β-Ga2O3 EPITAXIAL WAFER AND METHOD FOR PRODUCING β-Ga2O3 EPITAXIAL WAFER

Abstract

The present invention improves crystallinity of a β-Ga2O3 layer. This β-Ga2O3 epitaxial wafer (1) is provided with a sapphire substrate (2), a buffer layer (3), and a β-Ga2O3 layer (4). The sapphire substrate (2) has a first main surface (21), and a second main surface (22) that is on the reverse side from the first main surface (21). The buffer layer (3) is formed on the first main surface (21) of the sapphire substrate (2). The β-Ga2O3 layer (4) is formed on the buffer layer (3). The first main surface (21) of the sapphire substrate (2) is an m-plane, an r-plane, a crystal plane that has an off angle of 30 degrees or less with respect to the m-plane, or a crystal plane that has an off angle of 30 degrees or less with respect to the r-plane. The buffer layer (3) contains O and at least one element that is selected from the group consisting of Ga, Al, and In.

Description

β-Ga2O3 epitaxial wafer and method for manufacturing β-Ga2O3 epitaxial wafer

[0001] The present disclosure provides β-Ga ２ O ３ Epitaxial wafer and β-Ga ２ O ３ This invention relates to a method for manufacturing an epitaxial wafer, more particularly to a β-Ga epitaxial wafer having a sapphire substrate. ２ O ３ Epitaxial wafer and β-Ga with sapphire substrate ２ O ３ The present invention relates to a method for manufacturing an epitaxial wafer.

[0002] Patent Document 1 describes β-Ga ２ O ３ Sapphire substrate with single crystal layer and β-Ga ２ O ３ A method for manufacturing a single crystal layer is disclosed.

[0003] Furthermore, Patent Document 1 discloses the use of a sapphire substrate having an inclined surface inclined at a predetermined angle of 5 degrees to 25 degrees in the a-axis direction with respect to the (0001) plane.

[0004] β-Ga with sapphire substrate ２ O ３ In the epitaxial wafer, β-Ga ２ O ３ In some cases it may be desirable to improve the crystallinity of the layer.

[0005] International Publication No. 2015 / 147101

[0006] The purpose of this disclosure is to ２ O ３ β-Ga that can improve the crystallinity of the layer ２ O ３ Epitaxial wafer, β-Ga ２ O ３ The present invention aims to provide a method for manufacturing a silicon-based epitaxial wafer.

[0007] β-Ga according to one aspect of the present disclosure ２ O ３The epitaxial wafer is composed of a sapphire substrate, a buffer layer, and a β-Ga ２ O ３ The sapphire substrate has a first main surface and a second main surface opposite to the first main surface. The buffer layer is formed on the first main surface of the sapphire substrate. ２ O ３ a layer formed on the buffer layer, the first main surface of the sapphire substrate being an m-plane, an r-plane, a crystal plane having an off-angle of 30 degrees or less with respect to the m-plane, or a crystal plane having an off-angle of 30 degrees or less with respect to the r-plane, the buffer layer containing O and at least one element selected from the group consisting of Ga, Al, and In;

[0008] β-Ga according to one aspect of the present disclosure ２ O ３ The method for manufacturing an epitaxial wafer includes a substrate preparation step, a buffer layer formation step, and an epitaxial growth step. In the substrate preparation step, a sapphire substrate having a first main surface and a second main surface opposite to the first main surface is prepared. In the buffer layer formation step, a buffer layer is formed on the first main surface of the sapphire substrate. In the epitaxial growth step, β-Ga is grown on the buffer layer. ２ O ３ The first principal surface of the sapphire substrate is an m-plane, an r-plane, a crystal plane having an off-angle of 30 degrees or less with respect to the m-plane, or a crystal plane having an off-angle of 30 degrees or less with respect to the r-plane. The buffer layer contains O and at least one element selected from the group consisting of Ga, Al, and In.

