Group III element nitride substrate and method for producing group III element nitride substrate

Abstract

Provided is a group III element nitride substrate in which the occurrence of warpage is suppressed. A group III element nitride substrate according to an embodiment of the present invention is a group III element nitride substrate having a first main surface and a second main surface facing each other, wherein the variation range of Young's modulus in the thickness direction is 50% or less.

Description

Technical Field

[0001] The present invention relates to a group III nitride substrate and a method for manufacturing the group III nitride substrate. Background Art

[0002] As a substrate for various devices such as light-emitting diodes, semiconductor lasers, and power ICs, a group III nitride substrate is used.

[0003] For example, as described in Patent Document 1, the above-mentioned group III nitride substrate can be obtained as follows: a substrate made of a material having a different composition such as a sapphire substrate is used as a base substrate, and group III nitride crystals are heteroepitaxially grown on the base substrate, thereby obtaining a group III nitride substrate.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2005-136167 Summary of the Invention

[0007] However, the group III nitride substrate obtained by heteroepitaxial growth as described above has a problem that warping is likely to occur.

[0008] In view of the above problems, the main object of the present invention is to provide a group III nitride substrate in which the generation of warping is suppressed.

[0009] 1. The group III nitride substrate according to an embodiment of the present invention is a group III nitride substrate having a first main surface and a second main surface facing each other, wherein the variation range of the Young's modulus in the thickness direction is 50% or less.

[0010] 2. The group III nitride substrate described in 1 above may be a self-supporting substrate of group III nitride crystals.

[0011] 3. The thickness of the group III nitride substrate described in 1 or 2 above may be 250 μm or more and 800 μm or less.

[0012] 4. In the group III nitride substrate described in any one of 1 to 3 above, the variation range of the Young's modulus in the thickness direction may be 35% or less.

[0013] 5. In the group III nitride substrate described in any one of 1 to 4 above, the variation range of the Young's modulus in the thickness direction may be 1% or more.

[0014] 6. In the group-III nitride substrate described in any one of the above 1 to 5, it may be that the Young's modulus is higher as it approaches the first main surface side from the second main surface side.

[0015] 7. In the group-III nitride substrate described in any one of the above 1 to 6, the absolute value of the difference between the Young's modulus in the first main surface and the Young's modulus in the second main surface may be 100 GPa or less.

[0016] 8. In the group-III nitride substrate described in any one of the above 1 to 7, the thickness direction may substantially be the c-axis direction of the group-III nitride crystal.

[0017] 9. In the group-III nitride substrate described in any one of the above 1 to 8, the Young's modulus can be measured by nanoindentation.

[0018] 10. The method for manufacturing a group-III nitride substrate according to an embodiment of the present invention is the method for manufacturing a group-III nitride substrate described in any one of the above 1 to 9, and includes: preparing a seed substrate having a base substrate with an upper surface and a lower surface facing each other and a seed film formed on the upper surface of the base substrate; growing a group-III nitride crystal on the seed film of the seed substrate; and removing the base substrate from the group-III nitride crystal and growing the group-III nitride crystal by changing the growth rate of the group-III nitride crystal.

[0019] 11. In the manufacturing method described in the above 10, the base substrate may include a material having a composition different from that of the group-III nitride crystal.

[0020] Advantages of the Invention

[0021] According to an embodiment of the present invention, it is possible to provide a group-III nitride substrate in which the generation of warpage is suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic cross-sectional view showing a schematic configuration of a group-III nitride substrate according to one embodiment of the present invention.

[0023] Figure 2 is Figure 1 a plan view of the group-III nitride substrate shown.

[0024] Figure 3A It is a view showing a manufacturing process of a group-III nitride substrate according to one embodiment.

[0025] Figure 3B is the figure immediately following Figure 3A .

[0026] Figure 3C is the figure immediately following Figure 3B .

[0027] Figure 4A is a cross-sectional view showing an example of warpage that may occur in a stacked substrate.

[0028] Figure 4B is a cross-sectional view showing an example of warpage that may occur in a self-supporting substrate.

[0029] Figure 5 is a schematic cross-sectional view showing a schematic configuration of an element substrate according to one embodiment of the present invention.

