Base substrate

Abstract

Provided is a base substrate which has a lattice constant matching alpha-Ga2O3 and is not susceptible to edge breakage due to grinding and polishing. The base substrate is provided with an alignment layer for crystal growth of a semiconductor film comprising alpha-Ga2O3 or an alpha-Ga2O3-based solid solution. The orientation layer is composed of a material having a corundum-type crystal structure in which an a-axis length and / or a c-axis length is larger than that of sapphire, and a plurality of crystallites, which are defined as crystal particles having a long axis length of 1 nm to 2 [mu] m, are present inside the orientation layer.

Description

Technical Field

[0001] This invention relates to a substrate for the crystal growth of α-gallium oxide. Background Technology

[0002] In recent years, semiconductor devices using gallium nitride (GaN) have become practical. For example, devices formed by alternately stacking n-type GaN layers, quantum well layers containing InGaN layers, and barrier layers containing GaN layers on a sapphire substrate to obtain multiple quantum well (MQW) layers and p-type GaN layers have been mass-produced.

[0003] In addition, research and development of corundum-phase α-gallium oxide (α-Ga2O3), which has the same crystal structure as sapphire, is being actively pursued. In fact, α-Ga2O3 has a high band gap of 5.3 eV, making it a promising material for power semiconductor devices. For example, Patent Document 1 (Japanese Patent Application Publication No. 2014-72533) discloses a semiconductor device formed from a substrate with a corundum-type crystal structure, a semiconductor layer with a corundum-type crystal structure, and an insulating film with a corundum-type crystal structure, and discloses an example of forming an α-Ga2O3 film on a sapphire substrate as the semiconductor layer. Furthermore, Patent Document 2 (Japanese Patent Application Publication No. 2016-25256) discloses a semiconductor device comprising: an n-type semiconductor layer mainly composed of a crystalline oxide semiconductor having a corundum structure, a p-type semiconductor layer mainly composed of an inorganic compound having a hexagonal crystal structure, and an electrode. In an embodiment, a metastable phase, namely an α-Ga2O3 film having a corundum structure, is formed on a c-plane sapphire substrate as the n-type semiconductor layer, and an α-Rh2O3 film having a hexagonal crystal structure is formed as the p-type semiconductor layer to fabricate a diode.

[0004] However, it is known that semiconductor devices with fewer crystal defects exhibit better characteristics. In particular, in power semiconductors, the amount of crystal defects significantly affects the dielectric breakdown electric field characteristics; therefore, it is desirable to significantly reduce crystal defects. It should be noted that crystal defects referred to here include: through-edge dislocations, through-screw dislocations, through-mixed dislocations, and basal plane dislocations; the crystal defect density is the sum of the densities of each dislocation. However, since α-Ga₂O₃ is a metastable phase, single-crystal substrates with few crystal defects have not yet been practically implemented; they are usually formed on sapphire substrates, etc., through heteroepitaxial growth. In such cases, stress can sometimes be generated in the semiconductor film due to the difference in lattice constant between the sapphire and sapphire, leading to a large number of crystal defects. For example, when α-Ga₂O₃ is deposited on c-plane sapphire, the a-axis length of sapphire (α-Al₂O₃) (4.754 Å) differs from that of α-Ga₂O₃ (4.983 Å) by approximately 5%, and this difference constitutes a major cause of crystal defects.

[0005] As an effort to reduce the difference in lattice constant between α-Ga₂O₃ and sapphire, it is known to use an orientation layer comprising a corundum-type crystal structure having an a-axis length and / or c-axis length greater than that of sapphire. For example, Patent Document 3 (Japanese Patent No. 7159449) discloses a substrate having an orientation layer for the crystal growth of nitrides or oxides of group 13 elements. In this substrate, the surface of the orientation layer for crystal growth is made of a material having a corundum-type crystal structure having an a-axis length and / or c-axis length greater than that of sapphire. The orientation layer comprises two or more solid solutions selected from the group consisting of α-Al₂O₃, α-Cr₂O₃, α-Fe₂O₃, α-Ti₂O₃, α-V₂O₃, and α-Rh₂O₃.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2014-72533

[0009] Patent Document 2: Japanese Patent Application Publication No. 2016-25256

[0010] Patent Document 3: Japanese Patent No. 7159449 Summary of the Invention

[0011] Here, for example, in a substrate with an alignment layer disclosed in Patent Document 3, the surface of the alignment layer is planarized and mirror-finished by grinding or polishing the alignment layer. However, such substrates have the following problem: during the grinding and polishing process, chipping (defects such as notches or cracks) is easily generated at the ends of the alignment layer, resulting in a reduced yield.

[0012] The inventors of this invention have recently come to the insight that by having a substrate having an alignment layer for the crystal growth of α-gallium oxide containing specific microcrystals within its alignment layer, the lattice constant is matched with α-Ga2O3, and the substrate is less prone to edge chipping due to grinding and polishing.

[0013] Therefore, the object of the present invention is to provide a substrate with a lattice constant that matches α-Ga2O3 and is not prone to edge chipping due to grinding and polishing.

[0014] According to the present invention, the following solution is provided.

[0015] [Option 1]

[0016] A substrate having an alignment layer for the crystallization growth of a semiconductor film composed of α-Ga₂O₃ or an α-Ga₂O₃-based solid solution.

[0017] The substrate is characterized in that...

[0018] The orientation layer is composed of a corundum-type crystal structure having an a-axis length and / or a c-axis length greater than that of sapphire.

[0019] The orientation layer contains multiple microcrystals defined as crystalline particles with a major axis length of 1 nm to 2 μm.

[0020] [Option 2]

[0021] The substrate according to Scheme 1 is characterized in that,

[0022] The microcrystals have an average major axis length of 10 nm to 100 nm.

[0023] [Option 3]

[0024] The substrate according to scheme 1 or 2 is characterized in that,

[0025] The number density of the microcrystals per unit area in the orientation layer is 1.00 × 10⁻⁶. 5 ~1.00×10 12 pcs / cm 2 .

[0026] [Option 4]

[0027] The substrate according to Scheme 3 is characterized in that...

[0028] The number density of the microcrystals per unit area in the orientation layer is 1.00 × 10⁻⁶. 10 ~1.00×10 12 pcs / cm 2 .

[0029] [Option 5]

[0030] The substrate according to any one of claims 1 to 4 is characterized in that,

[0031] The microcrystals contain one or more elements selected from the group consisting of Ti, Zr, Hf, Ge, Si and Ce.

