Group III element nitride substrate, method for inspecting a Group III element nitride substrate, and method for manufacturing a Group III element nitride substrate.

Abstract

Provided is a group-III element nitride substrate with which a higher yield can be achieved. An group-III element nitride substrate according to an embodiment of the present invention has a first principal surface and second principal surface facing each other, wherein the value of (Dmax - Dmin / Dave calculated from the maximum value Dmax, minimum value Dmin, and average value Dave of crystal lattice spacing D1 to crystal lattice spacing D12 of (10-12) plane, (01-12) plane, (-1102) plane, (-1012) plane, (0-112) plane, and (1-102) plane at each of a first position of the first principal surface and a second position at the second principal surface is 5.0 × 10-4 or less.

Description

Technical Field

[0001] The present invention relates to a group III nitride substrate, a method for inspecting a group III nitride substrate, and a method for manufacturing a group III nitride substrate.

Background Art

[0002] For example, as described in Patent Document 1, a group III nitride substrate is used as a substrate for various semiconductor devices such as light-emitting devices and electronic devices. For example, various semiconductor devices can be manufactured by epitaxially growing crystals on a group III nitride substrate.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, cracks and fractures are likely to occur in group III nitride substrates, and an improvement in yield is desired. Specifically, cracks and fractures are likely to occur during the production of group III nitride substrates and / or during the production of semiconductor devices, and an improvement in yield is desired.

[0005] A main object of the present invention is to provide a group III nitride substrate capable of improving the yield.

Means for Solving the Problems

[0006] 1. A 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, and the crystal lattice plane spacings D1 to D12 of the (10-12) plane, (01-12) plane, (-1102) plane, (-1012) plane, (0-112) plane, and (1-102) plane at a first site on the first main surface and a second site on the second main surface, respectively, the maximum value D max , the minimum value D min and the average value D ave are calculated from (D max - D min ) / D ave is 5.0×10 -4 or less. 2. The group-III nitride substrate according to 1 above may be a freestanding substrate of a group-III nitride crystal. 3. The group-III nitride substrate according to 1 or 2 above may contain gallium nitride. 4. In the group-III nitride substrate according to any one of 1 to 3 above, the first site and the second site may be located on the same line extending in the thickness direction of the substrate. 5. A method for inspecting a group-III nitride substrate according to an embodiment of the present invention includes preparing a group-III nitride substrate having a first main surface and a second main surface facing each other, measuring the crystal lattice plane spacings D1 to D12 of the (10-12) plane, (01-12) plane, (-1102) plane, (-1012) plane, (0-112) plane, and (1-102) plane at a first site on the first main surface and a second site on the second main surface, respectively, and calculating the maximum value D max , the minimum value D min and the average value D ave from (D max - D min ) / D ave . 6. In the method for inspecting a group-III nitride substrate according to 5 above, the first site and the second site may be located on the same line extending in the thickness direction of the substrate. 7. In the method for inspecting a group-III nitride substrate according to 5 or 6 above, the measurement may be an X-ray diffraction measurement. 8. A method for manufacturing a group III element nitride substrate according to an embodiment of the present invention involves performing the inspection method for a group III element nitride substrate described in any of 5 to 7 above, and (D max -D min ) / D ave This includes selecting the above-mentioned Group III element nitride substrate based on the value of . 9. In the method for manufacturing a group III element nitride substrate as described in 8 above, the above (D max -D min ) / D ave The value is 5.0 × 10 -4 The following Group III element nitride substrates may be selected. 10. In the method for manufacturing a group III element nitride substrate described in 8 or 9 above, preparing the group III element nitride substrate may include preparing a base substrate having an upper surface and a lower surface facing each other, and growing a group III element nitride crystal on the base substrate. 11. Another embodiment of the present invention provides a method for manufacturing a group III element nitride substrate, the method for manufacturing a group III element nitride substrate described in any of 1 to 4 above, comprising: preparing a base substrate having an upper surface and a lower surface facing each other; and growing a group III element nitride crystal on the base substrate, wherein the base substrate contains a group III element nitride. 12. In the method for manufacturing a group III element nitride substrate described in 11 above, the group III element nitride crystal may be grown by the flux method. 13. A method for manufacturing an element substrate according to an embodiment of the present invention involves performing the inspection method for a group III element nitride substrate described in any of 5 to 7 above, and (D max -D min ) / D ave The method includes selecting the above-mentioned Group III element nitride substrate based on the value of and forming a functional layer on the main surface of the selected Group III element nitride substrate. 14. The method for manufacturing a bonded substrate according to an embodiment of the present invention involves performing the inspection method for a group III element nitride substrate described in any of 5 to 7 above, and the above (D max -D min ) / D aveThe process includes selecting the above-mentioned Group III element nitride substrate based on the value of and bonding the selected Group III element nitride substrate to a support substrate. [Effects of the Invention]