[0030] Figure 6 is a cross-sectional view for explaining a measurement site of Young's modulus. DETAILED DESCRIPTION OF THE INVENTION

[0031] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments. For the sake of clarity in the description, the width, thickness, shape, etc. of each part may be schematically shown in the drawings as compared with the embodiments, but this is merely an example and does not limit the interpretation of the present invention. In addition, regarding the drawings, the same reference numerals are assigned to the same elements or equivalent elements, and repeated description may be omitted.

[0032] A. Group III element nitride substrate

[0033] Figure 1 is a schematic cross-sectional view showing a schematic configuration of a group III element nitride substrate according to one embodiment of the present invention, Figure 2 is Figure 1 a plan view of the group III element nitride substrate shown. The group III element nitride substrate 10 has a plate shape and has a first main surface 11 and a second main surface 12 facing each other, and these main surfaces are connected by a side surface 13.

[0034] In the illustrated example, the group III element nitride substrate is disk-shaped (wafer), but is not limited thereto, and may have any appropriate shape. The size of the group III element nitride substrate can be appropriately set according to the purpose. The diameter of the disk-shaped group III element nitride substrate is, for example, 50 mm or more and 300 mm or less, can be 75 mm or more, and can be 100 mm or more. By using a group III element nitride substrate having a larger size (for example, 75 mm or more in diameter), it is possible to increase the productivity of, for example, a larger-sized element.

[0035] The thickness of the group III nitride substrate is, for example, 250 μm or more and 800 μm or less, preferably 300 μm or more and 750 μm or less, and more preferably 350 μm or more and 725 μm or less.

[0036] The group III nitride substrate is composed of a group III nitride crystal. As the group III element constituting the group III nitride, for example, aluminum (Al), gallium (Ga), and indium (In) are used. These elements can be used alone or in combination of two or more. As a specific example of the group III nitride, examples include: aluminum nitride (Al x N), gallium nitride (Ga y N), indium nitride (In z N), aluminum gallium nitride (Al x Ga y N), gallium indium nitride (Ga y In z N), aluminum indium nitride (Al x In z N), aluminum gallium indium nitride (Al x Ga y In z N). It should be noted that in each chemical formula in parentheses, typically, x + y + z = 1.

[0037] The above-mentioned group III nitride may contain dopants. As dopants, for example, p-type dopants such as beryllium (Be), magnesium (Mg), strontium (Sr), cadmium (Cd), iron (Fe), manganese (Mn), and zinc (Zn), and n-type dopants such as silicon (Si), germanium (Ge), tin (Sn), and oxygen (O) can be cited. These dopants can be used alone or in combination of two or more.

[0038] In the above-mentioned group III nitride crystal, typically, the <0001> direction is the c-axis direction, the <1 - 100> direction is the m-axis direction, and the <11 - 20> direction is the a-axis direction. In addition, the crystal plane orthogonal to the c-axis is the c-plane, the crystal plane orthogonal to the m-axis is the m-plane, and the crystal plane orthogonal to the a-axis is the a-plane. The relationship between the crystal axis of the group III nitride crystal and the thickness direction of the group III nitride substrate 10 is not particularly limited.

[0039] In one embodiment, the thickness direction of the group III nitride substrate 10 is substantially the c-axis direction. Specifically, the thickness direction of the group III nitride substrate 10 is parallel or substantially parallel to the c-axis. And, substantially, the first major surface 11 is a group III element polar surface on the (0001) plane side, and the second major surface 12 is a nitrogen polar surface on the (000-1) side. Specifically, the first major surface 11 may be parallel to the (0001) plane or may be inclined with respect to the (0001) plane. The inclination angle of the first major surface 11 with respect to the (0001) plane is, for example, 10° or less, may be 5° or less, may be 2° or less, may be 1° or less. The second major surface 12 may be parallel to the (000-1) plane or may be inclined with respect to the (000-1) plane. The inclination angle of the second major surface 12 with respect to the (000-1) plane is, for example, 10° or less, may be 5° or less, may be 2° or less, may be 1° or less. The first major surface 11 is not limited to a plane parallel to the (0001) plane or a plane inclined with respect to the (0001) plane. For example, it may be substantially parallel to a non-polar plane such as the a-plane (11-20) or the m-plane (1-100), or may be parallel to a semi-polar plane such as the (11-22) plane or the (1-101) plane. It should be noted that the thickness direction means the direction perpendicular to the major surface.