[0032] [Option 6]

[0033] The substrate according to embodiment 5 is characterized in that,

[0034] The microcrystals contain Ti.

[0035] [Option 7]

[0036] The substrate according to any one of claims 1 to 6 is characterized in that,

[0037] The microcrystals are needle-shaped crystals.

[0038] [Option 8]

[0039] The substrate according to any one of claims 1 to 7 is characterized in that,

[0040] Materials having the aforementioned corundum-type crystalline structure include α-Cr2O3 or α-Cr2O3-based solid solutions.

[0041] [Option 9]

[0042] The substrate according to any one of claims 1 to 8 is characterized in that,

[0043] The orientation layer also has a support substrate on the side opposite to the side used for crystal growth.

[0044] [Option 10]

[0045] The substrate according to Scheme 9 is characterized in that,

[0046] The supporting substrate is a sapphire substrate. Attached Figure Description

[0047] Figure 1 This is a simplified cross-sectional diagram showing the structure of an aerosol deposition (AD) device.

[0048] Figure 2 It is a diagram used to illustrate the position of the center point and four peripheral points on the surface of the alignment layer.

[0049] Figure 3 This is an example of a TEM image obtained by observing the alignment layer using a transmission electron microscope (TEM) in Example 1. Detailed Implementation

[0050] substrate

[0051] The substrate of the present invention comprises an alignment layer for the crystallization growth of a semiconductor film composed of α-Ga₂O₃ or an α-Ga₂O₃-based solid solution. The alignment layer is composed of a corundum-type crystalline structure having an a-axis length and / or a c-axis length larger than that of sapphire. Within the alignment layer, there are multiple microcrystals defined as crystalline particles with a long axis length of 1 nm to 2 μm. In this way, the substrate having an alignment layer for the crystallization growth of α-gallium oxide contains specific microcrystals within its alignment layer, thereby enabling the fabrication of a substrate with a lattice constant matching that of α-Ga₂O₃ and less prone to edge chipping due to grinding and polishing. That is, as described above, when the surface of the substrate is planarized and mirror-finished by grinding or polishing, conventional substrates suffer from the following problem: edge chipping (defects such as notches or cracks) easily occurs at the ends, reducing the yield. In this respect, the substrate according to the present invention effectively eliminates the above-mentioned problems.

[0052] When multiple crystallites, defined as having a long axis length of 1 nm to 2 μm, exist within the alignment layer, excessively large crystallites may cause detachment and damage to the polished surface. Therefore, from the viewpoint of suppressing damage, the size of the crystallites is preferably small. Accordingly, the average long axis length of the crystallites is preferably 1 μm or less, more preferably 500 nm or less, and even more preferably 100 nm or less. Although there is no lower limit to the size of the crystallites, the average long axis length of the crystallites is preferably 1 nm or more, more preferably 10 nm or more. Therefore, the crystallites preferably have an average long axis length of 1 nm to 1 μm, more preferably 10 nm to 1 μm, even more preferably 10 nm to 500 nm, and particularly preferably 10 nm to 100 nm. It should be noted that the size of the crystallites can be measured using scanning electron microscopy (SEM), transmission electron microscopy (TEM), optical microscopy (OM), electron backscatter diffraction (EBSD), etc. The crystallites in the alignment layer are preferably needle-like crystals.

[0053] From the perspective of suppressing edge breakage, a higher number of crystallites is preferable in the orientation layer. Therefore, the preferred crystallite density per unit area in the orientation layer is 1.00 × 10⁻⁶. 5 pcs / cm 2 The above, more preferably 1.0×10 7 pcs / cm 2 The above is further preferred to be 1.0×10 9 pcs / cm 2 The above is particularly preferred to be 1.00 × 10⁻⁶. 10 pcs / cm 2 That's all. While there is no upper limit to the number density of microcrystals, a density of 1.00 × 10⁻⁶ is preferred. 12 pcs / cm 2Therefore, the preferred crystallite density per unit area in the orientation layer is 1.00 × 10⁻⁶. 5 ~1.00×10 12 pcs / cm 2 More preferably 1.0×10 7 ~1.00×10 12 pcs / cm 2 More preferably 1.0×10 9 ~1.00×10 12 pcs / cm 2 The preferred value is 1.00×10. 10 ~1.00×10 12 pcs / cm 2 It should be noted that the number density of microcrystals can also be calculated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), optical microscopy (OM), electron backscatter diffraction (EBSD), etc.

[0054] The microcrystals in the orientation layer preferably contain one or more elements selected from the group consisting of Ti, Zr, Hf, Ge, Si, and Ce, and more preferably Ti. The elements contained in the microcrystals can be determined using known methods; however, for example, energy dispersive X-ray spectrometry (SEM-EDX), electron probe microanalysis (EPMA), scanning transmission electron microscopy (STEM-EDX), and time-of-flight secondary ion mass analysis (TOF-SIMS) can be used. It should be noted that the inclusion of the aforementioned elements in the microcrystals means that 0.1 at% or more of the aforementioned elements are detected in the microcrystals using any of the above methods. Therefore, the content of the aforementioned elements is preferably 0.1 at% or more relative to the total content of all elements in the microcrystals. In addition to the elements Ti, Zr, Hf, Ge, Si, and Ce, the composition of the microcrystals preferably also includes the components constituting the orientation layer (for example, Cr and O if the material constituting the orientation layer has a corundum-type crystal structure and contains α-Cr₂O₃).

[0055] The alignment layer typically has a configuration where the crystal orientation is substantially consistent in the general normal direction. By adopting such a configuration, a semiconductor layer of excellent quality, especially excellent orientation, can be formed on it. That is, when forming a semiconductor layer on the alignment layer, the crystal orientation of the semiconductor layer substantially mimics the crystal orientation of the alignment layer. Therefore, by making the substrate have a configuration with an alignment layer, the semiconductor film can be an alignment film. It should be noted that the alignment layer can be polycrystalline, mosaic crystal (a collection of crystals whose crystal orientation deviates from a certain value), or monocrystalline. When the alignment layer is polycrystalline, a biaxial alignment layer in which the twist direction (i.e., the rotation direction centered on the substrate normal which is given an orientation substantially perpendicular to the substrate surface) is also substantially consistent is preferred.

