant and the thermal expansion coefficient between the substrate and the GaN-based film. However, the GaN substrate is very expensive, and it is difficult to obtain a large-diameter GaN substrate having a main surface diameter exceeding 2 inches.

  For this reason, a sapphire substrate is generally used as a substrate for forming a GaN-based film. However, the sapphire substrate and the GaN crystal have greatly different lattice constants and thermal expansion coefficients.

  For this reason, in order to relax the mismatch of the lattice constant between the sapphire substrate and the GaN crystal and grow a GaN crystal having good crystallinity, for example, Japanese Patent Laid-Open No. 04-297023 (Patent Document 1) It is disclosed that when a GaN crystal is grown on a sapphire substrate, a GaN buffer layer is formed on the sapphire substrate and the GaN crystal layer is grown on the GaN buffer layer.

  In order to obtain a GaN film having a small warp using a substrate having a thermal expansion coefficient close to that of the GaN crystal, for example, JP-T-2007-523472 (Patent Document 2) Disclosed is a composite support substrate having one or more pairs of each pair of layers having substantially the same thermal expansion coefficient, the overall thermal expansion coefficient being substantially the same as the thermal expansion coefficient of the GaN crystal.

Japanese Patent Laid-Open No. 04-297023 Special table 2007-523472

  In the above-mentioned Japanese Patent Application Laid-Open No. 04-297023 (Patent Document 1), a GaN crystal grows while warping in a concave direction in the crystal growth direction because crystal defects such as dislocations associate and disappear during GaN crystal growth.

  However, as described above, the coefficient of thermal expansion of the sapphire substrate is very large compared to the coefficient of thermal expansion of the GaN crystal, so that the grown GaN crystal warps convexly in the crystal growth direction during cooling after crystal growth, and the crystal growth direction Thus, a GaN film having a large convex curvature is obtained. Here, as the diameter of the main surface of the sapphire substrate is increased, the warpage of the GaN crystal during the cooling increases (specifically, the warpage of the obtained GaN film is 2 times the diameter of the main surface of the sapphire substrate). Almost proportional to the power). For this reason, it is difficult to obtain a GaN film with a small warp as the diameter of the main surface increases.

  Moreover, since the thermal expansion coefficient of the composite support substrate disclosed in the above Japanese translation of PCT publication No. 2007-523472 (Patent Document 2) is substantially the same as the thermal expansion coefficient of the GaN crystal, a GaN layer is grown on it. Can reduce the warpage. However, since the structure of such a composite support substrate is complicated, it is difficult to design the structure, and it is difficult to form the structure, so the cost for designing and manufacturing becomes very high, and the GaN film is manufactured. The cost to do is very high.

  An object of the present invention is to solve the above-described problems and to provide a method for manufacturing a GaN-based film capable of manufacturing a GaN-based film having a large principal surface area and a small warpage.

  In the present invention, the thermal expansion coefficient in the main surface is larger than 1.0 times and smaller than 1.2 times the thermal expansion coefficient in the a-axis direction of the GaN crystal, and disposed on the main surface side of the support substrate. A single crystal film comprising: a single crystal film comprising: a single crystal film having a three-fold symmetry with respect to an axis perpendicular to a main surface of the single crystal film; And a step of forming a GaN-based film on the main surface of the crystal film.

In the GaN-based film manufacturing method according to the present invention, the area of the main surface of the single crystal film in the composite substrate can be 45 cm ² or more. Further, the support substrate in the composite substrate can be a sintered body. The step of forming the GaN-based film includes a sub-step of forming a GaN-based buffer layer on the main surface of the single crystal film and a sub-step of forming a GaN-based single crystal layer on the main surface of the GaN-based buffer layer. And can be included.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the GaN-type film | membrane which can manufacture the GaN-type film | membrane with a large area of a main surface and a small curvature can be provided.