[0040] The Young's modulus of the group III nitride substrate 10 can typically be 100 GPa to 300 GPa.

[0041] The Young's modulus of the group III nitride substrate 10 may vary in the thickness direction. The variation range of the Young's modulus in the thickness direction of the group III nitride substrate 10 is, for example, 50% or less, preferably 35% or less, more preferably 25% or less, further preferably 15% or less, and may be 5% or less. The variation range of the Young's modulus in the thickness direction is, for example, 0% or more, preferably 1% or more. By satisfying such a variation range, the generation of warpage can be well suppressed. It should be noted that the variation range of the Young's modulus can be calculated based on the measured values obtained by measuring the Young's modulus, for example, every 5 μm to 400 μm in the thickness direction.

[0042] The variation mode of the Young's modulus in the thickness direction is not particularly limited. In one embodiment, the Young's modulus in the first portion on the first major surface 11 side is higher than the Young's modulus in the second portion at a position closer to the second major surface 12 side than the first portion. For example, it may be that the Young's modulus becomes higher as it approaches the first major surface 11 side from the second major surface 12 side.

[0043] The absolute value of the difference between the Young's modulus in the first major surface 11 and the Young's modulus in the second major surface 12 is, for example, 100 GPa or less, preferably 80 GPa or less, more preferably 60 GPa or less, still more preferably 40 GPa or less, and may be 10 GPa or less. The absolute value of the difference between the Young's modulus in the first major surface 11 and the Young's modulus in the second major surface 12 is, for example, 0 GPa or more, preferably 3 GPa or more.

[0044] The value obtained by dividing the absolute value of the difference between the Young's modulus in the first major surface 11 and the Young's modulus in the second major surface 12 by the thickness of the group III nitride substrate 10 is, for example, 0.20 GPa / μm or less, preferably 0.18 GPa / μm or less, more preferably 0.14 GPa / μm or less, still more preferably 0.10 GPa / μm or less, and may be 0.05 GPa / μm or less. The value obtained by dividing the absolute value of the difference between the Young's modulus in the first major surface 11 and the Young's modulus in the second major surface 12 by the thickness of the group III nitride substrate 10 is, for example, 0 GPa / μm or more, preferably 0.02 GPa / μm or more.

[0045] The Young's modulus of the group III nitride substrate 10 can be measured by any suitable method. For example, in accordance with ISO14577, the Young's modulus can be measured using nanoindentation. In nanoindentation, the measurement direction of the Young's modulus is typically the thickness direction of the group III nitride substrate 10. Additionally, for example, the Young's modulus can be measured using a tensile test. Additionally, for example, the Young's modulus can be measured using a bending test. In the tensile test and the bending test, the measurement direction of the Young's modulus is typically the direction orthogonal to the thickness direction of the group III nitride substrate 10.

[0046] For example, a specified portion of the group III nitride substrate 10 can be exposed by grinding, polishing, etc. to measure the Young's modulus. Additionally, a measurement sample can be cut out from a specified portion of the group III nitride substrate 10, and the Young's modulus of the cut-out measurement sample can be measured. It should be noted that the Young's modulus can be evaluated at any position within the plane of the group III nitride substrate 10. However, regarding the variation range of the Young's modulus and the difference in Young's modulus in the above thickness direction, it is preferably evaluated substantially coaxially.

[0047] The group-III nitride substrate according to an embodiment of the present invention can well suppress the generation of warpage. Specifically, by making the group-III nitride substrate satisfy the above-mentioned relationship of Young's modulus, the generation of warpage can be well suppressed. Through repeated exploration of the problem of warpage, it was found that by controlling the distribution of Young's modulus in the thickness direction, warpage can be improved. It should be noted that the larger the size (e.g., diameter) of the group-III nitride substrate, the greater the warpage of the entire substrate. If the warpage of the entire substrate becomes large, for example, the characteristic deviation of the functional layer described later formed on the substrate will become large. Therefore, stricter warpage control is required. According to the embodiment of the present invention, even when the size of the group-III nitride substrate is large, the generation of warpage can be well suppressed.