[0056] The surface of the alignment layer used for crystal growth (hereinafter, sometimes simply referred to as the "surface" or "alignment layer surface") is made of a corundum-type crystalline structure with a length of a-axis and / or a length of c-axis that is larger than that of sapphire (α-Al₂O₃). By controlling the lattice constant of the alignment layer in this way, crystallization defects in the semiconductor layer formed thereon can be significantly reduced. That is, the lattice constant of α-Ga₂O₃ constituting the semiconductor layer is larger than that of sapphire (α-Al₂O₃). In fact, as shown in Table 1 below, the lattice constant (a-axis length and c-axis length) of α-Ga₂O₃, an oxide of a group 13 element, is larger than that of α-Al₂O₃. Therefore, by controlling the lattice constant of the alignment layer to be larger than that of α-Al₂O₃, the mismatch of lattice constants between the semiconductor layer and the alignment layer is suppressed when the semiconductor layer is formed on this alignment layer, resulting in a reduction of crystallization defects in the semiconductor layer. For example, when α-Ga₂O₃ is deposited on the c-plane of sapphire, the in-plane lattice length (a-axis length) of α-Ga₂O₃ is larger than that of sapphire, exhibiting a mismatch of approximately 4.8%. Therefore, by controlling the a-axis length of the alignment layer to be larger than that of α-Al₂O₃, the crystallization defects in the α-Ga₂O₃ layer are reduced. Similarly, when α-Ga₂O₃ is deposited on the m-plane of sapphire, the in-plane lattice length (c-axis and a-axis length) of α-Ga₂O₃ is larger than that of sapphire, with a c-axis mismatch of approximately 3.4% and an a-axis mismatch of approximately 4.8%. Therefore, by controlling the c-axis and a-axis lengths of the alignment layer to be larger than those of α-Al₂O₃, the crystallization defects in the α-Ga₂O₃ layer are reduced. In contrast, if the semiconductor layer is formed directly on the sapphire substrate, stress generated in the semiconductor layer due to lattice constant mismatch may lead to a large number of crystallization defects.

[0057] [Table 1]

[0058]

[0059] The alignment layer is preferably composed entirely of a material having a corundum-type crystal structure. This reduces crystal defects in both the alignment layer and the semiconductor layer. The alignment layer is preferably formed on the surface of a sapphire substrate. Since the α-Al₂O₃ constituting the sapphire substrate has a corundum-type crystal structure, by making the alignment layer composed of a material with a corundum-type crystal structure, its crystal structure is identical to that of the sapphire substrate. Consequently, crystal defects caused by mismatch in crystal structure within the alignment layer are suppressed. In this respect, if crystal defects in the alignment layer are reduced, crystal defects in the semiconductor layer formed thereon are also reduced, which is preferable. This is because if a large number of crystal defects exist in the alignment layer, these defects are inherited in the semiconductor layer formed thereon, resulting in crystal defects also occurring in the semiconductor layer.

[0060] The material constituting the alignment layer, having a corundum-type crystalline structure, preferably comprises α-Cr₂O₃ or an α-Cr₂O₃-based solid solution. As shown in Table 1 above, these materials have larger lattice constants (a-axis length and / or c-axis length) than α-Al₂O₃, and their lattice constants are close to or consistent with those of α-Ga₂O₃. Therefore, they can effectively suppress crystallization defects in the semiconductor layer. The aforementioned solid solution can be either a substitutional solid solution or an intrusive solid solution, but a substitutional solid solution is preferred. However, although the alignment layer is composed of a material having a corundum-type crystalline structure, the presence of trace components other than these, such as microcrystals, is not excluded.

[0061] The a-axis length of the material with a corundum-type crystalline structure in the surface of the orientation layer on the side for crystal growth is greater than 4.754 Å and less than 5.157 Å, more preferably 4.850 to 5.000 Å, and even more preferably 4.900 to 5.000 Å. Furthermore, the c-axis length of the material with a corundum-type crystalline structure in the surface of the orientation layer on the side for crystal growth is greater than 12.990 Å and less than 13.998 Å, more preferably 13.000 to 13.800 Å, and even more preferably 13.400 to 13.600 Å. By controlling the a-axis length and / or c-axis length of the orientation layer surface within the above ranges, it is possible to make it close to the lattice constant (a-axis length and / or c-axis length) of α-Ga₂O₃.

[0062] The thickness of the alignment layer is preferably 10 μm or more, more preferably 40 μm or more. There is no particular upper limit to the thickness, but it is typically 1000 μm or less. When used as a self-supporting substrate with only the alignment layer, from an operational point of view, the alignment layer can be thicker, for example, 1 mm or more; from a cost point of view, for example, the thickness can be 2 mm or less. By thickening the alignment layer in this way, crystal defects on the surface of the alignment layer can also be reduced. When the alignment layer is formed on a sapphire substrate, there is a difference in lattice constant between the sapphire substrate and the alignment layer, resulting in the easy generation of crystal defects at their interface, i.e., below the alignment layer. However, by thickening the alignment layer, the influence of such crystal defects generated below the alignment layer can be reduced on the surface of the alignment layer. The reason for this is not yet conclusive, but it is believed that the crystal defects generated below the alignment layer disappear before reaching the surface of the thicker alignment layer. Furthermore, it is also expected that by thickening the alignment layer, after forming a semiconductor layer on the alignment layer, the semiconductor layer can be peeled off, allowing the substrate to be reused. The density of crystal defects on the surface of the orientation layer is preferably 1.0 × 10⁻⁶. 8 / cm 2 Hereinafter, 1.0 × 10 is more preferred. 6 / cm 2 Hereinafter, 4.0×10 is further preferred. 3 / cm 2 There is no specific lower limit below. It should be noted that in this specification, crystallization defects refer to: through-edge dislocations, through-screw dislocations, through-mixed dislocations, and basal plane dislocations. The crystallization defect density is the sum of the densities of all dislocations. For example, if the material contains 3 × 10⁻⁶ through-edge dislocations... 8 / cm 2 6×10 through spiral dislocations 8 / cm 2 4×10 through mixed dislocations 8 / cm 2 The density of crystal defects is then 1.3 × 10⁻⁶. 9 / cm 2 For basal plane dislocations, a problem arises when the substrate containing the alignment layer has an off-angle, but not when there is no off-angle, since the surface of the alignment layer is not exposed.

[0063] The material constituting the alignment layer is not particularly limited as long as it has orientation relative to the surface of the substrate, such as c-axis orientation, a-axis orientation, or m-axis orientation. Accordingly, when a semiconductor layer is formed on the substrate, the semiconductor film can be a c-axis oriented film, an a-axis oriented film, or a m-axis oriented film.

