Group iii element nitride substrate, group iii element nitride substrate inspection method, and group iii element nitride substrate production method

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

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

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

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

[0003] Japanese Patent Application Laid-Open No. 2005-263609

[0004] However, Group III element nitride substrates are prone to cracks and breakage, and therefore, an improvement in yield is desired. Specifically, cracks and breakage are prone to occur during the fabrication of Group III element nitride substrates and / or during the fabrication of semiconductor devices, and therefore, an improvement in yield is desired.

[0005] A primary object of the present invention is to provide a Group III element nitride substrate that can improve yield.

[0006] 1. 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 a maximum value D of crystal lattice spacings D1 to D12 of the (10-12) plane, the (01-12) plane, the (-1102) plane, the (-1012) plane, the (0-112) plane, and the (1-102) plane in a first portion of the first main surface and a second portion of the second main surface, respectively, is ｍａｘ , minimum value D ｍｉｎ and the average value D ａｖｅ (D ｍａｘ -D ｍｉｎ ) / D ａｖｅ The value of is 5.0 × 10 －４The following are the details. 2. The Group III element nitride substrate described in 1 above may be a freestanding substrate of Group III element nitride crystal. 3. The Group III element nitride substrate described in 1 or 2 above may contain gallium nitride. 4. In the Group III element nitride substrate described in any one of 1 to 3 above, the first portion and the second portion may be located on the same line extending in the thickness direction of the substrate. 5. A method for inspecting a Group III element nitride substrate according to an embodiment of the present invention includes: preparing a Group III element nitride substrate having a first main surface and a second main surface opposing each other; measuring crystal lattice spacings D1 to D12 of the (10-12) plane, the (01-12) plane, the (-1102) plane, the (-1012) plane, the (0-112) plane, and the (1-102) plane in a first portion of the first main surface and a second portion of the second main surface, respectively; and determining a maximum value D of the crystal lattice spacings D1 to D12. ｍａｘ , minimum value D ｍｉｎ and the average value D ａｖｅ From (D ｍａｘ -D ｍｉｎ ) / D ａｖｅ and calculating the value of (D ｍａｘ -D ｍｉｎ ) / D ａｖｅ 9. The method for producing a Group III element nitride substrate according to the above item 8, further comprising the step of: ｍａｘ -D ｍｉｎ ) / D ａｖｅ The value is 5.0 x 10 －４The following Group III nitride substrates may be selected. 10. In the method for manufacturing a Group III nitride substrate recited in item 8 or 9 above, preparing the Group III nitride substrate may include preparing a base substrate having upper and lower surfaces opposing each other, and growing a Group III nitride crystal on the base substrate. 11. A method for manufacturing a Group III nitride substrate according to another embodiment of the present invention is the method for manufacturing a Group III nitride substrate recited in any of items 1 to 4 above, comprising preparing a base substrate having upper and lower surfaces opposing each other, and growing a Group III nitride crystal on the base substrate, the base substrate containing a Group III nitride. 12. In the method for manufacturing a Group III nitride substrate recited in item 11 above, the Group III nitride crystal may be grown by a flux method. 13. A method for manufacturing a device substrate according to an embodiment of the present invention comprises carrying out the method for inspecting a Group III nitride substrate recited in any of items 5 to 7 above, and ｍａｘ -D ｍｉｎ ) / D ａｖｅ 14. A method for manufacturing a bonded substrate according to an embodiment of the present invention includes carrying out the method for inspecting a Group III element nitride substrate according to any one of the above items 5 to 7, and ｍａｘ -D ｍｉｎ ) / D ａｖｅ and bonding the selected Group III element nitride substrate to a support substrate.

[0007] According to an embodiment of the present invention, a Group III element nitride substrate capable of improving yield can be provided.

[0008] FIG. 1 is a schematic cross-sectional view showing the general configuration of a group III element nitride substrate according to one embodiment of the present invention. FIG. 2 is a plan view of the group III element nitride substrate shown in FIG. 1. FIG. 3 is a view showing a manufacturing process of a group III element nitride substrate according to one embodiment. FIG. 4 is a view continuing from FIG. 3A. FIG. 4 is a view continuing from FIG. 3B. FIG. 5 is a view for explaining a method for manufacturing a base substrate according to one embodiment. FIG. 6 is a view continuing from FIG. 6A. FIG. 7 is a view continuing from FIG. 7B. FIG. 8 is a schematic cross-sectional view showing the general configuration of an element substrate according to one embodiment of the present invention. FIG. 9 is a schematic cross-sectional view showing the general configuration of a bonded substrate according to one embodiment of the present invention.