[0048] The above-mentioned warpage can be evaluated by, for example, a laser displacement meter. As the measurement method of the laser displacement meter, for example, the confocal method, the triangulation method, and the optical interference method can be cited, and can be appropriately selected according to the surface roughness of the measurement object surface. The radius of curvature of the group-III nitride substrate calculated from the warpage measured by the laser displacement meter is preferably 15 m or more, more preferably 20 m or more, further preferably 25 m or more, particularly preferably 30 m or more, and most preferably 35 m or more.

[0049] B. Manufacturing method

[0050] The manufacturing method of the group-III nitride substrate according to an embodiment of the present invention includes: preparing a seed substrate having a base substrate and a seed film, growing a group-III nitride crystal on the seed film of the seed substrate, and removing the base substrate from the group-III nitride crystal.

[0051] Figures 3A to 3C It is a diagram showing the manufacturing process of the group-III nitride substrate according to an embodiment. Figure 3A It shows a state in which a seed film 22 is formed on the upper surface 21a of a base substrate 21 having an upper surface 21a and a lower surface 21b facing each other to complete a seed substrate 20.

[0052] As the above-mentioned base substrate, for example, a substrate having a shape and size capable of manufacturing a group-III nitride substrate having a desired shape and size is used. Representatively, the base substrate is a disk shape with a diameter of 50 mm to 350 mm. The thickness of the base substrate is, for example, 300 μm to 2000 μm.

[0053] As the base substrate, any suitable substrate can be used. The base substrate is typically composed of a single crystal. Examples of the material constituting the base substrate include: sapphire, crystal-oriented alumina, silicon, gallium oxide, aluminum gallium nitride, gallium arsenide, and silicon carbide (SiC).

[0054] The thickness of the above-mentioned seed film is, for example, 0.2 μm to 5 μm, preferably 1 μm to 4 μm. As the material constituting the seed film, any suitable material can be used. As the material constituting the seed film, group III element nitrides are typically used. In one embodiment, gallium nitride is used.

[0055] The seed film can be formed by any suitable method. As the film formation method of the seed film, a vapor growth method is typically used. Specific examples of the vapor growth method include: metalorganic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), pulsed-excitation deposition (PXD), molecular beam epitaxy (MBE), and sublimation method. Among them, the MOCVD method is preferably used.

[0056] The seed film formation based on the above MOCVD method includes, for example, a first formation step and a second formation step in sequence. Specifically, in the first formation step, a first layer (low-temperature growth buffer layer) (not shown) is formed on the base substrate at a temperature T1 (for example, 450 °C to 550 °C), and in the second formation step, a second layer (not shown) is formed at a temperature T2 (for example, 1000 °C to 1200 °C) higher than the temperature T1. The thickness of the first layer is, for example, 20 nm to 50 nm. The thickness of the second layer is, for example, 1 μm to 4 μm.

[0057] Next, group III element nitride crystals are grown on the seed film 22 of the seed substrate 20 to form a group III element nitride crystal layer 16, as Figure 3B shown to obtain a laminated substrate 30. The growth degree of the group III element nitride crystals (the thickness of the group III element nitride crystal layer 16) can be adjusted according to the desired thickness of the group III element nitride substrate. As the growth direction of the group III element nitride crystals, any suitable direction can be selected according to the use, purpose, etc. Specific examples include: the normal directions of the above-mentioned c-plane, a-plane, and m-plane, and the normal directions of the planes inclined with respect to the above-mentioned c-plane, a-plane, and m-plane.

[0058] Group III nitride crystals can be grown by any suitable method. As a method for growing Group III nitride crystals, any method can be used as long as it can achieve a crystal orientation that roughly imitates the crystal orientation of the above-mentioned seed film, and there is no particular limitation. Specific examples of the method for growing Group III nitride crystals include: vapor growth methods such as metalorganic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), pulsed laser deposition (PXD), molecular beam epitaxy (MBE), and sublimation method; liquid growth methods such as flux method, ammonothermal method, hydrothermal method, and sol-gel method; and solid growth methods using grain growth of powders. These methods can be used alone or in combination of two or more.