[0009] FIG. 1 is a diagram showing a β-Ga ２ O ３ FIG. 2 is a plan view of the epitaxial wafer. ２ O ３ 1, which is a cross-sectional view of the epitaxial wafer taken along line II-II in FIG. 1. FIG. 3 is an explanatory diagram of the crystal plane of a sapphire substrate. FIGS. 4A to 4C are diagrams illustrating the β-Ga ２ O ３5 is a cross-sectional view illustrating the main steps of a method for manufacturing an epitaxial wafer according to a second embodiment of the present invention. ２ O ３ 6A to 6D are cross-sectional views of the β-Ga epitaxial wafer. ２ O ３ 7 is a cross-sectional view illustrating the main steps of a method for manufacturing an epitaxial wafer. ２ O ３ 8 is an explanatory diagram of a buffer layer forming step in the epitaxial wafer manufacturing method according to the second embodiment. ２ O ３ FIG. 9 is a diagram showing the results of measuring an X-ray rocking curve by ω-scanning of X-ray diffraction, regarding the crystallinity of a sample on which a buffer layer is formed in a manufacturing method of an epitaxial wafer. FIG. 10 is a diagram showing the results of measuring an X-ray rocking curve by ω-scanning of X-ray diffraction, regarding the crystallinity of a sample of a comparative example. FIG. 11 is a diagram showing the results of measuring an X-ray rocking curve by ω-scanning of X-ray diffraction, regarding the crystallinity of a sample of a comparative example. ２ O ３ FIG. 10 is another explanatory view of the buffer layer forming step in the epitaxial wafer manufacturing method.

[0010] 1 to 7 and 10 described in the following embodiments 1 and 2 are schematic diagrams, and the ratios of the sizes and thicknesses of the components in the diagrams do not necessarily reflect the actual dimensional ratios.

[0011] (Embodiment 1) Hereinafter, β-Ga according to embodiment 1 will be described. ２ O ３ The epitaxial wafer 1 and its manufacturing method will be described with reference to FIGS. 1 to 3 and 4A to 4C.

[0012] (1) β-Ga ２ O ３ Epitaxial wafer β-Ga according to embodiment 1 ２ O ３ As shown in FIG. 2, the epitaxial wafer 1 includes a sapphire substrate 2, a buffer layer 3, and a β-Ga ２ O ３The sapphire substrate 2 has a first main surface 21 and a second main surface 22 opposite to the first main surface 21. The buffer layer 3 is formed on the first main surface 21 of the sapphire substrate 2. ２ O ３ The layer 4 is formed on the buffer layer 3 .

[0013] β-Ga ２ O ３ The epitaxial wafer 1 has a buffer layer 3 formed on a sapphire substrate 2, and a β-Ga ２ O ３ As shown in FIG. 1, in a plan view from the thickness direction D1 of the sapphire substrate 2 (see FIG. 2), the β-Ga ２ O ３ The epitaxial wafer 1 has a substantially circular shape.

[0014] When viewed from the thickness direction D1 of the sapphire substrate 2 (see FIG. 2), the sapphire substrate 2 is ２ O ３ The sapphire substrate 2 has the same approximately circular shape as the epitaxial wafer 1. The diameter of the sapphire substrate 2 is, for example, 50 mm or more and 150 mm or less, and the thickness of the sapphire substrate 2 is, for example, 430 μm or more and 1300 μm or less.

[0015] The crystal planes in the crystal structure of sapphire include, for example, the c-plane, a-plane, m-plane, and r-plane, and the first main surface 21 of the sapphire substrate 2 is, for example, the m-plane. As shown in FIG. 3, the crystal structure of sapphire is approximately represented by a hexagonal system, and the c-axis, a １ axis, a ２ axis, a ３ The a1 axis, a2 axis, and a3 axis are defined. The a1 axis, a2 axis, and a3 axis are axes that are perpendicular to the c axis. In other words, the a1 axis, a2 axis, and a3 axis are axes that are parallel to the c plane. The angle between the a1 axis and each of the a2 axis and a3 axis is 120 degrees. The crystal structure of sapphire has three-fold rotational symmetry.

[0016] The m-plane of the sapphire substrate 2 is the {10-10} plane of sapphire. The {10-10} plane of sapphire is a crystal plane defined by Miller indices, which are expressed by placing four indices in parentheses. A "-" sign added to an index in the Miller indices indicates the inversion of the index following the sign. The {10-10} plane includes multiple crystallographically equivalent crystal planes. For example, the (1010) plane included in the {10-10} plane of sapphire is a plane equivalent to the (10-10) plane of sapphire.