It is a schematic sectional drawing which shows an example of the manufacturing method of the GaN-type film | membrane concerning this invention. Here, (A) shows a step of preparing a composite substrate, and (B) shows a step of forming a GaN-based film. It is a schematic sectional drawing which shows an example of the process of preparing the composite substrate used for the manufacturing method of the GaN-type film | membrane concerning this invention. Here, (A) shows a sub-process for preparing a support substrate, (B) shows a sub-process for forming a single crystal film on the base substrate, and (C) attaches the single crystal film to the support substrate. (D) shows a sub-process for separating the base substrate from the single crystal film.

Referring to FIG. 1, in one embodiment of the method for producing a GaN-based film according to the present invention, the thermal expansion coefficient in the main surface 11m is 1.0 times the thermal expansion coefficient in the a-axis direction of the GaN crystal. A support substrate 11 that is larger and smaller than 1.2 times, and a single crystal film 13 disposed on the main surface 11 m side of the support substrate 11, and the single crystal film 13 is perpendicular to the main surface 13 m of the single crystal film 13. A step of preparing a composite substrate 10 having a three-fold symmetry with respect to an arbitrary axis (FIG. 1A), and a step of forming a GaN-based film 20 on the main surface 13m of the single crystal film 13 of the composite substrate 10 (FIG. 1B). Here, the GaN-based film refers to a film formed of a group III nitride containing Ga as a group III element. For example, a Ga _x In _y Al _1-xy N film (x> 0, y ≧ 0, x + y ≦ 1).

  According to the method for manufacturing a GaN-based film of this embodiment, the support substrate has a thermal expansion coefficient in the main surface that is greater than 1.0 times and less than 1.2 times the thermal expansion coefficient of the GaN crystal in the a-axis direction. And a single crystal film disposed on the main surface side of the support substrate, and using a composite substrate in which the single crystal film has a three-fold symmetry with respect to an axis perpendicular to the main surface of the crystal film, A GaN-based film having a large principal surface area (ie, a large diameter) and small warpage can be obtained.

(Preparation process of composite substrate)
Referring to FIG. 1A, in the method for manufacturing a GaN-based film of this embodiment, the thermal expansion coefficient in the main surface 11m is 1.0 times larger than the thermal expansion coefficient in the a-axis direction of the GaN crystal. Including a support substrate 11 that is larger than 1.2 times and a single crystal film 13 disposed on the main surface 11 m side of the support substrate 11, and the single crystal film 13 is perpendicular to the main surface 13 m of the single crystal film 13. A step of preparing a composite substrate 10 having a three-fold symmetry with respect to an axis.

  The composite substrate 10 has a slightly larger thermal expansion coefficient in the main surface 11m than the thermal expansion coefficient in the a-axis direction of the GaN crystal (specifically, larger than 1.0 times and smaller than 1.2 times). The support substrate 11 and the single crystal film 13 disposed on the main surface 11m side of the support substrate 11 are included, and the single crystal film 13 is three times symmetrical with respect to an axis perpendicular to the main surface 13m of the single crystal film 13 Therefore, a large-diameter GaN-based film with low warpage and low dislocation density can be grown on the main surface 13 m of the single crystal film 13 of the composite substrate 10.

  From the viewpoint of growing a large-diameter GaN-based film with low warpage and low dislocation density on the single crystal film 13 of the composite substrate 10, the support substrate 11 included in the composite substrate 10 has a thermal expansion within the main surface 11m. The coefficient needs to be larger than 1.0 times and smaller than 1.2 times compared with the thermal expansion coefficient in the a-axis direction of the GaN crystal, preferably larger than 1.04 times and smaller than 1.15 times, More preferably, it is larger than 1.04 times and smaller than 1.10 times.