[0007] According to embodiments of the present invention, it is possible to provide a group III element nitride substrate that can improve yield. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view showing the general structure of a group III element nitride substrate according to one embodiment of the present invention. [Figure 2] Figure 1 is a plan view of a group III element nitride substrate. [Figure 3A] This figure shows the manufacturing process of a group III element nitride substrate according to one embodiment. [Figure 3B] This figure follows Figure 3A. [Figure 3C] This figure follows Figure 3B. [Figure 4A] This is a diagram illustrating a method for manufacturing a substrate according to one embodiment. [Figure 4B] This figure follows Figure 4A. [Figure 4C] This figure follows Figure 4B. [Figure 5] This is a schematic cross-sectional view showing the general configuration of an element substrate according to one embodiment of the present invention. [Figure 6] This is a schematic cross-sectional view showing the general configuration of a bonded substrate according to one embodiment of the present invention. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. While the drawings may schematically represent the width, thickness, shape, etc., of each part compared to the embodiments in order to clarify the explanation, these are merely examples and do not limit the interpretation of the present invention. Furthermore, in the drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant explanations may be omitted.

[0010] A. Group III element nitride substrate Figure 1 is a schematic cross-sectional view showing the general structure of a group III element nitride substrate according to one embodiment of the present invention, and Figure 2 is a plan view of the group III element nitride substrate shown in Figure 1. The group III element nitride substrate 10 is plate-shaped and has a first main surface 11 and a second main surface 12 facing each other, which are connected via a side surface 13. As shown in Figure 2, the group III element nitride substrate 10 has an outer peripheral edge 14. In the illustrated example, the outer peripheral edge 14 has an arc-shaped portion 14a and a linear orientation flat 14b, and the arc-shaped portion 14a is connected to the orientation flat 14b.

[0011] The main surface may be, for example, a mirror surface or a non-mirror surface. The main surface on the side where the functional layer described later is formed is preferably a mirror surface. A mirror surface is a surface on which light is reflected and an object is visible reflected in the surface, and the roughness and undulation of the surface are reduced to a degree that is negligible with respect to the wavelength of visible light.

[0012] In the illustrated example, the group III element nitride substrate is disc-shaped (wafer), but it is not limited to this and can be any suitable shape. The size of the group III element nitride substrate can be appropriately set according to the purpose. The diameter of the disc-shaped group III element nitride substrate is, for example, 25 mm or more and 350 mm or less, and may be 45 mm or more, or 50 mm or more.

[0013] The thickness of the group III element nitride substrate is, for example, 200 μm or more and 1000 μm or less, preferably 250 μm or more and 900 μm or less, and more preferably 300 μm or more and 800 μm or less.

[0014] Group III element nitride substrates are composed of Group III element nitride crystals. Examples of Group III elements used to make up Group III element nitrides include aluminum (Al), gallium (Ga), and indium (In). These can be used individually or in combination of two or more. Specific examples of Group III element nitrides include aluminum nitride (typically AlN), gallium nitride (typically GaN), indium nitride (typically InN), and 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) is one example. Note that, in each chemical formula within parentheses, x+y+z=1 is typical.

[0015] The above-mentioned Group III element nitrides may contain dopants. Examples of dopants include 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). These can be used individually or in combination of two or more.

[0016] In the above-mentioned Group III element nitride crystals, typically, <0001> The 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. Furthermore, a crystal plane perpendicular to the c-axis is a c-plane, a crystal plane perpendicular to the m-axis is an m-plane, and a crystal plane perpendicular to the a-axis is an a-plane.

[0017] In one embodiment, the thickness direction of the group III element nitride substrate 10 is substantially the c-axis direction. Specifically, the thickness direction of the group III element nitride substrate 10 is parallel to or substantially parallel to the c-axis. Substantially, the first main surface 11 is the group III element polar surface on the (0001) plane side, and the second main surface 12 is the nitrogen polar surface on the (000-1) plane side. Specifically, the first main surface 11 may be parallel to the (0001) plane or inclined with respect to the (0001) plane. The inclination angle of the first main surface 11 with respect to the (0001) plane is, for example, 10° or less, 5° or less, 2° or less, or 1° or less. The second main surface 12 may be parallel to the (000-1) plane or inclined with respect to the (000-1) plane. The inclination angle of the second main surface 12 with respect to the (000-1) surface is, for example, 10° or less, may be 5° or less, may be 2° or less, or may be 1° or less. Here, the thickness direction is the direction perpendicular to the main surface and is the normal direction of the main surface.

[0018] B. Testing Methods A method for inspecting a group III element nitride substrate according to one embodiment of the present invention involves measuring the crystal lattice plane spacings D1 to D12 of the (10-12), (01-12), (-1102), (-1012), (0-112), and (1-102) planes in the first portion of the first main surface and the second portion of the second main surface of the prepared group III element nitride substrate, and measuring the maximum value D of the obtained crystal lattice plane spacings D1 to D12. max , minimum value D min and mean D ave From (D max -D min ) / D ave This includes calculating the value of [the specified value]. By selecting the first and second main surfaces as measurement points, measurements can be taken without damaging the substrate (non-destructively). Furthermore, the intrinsic stress described later can be evaluated more accurately.