[0059] Preferably, as a method for growing Group III nitride crystals, the flux method (for example, Na flux method) is adopted. The detailed content of such a growth method is described, for example, in Japanese Patent No. 5244628, and various conditions of the described growth method can be appropriately controlled for growth.

[0060] For example, by changing the growth rate (growth speed) of Group III nitride crystals, the above-mentioned Young's modulus distribution can be achieved in the obtained Group III nitride substrate. Specifically, by reducing the growth rate of Group III nitride crystals in the initial stage of growth compared to the later stage of growth, the above-mentioned Young's modulus distribution can be achieved in the obtained Group III nitride substrate. In the initial stage of growth compared to the later stage of growth, there is a tendency for more defects such as dislocations to be generated more easily due to the lattice constant mismatch between the substrate 21 and the grown Group III nitride crystals. It is considered that if there are more such defects, the Young's modulus decreases. It has been found that by reducing the growth rate of Group III nitride crystals in the initial stage of growth compared to the later stage of growth, the decrease in Young's modulus in the initial stage of growth can be suppressed. Regarding the suppression of the decrease in Young's modulus, it is considered that, for example, changes in hole density and impurity concentration are the main reasons.

[0061] The change in growth rate can be achieved, for example, by adjusting the pressure. In one embodiment, when growing Group III nitride crystals with respect to the seed substrate 20, by reducing the pressure in the initial stage of growth compared to the later stage of growth to reduce the growth rate, the above-mentioned Young's modulus distribution can be achieved. As the growth progresses, the pressure can be increased continuously or stepwise.

[0062] The change in the growth rate can be achieved by adjusting, for example, the temperature. In addition, in the vapor phase growth method, the change in the growth rate of, for example, group III nitride crystals can be achieved by adjusting the supply mode (flow rate, flow velocity) of the source gas, the flow rate ratio of the source gas, and the like.

[0063] After the growth of the group III nitride crystal, as Figure 3C shown, the substrate 21 is removed from the group III nitride crystal (group III nitride crystal layer 16) to obtain a free-standing substrate 32. Representatively, as shown in the figure, the free-standing substrate 32 may include a group III nitride crystal layer 16 and a seed film 22. For example, the group III nitride crystal layer 16 is separated from the substrate 21 to obtain a free-standing substrate 32. The group III nitride crystal can be separated from the substrate by any suitable method. As a method for separating the group III nitride crystal, for example, a method in which the group III nitride crystal spontaneously separates from the substrate by using the thermal shrinkage difference with the substrate during the cooling process after the growth of the group III nitride crystal, a method of separating by chemical etching, and a laser lift-off method based on laser irradiation can be cited. When the group III nitride crystal is separated by the laser lift-off method, typically, the laser is irradiated from the lower surface 21b side of the substrate 21 of the stacked substrate 30. In addition, a free-standing substrate can be obtained by, for example, grinding or cutting using a cutting machine such as a wire saw.

[0064] Warpage sometimes occurs in the stacked substrate. Figure 4A is a cross-sectional view showing an example of the warpage that may occur in the stacked substrate, Figure 4B is a cross-sectional view showing an example of the warpage that may occur in the free-standing substrate. It should be noted that in FIG. 4, for easy observation of the figure, the cross-sections of the stacked substrate and the free-standing substrate are omitted of hatching. In addition, for convenience, the illustration of the seed film is omitted.

[0065] Figure 4AIn the example shown, convex warping occurs on the side of the group III nitride crystal layer 16 of the stacked substrate 30. The base substrate 21 may be made of a material having a different composition (chemical composition) from that of the group III nitride crystal layer 16. If a group III nitride crystal is heteroepitaxially grown on such a base substrate 21, warping tends to easily occur in the resulting stacked substrate 30. As the cause of the warping, it is considered that, for example, stress may be generated due to the lattice constant mismatch and the difference in thermal expansion coefficient between the base substrate 21 and the grown group III nitride crystal. For example, if the stacked substrate 30 is cooled after growing a group III nitride crystal at a high temperature (e.g., 800 °C to 1100 °C), warping may occur. When the thermal expansion coefficient of the base substrate 21 is larger than that of the grown group III nitride crystal (e.g., when a sapphire substrate is used as the base substrate), as Figure 4A shown, convex warping may occur on the side of the group III nitride crystal layer 16. On the other hand, when the thermal expansion coefficient of the base substrate 21 is smaller than that of the grown group III nitride crystal (e.g., when a silicon substrate or a SiC substrate is used as the base substrate), contrary to the illustrated example, convex warping may occur on the side of the base substrate 21.