Here, the support substrate 11 is not particularly limited as long as the thermal expansion coefficient in the main surface 11m is a substrate that is larger than 1.0 times and smaller than 1.2 times the thermal expansion coefficient in the a-axis direction of the GaN crystal. There may be a single crystal, a polycrystal, or an amorphous. The support substrate 11 is a sintered body from the viewpoint of easily adjusting the thermal expansion coefficient by changing the kind and ratio of the raw material and easily obtaining the thermal expansion coefficient within the above range. preferable. For example, an Al ₂ O ₃ —SiO ₂ sintered body, a SiO ₂ —MgO sintered body, a SiO ₂ —ZrO ₂ sintered body and the like are preferable.

  At this time, since the thermal expansion coefficients of the support substrate 11 and the GaN crystal generally vary greatly depending on their temperatures, it is important to determine the temperature or thermal range in which temperature range. The purpose of the present invention is to produce a GaN-based film having a small warp on a composite substrate, and the GaN-based film is formed on the composite substrate at the film formation temperature of the GaN-based film by raising the temperature from room temperature. After the film formation, the temperature is lowered to room temperature and the GaN-based film formed on the composite substrate is taken out, so that the average thermal expansion coefficient of the support substrate and the GaN crystal from room temperature to the film-forming temperature of the GaN-based film is It is considered appropriate to handle it as the thermal expansion coefficient of GaN crystals. However, GaN crystals decompose when the temperature exceeds 800 ° C. even in an inert gas atmosphere. Therefore, in the present invention, the thermal expansion coefficients of the support substrate and the GaN crystal are determined by the average thermal expansion coefficient from room temperature (specifically 25 ° C.) to 800 ° C.

  Further, from the viewpoint of growing a large-diameter GaN-based film with low warpage and low dislocation density on the single crystal film 13 of the composite substrate 10, it is disposed on the main surface 11 m side of the support substrate 11 included in the composite substrate 10. The single crystal film 13 is required to have three-fold symmetry with respect to an axis perpendicular to the main surface 13m of the single crystal film 13, and the sapphire film whose main surface 13m is the (0001) plane, the main surface Preferred are an SiC film in which 13m is the (0001) plane, an Si film in which the main surface 13m is the (111) plane, a GaAs film in which the main surface 13m is the (111) plane, and the like. Here, the fact that the single crystal film has a three-fold symmetry with respect to an axis perpendicular to the main surface of the single crystal film means that the crystal has a strict three-fold symmetry in terms of crystal geometry. Rather, it means that the actual single crystal film has a substantial three-fold symmetry. Specifically, the crystal geometrically strict three-fold symmetry axis of the single crystal film and its This means that the absolute value of the angle formed with the axis perpendicular to the main surface of the single crystal film is 10 ° or less.

  In the composite substrate 10, it is preferable that the main surface 11 m of the support substrate 11 and the main surface 13 m of the single crystal film 13 are substantially parallel from the viewpoint of reducing warpage and reducing dislocation density. Here, two surfaces being substantially parallel means that the absolute value of the angle formed by these two surfaces is 10 ° or less.

  Further, the method for disposing the single crystal film 13 on the main surface 11m side of the support substrate 11 of the composite substrate 10 is not particularly limited, and a method for growing the single crystal film 13 directly on the main surface 11m of the support substrate 11 (first step). 1), a method of removing the base substrate after bonding the single crystal film 13 formed on the main surface of the base substrate to the main surface 11m of the support substrate 11 (second method), and the support substrate 11 A single crystal (not shown) is bonded to the main surface 11m of the support substrate 11, and then the single crystal is separated from the bonded surface at a predetermined depth to form a single crystal film 13 on the main surface 11m of the support substrate 11. A forming method (third method) is exemplified. When the support substrate is a polycrystalline sintered body, the first method is difficult, and therefore any one of the second and third methods is preferably used. In the second method, the method for bonding the single crystal film 13 to the support substrate 11 is not particularly limited. The method for bonding the single crystal film 13 directly to the main surface 11m of the support substrate 11, Examples thereof include a method in which the single crystal film 13 is bonded to the main surface 11m with the adhesive layer 12 interposed. In the third method, the method for attaching the single crystal to the support substrate 11 is not particularly limited, and the method of attaching the single crystal directly to the main surface 11m of the support substrate 11 or the main surface 11m of the support substrate 11 may be used. Examples thereof include a method of bonding single crystals with the adhesive layer 12 interposed.