[0019] Typically, X-ray diffraction measurement is employed to measure the crystal lattice plane spacing D described above. X-ray diffraction measurement allows for non-destructive measurement. It is preferable to measure the crystal lattice plane spacing D at multiple locations (for example, two locations) on the group III element nitride substrate. In one embodiment, for example, from the viewpoint of simplifying the measurement, the crystal lattice plane spacing D is measured at one location each on the first main surface and the second main surface of the group III element nitride substrate. For example, as shown by the black circles in Figures 1 and 2, the crystal lattice plane spacing D is measured at the first part 11a located at the center of the circular first main surface 11 and at the second part 12a located at the center of the second main surface 12. The first part 11a and the second part 12a are located on the same line extending in the thickness direction of the group III element nitride substrate 10. Here, the first part 11a and the second part 12a do not need to be strictly located on the same line extending in the thickness direction, but it is sufficient if they are substantially located on the same line extending in the thickness direction. For example, when viewing the group III element nitride substrate 10 from above, the distance between the first portion 11a and the second portion 12a should be 5 mm or less.

[0020] For example, by measurement, the values ​​D1, D2, D3, D4, D5, and D6 of the lattice plane spacing D of the (10-12), (01-12), (-1102), (-1012), (0-112), and (1-102) planes in the first part of the group III element nitride substrate, and the values ​​D7, D8, D9, D10, D11, and D12 of the lattice plane spacing D of the (10-12), (01-12), (-1102), (-1012), (0-112), and (1-102) planes in the second part of the group III element nitride substrate are obtained, and the maximum value D from D1 to D12 is obtained. max , minimum value D min and mean D ave The value calculated from (D max -D min ) / D ave By satisfying a predetermined value (by having a value less than or equal to a predetermined value), a high-quality group III element nitride substrate and / or semiconductor device can be obtained. Specifically, a group III element nitride substrate in which crack occurrence is well suppressed can be obtained. And, by satisfying a predetermined (D max-D min ) / D ave By selecting and using Group III element nitride substrates that satisfy the specified requirements, the yield of semiconductor device fabrication can be significantly improved. For example, the occurrence of defects such as cracks and chips in the substrate can be significantly suppressed during the device fabrication process.

[0021] In one embodiment, the group III element nitride substrate is (D max -D min ) / D ave 5.0 × 10 -4 The following is preferable. In this case, in the above selection, (D max -D min ) / D ave 5.0 × 10 -4 The following Group III element nitride substrates will be selected.

[0022] In group III element nitride crystals, the (10-12), (01-12), (-1102), (-1012), (0-112), and (1-102) planes are generally considered crystallographically equivalent. However, the inventors investigated the relationship between the lattice plane spacing D of these planes, which are considered equivalent, and the quality of the group III element nitride substrate, and found that there is a correlation between the lattice plane spacing D of the above planes and the quality of the group III element nitride substrate. Specifically, they found a correlation between the lattice plane spacing D and the susceptibility of the group III element nitride substrate to cracking. Since group III element nitride substrates that are prone to cracking tend to experience defects such as cracking and chipping during the device fabrication process, the inspection method according to this embodiment may contribute to improving the yield of device fabrication. The susceptibility of a substrate to cracking is thought to be correlated with the intrinsic stress of the substrate, and this can be evaluated, for example, by Raman spectroscopy. Stresses evaluated by Raman spectroscopy can be calculated assuming isotropic stress in the plane, which may prevent a complete assessment of the substrate's brittleness. According to this embodiment, the substrate's brittleness can be evaluated with extremely high accuracy. Intrinsic stress can cause crystal strain and change the lattice length, and by measuring this, the substrate's brittleness can be evaluated more accurately.

[0023] C. Manufacturing method A method for manufacturing a group III element nitride substrate according to one embodiment of the present invention includes preparing a base substrate and growing a group III element nitride crystal on the base substrate.

[0024] Figures 3A to 3C show the manufacturing process of a group III element nitride substrate according to one embodiment.

[0025] C-1. Preparation of the substrate Figure 3A shows a base substrate 20 having an upper surface 20a and a lower surface 20b that are opposite to each other.

[0026] As the base substrate 20, for example, a substrate having a shape and size that allows for the manufacture of a Group III element nitride substrate of a desired shape and size is used. Typically, the base substrate is disc-shaped with a diameter of 25 mm to 350 mm. The thickness of the base substrate is, for example, 300 μm to 2000 μm.

[0027] Any suitable substrate can be used as the base substrate. Typically, the base substrate is composed of a single crystal. Any suitable material can be used as the material constituting the base substrate. Specific examples of materials constituting the base substrate include sapphire, crystal-oriented alumina, silicon, gallium oxide, gallium arsenide, silicon carbide (SiC), and group III element nitrides. Preferably, the base substrate is composed of a material having the same composition (chemical composition) as the group III element nitride crystal layer to be grown, and may contain group III element nitrides. Specifically, a group III element nitride base substrate can be used as the base substrate. Details of group III element nitrides are as described above.