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. In order to clarify the description, the drawings may schematically show the width, thickness, shape, etc. of each part compared to the embodiments, but these are merely examples and do not limit the interpretation of the present invention. Furthermore, in the drawings, the same or equivalent elements are given the same reference numerals, and duplicate explanations may be omitted.

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

[0011] The main surface may be, for example, a mirror surface or a non-mirror surface. The main surface on which a functional layer (described later) is formed is preferably a mirror surface. Note that a mirror surface refers to a surface on which light is reflected and objects are visible, and refers to a state in which the roughness and waviness of the surface are reduced to a negligible level relative to the wavelength of visible light.

[0012] In the illustrated example, the Group III element nitride substrate is disk-shaped (wafer), but is not limited thereto and may be any suitable shape. The size of the Group III element nitride substrate may be appropriately set depending on the purpose. The diameter of the disk-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] The group III element nitride substrate is composed of group III element nitride crystals. Examples of group III elements that make up the group III element nitride include aluminum (Al), gallium (Ga), and indium (In). These may be used alone 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 In each chemical formula in parentheses, typically, x+y+z=1.

[0015] The Group III element nitride may contain a dopant. Examples of the dopant 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 may be used alone or in combination.

[0016] In the above-mentioned Group III element nitride crystal, the <0001> direction is typically the c-axis direction, the <1-100> direction is typically the m-axis direction, and the <11-20> direction is typically the a-axis direction. Furthermore, the crystal plane perpendicular to the c-axis is the c-plane, the crystal plane perpendicular to the m-axis is the m-plane, and the crystal plane perpendicular to the a-axis is the 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 or approximately parallel to the c-axis. The first main surface 11 is substantially a Group III element polar plane on the (0001) plane side, and the second main surface 12 is substantially a nitrogen polar plane on the (000-1) plane side. Specifically, the first main 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 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 may be inclined with respect to the (000-1) plane. The inclination angle of the second main surface 12 with respect to the (000-1) plane is, for example, 10° or less, or may be 5° or less, 2° or less, or 1° or less. Here, the thickness direction is the direction perpendicular to the main surface, that is, the normal direction to the main surface.

[0018] B. Inspection Method A method for inspecting a Group III element nitride substrate according to one embodiment of the present invention includes measuring crystal lattice spacings D1 to D12 of the (10-12) plane, (01-12) plane, (-1102) plane, (-1012) plane, (0-112) plane, and (1-102) plane in a first portion of the first main surface and a second portion of the second main surface of the prepared Group III element nitride substrate, and finding the maximum value D of the obtained crystal lattice spacings D1 to D12. ｍａｘ , minimum value D ｍｉｎ and the average value D ａｖｅ From (D ｍａｘ -D ｍｉｎ ) / D ａｖｅ By selecting the first and second principal surfaces as measurement points, the measurement can be performed without destroying the substrate (non-destructively). Also, the intrinsic stress, which will be described later, can be evaluated more accurately.

[0019] X-ray diffraction measurement is typically employed to measure the crystal lattice spacing D. X-ray diffraction measurement can achieve non-destructive measurement. The measurement of the crystal lattice spacing D is preferably performed at multiple locations (e.g., two locations) on the Group III element nitride substrate. In one embodiment, for example, from the perspective of simplifying the measurement, the crystal lattice spacing D is measured at one location on each of the first and second main surfaces of the Group III element nitride substrate. For example, as shown by the black circles in FIGS. 1 and 2 , the crystal lattice spacing D is measured at a first portion 11a located at the center of the circular first main surface 11 and a second portion 12a located at the center of the second main surface 12. The first portion 11a and the second portion 12a are located on the same line extending in the thickness direction of the Group III element nitride substrate 10. Here, the first portion 11a and the second portion 12a do not need to be located strictly on the same line extending in the thickness direction, but may be located substantially on the same line extending in the thickness direction. For example, when the group III element nitride substrate 10 is viewed from above, the distance between the first portion 11a and the second portion 12a may be 5 mm or less.