  The step of preparing the composite substrate 10 is not particularly limited, but from the viewpoint of efficiently preparing a composite substrate 10 with high quality, for example, referring to FIG. A sub-process for preparing the support substrate 11 (FIG. 2A), a sub-process for forming the single crystal film 13 on the main surface 30n of the base substrate 30 (FIG. 2B), the support substrate 11 and the single substrate A sub-process for bonding the crystal film 13 (FIG. 2C) and a sub-process for removing the base substrate 30 (FIG. 2D) can be included.

  In FIG. 2C, in the sub-process for bonding the support substrate 11 and the single crystal film 13, an adhesive layer 12a is formed on the main surface 11m of the support substrate 11 (FIG. 2C1). After forming the adhesive layer 12b on the main surface 13n of the single crystal film 13 grown on the main surface 30n (FIG. 2 (C2)), the main surface 12am of the adhesive layer 12a formed on the support substrate 11 and The adhesive layer 12 formed by bonding the adhesive layer 12a and the adhesive layer 12b to each other by bonding the main surface 12bn of the adhesive layer 12b formed on the single crystal film 13 formed on the base substrate 30. The support substrate 11 and the single crystal film 13 are bonded to each other with the intervening layer (FIG. 2 (C3)). However, as long as the support substrate 11 and the single crystal film 13 can be bonded to each other, the support substrate 11 and the single crystal film 13 can be directly bonded together without the adhesive layer 12 interposed.

  A specific method for bonding the support substrate 11 and the single crystal film 13 is not particularly limited, but from the viewpoint of maintaining the bonding strength even at a high temperature after bonding, the bonded surface is washed and bonded as it is. Direct bonding method in which bonding is performed by raising the temperature to about 1 to 1200 ° C., surface activation for bonding at a low temperature of about room temperature (for example, 25 ° C.) to about 400 ° C. after cleaning the bonded surfaces and activating them with plasma or ions. The method is preferably used.

(GaN film formation process)
With reference to FIG. 1B, the GaN-based film manufacturing method of this embodiment includes a step of forming a GaN-based film 20 on the main surface 13 m of the single crystal film 13 in the composite substrate 10.

  In the composite substrate 10 prepared in the composite substrate preparation step, the thermal expansion coefficient in the main surface 11m is slightly larger than the thermal expansion coefficient in the a-axis direction of the GaN crystal (specifically, 1.0 times). And a single crystal film 13 disposed on the main surface 11 m side of the support substrate 11, and the single crystal film 13 is formed on the main surface 13 m of the single crystal film 13. Since it has three-fold symmetry with respect to the vertical axis, a large-diameter GaN-based film 20 with a small warpage and a low dislocation density is formed on the main surface 13 m of the single crystal film 13 of the composite substrate 10. Can do.

  The method for forming the GaN-based film is not particularly limited. From the viewpoint of forming a GaN-based film having a low dislocation density, the MOCVD (metal organic chemical vapor deposition) method and the HVPE (hydride vapor deposition) method are used. Preferred examples include gas phase methods such as MBE (molecular beam epitaxy) method and sublimation method, liquid phase methods such as flux method and high nitrogen pressure solution method.

  The step of forming the GaN-based film is not particularly limited, but from the viewpoint of forming a GaN-based film having a low dislocation density, the GaN-based buffer layer 21 is formed on the main surface 13m of the single crystal film 13 of the composite substrate 10. It is preferable to include a sub-process for forming and a sub-process for forming the GaN-based single crystal layer 23 on the main surface 21 m of the GaN-based buffer layer 21. Here, the GaN-based buffer layer 21 is a part of the GaN-based film 20 and has a crystallinity that is grown at a temperature lower than the growth temperature of the GaN-based single crystal layer 23 that is another part of the GaN-based film 20. Refers to a low or amorphous layer.