[0064] The orientation layer is preferably a heteroepitaxial growth layer. For example, when the orientation layer is grown on a sapphire substrate, both the sapphire substrate and the orientation layer have a corundum-type crystal structure. Therefore, when their lattice constants are similar, epitaxial growth sometimes occurs during heat treatment, where the crystal planes of the orientation layer align with the crystal orientation of the sapphire substrate. By epitaxially growing the orientation layer in this way, the orientation layer can inherit the high crystallinity and crystal orientation characteristic of a single crystal of the sapphire substrate.

[0065] The arithmetic mean roughness Ra of the surface of the alignment layer is preferably 1 nm or less, more preferably 0.5 nm or less, and even more preferably 0.2 nm or less. It is believed that smoothing the surface of the alignment layer in this way further improves the crystallinity of the semiconductor layer disposed thereon.

[0066] The substrate has a preferred single-sided diameter of 20 cm. 2 The above, and more preferably 70cm 2 The above, and more preferably 170cm 2 The area mentioned above. By increasing the area of ​​the substrate in this way, it is possible to increase the area of ​​the semiconductor layer formed on it. Therefore, multiple semiconductor devices can be obtained from a single semiconductor layer, and further reductions in manufacturing costs can be expected. There is no particular upper limit to the size of the substrate; a typical size is 700 cm² on one side. 2 the following.

[0067] The substrate of the present invention preferably also includes a support substrate on the side opposite to the side used for crystal growth (i.e., the back side) of the alignment layer. That is, the substrate of the present invention can be a substrate having a support substrate and an alignment layer disposed on the support substrate. Furthermore, the support substrate is preferably a sapphire substrate, a corundum single crystal such as Cr2O3, and particularly preferably a sapphire substrate. By making the support substrate a corundum single crystal, it can also act as a seed crystal for heteroepitaxial growth of the alignment layer. In addition, by adopting such a configuration with a corundum single crystal, a semiconductor layer of excellent quality can be obtained. That is, corundum single crystal has excellent mechanical properties, thermal properties, chemical stability, and other characteristics. In particular, sapphire has a thermal conductivity as high as 42 W / m·K at room temperature, exhibiting excellent thermal conductivity. Therefore, by using a substrate having a sapphire substrate, the overall thermal conductivity of the substrate can be excellent. As a result, it is expected that when forming a semiconductor layer on the substrate, uneven temperature distribution within the substrate surface will be suppressed, and a semiconductor layer with a uniform film thickness can be obtained. In addition, it has the following effects: it makes it easy to obtain large-area sapphire substrates, which can reduce the overall cost, and it can obtain large-area semiconductor layers.

[0068] The sapphire substrate used as the support substrate can have any orientation plane. That is, for example, it can have an a-plane, a c-plane, an r-plane, and an m-plane, and can also have a specified angle relative to these planes. In addition, in order to adjust the electrical properties, the sapphire can be doped. Known dopants can be used as such dopants.

[0069] Using the alignment layer of the substrate of the present invention, a semiconductor layer composed of α-Ga₂O₃ can be formed. The semiconductor layer can be formed using known methods; however, any one of various vapor phase film formation methods such as CVD, HVPE, sublimation, MBE, PLD, and sputtering, as well as liquid phase film formation methods such as hydrothermal methods and Na flux methods, is preferred. Examples of CVD methods include thermal CVD, plasma CVD, atomization CVD, and MO (organometallic) CVD. Among these, atomization CVD, hydrothermal methods, or HVPE are particularly preferred for forming a semiconductor layer composed of α-Ga₂O₃.

[0070] The substrate of this invention can be a self-standing substrate with only the alignment layer, or a substrate with a supporting substrate such as a sapphire substrate. Therefore, the alignment layer can ultimately be separated from the supporting substrate such as the sapphire substrate as needed. Separation of the supporting substrate can be performed using known methods and is not particularly limited. Examples include: methods for separating the alignment layer by applying mechanical impact, methods for separating the alignment layer by applying heat and using thermal stress, methods for separating the alignment layer by applying vibration such as ultrasound, methods for separating the alignment layer by etching unwanted portions, methods for separating the alignment layer by laser lift-off, and methods for separating the alignment layer by machining such as cutting and grinding. Furthermore, in the case where the alignment layer is heteroepitaxially grown on a sapphire substrate, the alignment layer can be placed on another supporting substrate after separating the sapphire substrate. The material of the other supporting substrate is not particularly limited; a suitable material can be selected from the viewpoint of material properties. Examples include: metal substrates or substrates such as Cu, and ceramic substrates such as SiC and AlN, from the viewpoint of thermal conductivity.

[0071] Manufacturing method

[0072] The substrate of the present invention can preferably be manufactured as follows: (a) preparing a sapphire substrate; (b) fabricating an orientation precursor layer comprising elements constituting microcrystals; (c) heat-treating the orientation precursor layer on the sapphire substrate, so that at least a portion of the orientation precursor layer near the sapphire substrate is transformed into an orientation layer; and (d) performing grinding, polishing, or other processing to smooth the surface of the orientation layer. The orientation precursor layer, which becomes an orientation layer through heat treatment, comprises: a material having a corundum-type crystal structure with an a-axis length and / or a c-axis length larger than that of sapphire, or a material that, through heat treatment described later, becomes a corundum-type crystal structure with an a-axis length and / or a c-axis length larger than that of sapphire. According to this manufacturing method, the growth of the orientation layer can be promoted using the sapphire substrate as a seed crystal. That is, the high crystallinity and crystal orientation characteristic of a single crystal of the sapphire substrate are inherited by the orientation layer.

[0073] (a) Preparation of sapphire substrate

[0074] To fabricate the substrate, firstly, a sapphire substrate is prepared. The sapphire substrate used can have any orientation plane. That is, for example, it can have an a-plane, a c-plane, an r-plane, and an m-plane, and can also have a predetermined angle relative to these planes. For example, when using c-plane sapphire, it is c-axis oriented relative to the surface; therefore, a c-axis oriented alignment layer can be easily heteroepitaxially grown on it. Furthermore, to adjust the electrical properties, a sapphire substrate with added dopant can be used. Known dopants can be used as this dopant.