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

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

[0022] In Group III element nitride crystals, the (10-12) plane, (01-12) plane, (-1102) plane, (-1012) plane, (0-112) plane, and (1-102) plane are generally considered to be crystallographically equivalent. However, the present inventors have closely examined the relationship between the crystal lattice spacing D of these planes, which are considered to be equivalent, and the quality of Group III element nitride substrates, and have found that there is a correlation between the crystal lattice spacing D of the above planes and the quality of Group III element nitride substrates. Specifically, they have found a correlation between the crystal lattice spacing D and the susceptibility to cracking in Group III element nitride substrates. Group III element nitride substrates that are prone to cracking tend to be prone to defects such as cracking and chipping in device fabrication processes, and therefore the inspection method according to this embodiment can also contribute to improving the yield of device fabrication. The susceptibility of a substrate to cracking is thought to be correlated with the substrate's intrinsic stress, and it is known that this can be evaluated, for example, by Raman spectroscopy. Since the stress evaluated by Raman spectroscopy can be calculated assuming that the stress is isotropic within the plane, there is a possibility that the susceptibility of the substrate to cracking cannot be fully evaluated. According to this embodiment, the susceptibility of the substrate to cracking can be evaluated with extremely high accuracy. The inherent stress can cause distortion in the crystal, which can change the lattice length, and by measuring this, it is thought that the susceptibility of the substrate to cracking can be evaluated more accurately.

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

[0024] 3A to 3C are diagrams illustrating a manufacturing process for a group III nitride substrate according to one embodiment.

[0025] C-1. Preparation of Underlying Substrate Fig. 3A shows an underly- ing substrate 20 having an upper surface 20a and a lower surface 20b opposite to each other.

[0026] The base substrate 20 may be, for example, a substrate having a shape and size that allows a Group III nitride substrate having the desired shape and size to be manufactured. Typically, the base substrate is disk-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 appropriate substrate can be used as the base substrate. The base substrate is typically composed of a single crystal. Any appropriate material can be adopted as the material for the base substrate. Specific examples of materials for the base substrate include sapphire, crystal-oriented alumina, silicon, gallium oxide, gallium arsenide, silicon carbide (SiC), and group III element nitrides. The base substrate is preferably composed of a material having the same type of 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. Note that the details of the group III element nitride are as described above.

[0028] 4A to 4C are diagrams illustrating a method for fabricating a base substrate according to one embodiment. For example, as shown in FIG. 4A , a seed crystal film 52 is formed on a growth substrate 51 to prepare a seed crystal substrate 50. As shown in FIG. 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 FIG. 4C , the growth substrate 51 is removed from the grown Group III element nitride crystal (growth layer) 22, thereby obtaining a Group III element nitride base substrate 20. The growth substrate 51 can be made of any appropriate material. A sapphire substrate is preferably 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. A typical material for the seed crystal film is a Group III element nitride. Details of the Group III element nitride are as described above.

[0030] The seed crystal film can be formed by any appropriate method. A typical method for forming the seed crystal film is a vapor phase growth method. Specific examples of the vapor phase growth method include metal organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), pulsed excited deposition (PXD), molecular beam epitaxy (MBE), and sublimation. Among these, the MOCVD method is preferably used.

[0031] The formation of the seed crystal film by the MOCVD method 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 formed on a growth substrate at a temperature T1 (e.g., 450°C to 600°C), and in the second formation step, a second layer is formed at a temperature T2 (e.g., 1000°C to 1200°C) higher than 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 a Group III element nitride crystal on the seed crystal substrate is not particularly limited as long as it is a method that can achieve a crystal orientation that roughly follows the crystal orientation of the seed crystal film. Specific examples of methods for growing a Group III element nitride crystal will be described later.

[0033] 4C , after removing the growth substrate 51 from the growth layer 22, for example, the peripheral portion of the growth layer 22 may be ground (e.g., by using a diamond grinding wheel). Typically, the growth layer 22 may be ground to have the desired shape and size (e.g., a disk shape having a desired diameter).