  By forming the GaN-based buffer layer 21, the lattice constant mismatch between the GaN-based single crystal layer 23 and the single crystal film 13 formed on the GaN-based buffer layer 21 is alleviated. The crystallinity of the crystal layer 23 is improved and the dislocation density is lowered. As a result, the crystallinity of the GaN-based film is improved and the dislocation density is lowered.

  Note that the GaN-based single crystal layer 23 can be grown as the GaN-based film 20 on the single-crystal film 13 without growing the GaN-based buffer layer 21. Such a method is suitable when the lattice constant mismatch between the single crystal film 13 and the GaN-based film 20 formed thereon is small.

Example 1
1. Measurement of thermal expansion coefficient of GaN crystal Dislocation density 1 × 10 ⁶ cm ⁻² , Si concentration 1 × 10 ¹⁸ cm ⁻² , oxygen concentration 1 × 10 ¹⁷ cm ⁻² , carbon concentration grown by HVPE method Is a 1 × 10 ¹⁶ cm ⁻² GaN single crystal and has a size of 2 × 2 × 20 mm (the longitudinal direction is a-axis, and the plane parallel to the longitudinal direction is composed of either the C plane or the M plane. A sample for evaluation having an accuracy of within ± 0.1 ° was cut out.

About said sample for evaluation, the average thermal expansion coefficient when it heated up from room temperature (25 degreeC) to 800 degreeC was measured by TMA (thermomechanical analysis). Specifically, the thermal expansion coefficient of the evaluation sample was measured in a nitrogen gas circulation atmosphere by the suggested expansion method using TMA8310 manufactured by Rigaku Corporation. The average thermal expansion coefficient α _GaN-a from 25 ° C. to 800 ° C. in the a-axis direction of the GaN crystal obtained by such measurement was 5.84 × 10 ⁻⁶ / ° C.

2. Preparation Step of Composite Substrate (1) Sub-Step of Preparing Support Substrate With reference to FIG. 2A, as a material for the support substrate 11, eight commercially available Al ₂ O ₃ —SiO ₂ based sintered bodies A to H For each, a measurement sample having a size of 2 × 2 × 20 mm (the longitudinal direction is a direction substantially parallel to the main surface of the support substrate cut out from the sintered body) was cut out. Here, since the Al ₂ O ₃ —SiO ₂ sintered body has no direction specificity, the cutting direction is arbitrary. For these measurement samples, the average thermal expansion coefficient α _S at the time of temperature increase from room temperature (25 ° C.) to 800 ° C. was measured in the same manner as described above.

For the Al ₂ O ₃ —SiO ₂ sintered body A, the average thermal expansion coefficient α _S from 25 ° C. to 800 ° C. is 5.5 × 10 ⁻⁶ / ° C., and the average thermal expansion in the a-axis direction of the GaN crystal is The ratio of the thermal expansion coefficient α _S of the sintered body to the coefficient α _GaN-a (hereinafter referred to as α _S / α _GaN-a ratio) was 0.942. For the Al ₂ O ₃ —SiO ₂ sintered body B, the average coefficient of thermal expansion α _S from 25 ° C. to 800 ° C. is 5.9 × 10 ⁻⁶ / ° C., and the α _S / α _GaN-a ratio is 1. .010. For the Al ₂ O ₃ —SiO ₂ sintered body C, the average coefficient of thermal expansion α _S from 25 ° C. to 800 ° C. is 6.1 × 10 ⁻⁶ / ° C., and the α _S / α _GaN-a ratio is 1. 0.045. For the Al ₂ O ₃ —SiO ₂ sintered body D, the average coefficient of thermal expansion α _S from 25 ° C. to 800 ° C. is 6.4 × 10 ⁻⁶ / ° C., and the α _S / α _GaN-a ratio is 1. 0.096. For the Al ₂ O ₃ —SiO ₂ sintered body E, the average coefficient of thermal expansion α _S from -25 ° C. to 800 ° C. is 6.6 × 10 ⁻⁶ / ° C., and the α _S / α _GaN-a ratio is 1. .130. For the Al ₂ O ₃ —SiO ₂ sintered body F, the average coefficient of thermal expansion α _S from 25 ° C. to 800 ° C. is 7.0 × 10 ⁻⁶ / ° C., and the α _S / α _GaN-a ratio is 1. 199. For the Al ₂ O ₃ —SiO ₂ sintered body G, the average coefficient of thermal expansion α _S from 25 ° C. to 800 ° C. is 7.2 × 10 ⁻⁶ / ° C., and the α _S / α _GaN-a ratio is 1. .233. For the Al ₂ O ₃ —SiO ₂ based sintered body H, the average thermal expansion coefficient α _S from 25 ° C. to 800 ° C. is 7.5 × 10 ⁻⁶ / ° C., and the α _S / α _GaN-a ratio is 1. .284.