[0066] Regarding the free-standing substrate 32 obtained by removing the base substrate 21 from the Figure 4A stacked substrate 30 shown, for example, as Figure 4B shown, the orientation of the warping may be reversed, and convex warping may occur on the lower surface 33 side where the base substrate 21 was disposed.

[0067] As described above, the free-standing substrate according to the embodiment of the present invention suppresses the decrease in Young's modulus in the initial stage of its cultivation, and the generation of warping as described above can be well suppressed.

[0068] The free-standing substrate 32 may be directly used as the above-mentioned group III nitride substrate, or the free-standing substrate 32 may be arbitrarily and appropriately processed to obtain the above-mentioned group III nitride substrate.

[0069] As an example of the processing performed on the above free-standing substrate, grinding of the peripheral portion (e.g., grinding using a diamond grindstone) can be cited. Typically, by grinding, it is processed into the above-mentioned desired shape and size (e.g., a disc shape having a desired diameter).

[0070] As another example of the processing performed on the self-supporting substrate described above, processing such as grinding and polishing (e.g., lapping, chemical mechanical polishing (CMP)) of the main surface (upper surface, lower surface) can be cited. Typically, thinning and planarization to a desired thickness are performed using grinding and polishing. In one embodiment, the seed film 22 can be removed by processing the main surface, and a state where only the group III nitride crystal layer 16 (only a single crystal growth layer) remains can be achieved.

[0071] In addition, for example, as the processing performed on the self-supporting substrate described above, chamfering of the outer peripheral edge, removal of the processed damaged layer, and removal of residual stress that may be generated due to the processed damaged layer can be cited.

[0072] C. Use

[0073] A functional layer can be formed on the group III nitride substrate described above. Figure 5 FIG. is a schematic cross-sectional view showing a schematic configuration of an element substrate according to one embodiment of the present invention. The element substrate 40 has a group III nitride substrate 10 and a functional layer 42 formed on the first main surface (e.g., group III element polar surface) 11 of the group III nitride substrate 10. Typically, the functional layer 42 is formed by epitaxial growth of crystals. As described above, warpage generation in the group III nitride substrate 10 can be well suppressed, and thus the functional layer 42 can be formed extremely well. Specifically, when forming the functional layer 42, for example, uneven heating during heating from the group III nitride substrate 10 side can be prevented, and excellent in-plane property uniformity of the obtained functional layer 42 can be achieved. In addition, by using the group III nitride substrate 10 in which warpage generation is suppressed, excellent workability in manufacturing the element substrate 40 can be achieved.

[0074] The above functional layer can function as, for example, a light-emitting layer, a rectifying element layer, a switching element layer, or a power semiconductor layer. In one embodiment, group III nitride crystals are used as the material constituting the above functional layer. As the group III elements constituting the group III nitride, for example, Ga (gallium), Al (aluminum), and In (indium) are used. These elements can be used alone or in combination of two or more.

[0075] It should be noted that the second main surface (e.g., nitrogen polar surface) 12 of the group III nitride substrate 10 can be processed such as grinding and polishing in a state where the functional layer 42 is formed on the group III nitride substrate 10 (in a state where the element substrate 40 is manufactured).

[0076] Examples

[0077] Hereinafter, the present invention will be specifically described using examples, but the present invention is not limited to these examples.

[0078] [Comparative Example 1]

[0079] (Fabrication of Seed Substrate)

[0080] On a 2-inch diameter c-plane sapphire substrate, a 2-μm thick gallium nitride film was formed by MOCVD method to fabricate a seed substrate.

[0081] (Cultivation of Gallium Nitride Crystals)

[0082] The cultivation of gallium nitride crystals was carried out using a crystal manufacturing apparatus, which includes: a pressure-resistant container capable of supplying pressurized nitrogen, a rotating table capable of rotating within the pressure-resistant container, and an outer container placed on the rotating table.