[0034] For example, the main surface (e.g., the group III element polar surface) of the growth layer 22 may be ground or polished. For example, lapping, chemical mechanical polishing (CMP), or other processing may be performed. After processing the main surface, it is preferable to perform a removal process on the processed surface. By such a process, a base substrate can be obtained from which the process-affected layer and latent scratches have been removed. For example, reactive ion etching (RIE) can be used as a removal process on the processed surface.

[0035] C-2. Growth of Group III Element Nitride Crystal Next, as shown in FIG. 3B , 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 layered 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 depending on the desired thickness of the Group III element nitride substrate. Any appropriate direction can be selected as the growth direction of the Group III element nitride crystal depending on the application, purpose, etc. Specific examples include the normal direction to the c-plane and the normal direction of a plane tilted relative to the c-plane.

[0036] Group III element nitride crystals can be grown by any appropriate method. The method for growing Group III element nitride crystals is not particularly limited, as long as it is a method that can achieve a crystal orientation that roughly mimics the crystal orientation of the base 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 phase epitaxy (HVPE), pulsed excited deposition (PXD), molecular beam epitaxy (MBE), and sublimation; and liquid phase growth methods such as flux deposition, ammonothermal deposition, hydrothermal deposition, and sol-gel deposition. These methods can be used alone or in combination of two or more.

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

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

[0039] The raw material is, for example, a melt composition containing a flux, a Group III element, and, if necessary, a dopant. The flux preferably contains at least one of an alkali metal and an alkaline earth metal, and more preferably metallic sodium. Typically, the flux and a metal source material are mixed together. As the metal source material, an elemental metal, an alloy, a metal compound, etc. can be used, but from the viewpoint of ease of handling, an elemental metal is preferably used.

[0040] The crucible (including the lid) can be made of any suitable material that can be used in the flux method. Examples of the crucible material include alumina, yttria, and YAG (yttrium aluminum garnet). The crucible material may be a single crystal or a polycrystal (ceramic). The ceramic may have a high relative density, such as by HIP treatment, to give it translucency.

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

[0042] The pressure of the atmosphere during growth can be set to any appropriate pressure. For example, from the viewpoint of preventing evaporation of the flux, the pressure of the atmosphere during growth is, for example, 1 MPa or more, and may be 2 MPa or more, or 3 MPa or more. On the other hand, for example, from the viewpoint of preventing the growth apparatus from becoming large-scale, the pressure of the atmosphere during growth may be, for example, 50 MPa or less, or may be 10 MPa or less. In one embodiment, the pressure of the atmosphere during growth of the Group III element nitride crystal on the base substrate is preferably 4.3 MPa or less, and more preferably 4.0 MPa or less. With such a pressure, the above-mentioned predetermined (D ｍａｘ -D ｍｉｎ ) / D ａｖｅ Therefore, a group III element nitride substrate that satisfies the above 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 is, for example, 700°C to 1000°C, or may be 800°C to 900°C. In one embodiment, the temperature of the atmosphere during growth of the Group III element nitride crystal on the starting substrate is preferably 840°C or higher, and more preferably 850°C or higher. At such a temperature, the above-mentioned predetermined (D ｍａｘ -D ｍｉｎ ) / D ａｖｅ Therefore, a group III element nitride substrate that satisfies the above requirements can be successfully fabricated.

[0044] The growth is preferably carried out while rotating the crucible (base substrate). For example, the covered crucible is placed in the outer container of the crystal manufacturing apparatus and placed on a turntable, and the turntable is rotated in this state (for example, on its axis) to rotate the crucible. The rotation speed is, for example, 5 rpm to 40 rpm. In one embodiment, the rotation speed during growth of the Group III element nitride crystal relative to the base substrate is preferably 15 rpm or less, and more preferably 14 rpm or less. At such a rotation speed, the above-mentioned predetermined (D ｍａｘ -D ｍｉｎ ) / D ａｖｅ It is possible to satisfactorily produce a Group III element nitride substrate that can satisfy the above requirement. The rotation direction can be set to any appropriate direction. In a preferred embodiment, during growth, clockwise and counterclockwise rotations are repeated at a predetermined cycle. The time (holding time) for maintaining rotation at a predetermined rotation speed in one direction is, for example, 10 to 1000 seconds. In one embodiment, the holding time for the Group III element nitride crystal on the starting substrate during growth 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, it is possible to achieve the above-mentioned predetermined (D ｍａｘ -D ｍｉｎ ) / D ａｖｅ Therefore, a group III element nitride substrate that satisfies the above requirements can be successfully fabricated.