[0028] Figures 4A to 4C illustrate a method for manufacturing a base substrate according to one embodiment. For example, as shown in Figure 4A, a seed crystal film 52 is deposited on a growth substrate 51 to prepare a seed crystal substrate 50. As shown in Figure 4B, a group III element nitride crystal 22 is grown on the seed crystal film 52 side of the seed crystal substrate 50. As shown in Figure 4C, the growth substrate 51 is removed from the grown group III element nitride crystal (growth layer) 22 to obtain a group III element nitride base substrate 20. The growth substrate 51 can be made of any suitable material. Preferably, a sapphire substrate is used as the growth substrate 51.

[0029] The thickness of the seed crystal film is, for example, 0.2 μm to 10 μm, preferably 1 μm to 5 μm. Typical materials used to constitute the seed crystal film are group III element nitrides. Details of the group III element nitrides are as described above.

[0030] Seed crystal films can be deposited by any suitable method. Typical methods for depositing seed crystal films include vapor deposition (VPD). Specific examples of VPD methods include metal-organic chemical vapor deposition (MOCVD), hydride vapor deposition (HVPE), pulsed excitation deposition (PXD), molecular beam epitaxy (MBE), and sublimation. Among these, MOCVD is preferred.

[0031] The deposition of the seed crystal film by the MOCVD method described above includes, for example, a first formation step and a second formation step in this order. In one embodiment, in the first formation step, a first layer (buffer layer) not shown is deposited on the growth substrate at a temperature T1 (e.g., 450°C to 600°C), and in the second formation step, a second layer is deposited at a temperature T2 (e.g., 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.

[0032] The method for growing the group III element nitride crystal on the above-mentioned seed crystal substrate is not particularly limited, as long as it can achieve a crystal orientation that generally follows the crystal orientation of the seed crystal film. Specific examples of methods for growing group III element nitride crystals will be described later.

[0033] As shown in Figure 4C, after removing the growth substrate 51 from the growth layer 22, the growth layer 22 may be subjected to grinding of its peripheral edges (for example, grinding using a diamond grinding wheel). Typically, the growth layer 22 may be processed by grinding to achieve the desired shape and size (for example, a disc shape with a desired diameter).

[0034] For example, the main surface (e.g., the polar surface of group III elements) of the growth layer 22 may be ground and polished. For example, lapping or chemical mechanical polishing (CMP) may be performed. After processing the main surface, it is preferable to perform a treatment to remove the processed surface. Through such a treatment, a substrate from which the processed altered layer and latent scratches have been removed can be obtained. Examples of treatments to remove the processed surface include reactive ion etching (RIE).

[0035] Growth of C-2.III element nitride crystals Next, as shown in Figure 3B, a group III element nitride crystal is grown on the base substrate 20 to form a group III element nitride crystal layer 16, thereby obtaining a laminated substrate 30. The degree of growth of the group III element nitride crystal (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. Any appropriate direction can be selected for the growth direction of the group III element nitride crystal depending on the application, purpose, etc. Specific examples include the direction normal to the c-plane and the direction normal to a plane inclined to the c-plane.

[0036] Group III element nitride crystals can be grown by any suitable method. The method for growing Group III element nitride crystals is not particularly limited, as long as it can achieve a crystal orientation that generally follows the crystal orientation of the underlying substrate. Specific examples of methods for growing Group III element nitride crystals include vapor phase growth methods such as metal-organic chemical vapor deposition (MOCVD), hydride vapor deposition (HVPE), pulsed excitation deposition (PXD), molecular beam epitaxy (MBE), and sublimation; and liquid phase growth methods such as flux, amonothermal, hydrothermal, and sol-gel methods. These can be used individually or in combination of two or more.

[0037] Preferably, a flux method (e.g., the Na flux method) is used as a method for growing group III element nitride crystals. Details of such a growth method are described, for example, in Japanese Patent Publication No. 5244628, and the crystals may be grown by adjusting the various conditions of the described growth method as appropriate. Specifically, the growth of group III element nitride crystals can be carried out by adjusting various conditions using a crystal manufacturing apparatus that includes a pressure vessel capable of supplying pressurized nitrogen gas, a turntable that can rotate within the pressure vessel, and an outer vessel placed on the turntable.

[0038] The growth of Group III element nitride crystals by the flux method is typically carried out using a crucible as the growth container. Specifically, the substrate or seed crystal substrate is placed in a predetermined position within the crucible, and then the raw material is filled in. The crucible containing the substrate or seed crystal substrate is typically placed with a lid on, under a nitrogen-containing atmosphere, and under predetermined pressure and temperature, and subjected to the growth process.

[0039] The above raw materials are, for example, a molten composition containing flux, a group III element, and optionally a dopant. The flux preferably contains at least one of an alkali metal and an alkaline earth metal, and more preferably contains metallic sodium. Typically, the flux and the metal raw material are used in mixture form. As the metal raw material, elemental metals, alloys, metal compounds, etc., can be used, but from the viewpoint of handling, elemental metals are preferably used.

[0040] The crucible (including the lid) can be formed from any suitable material that can be used in the flux process. Examples of crucible materials include alumina, yttria, and YAG (yttrium-aluminum-garnet). The crucible material may be single crystal or polycrystalline (ceramic). The ceramic may have its relative density increased by HIP treatment or other methods, giving it so-called translucency.