[0075] (b) Fabrication of orientation precursor layers

[0076] An orientation precursor layer is fabricated comprising a material having a corundum-type crystalline structure with an a-axis length and / or c-axis length greater than that of sapphire, or a material having a corundum-type crystalline structure with an a-axis length and / or c-axis length greater than that of sapphire obtained through heat treatment. Furthermore, the orientation precursor layer preferably contains one or more elements selected from the group consisting of Ti, Zr, Hf, Ge, Si, and Ce, as the material constituting the microcrystals. These elements are preferably contained in the orientation precursor layer in the form of metallic elements or compounds other than oxides (e.g., nitrides). The method for forming the orientation precursor layer is not particularly limited, and known methods can be used. Examples of methods for forming the orientation precursor layer include: aerosol deposition (AD), hydrothermal methods, sputtering, evaporation, various CVD (chemical vapor deposition) methods, HVPE, PLD, CVT (chemical vapor transport), sublimation, etc. Examples of CVD methods include thermal CVD, plasma CVD, atomization CVD, and MO (metal-organic) CVD. Alternatively, a pre-formed alignment precursor can be fabricated and placed on a sapphire substrate. This pre-formed material can be shaped using methods such as tape casting or pressing. Another method involves using a polycrystalline material pre-fabricated using various CVD methods or sintering techniques, and placing it on a sapphire substrate as the alignment precursor layer.

[0077] However, the preferred methods are algebraic deposition (AD), various CVD methods, or sputtering. These methods allow for the formation of a dense orientation precursor layer in a relatively short time, facilitating heteroepitaxial growth using a sapphire substrate as a seed crystal. In particular, the AD method does not require a high-vacuum process and has a relatively fast film formation rate, making it cost-effective. When using sputtering, a target made of the same material as the orientation precursor layer can be used for film formation; however, reactive sputtering using a metal target in an oxygen atmosphere can also be employed. Placing a pre-formed structure on sapphire is also preferred as a simple method; however, the orientation precursor layer is not dense, thus requiring a densification process in the heat treatment step described later. Using a pre-formed polycrystalline material as the orientation precursor layer requires two steps: fabricating the polycrystalline material and heat treatment on the sapphire substrate. Furthermore, to improve the adhesion between the polycrystalline material and the sapphire substrate, the surface of the polycrystalline material needs to be thoroughly smoothed beforehand. Either method can be used under known conditions; however, the following describes the method of directly forming the orientation precursor layer using the AD method and the method of placing the pre-made molded body on a sapphire substrate.

[0078] Aerosol deposition (AD) is a technique in which particulate matter or particulate material is mixed with a gas, atomized, and then sprayed at high speed from a nozzle to impinge on a substrate, forming a film. This AD method is characterized by its ability to form a densified film at room temperature. An example of the film-forming apparatus (aerosol deposition (AD) apparatus) used in this AD method is shown below. Figure 1 . Figure 1 The film-forming apparatus 20 shown is configured as an apparatus used in the AD process for spraying raw material powder onto a substrate in an atmosphere with a pressure lower than atmospheric pressure. The film-forming apparatus 20 includes: an aerosol generation unit 22 that generates an aerosol containing raw material components; and a film-forming unit 30 that sprays the raw material powder onto a sapphire substrate 21 to form a film containing the raw material components. The aerosol generation unit 22 includes: an aerosol generation chamber 23 that receives the raw material powder and receives a carrier gas supply from a gas cylinder (not shown) to generate an aerosol; a raw material supply pipe 24 that supplies the generated aerosol to the film-forming unit 30; and a vibrator 25 that vibrates the aerosol generation chamber 23 and the aerosol therein at a vibration frequency of 10–100 Hz. The film-forming unit 30 includes: a film-forming chamber 32 that sprays aerosol onto a sapphire substrate 21; a substrate holder 34 disposed inside the film-forming chamber 32 and fixing the sapphire substrate 21; and an X-Y stage 33 that moves the substrate holder 34 in the X-Y axis direction. Additionally, the film-forming unit 30 includes: a spray nozzle 36 with a slit 37 formed at its tip to spray aerosol onto the sapphire substrate 21; and a vacuum pump 38 that depressurizes the film-forming chamber 32.

[0079] For the aerosol deposition (AD) method, it is known that film thickness and film quality can be controlled through film formation conditions. For example, the morphology of the AD film is easily affected by the impact velocity of the raw material powder against the substrate, the particle size of the raw material powder, the aggregation state of the raw material powder in the aerosol, and the spraying rate per unit time. The impact velocity of the raw material powder against the substrate is affected by the differential pressure between the film formation chamber 32 and the spray nozzle 36, or the opening area of ​​the spray nozzle. Without appropriate conditions, the film may sometimes become compacted or porous; therefore, it is best to control these factors appropriately.

[0080] When using a molded body with a pre-formed orientation precursor layer, the orientation precursor raw material powder can be molded to produce the molded body. For example, when compression molding is used, the orientation precursor layer is a compression molded body. A compression molded body can be produced by compressing the orientation precursor raw material powder using known methods; for example, the raw material powder is placed in a mold and pressurized at a rate preferably 100–400 kgf / cm³. 2 More preferably, it is 150–300 kgf / cm³. 2It can be manufactured by pressing under pressure. Furthermore, the molding method is not particularly limited; besides compression molding, casting, extrusion molding, scraping, and any combination of these methods can also be used. For example, in the case of casting, it is preferable to add appropriate additives such as binders, plasticizers, dispersants, and dispersion media to the raw material powder to form a slurry, and then pass the slurry through a narrow, slit-shaped nozzle, thereby extruding and molding it into a sheet. The thickness of the molded sheet is not limited, but from an operational point of view, 5 to 500 μm is preferred. Additionally, if a thicker orientation precursor layer is required, multiple sheets of this molded sheet can be stacked and used to achieve the desired thickness.

[0081] For these molded articles, subsequent heat treatment on a sapphire substrate causes the portion near the sapphire substrate to become an alignment layer. As described above, in this method, densification is achieved by sintering the molded article in the subsequent heat treatment process. Therefore, in addition to materials having or providing a corundum-type crystalline structure, the molded article may also contain trace components such as sintering aids.

[0082] (c) Heat treatment of the alignment precursor layer on the sapphire substrate

[0083] A sapphire substrate with an oriented precursor layer is heat-treated at a temperature of 1000°C or higher. This heat treatment transforms at least a portion of the oriented precursor layer near the sapphire substrate into a dense oriented layer. Furthermore, this heat treatment enables heteroepitaxial growth of the oriented layer. Specifically, by forming the oriented layer from a material with a corundum-type crystal structure, heteroepitaxial growth occurs during heat treatment, where the material with the corundum-type crystal structure crystallizes using the sapphire substrate as a seed crystal. At this time, a rearrangement of the crystals occurs, with the crystals aligning to mimic the crystal planes of the sapphire substrate. As a result, the crystal axes of the sapphire substrate and the oriented layer are aligned. For example, when using a c-plane sapphire substrate, both the sapphire substrate and the oriented layer are c-axis oriented relative to the surface of the substrate.