From the Al ₂ O ₃ —SiO ₂ sintered bodies A to H, a support substrate having a diameter of 4 inches (101.6 mm) and a thickness of 1 mm is cut out, and both main surfaces of each support substrate are polished to mirror surfaces. And it was set as support substrate AH. That is, the average thermal expansion coefficient of the support substrates A to H from 25 ° C. to 800 ° C. is equal to the average thermal expansion coefficient of the Al ₂ O ₃ —SiO ₂ based sintered bodies A to H from 25 ° C. to 800 ° C., respectively. . The results are summarized in Table 1.

(2) Sub-Process for Forming Single Crystal Film on Base Substrate With reference to FIG. 2B, the base substrate 30 has a diameter of 5 inches (having a (111) principal surface 30n polished to a mirror surface). 127 mm) and a 0.5 mm thick Si substrate was prepared.

On the main surface 30n of the Si substrate (underlying substrate 30), an SiC film having a thickness of 0.4 μm was formed as a single crystal film 13 by a CVD (chemical vapor deposition) method. The film formation conditions were as follows: SiH ₄ gas and C ₃ H ₈ gas were used as source gases, H ₂ gas was used as a carrier gas, the film formation temperature was 1300 ° C., and the film formation pressure was atmospheric pressure. In addition, Si atomic plane ((0001) plane) and C atomic plane ((000-1) plane) were mixed in a mosaic pattern on main surface 13m of thus obtained SiC film (single crystal film 13). .

(3) Sub-process for bonding support substrate and single crystal film Referring to (C1) in FIG. 2 (C), each of the main substrates A to H (support substrate 11) in FIG. 2 (A) A SiO ₂ film having a thickness of 2 μm was formed on the surface 11 m by the CVD method. Next, the SiO ₂ film having a thickness of 2 μm on each main surface 11 m of the support substrates A to H (support substrate 11) is polished by using CeO ₂ slurry, so that only the SiO ₂ film having a thickness of 0.2 μm is obtained. The adhesive layer 12a was made to remain. Thus, the gap of each main surface 11m is filled in the supporting substrate A to H (the supporting substrate 11), SiO ₂ film having a thickness of 0.2μm having a flat main surface 12am (adhesive layer 12a) was obtained .

2C, the main surface 13n of the SiC film (single crystal film 13) formed on the Si substrate (underlying substrate 30) in FIG. An SiO ₂ layer (adhesive layer 12b) having a thickness of 0.2 μm was formed on the main surface 13n of the SiC film (single crystal film 13) by oxidation at 1000 ° C. in an atmosphere.

2C, the main surface 12am of the SiO ₂ film (adhesive layer 12a) formed on each of the support substrates A to H (support substrate 11) and the Si substrate (underlayer) After the main surface 12bn of the SiO ₂ layer (adhesive layer 12b) formed on the SiC film (single crystal film 13) formed on the substrate 30) is cleaned and activated by argon plasma, the SiO ₂ film The main surface 12am of the (adhesive layer 12a) and the main surface 12bn of the SiO ₂ layer (adhesive layer 12b) were bonded together and heat-treated at 300 ° C. for 2 hours in a nitrogen atmosphere.