[0045] After growth of the group III element nitride crystal, as shown in FIG. 3C , a free-standing substrate 32 may be obtained by removing part or all of the base substrate 20 from the group III element nitride crystal (group III element nitride crystal layer 16), or, unlike the illustrated example, the laminated substrate 30 may be used as is as the free-standing substrate. When removing the base substrate 20 from the group III element nitride crystal layer 16 as shown in the figure, for example, the free-standing substrate 32 is obtained by separating the group III element nitride crystal layer 16 from the base substrate 20. The group III element nitride crystal may be separated from the base substrate by any appropriate method. Examples of methods for separating the group III element nitride crystal include spontaneous separation from the base substrate by utilizing the difference in thermal contraction between the base substrate and the base substrate during a cooling step after growth of the group III element nitride crystal, separation by chemical etching, and laser lift-off using laser light irradiation. When separating the group III element nitride crystal 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 free-standing substrate may be obtained by, for example, grinding or cutting using a cutting machine such as a wire saw.

[0046] The free-standing substrate 32 may be the above-mentioned Group III element nitride substrate as it is, or the free-standing 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 free-standing substrate is grinding of the peripheral portion (e.g., grinding using a diamond grinding wheel). Typically, the free-standing substrate is ground to have the desired shape and size (e.g., a disk shape having a desired diameter).

[0048] Other examples of processing performed on the freestanding substrate include grinding and polishing (e.g., lapping and chemical mechanical polishing (CMP)) of the main surfaces (upper and lower surfaces). Typically, the substrate is thinned and flattened to a desired thickness by grinding and polishing.

[0049] Furthermore, examples of processing performed on the freestanding substrate include chamfering the outer peripheral edge, removing process-affected layers and latent scratches, and removing residual stress that may be caused by process-affected layers.

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

[0051] The 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, a Group III element nitride crystal is used as the material constituting the functional layer. Examples of Group III elements constituting the Group III element nitride include Ga (gallium), Al (aluminum), and In (indium). These elements can be used alone or in combination of two or more.

[0052] In addition, in a state where the functional layer 42 is formed on the group III element nitride substrate 10 (in a state where it has been made into the element substrate 40), the second main surface (e.g., 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 can be bonded to a support substrate. Fig. 6 is a schematic cross-sectional view showing an outline of the 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 arranged on the second main surface (e.g., nitrogen-polar surface) 12 side of the group III element nitride substrate 10. Although not shown, any appropriate epitaxial film can 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 appropriate 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, the laminated substrate may further include any appropriate layer, the type, function, number, combination, arrangement, etc. of such layers may be appropriately determined depending on the purpose.

[0056] In one embodiment, the bonded substrate can be obtained by directly bonding the Group III element nitride substrate and the support substrate. For example, the bonding surface of the support substrate and / or the bonding surface of the Group III element nitride substrate can be surface-activated, and then the Group III element nitride substrate and the support substrate can be bonded to each other to obtain a bonded substrate.

[0057] The bonded substrate according to the embodiment of the present invention may have, for example, a bonding layer (not shown) disposed between the Group III element nitride substrate and the support substrate. In this case, the bonded substrate can be obtained by, for example, 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 surfaces may be surface-activated.

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

[0059] Typically, the sialon is a ceramic obtained by sintering a mixture of silicon nitride and alumina, and for example, Si ６－ａ Al ａ O ａ N ８－ａ 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 silicon oxide is typically Si （１－ｂ） O ｂ (wherein 0.008≦b≦0.408).

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

[0061] Example 1 Preparation of Base Substrate A c-plane freestanding gallium nitride substrate having a disk shape with a diameter of 55 cm and a thickness of 500 μm was prepared.