[0084] It should be noted that, in various methods such as CVD, sputtering, HVPE, PLD, CVT, and sublimation, heteroepitaxial growth sometimes occurs on sapphire substrates without heat treatment at temperatures above 1000°C. However, the orientation precursor layer is preferably in an unoriented state during its fabrication, i.e., amorphous or non-oriented polycrystalline, and undergoes a crystal rearrangement using sapphire as a seed crystal during this heat treatment process. This effectively reduces crystallization defects reaching the surface of the orientation layer. The reason for this is not yet definitively established, but it is believed that crystallization defects generated in the lower part of the orientation layer are more easily offset.

[0085] Regarding the heat treatment method, there are no particular limitations as long as a corundum-type crystalline structure is obtained and heteroepitaxial growth occurs using a sapphire substrate as a seed crystal. It can be carried out in known heat treatment furnaces such as tubular furnaces or heated plates. Furthermore, not only can these atmospheric (pressureless) heat treatments be used, but also pressurized heat treatments such as hot pressing and HIP, or combinations of atmospheric and pressurized heat treatments. The heat treatment conditions can be appropriately selected depending on the material used for the alignment layer. For example, the heat treatment atmosphere can be selected from atmosphere, vacuum, nitrogen, and inert gas atmospheres. The preferred heat treatment temperature also varies depending on the material used for the alignment layer; however, for example, 1000–2000°C is preferred, and 1200–2000°C is more preferred. The heat treatment temperature and holding time are related to the thickness of the alignment layer produced during heteroepitaxial growth, and can be appropriately adjusted according to the type of material and the target alignment layer thickness. However, when a pre-formed molded body is used as an alignment precursor layer, it needs to be sintered during heat treatment to densify it; atmospheric sintering at high temperature, hot pressing, HIP, or a combination thereof are preferred. For example, when hot pressing is used, the surface pressure is preferably 50 kgf / cm. 2 The above, more preferably 100 kgf / cm 2 The above is particularly preferred, with 200 kgf / cm² being the optimal value. 2 The upper limit is not specifically limited. Regarding the firing temperature, any temperature that allows sintering, densification, and heteroepitaxial growth to occur is acceptable and is not particularly limited; preferably 1000°C or higher, more preferably 1200°C or higher, even more preferably 1400°C or higher, and particularly preferably 1600°C or higher. The firing atmosphere can also be selected from atmospheric, vacuum, nitrogen, and inert gas atmospheres. The firing fixtures, such as the outer mold, can be made of graphite or alumina.

[0086] (d) Exposure of the orientation layer surface

[0087] On the alignment layer formed near the sapphire substrate through heat treatment, there may be or remain an alignment precursor layer or a surface layer with poor or no alignment. In this case, it is preferable to apply a grinding or polishing process to the surface originating from the alignment precursor layer to expose the surface of the alignment layer. Accordingly, a material with excellent alignment properties is exposed on the surface of the alignment layer, thus enabling the effective epitaxial growth of a semiconductor layer on it. The method for removing the alignment precursor layer and the surface layer is not particularly limited, and examples include grinding and polishing methods, and ion beam milling methods. It is preferable to use abrasive finishing or chemical mechanical polishing (CMP) to polish the surface of the alignment layer.

[0088] Specific grinding and polishing methods for the alignment layer can be exemplified by the following method: Three identical substrates are fixed at three points on a ceramic platform. Using abrasive stones with grit sizes #320 to #2000, the film-forming surface of the substrates is ground until the alignment layer is exposed. Then, a fine polishing process using diamond abrasive grains is performed to further smooth the surface of the alignment layer. During this process, the size of the diamond abrasive grains is progressively reduced while performing the fine polishing, thereby improving the flatness of the surface. Next, a mirror finish is achieved on the alignment layer surface using chemical mechanical polishing (CMP) with colloidal silica, resulting in a composite substrate substrate with an alignment layer on a sapphire substrate. Preferably, the arithmetic mean roughness Ra of the finished alignment layer surface is 0.2 nm or less. The arithmetic mean roughness Ra of the alignment layer surface can be confirmed using a commercially available surface roughness meter.

[0089] Example

[0090] The invention will be further illustrated by the following examples.

[0091] Example 1

[0092] (1) Fabrication of composite substrate

[0093] (1a) Fabrication of orientation precursor layers

[0094] Commercially available Cr2O3 powder (volume average particle size 3 μm) and commercially available TiN powder (volume average particle size 0.8 μm) were prepared as raw material powders. Using a mixture of 1.5 parts by weight of TiN powder added to 100 parts by weight of Cr2O3 powder and mixed in a jar mill for 48 hours, a sapphire substrate (diameter 50.8 mm (2 inches), thickness 0.43 mm, c-face, off-center angle 0.3°) was prepared. Figure 1 The aerosol deposition (AD) apparatus 20 shown forms an AD film (orientation precursor layer) with Cr2O3 as the main component on a seed substrate (sapphire substrate). The configuration of the aerosol deposition (AD) apparatus 20 is as described above.

[0095] The AD film formation conditions are as follows: The carrier gas is Ar, and a ceramic nozzle with a slit having a long side of 5 mm and a short side of 0.3 mm is used. The nozzle scanning conditions are as follows: at a scanning speed of 0.5 mm / s, the nozzle moves 55 mm along the direction perpendicular to the long side of the slit and forward, then moves 5 mm along the direction of the long side of the slit, then moves 55 mm along the direction perpendicular to the long side of the slit and back, then moves 5 mm along the direction of the long side of the slit and in the opposite direction to the initial position. This scanning is repeated. At the moment when the nozzle has moved 55 mm from the initial position along the direction of the long side of the slit, it scans in the opposite direction and returns to the initial position. This cycle is considered one cycle, and 500 cycles are repeated. In one cycle of film formation at room temperature, the set pressure of the delivery gas is adjusted to 0.07 MPa, the flow rate is adjusted to 8 L / min, and the chamber pressure is adjusted to below 100 Pa. The thickness of the AD film (oriented precursor layer) formed in this way is 120 μm.