[0041] As described above, growth can be carried out in a nitrogen-containing atmosphere. In addition to nitrogen, the growth atmosphere may contain other gases. Inert gases such as argon, helium, and neon are preferably used as other gases.

[0042] The atmospheric pressure during growth can be set to any appropriate pressure. The atmospheric pressure during growth may be, for example, 1 MPa or more, 2 MPa or more, or 3 MPa or more, from the viewpoint of preventing flux evaporation. On the other hand, the atmospheric pressure during growth may be, for example, 50 MPa or less, or 10 MPa or less, from the viewpoint of preventing the growth apparatus from becoming too large. In one embodiment, the atmospheric pressure during the growth of the group III element nitride crystal on the substrate is preferably 4.3 MPa or less, more preferably 4.0 MPa or less. Such pressure allows for the above-mentioned predetermined (D max -D min ) / D ave A group III element nitride substrate that satisfies the requirements can be successfully fabricated.

[0043] The temperature of the atmosphere during growth can be set to any appropriate temperature. The temperature of the atmosphere during growth may be, for example, 700°C to 1000°C, or 800°C to 900°C. In one embodiment, the temperature of the atmosphere during growth of the group III element nitride crystal on the substrate is preferably 840°C or higher, more preferably 850°C or higher. According to such a temperature, the above predetermined (D max -D min ) / D ave A group III element nitride substrate that satisfies the requirements can be successfully fabricated.

[0044] Growth is preferably carried out while rotating the crucible (substrate). For example, a covered crucible is placed in the outer container of the crystal manufacturing apparatus and placed on a turntable, and the crucible is rotated by rotating the turntable (for example, by rotation on its own axis). The rotation speed is, for example, 5 rpm to 40 rpm. In one embodiment, the rotation speed when growing the group III element nitride crystal on the substrate is preferably 15 rpm or less, more preferably 14 rpm or less. With such a rotation speed, the predetermined (D max -D min ) / D ave A group III element nitride substrate that satisfies the above can be successfully fabricated. The rotation direction can be set to any suitable direction. In a preferred embodiment, during growth, clockwise and counterclockwise rotations are repeated at predetermined intervals. The time for maintaining rotation at a predetermined rotational speed in one rotation direction (holding time) is, for example, 10 seconds to 1000 seconds. In one embodiment, the holding time for growing the group III element nitride crystal on the substrate is preferably 100 seconds or more, more preferably 200 seconds or more, and even more preferably 300 seconds or more. With such a holding time, the above predetermined (D max -D min ) / D ave A group III element nitride substrate that satisfies the requirements can be successfully fabricated.

[0045] After growing the group III element nitride crystals, as shown in Figure 3C, a part or all of the base substrate 20 may be removed from the group III element nitride crystals (group III element nitride crystal layer 16) to obtain a self-supporting substrate 32, or, unlike the illustrated example, the laminated substrate 30 may be used as a self-supporting substrate as is. As shown in the illustration, when removing the base substrate 20 from the group III element nitride crystal layer 16, for example, the group III element nitride crystal layer 16 is separated from the base substrate 20 to obtain a self-supporting substrate 32. The group III element nitride crystals can be separated from the base substrate by any suitable method. Examples of methods for separating the group III element nitride crystals include a method that utilizes the difference in thermal shrinkage with the base substrate during the cooling process after growing the group III element nitride crystals to allow spontaneous separation from the base substrate, a method of separation by chemical etching, and a laser lift-off method using laser light irradiation. When separating the group III element nitride crystals by the laser lift-off method, typically, laser light is irradiated from the lower surface 20b side of the base substrate 20 of the laminated substrate 30. Alternatively, a self-supporting substrate may be obtained by cutting using a cutting machine such as a grinder or wire saw.

[0046] The self-supporting substrate 32 may be used as the above-mentioned Group III element nitride substrate as is, or the self-supporting substrate 32 may be subjected to any appropriate processing to obtain the above-mentioned Group III element nitride substrate.

[0047] One example of processing performed on the above-mentioned self-supporting substrate is grinding of the peripheral edge (for example, grinding using a diamond grinding wheel). Typically, grinding is performed to process the substrate into the desired shape and size (for example, a disc shape with a desired diameter).

[0048] Another example of processing performed on the above-mentioned self-supporting substrate is grinding and polishing (e.g., lapping, chemical mechanical polishing (CMP)) of the main surfaces (top and bottom surfaces). Typically, grinding and polishing are used to thin and flatten the substrate to the desired thickness.

[0049] Furthermore, examples of processing performed on the above-mentioned self-supporting substrate include chamfering of the outer edge, removal of the processed altered layer and latent scratches, and removal of residual stress that may be caused by the processed altered layer.

[0050] D.Applications In one embodiment, a functional layer may be formed on the Group III element nitride substrate. Figure 5 is a schematic cross-sectional view showing the general configuration of an element substrate according to one embodiment of the present invention. The element substrate 40 has a Group III element nitride substrate 10 and a functional layer 42 formed on the first main surface (e.g., the Group III element polar surface) 11 of the Group III element nitride substrate 10. The functional layer 42 is typically formed by epitaxial growth of a crystal.