[0083] The obtained seed substrate was placed in a 200-mm diameter alumina crucible in a nitrogen atmosphere glove box. Next, metallic gallium and metallic sodium were filled into the crucible such that the atomic ratio Ga / (Ga + Na) (mol%) was 15 mol%, and then covered with an alumina plate. In this state, the crucible was placed into a stainless-steel inner container, and further into a stainless-steel outer container capable of accommodating the inner container. The outer container was closed with a lid equipped with a nitrogen inlet tube. In this state, the outer container was placed on a rotating table provided in the heating section within the crystal manufacturing apparatus, and the lid of the pressure-resistant container of the crystal manufacturing apparatus was covered to seal it.

[0084] Next, the inside of the pressure-resistant container was evacuated using a vacuum pump. Next, the heating section was operated to heat the temperature of the heating space to 870 °C. At the same time, nitrogen was introduced into the pressure-resistant container until it reached 4.3 MPa, and the outer container was rotated around the central axis at a speed of 20 rpm in a clockwise and counterclockwise direction with a certain period. This state was maintained for 100 hours to cultivate 700-μm thick gallium nitride crystals.

[0085] After that, it was naturally cooled to room temperature and depressurized to atmospheric pressure, then the lid of the pressure-resistant container was opened, and the crucible was taken out. The solidified metallic sodium in the crucible was removed, and the seed substrate with gallium nitride crystals grown thereon was recovered.

[0086] After that, at room temperature, ultraviolet laser was irradiated from the sapphire substrate side of the seed substrate with gallium nitride crystals grown thereon to decompose the gallium nitride film of the seed substrate, and the grown gallium nitride crystals were separated from the sapphire substrate.

[0087] Using a diamond grindstone, grind the peripheral part of the separated gallium nitride crystal to adjust the diameter to 50 mm. Next, fix the gallium nitride crystal to a ceramic processing platform, and use a grinding device and a lapping device to grind and lap the gallium-polarity surface of the gallium nitride. Then, use diamond abrasive grains with a particle size of 0.1 μm for mirror finishing. Next, turn over the gallium nitride crystal and fix it to the ceramic processing platform, and perform grinding and lapping on its nitrogen-polarity surface in the same manner as the gallium-polarity surface. After that, use diamond abrasive grains with a particle size of 0.1 μm for mirror finishing.

[0088] In this way, a gallium nitride substrate (wafer) with a thickness direction corresponding to the c-axis direction and a thickness of 450 μm is fabricated.

[0089] [Example 1]

[0090] Cultivate gallium nitride crystals by linearly changing the pressure (atmospheric pressure) in the heat-resistant container from 4.1 MPa to 4.3 MPa over 105 hours. Except for this, fabricate the gallium nitride substrate in the same manner as Comparative Example 1.

[0091] [Example 2]

[0092] Cultivate gallium nitride crystals by linearly changing the pressure (atmospheric pressure) in the heat-resistant container from 3.9 MPa to 4.3 MPa over 110 hours. Except for this, fabricate the gallium nitride substrate in the same manner as Comparative Example 1.

[0093] [Example 3]

[0094] Cultivate gallium nitride crystals by linearly changing the pressure (atmospheric pressure) in the heat-resistant container from 3.7 MPa to 4.3 MPa over 115 hours. Except for this, fabricate the gallium nitride substrate in the same manner as Comparative Example 1.

[0095] <Evaluation>

[0096] Evaluate the gallium nitride substrates (wafers) obtained in the examples and comparative examples as follows. The evaluation results are summarized in Table 1.

[0097] 1. Young's modulus

[0098] As Figure 6 shown by the black circles in, measure the Young's modulus at four points in the thickness direction at the center of the plane of the obtained gallium nitride substrate (wafer, thickness 450 μm). Specifically, after measuring the Young's modulus at the center of the upper surface and the center of the lower surface of the obtained gallium nitride substrate, grind and lap the upper surface and the lower surface at a thickness of 150 μm respectively, and measure the Young's modulus at the center of the ground and lapped upper surface and the center of the lower surface.