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

[0063] (Growth of First Crystal Layer) Gallium nitride crystals were grown using a crystal manufacturing apparatus equipped with a pressure-resistant container capable of supplying pressurized nitrogen gas, a turntable rotatable within the pressure-resistant container, and an outer container placed on the turntable. The obtained seed crystal substrate was placed in an alumina crucible in a nitrogen atmosphere glove box. Next, the crucible was filled with metallic gallium as a raw material, metallic sodium as a solvent, and metallic germanium as a dopant, so that the mass ratio of Ga / (Ga + Na) was 20 mol % and Ge / (Ga + Na) was 0.40 mol %, and the crucible was 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 containing the inner container, and the outer container was closed with a lid equipped with a nitrogen inlet pipe. In this state, the outer container was placed on a turntable installed in the heating section of the crystal manufacturing apparatus, and the pressure-resistant container of the crystal manufacturing apparatus was sealed with a lid. Next, the pressure vessel was evacuated to 0.1 Pa or less using a vacuum pump. Subsequently, the heating unit was operated to heat the heating space to 870 ° C., while introducing nitrogen gas into the pressure vessel until the pressure reached 4.0 MPa. The outer vessel was rotated around the central axis at a speed of 20 rpm in a constant cycle clockwise and counterclockwise direction. The rotation conditions were an acceleration time of 10 seconds, a holding time of 300 seconds, and a deceleration time of 10 seconds. This state was maintained for 100 hours, and a gallium nitride crystal with a thickness of 1000 μm was grown. The pressure was then naturally cooled from 870 ° C. to room temperature and reduced to atmospheric pressure, after which the lid of the pressure vessel was opened and the crucible was removed. The solidified metallic sodium in the crucible was removed, and the seed crystal substrate on which the first gallium nitride crystal had been grown as the first crystal layer was recovered.

[0064] Thereafter, 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 of the seed crystal substrate, and the grown first gallium nitride crystal was separated from the sapphire substrate. The peripheral portion of the separated first gallium nitride crystal (base substrate) was ground to form a disk shape with a diameter of 53 mm. Next, the first gallium nitride crystal (base substrate) was fixed to a ceramic processing table using wax, and the gallium polar surface of the gallium nitride was ground and smoothed, and then polished to a mirror finish. Next, it was washed with a mixture of alcohol ethoxylate and water, and then rinsed with pure water to remove processing residues adhering to the surface of the base substrate. Next, a chlorine-based gas, BCl ３ Gas and Cl ２ The substrate was subjected to reactive ion etching (RIE) using a mixture of SiO 2 and SiO 2 gas. The reaction residues adhering to the surface of the substrate were then removed by rinsing with pure water. Thus, a substrate with a diameter of 55 mm and a thickness of 500 μm was prepared.

[0065] <Preparation of Gallium Nitride Substrate> Gallium nitride substrates were prepared using the above-described base substrate. Specifically, the procedure is as follows.

[0066] (Growth of second crystal layer) A second gallium nitride crystal was grown as a second crystal layer on the crystal growth surface (gallium polarity surface) of the base substrate. 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] The base substrate on which the second gallium nitride crystal had been grown was then removed from the crucible, and the base substrate was scraped off from the second gallium nitride crystal. The peripheral edge of the resulting second gallium nitride crystal was then ground, and the second gallium nitride crystal was then fixed to a ceramic processing platen using wax, and the gallium polarity surface and nitrogen polarity surface of the gallium nitride were ground to smoothen them, and then polished to a mirror finish. Next, BCl ３ Gas and Cl ２The second gallium nitride crystal was subjected to reactive ion etching (RIE) using a mixed gas of 1,000 sulphur dioxide and 1,000 sulphur dioxide, to remove any process-affected layers or latent scratches on the surface of the second gallium nitride crystal. In this way, a gallium nitride substrate having a diameter of 50.8 mm and a thickness of 400 μm was produced.

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

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

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

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

[0072] Example 6 A gallium nitride substrate was fabricated in the same manner as in Example 1, except that the rotation hold time during growth of the first gallium nitride crystal was changed from 300 seconds to 600 seconds, and the rotation hold time during growth of 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 during growth of the second gallium nitride crystal was changed from 10 rpm to 20 rpm.

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

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

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

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

[0078] Comparative Example 6 A gallium nitride substrate was fabricated in the same manner as in Example 1, except that the rotation hold time in growing the first gallium nitride crystal was changed from 300 seconds to 600 seconds, that RIE was not performed on the first gallium nitride crystal (base substrate) in preparing the base substrate, and that the rotation hold time in growing the second gallium nitride crystal was changed from 300 seconds to 600 seconds.