[0096] (1b) Heat treatment of orientation precursor layer

[0097] The sapphire substrate with the AD film (orientation precursor layer) formed is removed from the AD device and annealed at 1700°C for 4 hours in a nitrogen atmosphere.

[0098] (1c) Grinding and polishing

[0099] The obtained substrate was fixed on a ceramic platform, and the side originating from the AD film was ground using abrasive stones with grit sizes #320 to #2000 until the alignment layer was exposed. Then, the surface was further smoothed using a diamond abrasive. During this process, the diamond abrasive grain size was progressively reduced from 3 μm to 0.5 μm to improve the flatness of the surface. Next, a mirror finish was achieved using chemical mechanical polishing (CMP) with colloidal silica, resulting in a composite substrate with an alignment layer on a sapphire substrate. The arithmetic mean roughness Ra of the processed alignment layer surface was 0.1 nm, the grinding and polishing amount was 70 μm, and the thickness of the polished composite substrate was 0.48 mm. It should be noted that the side with the AD film is referred to as the "surface". Furthermore, by repeatedly performing the above steps (1a) to (1c), 101 composite substrates were fabricated.

[0100] (2) Evaluation of orientation layer

[0101] (2a) Surface EDX

[0102] Compositional analysis of the exposed substrate surface of the alignment layer was performed using an energy-dispersive X-ray diffractometer (EDX). The results showed that Cr and O were detected as major components, and Ti was detected as a trace component, indicating that the alignment layer is dominated by Cr oxide. Furthermore, it is presumed that the alignment layer contains Ti-containing microcrystals.

[0103] (2b) Surface EBSD

[0104] Using a SEM (Hitachi High Technology Co., Ltd., SU-5000) equipped with an electron backscatter diffraction (EBSD) device (Nordlys Nano, Oxford Instruments), inverse pole figure orientation mapping of the Cr oxide-dominant orientation layer surface was performed within a 500 μm × 500 μm field of view. The conditions for this EBSD measurement are as follows.

[0105] <EBSD Measurement Conditions>

[0106] Accelerating voltage: 15kV

[0107] • Point strength: 70

[0108] • Working distance: 22.5mm

[0109] • Step size: 0.5μm

[0110] • Sample tilt angle: 70°

[0111] • Measurement procedure: Aztec (version 3.3)

[0112] The orientation mapping of the inverse pole figure shows that the surface of the orientation layer with Cr oxide as the main phase has a biaxially oriented corundum-type crystalline structure, which is c-axis oriented in the substrate normal direction and also oriented in the in-plane direction. This indicates that an orientation layer with α-Cr2O3 as the main phase is formed on the substrate surface.

[0113] (2c) Planar TEM and STEM-EDX of the orientation layer

[0114] To evaluate the microstructure of the alignment layer, planar TEM observation (top view) was performed. Five samples for TEM observation were cut from five locations within a region approximately 10 μm deep from the surface of the alignment layer, with a sample thickness of approximately 400 nm around the perimeter of the measurement field of view, using focused ion beam (FIB). It should be noted that... Figure 2 As shown, the sampling points are set as the center point of the substrate and four peripheral points on the line about 20 mm away from the center point when two intersecting lines are drawn from the center point on the substrate.

[0115] The obtained slices were observed using a transmission electron microscope (Hitachi H-9000UHR-II) at an accelerating voltage of 300kV. Specifically, TEM images with a measurement field of approximately 10μm × 10μm to 161nm × 161nm were observed in each slice using two fields of view, totaling ten fields. As a result, needle-like crystallites were observed in the TEM images obtained at a 161nm × 161nm field of view, with 20 to 30 crystallites observed in each field. The number of crystallites was determined by counting the crystalline particles with a long axis length of 1nm to 2μm. An example of the obtained TEM image is shown below. Figure 3 The long axis lengths of the crystallites observed by TEM were measured, and the average long axis length of 10 fields of view was calculated. Additionally, the total number of crystallites observed by TEM in the 10 fields of view was divided by the total area of ​​all observed fields of view to obtain the crystallite density per unit area (crystals / cm²). 2 The results are shown in Table 2. Additionally, for each section, EDX measurements were performed using a scanning transmission electron microscope (JEOL JEM-ARM200F Dual-X, EDX: JEOL JED-2300) at an accelerating voltage of 200 kV. The beam spot size was set to approximately 0.2 nm in diameter, and point analysis was performed using an electron beam. The results showed that 2.71 at% Ti was detected in the crystallites, indicating that Ti was enriched in the crystallites.

[0116] (3) Evaluation of composite substrate

[0117] (3a) Evaluation of edge collapse

[0118] Using 100 of the 101 composite substrates prepared in (1) above, excluding those used for evaluating the alignment layer in (2) above, the chipping condition of the outer edge (edge) of the alignment layer was evaluated. Specifically, the outer edge of the ground and polished alignment layer was observed using an optical microscope at 50x magnification. Notches with a longest side of 50 μm or more were considered chipped edges, and their presence or absence was confirmed. Substrates without chipping were designated as acceptable, and those with chipping were designated as unacceptable. The number of acceptable substrates was calculated. The yield R1 was calculated by dividing the number of acceptable substrates by the total number of ground and polished substrates (100). The yield R1 is preferably 0.75 or higher, more preferably 0.85 or higher. The results are shown in Table 2.

[0119] (3b) Evaluation of damage

[0120] Using 100 of the 101 composite substrates prepared in (1) above, excluding those used for evaluating the alignment layer in (2) above, the damage state of the alignment layer surface was evaluated. In practice, the surface of the grinding and polishing alignment layer was observed using an optical microscope at 50x magnification to confirm the presence or absence of damage. Substrates with 3 or fewer visible damage points were considered acceptable, while substrates with 4 or more visible damage points were considered unacceptable, and the number of acceptable substrates was calculated. The yield R2 was calculated by dividing the number of acceptable substrates by the total number of grinding and polishing substrates (100). The yield R2 is preferably 0.75 or higher, more preferably 0.95 or higher. The results are shown in Table 2.

[0121] Examples 2~4

[0122] The amount of TiN powder added in (1a) above is shown in Table 2. Otherwise, a composite substrate was fabricated using the same method as in Example 1, and the alignment layer and composite substrate were evaluated. The results are shown in Table 2. It should be noted that, using EDX and EBSD measurements, it was found that the alignment layer is mainly composed of α-Cr₂O₃, and its surface has a biaxially oriented corundum-type crystalline structure with c-axis orientation in the substrate normal direction and also in the in-plane direction. Furthermore, using STEM-EDX measurements, it was found that the alignment layer contains Ti-containing microcrystals.