(4) Sub-process for removing base substrate Referring to FIG. 2D, the main surface and side surfaces of the back side of support substrate A to H (support substrate 11) (the side where single crystal film 13 is not bonded) are After protection by covering with wax 40, the Si substrate (underlying substrate 30) was removed by etching using a mixed acid aqueous solution of hydrofluoric acid and nitric acid. Thus, composite substrates A to H were obtained in which the SiC film (single crystal film 13) was arranged on the main surface 11m side of each of the support substrates A to H (support substrate 11).

3. Step of Forming GaN-Based Film Referring to FIG. 1B, main surface 13m of SiC film (single crystal film 13) of composite substrates A to H (composite substrate 10) (the main surface is (0001) surface and (000-1) plane)) and on the main surface of a sapphire substrate having a diameter of 4 inches (101.6 mm) and a thickness of 1 mm (the main surface is the (0001) plane). A GaN film (GaN-based film 20) was formed by MOCVD. In the formation of the GaN film (GaN-based film 20), TMG (trimethylgallium) gas and NH ₃ gas are used as the source gas, H ₂ gas is used as the carrier gas, and the thickness is 0.1 μm at 500 ° C. A GaN buffer layer (GaN-based buffer layer 21) was grown, and then a GaN single crystal layer (GaN-based single crystal layer 23) having a thickness of 5 μm was grown at 1050 ° C. Here, the growth rate of the GaN single crystal layer was 1 μm / hr. Thereafter, wafers A to H and R each having a GaN film formed on each of the composite substrates A to H and the sapphire substrate were cooled to room temperature (25 ° C.) at a rate of 10 ° C./min.

  For wafers A to H and R taken out from the film forming apparatus after cooling to room temperature, the warpage of the wafer, the appearance of the GaN film, and the dislocation density were measured. Here, the shape and amount of warpage of the wafer were measured with a Corning Tropel FM200EWafer on the main surface of the GaN film, the appearance of the GaN film was observed with a Nomarski microscope, and the dislocation density of the GaN film was CL (cathode luminescence). The dark spot was measured.

The wafer A warped in a concave shape on the GaN film side, the warpage amount was 60 μm, and many cracks were generated in the GaN film. The wafer B warped in a concave shape on the GaN film side, the warpage amount was 320 μm, no crack was generated in the GaN film, and the dislocation density of the GaN film was 3 × 10 ⁸ cm ⁻² . The wafer C warped in a concave shape on the GaN film side, the warpage amount was 10 μm, no crack was generated in the GaN film, and the dislocation density of the GaN film was 1 × 10 ⁸ cm ⁻² . The wafer D warped in a convex shape on the GaN film side, the warpage amount was 20 μm, no crack was generated in the GaN film, and the dislocation density of the GaN film was 1 × 10 ⁸ cm ⁻² . The wafer E was warped convexly on the GaN film side, the warpage amount was 110 μm, no crack was generated in the GaN film, and the dislocation density of the GaN film was 2 × 10 ⁸ cm ⁻² . The wafer F was warped convexly on the GaN film side, the warpage amount was 230 μm, no crack was generated in the GaN film, and the dislocation density of the GaN film was 3 × 10 ⁸ cm ⁻² . The wafer G warped in a convex shape on the GaN film side, the warpage amount was 740 μm, no crack was generated in the GaN film, and the dislocation density of the GaN film was 4 × 10 ⁸ cm ⁻² . In wafer H, the support substrate was cracked, and a sufficient GaN film could not be obtained. The wafer R warped in a convex shape on the GaN film side, the warpage amount was 750 μm, no crack was generated in the GaN film, and the dislocation density of the GaN film was 4 × 10 ⁸ cm ⁻² . These results are summarized in Table 1. In Table 1, “-” indicates that the physical property value is not measured.