[0079] <Evaluation> The following evaluations were performed on the obtained gallium nitride substrates. The evaluation results are summarized in Table 1. 1. X-ray Diffraction Measurement The crystal lattice spacing of the obtained gallium nitride substrates was evaluated by high-resolution X-ray diffraction (HR-XRD). The crystal lattice spacing D at the center of the front surface and the center of the back surface of the substrate was measured by 2θ-ω scanning using an X-ray diffractometer ("D8 Discover" manufactured by Bruker AXS). Specifically, the crystal lattice spacings D1 to D12 of the (10-12) plane, (01-12) plane, (-1102) plane, (-1012) plane, (0-112) plane, and (1-102) plane were measured at the measurement positions (center of the front surface and center of the back surface of the substrate) indicated by the black circles in Figures 1 and 2. The measurement conditions were as follows: X-ray source: Cu-Kα ray Voltage: 40 kV Current: 40 mA Diffraction angle 2θ: 48.05° to 48.15° Step width: 0.0005° / step Scan speed: 1.0 sec / step The measurement results (D1 to D12) of Example 1 are shown in Table 1, and the measurement results (D1 to D12) of Comparative Example 1 are shown in Table 2. ｍａｘ -D ｍｉｎ ) / D ａｖｅ is the maximum value D of D1 to D12 ｍａｘ , minimum value D ｍｉｎ and the average value D ａｖｅ2. Crack occurrence rate In each example and comparative example, 11 more gallium nitride substrates were produced (a total of 12 substrates were produced), and their appearances were observed visually and with an optical microscope to confirm the number of gallium nitride substrates in which cracks had occurred, and the crack occurrence rate (%) was calculated. The evaluation results are summarized in Table 3.

[0080]

[0081]

[0082]

[0083] In each example, almost no cracks were observed after grinding, polishing, and RIE of the second crystal layer, whereas in each comparative example, visually noticeable cracks occurred in multiple substrates during grinding or polishing of the second crystal layer, and these cracks were also observed after RIE.

[0084] Group III nitride substrates according to embodiments of the present invention can be used, for example, as substrates for various semiconductor devices.

[0085] REFERENCE SIGNS LIST 10 Group III element nitride substrate 11 First main surface 12 Second main surface 13 Side surface 14 Outer periphery 16 Group III element nitride crystal layer 20 Base substrate 20a Upper surface 20b Lower surface 22 Group III element nitride crystal 30 Laminated substrate 32 Freestanding substrate 40 Element substrate 42 Functional layer 50 Seed crystal substrate 51 Growth substrate 52 Seed crystal film 60 Bonded substrate 62 Support substrate

Claims

1. Providing a group-III nitride substrate having a first major surface and a second major surface facing each other; Measure the 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 the first part of the first main surface and the second part of the second main surface respectively, and from the maximum value D ｍａｘ , minimum value D ｍｉｎ and average value D ａｖｅ calculate the value of (D ｍａｘ - D ｍｉｎ ) / D ａｖｅ , and A method for inspecting a group-III nitride substrate, comprising the above.

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

4. Performing the method for inspecting a group-III 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 nitride substrate as described above; A method for manufacturing a group-III nitride substrate, comprising the above.

5. The above (D ｍａｘ -D ｍｉｎ ) / D ａｖｅ value is 5.0×10 －４ or less to select the above-mentioned group III element nitride substrate, the method for manufacturing a group III element nitride substrate according to claim 4.

6. The providing of the group-III nitride substrate comprises: Providing a base substrate having an upper surface and a lower surface facing each other; Growing a group-III nitride crystal on the base substrate; The method for manufacturing a group-III nitride substrate according to Claim 4.

7. Performing the method for inspecting a group-III nitride substrate according to any one of Claims 1 to 3; Based on the value of the aforementioned (D ｍａｘ -D ｍｉｎ ) / D ａｖｅ , sorting the Group III element nitride substrate and Forming a functional layer on the major surface of the selected group-III nitride substrate; A method for manufacturing an element substrate, comprising the above.

8. Performing the method for inspecting a group-III nitride substrate according to any one of Claims 1 to 3; Based on the value of the foregoing (D ｍａｘ -D ｍｉｎ ) / D ａｖｅ , sorting the group III nitride substrate Bonding the selected group-III nitride substrate to a support substrate; A method for manufacturing a bonded substrate, comprising the above.