[0051] The above-mentioned functional layer can function, for example, as a light-emitting layer, a rectifier layer, a switching element layer, or a power semiconductor layer. In one embodiment, a group III element nitride crystal is used as the material constituting the above-mentioned functional layer. Examples of group III elements that constitute the group III element nitride include Ga (gallium), Al (aluminum), and In (indium). These can be used individually or in combination of two or more.

[0052] Furthermore, while the functional layer 42 is formed on the group III element nitride substrate 10 (in the state of being an element substrate 40), the second main surface (for example, the nitrogen polar surface) 12 of the group III element nitride substrate 10 may be subjected to processing such as grinding or polishing.

[0053] In another embodiment, the Group III element nitride substrate may be bonded to a support substrate. Figure 6 is a schematic cross-sectional view showing the general configuration of a bonded substrate according to one embodiment of the present invention. The bonded substrate 60 has a Group III element nitride substrate 10 and a support substrate 62 positioned on the second main surface (e.g., nitrogen polar surface) 12 side of the Group III element nitride substrate 10. Although not shown, any suitable epitaxial film may be formed on the Group III element nitride substrate 10 of the bonded substrate 60.

[0054] The thickness of the support substrate 62 is, for example, 100 μm to 1000 μm. Any suitable substrate can be used as the support substrate. Specifically, the support substrate may be made of a single crystal or a polycrystalline material.

[0055] Although not shown in the diagram, the bonded substrate may further have any suitable layers. The type, function, number, combination, and arrangement of such layers can be appropriately determined according to the purpose.

[0056] In one embodiment, the bonded substrate can be obtained by directly bonding a group III element nitride substrate and a support substrate. For example, the bonded substrate can be obtained by surface activating the bonding surface of the support substrate and / or the bonding surface of the group III element nitride substrate, thereby bonding the group III element nitride substrate and the support substrate.

[0057] A bonded substrate according to an embodiment of the present invention may have, for example, a bonding layer (not shown) disposed between a group III element nitride substrate and a support substrate. In this case, the bonded substrate can be obtained, for example, by forming a bonding layer on the support substrate and / or the group III element nitride substrate, and then bonding the group III element nitride substrate and the support substrate via the bonding layer. During bonding, the bonding surface may be surface activated.

[0058] The bonding layer preferably contains, for example, at least one selected from the group consisting of tantalum oxide, alumina, aluminum nitride, silicon carbide, sialon, and silicon oxide, from the viewpoint of obtaining excellent bonding strength.

[0059] Typically, the above-mentioned SiAlON is a ceramic obtained by sintering a mixture of silicon nitride and alumina, for example, Si 6-a Al a O a N 8-a It has a composition represented by the formula. Specifically, SiAlON has a composition in which alumina is mixed in silicon nitride, and a in the formula indicates the mixing ratio of alumina. a is preferably 0.5 or more and 4.0 or less. The above silicon oxide is typically Si (1-b) O b This can be expressed as (where 0.008 ≤ b ≤ 0.408). [Examples]

[0060] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0061] [Example 1] <Preparation of the base substrate> A disc-shaped c-plane self-supporting gallium nitride substrate with a diameter of 55 cm and a thickness of 500 μm was prepared. Specifically, it is as follows:

[0062] (Preparation of seed crystal substrate) A 60 mm diameter sapphire substrate with the c-plane as the main surface was prepared. A gallium nitride film was deposited on this sapphire substrate by MOCVD to fabricate a seed crystal substrate. Specifically, a 30 nm thick low-temperature grown gallium nitride film was deposited on the sapphire substrate as a buffer layer at a susceptor temperature of 550 °C in a hydrogen atmosphere. Then, the susceptor temperature was raised to 1050 °C in a nitrogen-hydrogen atmosphere to deposit a 3 μm thick gallium nitride film and obtain a seed crystal substrate.

[0063] (Growth of the first crystal layer) The growth of gallium nitride crystals was carried out using a crystal manufacturing apparatus comprising a pressure vessel capable of supplying pressurized nitrogen gas, a rotating platform that can rotate within the pressure vessel, and an outer container placed on the rotating platform. The obtained seed crystal substrate was placed in an alumina crucible in a glove box under a nitrogen atmosphere. Next, the crucible was filled with metallic gallium (the raw material), metallic sodium (the solvent), and metallic germanium (the dopant) in molar ratios of 20 mol% Ga / (Ga+Na) and 0.40 mol% Ge / (Ga+Na), and then covered with an alumina plate. In this state, the crucible was placed in a stainless steel inner container, which was then placed in a stainless steel outer container capable of housing the inner container, and the outer container was closed with a lid equipped with a nitrogen introduction pipe. In this state, the outer container was placed on a rotating platform installed in the heating section of the crystal manufacturing apparatus, and the pressure vessel of the crystal manufacturing apparatus was sealed with a lid. Next, the pressure vessel was evacuated to below 0.1 Pa using a vacuum pump. Subsequently, the heating unit was operated to heat the heating space to 870°C while nitrogen gas was introduced into the pressure vessel until the pressure reached 4.0 MPa. The outer vessel was then rotated clockwise and counterclockwise at a constant period of 20 rpm around its central axis. The rotation conditions were set as follows: acceleration time of 10 seconds, holding time of 300 seconds, and deceleration time of 10 seconds. This state was maintained for 100 hours to grow a gallium nitride crystal with a thickness of 1000 μm. Afterward, the temperature was allowed to cool naturally from 870°C to room temperature and then reduced to atmospheric pressure. The lid of the pressure vessel was then opened and the crucible was removed. The solidified metallic sodium inside the crucible was removed, and the seed crystal substrate on which the first gallium nitride crystal was grown as the first crystal layer was recovered.