[0123] Example 5

[0124] The volume average particle size of the TiN powder in (1a) above and the heat treatment temperature of the orientation precursor layer in (1b) above are shown in Table 2. Otherwise, a composite substrate was fabricated using the same method as in Example 1, and the orientation layer and the composite substrate were evaluated. The results are shown in Table 2. It should be noted that, using EDX and EBSD measurements, it was found that the orientation layer is dominated by α-Cr₂O₃, and its surface has a biaxially oriented corundum-type crystalline structure with c-axis orientation in the substrate normal direction and also in the in-plane direction. Furthermore, using STEM-EDX measurements, it was found that the orientation layer contains Ti-containing microcrystals.

[0125] Examples 6~8

[0126] The amount of TiN powder added, the volume average particle size, and the heat treatment temperature of the orientation precursor layer in (1b) are shown in Table 2. Otherwise, a composite substrate was fabricated using the same method as in Example 1, and the orientation layer and the composite substrate were evaluated. The results are shown in Table 2. It should be noted that EDX and EBSD measurements show that the orientation layer is dominated by α-Cr₂O₃, and its surface has a biaxially oriented corundum-type crystalline structure with c-axis orientation in the substrate normal direction and also in the in-plane direction. Furthermore, STEM-EDX measurements show that the orientation layer contains Ti-containing microcrystals.

[0127] Example 9

[0128] The volume average particle size of the TiN powder in (1a) above, the mixing time of the raw material powder, and the heat treatment temperature of the orientation precursor layer in (1b) above are shown in Table 2. Otherwise, a composite substrate was fabricated using the same method as in Example 1, and the orientation layer and the composite substrate were evaluated. The results are shown in Table 2. It should be noted that, using EDX and EBSD measurements, it was found that the orientation layer is dominated by α-Cr₂O₃, and its surface has a biaxially oriented corundum-type crystalline structure with c-axis orientation in the substrate normal direction and also in the in-plane direction. Furthermore, using STEM-EDX measurements, it was found that the orientation layer contains Ti-containing microcrystals.

[0129] Examples 10~12

[0130] The amount of TiN powder added, the volume average particle size, and the mixing time of the raw material powder in (1a) above, and the heat treatment temperature of the orientation precursor layer in (1b) above, are shown in Table 2. Otherwise, a composite substrate was fabricated using the same method as in Example 1, and the orientation layer and the composite substrate were evaluated. The results are shown in Table 2. It should be noted that, using EDX and EBSD measurements, it was found that the orientation layer is mainly composed of α-Cr2O3, and its surface has a biaxially oriented corundum-type crystal structure with c-axis orientation in the substrate normal direction and also in the in-plane direction. Furthermore, using STEM-EDX measurements, it was found that the orientation layer contains Ti-containing microcrystals.

[0131] Example 13

[0132] In (1a) above, TiC is added 0.5 N 0.5Powder was used instead of TiN powder. The volume average particle size, mixing time of the raw material powder, and heat treatment temperature of the orientation precursor layer in (1b) above are shown in Table 2. Otherwise, a composite substrate was fabricated using the same method as in Example 1, and the orientation layer and the composite substrate were evaluated. The results are shown in Table 2. It should be noted that, according to EDX and EBSD measurements, the orientation layer is mainly composed of α-Cr2O3, and its surface has a biaxially oriented corundum-type crystal structure with c-axis orientation in the substrate normal direction and also in the in-plane direction. In addition, according to STEM-EDX measurements, the orientation layer contains Ti-containing microcrystals.

[0133] Examples 14~16

[0134] In (1a) above, TiC is added 0.5 N 0.5 The amount of powder used instead of TiN powder, the volume average particle size, the mixing time of the raw material powder, and the heat treatment temperature of the orientation precursor layer in (1b) above are shown in Table 2. Otherwise, a composite substrate was fabricated using the same method as in Example 1, and the orientation layer and the composite substrate were evaluated. The results are shown in Table 2. It should be noted that, using EDX and EBSD measurements, it was found that the orientation layer is mainly composed of α-Cr2O3, and its surface has a biaxially oriented corundum-type crystal structure with c-axis orientation in the substrate normal direction and also in the in-plane direction. Furthermore, using STEM-EDX measurements, it was found that the orientation layer contains Ti-containing microcrystals.

[0135] Example 17 (Compare)

[0136] In (1a) above, no TiN powder or TiC is added. 0.5 N 0.5 Commercially available Cr2O3 powder was used as the raw material. Otherwise, a composite substrate was fabricated using the same method as in Example 1, and the alignment layer and composite substrate were evaluated. The results are shown in Table 2. It should be noted that no microcrystals were observed even during TEM observation of the alignment layer.

[0137] [Table 2]

[0138]

Claims

1. A substrate having an alignment layer for the crystallization growth of a semiconductor film composed of α-Ga₂O₃ or an α-Ga₂O₃-based solid solution. The substrate is characterized in that... The orientation layer is composed of a corundum-type crystal structure having an a-axis length and / or a c-axis length greater than that of sapphire. The orientation layer contains multiple microcrystals defined as crystalline particles with a major axis length of 1 nm to 2 μm.

2. The substrate according to claim 1, characterized in that, The microcrystals have an average major axis length of 10 nm to 100 nm.

3. The substrate according to claim 1 or 2, characterized in that, The number density of the microcrystals per unit area in the orientation layer is 1.00 × 10⁻⁶. 5 ~1.00×10 12 pcs / cm 2 .

4. The substrate according to claim 3, characterized in that, The number density of the microcrystals per unit area in the orientation layer is 1.00 × 10⁻⁶. 10 ~1.00×10 12 pcs / cm 2 .

5. The substrate according to claim 1 or 2, characterized in that, The microcrystals contain one or more elements selected from the group consisting of Ti, Zr, Hf, Ge, Si and Ce.

6. The substrate according to claim 5, characterized in that, The microcrystals contain Ti.

7. The substrate according to claim 1 or 2, characterized in that, The microcrystals are needle-shaped crystals.

8. The substrate according to claim 1 or 2, characterized in that, Materials having the aforementioned corundum-type crystalline structure include α-Cr2O3 or α-Cr2O3-based solid solutions.

9. The substrate according to claim 1 or 2, characterized in that, The orientation layer also has a support substrate on the side opposite to the side used for crystal growth.

10. The substrate according to claim 9, characterized in that, The supporting substrate is a sapphire substrate.

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