Referring to Table 1, the thermal expansion coefficient α _S in the main surface is larger than 1.0 times and smaller than 1.2 times the thermal expansion coefficient α _GaN-a in the a-axis direction of the GaN crystal (that is, 1.0 <(Α _S / α _GaN-a ratio) <1.2) By using a composite substrate having a supporting substrate (wafers B to F), warpage is extremely small compared to the case of using a sapphire substrate (wafer R). A GaN film could be formed. Further, from the viewpoint of further reducing the warpage and dislocation density of the GaN film on the wafer, the thermal expansion coefficient α _S in the main surface of the support substrate of the composite substrate is the thermal expansion coefficient α _{GaN-a in} the a-axis direction of the GaN crystal. It is preferably larger than 1.04 times and smaller than 1.15 times (that is, 1.04 <(α _S / α _GaN-a ratio) <1.15) (wafers C to E), and the a-axis direction of the GaN crystal The coefficient of thermal expansion of α _GaN-a is larger than 1.04 times and smaller than 1.10 times (that is, 1.04 <(α _S / α _GaN-a ratio) <1.10) (wafers C and D) Is more preferable.

  In the above embodiment, an example is shown in which an undoped GaN film is formed on a composite substrate. However, when an n-type or p-type conductivity imparted by doping is formed, doping is performed. Even when a GaN film with increased specific resistance was formed, the same results as in the above example were obtained.

Further, when a GaN-based film such as a Ga _x In _y Al _1-xy N film (0 <x <1, y ≧ 0, x + y ≦ 1) is formed instead of the GaN film, the same as in the above embodiment Results were obtained. In particular, when a Ga _x In _y Al _1-xy N film (x> 0.5, y ≧ 0, x + y ≦ 1) is formed in place of the GaN film, almost the same result as in the above example is obtained. It was.

A GaN-based film (specifically, Ga _x In _y Al _1-xy N film (x> 0, y ≧ 0, x + y ≦ 1), etc.) is a composition ratio of group III elements such as Ga, In, and Al. It is also possible to form a plurality of films by changing. Further, a plurality of GaN-based films such as Ga _x In _y Al _1-xy N films (x> 0, y ≧ 0, x + y ≦ 1) can be formed instead of Ga.

  In the practice of the present invention, a known dislocation reduction technique such as an ELO (Epitaxially Lateral Overgrowth) technique can be applied when forming a GaN-based film.

  Alternatively, after forming a GaN-based film on the composite substrate, only the support substrate of the composite substrate or the entire composite substrate (support substrate and single crystal film) may be removed by etching. At this time, the GaN-based film may be transferred to another support substrate.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 10 Composite substrate, 11 Support substrate, 11m, 12m, 12am, 12bn, 13m, 13n, 21m, 23m, 30n Main surface, 12, 12a, 12b Adhesion layer, 13 Single crystal film, 20 GaN system film, 21 GaN system buffer Layer, 23 GaN-based single crystal layer, 30 base substrate, 40 wax.

Claims (4)

The thermal expansion coefficient in the main surface is arranged on the main surface side of the support substrate, which is larger than 1.0 times and smaller than 1.2 times the thermal expansion coefficient in the a-axis direction of the GaN crystal. Preparing a composite substrate, wherein the single crystal film is a SiC film having a three-fold symmetry with respect to an axis perpendicular to the main surface of the single crystal film;
Forming a GaN-based film on a main surface of the single crystal film in the composite substrate. The method for producing a GaN-based film according to claim 1, wherein an area of a main surface of the single crystal film in the composite substrate is 45 cm ² or more. The method for producing a GaN-based film according to claim 1, wherein the support substrate in the composite substrate is a sintered body.   The step of forming the GaN-based film includes a sub-step of forming a GaN-based buffer layer on the main surface of the single crystal film and a sub-step of forming a GaN-based single crystal layer on the main surface of the GaN-based buffer layer. A method for producing a GaN-based film according to any one of claims 1 to 3, comprising a step.

Images