[0064] Subsequently, at room temperature, an ultraviolet laser was irradiated from the sapphire substrate side of the seed crystal substrate on which the first gallium nitride crystal was grown to decompose the gallium nitride film on the seed crystal substrate, and the grown first gallium nitride crystal was separated from the sapphire substrate. The periphery of the separated first gallium nitride crystal (substrate) was ground to form a disc shape with a diameter of 53 mm. Next, the first gallium nitride crystal (substrate) was fixed to a ceramic processing plate using wax, and the gallium polar surface of the gallium nitride was ground to smooth it, then polished to a mirror finish. Next, the substrate was washed with a mixture of alcohol ethoxylate and water, then rinsed with pure water to remove any processing residue adhering to the surface. Then, reactive ion etching (RIE) was performed using a mixed gas of chlorine-based gases, BCl3 and Cl2. Finally, any reaction residue adhering to the surface of the substrate was removed by washing with pure water. Thus, a base substrate with a diameter of 55 mm and a thickness of 500 μm was prepared.

[0065] <Fabrication of gallium nitride substrates> A gallium nitride substrate was fabricated using the above-mentioned substrate. Specifically, the process was as follows:

[0066] (Growth of the second crystal layer) A second gallium nitride crystal was grown as a second crystal layer on the crystal growth surface (gallium polar surface) of the substrate mentioned above. The growth of the second gallium nitride crystal was carried out in the same manner as the growth of the first gallium nitride crystal, except that the rotation speed was changed from 20 rpm to 10 rpm.

[0067] Subsequently, the substrate on which the second gallium nitride crystal was grown was recovered from the crucible, and the substrate was scraped off from the second gallium nitride crystal. The peripheral edge of the obtained second gallium nitride crystal was ground, and then the second gallium nitride crystal was fixed to a ceramic processing plate using wax, and the gallium polar surface and nitrogen polar surface of the gallium nitride were ground to smooth them, and then polished to a mirror finish. Next, reactive ion etching (RIE) was performed using a mixed gas of BCl3 and Cl2 to remove the processed altered layer and latent scratches on the surface of the second gallium nitride crystal. In this way, a gallium nitride substrate with a diameter of 50.8 mm and a thickness of 400 μm was fabricated.

[0068] [Example 2] A gallium nitride substrate was fabricated in the same manner as in Example 1, except that the rotation speed was changed from 10 rpm to 14 rpm during the growth of the second gallium nitride crystal.

[0069] [Example 3] A gallium nitride substrate was fabricated in the same manner as in Example 1, except that the temperature was changed from 870°C to 850°C during the growth of the second gallium nitride crystal.

[0070] [Example 4] A gallium nitride substrate was fabricated in the same manner as in Example 1, except that the pressure was changed from 4.0 MPa to 3.5 MPa during the growth of the second gallium nitride crystal.

[0071] [Example 5] A gallium nitride substrate was fabricated in the same manner as in Example 1, except that the rotation holding time was changed from 300 seconds to 600 seconds during the growth of the second gallium nitride crystal.

[0072] [Example 6] A gallium nitride substrate was fabricated in the same manner as in Example 1, except that the rotation holding time for the first gallium nitride crystal was changed from 300 seconds to 600 seconds, and the rotation holding time for the second gallium nitride crystal was changed from 300 seconds to 600 seconds.

[0073] [Comparative Example 1] A gallium nitride substrate was fabricated in the same manner as in Example 1, except that the rotation speed was changed from 10 rpm to 20 rpm during the growth of the second gallium nitride crystal.

[0074] [Comparative Example 2] A gallium nitride substrate was fabricated in the same manner as in Example 1, except that the rotation speed was changed from 10 rpm to 16 rpm during the growth of the second gallium nitride crystal.

[0075] [Comparative Example 3] A gallium nitride substrate was fabricated in the same manner as in Example 1, except that the temperature was changed from 870°C to 830°C during the growth of the second gallium nitride crystal.

[0076] [Comparative Example 4] A gallium nitride substrate was fabricated in the same manner as in Example 1, except that the pressure was changed from 4.0 MPa to 4.5 MPa during the growth of the second gallium nitride crystal.

[0077] [Comparative Example 5] A gallium nitride substrate was fabricated in the same manner as in Example 1, except that the rotation holding time was changed from 300 seconds to 30 seconds during the growth of the second gallium nitride crystal.