[0099] The Young's modulus was measured using nanoindentation. Specifically, an ultra-micro indentation hardness testing machine ("ENT-NEXUS" manufactured by ELIONIX Corporation) was used as the measuring device, a Berkovich-type diamond indenter was used as the indenter, and it was indented in the thickness direction under the conditions of a maximum load of 10 mN and a loading speed of 1 mN / second. After holding for 5 seconds, it was unloaded at an unloading speed of 1 mN / second. The curve of the indentation depth and the load was measured, and the Young's modulus was calculated.

[0100] It should be noted that the minimum and maximum measured values are shown in Table 1, and the variation range (%) was calculated according to the following formula (I).

[0101] Variation range = (maximum value - minimum value) / average value × 100 ····· (I)

[0102] 2. Radius of curvature

[0103] The warpage of the gallium nitride substrate (wafer, thickness 450 μm) was measured using a laser displacement meter ("CL-P015" manufactured by Keyence Corporation), and the radius of curvature was calculated based on the warpage. Specifically, a laser with a wavelength of 655 nm was irradiated onto the main surface on the side opposite to the side where the sapphire substrate was disposed, and the displacement of the main surface was measured using the confocal method to obtain the waveform of the region obtained by removing 3 mm from the end of the gallium nitride substrate. Based on the obtained waveform, an approximate curve was calculated by the least squares method using a quadratic function, and the difference between the highest value and the lowest value of the approximate curve was measured on two axes orthogonal to the substrate surface, and their average value was set as the warpage S. In addition, based on the obtained warpage S, the radius of curvature R was calculated using the following formula (II).

[0104] R = D 2 / (8 × S) ····· (II)

[0105] Here, R represents the radius of curvature, D represents the substrate diameter, and S represents the warpage, and the units are all [m].

[0106] Table 1

[0107]

[0108] In each of the examples and comparative examples, convex warpage was confirmed on the side where the sapphire substrate was disposed, but the degree was particularly small in the examples.

[0109] Industrial applicability

[0110] The group III nitride substrate according to the embodiment of the present invention can be used as a substrate for various semiconductor devices, for example.

[0111] Symbol description

[0112] 10…Group III nitride substrate

[0113] 11…First major surface

[0114] 12…Second major surface

[0115] 13…Side surface

[0116] 16…Group III nitride crystal layer

[0117] 20…Seed substrate

[0118] 21…Base substrate

[0119] 21a…Upper surface

[0120] 21b…Lower surface

[0121] 22…Seed film

[0122] 30…Stacked substrate

[0123] 32…Self-supporting substrate

[0124] 40…Component substrate

[0125] 42…Functional layer

Claims

1. A group III nitride substrate having a first major surface and a second major surface facing each other, The group III nitride substrate is characterized in that The variation range of the Young's modulus in the thickness direction is 50% or less.

2. The group III nitride substrate according to claim 1, characterized in that The group III nitride substrate is a self-supporting substrate of group III nitride crystal.

3. The group III nitride substrate according to claim 1, characterized in that The thickness is 250 μm or more and 800 μm or less.

4. The group III nitride substrate according to claim 1, characterized in that The variation range of the Young's modulus in the thickness direction is 35% or less.

5. The group III nitride substrate according to claim 1, characterized in that The variation range of the Young's modulus in the thickness direction is 1% or more.

6. The group III nitride substrate according to claim 1, characterized in that The closer to the first major surface side from the second major surface side, the higher the Young's modulus.

7. The group III nitride substrate according to claim 1, characterized in that The absolute value of the difference between the Young's modulus in the first major surface and the Young's modulus in the second major surface is 100 GPa or less.

8. The group III nitride substrate according to claim 1, characterized in that The thickness direction is substantially the c-axis direction of the group III nitride crystal.

9. The group III nitride substrate according to claim 1, characterized in that The Young's modulus is measured by nanoindentation method.

10. A method for manufacturing a group III nitride substrate according to any one of claims 1 to 9, characterized in that, Comprising: Preparing a seed substrate, which includes a base substrate having an upper surface and a lower surface facing each other and a seed film formed on the upper surface of the base substrate; Culturing group III nitride crystals on the seed film of the seed substrate; And Removing the base substrate from the group III nitride crystals, Changing the growth rate of the group III nitride crystals to perform the growth of the group III nitride crystals.

11. The manufacturing method according to claim 10, characterized in that The base substrate contains a material having a different composition from the group III nitride crystal.

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