[0078] [Comparative Example 6] A gallium nitride substrate was fabricated in the same manner as in Example 1, except that the rotation holding time for the first gallium nitride crystal was changed from 300 seconds to 600 seconds, RIE was not applied to the first gallium nitride crystal (substrate) in the preparation of the substrate, and the rotation holding time for the second gallium nitride crystal was changed from 300 seconds to 600 seconds.

[0079] <Rating> The obtained gallium nitride substrates were evaluated as follows. The evaluation results are summarized in Table 1. 1. X-ray diffraction measurement The interplanar spacing of the obtained gallium nitride substrate was evaluated by high-resolution X-ray diffraction (HR-XRD). The interplanar spacing D of the crystal lattice planes at the center of the substrate surface and the center of the substrate back surface was measured using an X-ray diffractometer (Bruker AXS "D8 Discover") with a 2θ-ω scan. Specifically, the interplanar spacings D1 to D12 of the (10-12), (01-12), (-1102), (-1012), (0-112), and (1-102) planes were measured at the measurement positions indicated by black circles in Figures 1 and 2 (center of the substrate surface and center of the substrate back surface). The measurement conditions are as follows: ·X-ray source: Cu-Kα ray Voltage: 40kV ·Current: 40mA • Diffraction angle 2θ: 48.05°~48.15° • Step width: 0.0005° / step • Scan speed: 1.0 sec / step The measurement results (D1-D12) for Example 1 are shown in Table 1, and the measurement results (D1-D12) for Comparative Example 1 are shown in Table 2. Note that (D max -D min ) / D ave This is the maximum value D from D1 to D12. max , minimum value D min and mean D ave It is calculated from. 2. Crack occurrence rate In each example and comparative example, 11 additional gallium nitride substrates were prepared (a total of 12 substrates). Their appearance was observed visually and under an optical microscope to determine the number of gallium nitride substrates with cracks, and the crack occurrence rate (%) was calculated. The evaluation results are summarized in Table 3.

[0080] [Table 1]

[0081] [Table 2]

[0082] [Table 3]

[0083] In each example, virtually no cracks were observed after grinding, polishing, and RIE of the second crystal layer. In contrast, in each comparative example, visible cracks occurred in multiple substrates during grinding or polishing of the second crystal layer, and these cracks were also observed after RIE. [Industrial applicability]

[0084] The group III element nitride substrate according to the embodiment of the present invention can be used, for example, as a substrate for various semiconductor devices. [Explanation of Symbols]

[0085] 10 Group III element nitride substrates 11 First principal surface 12 Second principal surface 13 Side view 14 Outer edge 16 Group III element nitride crystal layer 20 Substrate 20a top surface 20b Bottom side Group 22 III element nitride crystals 30 Multilayer substrates 32 Self-supporting circuit board 40-element substrate 42 Functional Layers 50 seed crystal substrate 51. Growing substrate 52 Seed crystal film 60 Laminated substrates 62 Support substrate

Claims

1. A group III element nitride substrate having a first principal surface and a second principal surface facing each other is prepared, The crystal lattice plane spacings D1 to D12 of the (10-12) plane, (01-12) plane, (-1102) plane, (-1012) plane, (0-112) plane, and (1-102) plane in the first portion of the first principal surface and the second portion of the second principal surface are measured, and the maximum value D of the crystal lattice plane spacings D1 to D12 is measured. ｍａｘ , minimum value D ｍｉｎ and average value D ａｖｅ From (D ｍａｘ -D ｍｉｎ ) / D ａｖｅ To calculate the value, A method for inspecting a Group III element nitride substrate, including the element in question.

2. The method for inspecting a group III element nitride substrate according to claim 1, wherein the first portion and the second portion are located on the same line extending in the thickness direction of the substrate.

3. The method for inspecting a group III element nitride substrate according to claim 1, wherein the measurement is an X-ray diffraction measurement.

4. The method for inspecting a group III element nitride substrate according to any one of claims 1 to 3, Based on the value of the above (D ｍａｘ -D ｍｉｎ ) / D ａｖｅ , sorting the group III element nitride substrate, A method for manufacturing a group III element nitride substrate, including the element in question.

5. The above (D ｍａｘ -D ｍｉｎ ) / D ａｖｅ The value is 5.0 × 10 －４ A method for producing a group III element nitride substrate according to claim 4, wherein the group III element nitride substrate is selected as follows.

6. Preparing the aforementioned Group III element nitride substrate is Prepare a base substrate having an upper surface and a lower surface that face each other, This includes growing a group III element nitride crystal on the aforementioned substrate. A method for producing a group III element nitride substrate according to claim 4.

7. The method for inspecting a group III element nitride substrate according to any one of claims 1 to 3, The above (D ｍａｘ -D ｍｉｎ ) / D ａｖｅ Based on the value, the group III element nitride substrate is selected, Forming a functional layer on the main surface of the selected Group III element nitride substrate, A method for manufacturing an element substrate, including the method described above.

8. The method for inspecting a group III element nitride substrate according to any one of claims 1 to 3, The above (D ｍａｘ -D ｍｉｎ ) / D ａｖｅ Based on the value, the group III element nitride substrate is selected, The selected group III element nitride substrate is bonded to the support substrate, A method for manufacturing laminated substrates, including [the specified part of the method].

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