[0017] The first main surface 21 of the sapphire substrate 2 is not limited to the m-plane, but may be, for example, the r-plane, which is the {01-12} plane of sapphire.

[0018] In the present disclosure, the first main surface 21 of the sapphire substrate 2 may be a crystal plane having an off-angle with respect to the m-plane. The "crystal plane having an off-angle with respect to the m-plane" means, for example, a crystal plane tilted by an off-angle in a direction in which the angle between the m-plane and the c-plane changes with respect to the m-plane, or in a direction in which the angle between the m-plane and the a-plane changes with respect to the m-plane. Therefore, if the off-angle with respect to the m-plane is 0 degrees, the first main surface 21 of the sapphire substrate 2 is an m-plane. In the present disclosure, the "crystal plane having an off-angle with respect to the m-plane" is a crystal plane having an off-angle of 30 degrees or less with respect to the m-plane. ２ O ３ In order to improve the crystallinity of the layer 4, the off angle with respect to the m-plane is preferably 5 degrees or more and 30 degrees or less.

[0019] In the present disclosure, the first main surface 21 of the sapphire substrate 2 may be a crystal plane having an off-angle with respect to the r-plane. The term "crystal plane having an off-angle with respect to the r-plane" refers to a crystal plane tilted by the off-angle in the direction in which the angle between the r-plane and the c-plane changes with respect to the r-plane. Therefore, if the off-angle with respect to the r-plane is 0 degrees, the first main surface 21 of the sapphire substrate 2 is an r-plane. In the present disclosure, the term "crystal plane having an off-angle with respect to the r-plane" refers to a crystal plane having an off-angle of 30 degrees or less with respect to the r-plane. ２ O ３From the viewpoint of improving the crystallinity of the layer 4, the off-angle with respect to the r-plane is preferably 5 degrees or more and 30 degrees or less. When the first main surface 21 of the sapphire substrate 2 has an off-angle, the first main surface 21 has a stepped undulation with a plurality of steps and a plurality of terraces arranged alternately. Therefore, when the buffer layer 3 is heteroepitaxially grown on the sapphire substrate 2, the surface 31 of the buffer layer 3 has a stepped undulation. As a result, β-Ga ２ O ３ When the layer 4 is grown heteroepitaxially, the β-Ga ２ O ３ The direction in which the crystals of layer 4 preferentially grow is easily determined, and the β-Ga ２ O ３ It is possible to grow layer 4 heteroepitaxially.

[0020] The buffer layer 3 contains at least one element selected from the group consisting of Ga, Al, and In, and O. That is, the buffer layer 3 contains, for example, α-(In ｙ Al ｘ Ga １－ｘ－ｙ ) ２ O ３ (where 0<x≦1, 0≦y<1, 0<x+y≦1). ２ O ３ In the epitaxial wafer 1, the buffer layer 3 is α-(Al ｘ Ga １－ｘ ) ２ O ３ layer (where 0.2≦x<1), so β-Ga ２ O ３ Layer 4 is a heteroepitaxial layer. ｘ Ga １－ｘ ) ２ O ３ In the case of the β-Ga layer, the growth temperature is higher (for example, 700° C. or higher and 900° C. or lower) than the growth temperature of the buffer layer 3 (for example, 600° C. or higher and lower than 700° C.). ２ O ３ In order to prevent the phase state of the buffer layer 3 from changing from the α phase to the β phase when the layer 4 is epitaxially grown, the α-(Al ｘGa １－ｘ ) ２ O ３ In other words, if x is 0.2 or less, the α-(Al ｘ Ga １－ｘ ) ２ O ３ The layer is unlikely to change to the β phase up to 900°C. ｘ Ga １－ｘ ) ２ O ３ In the case of the layer, the buffer layer 3 and the β-Ga ２ O ３ The difference in lattice constant with layer 4 is reduced to β-Ga ２ O ３ In order to improve the crystallinity of the layer 4, α-(Al ｘ Ga １－ｘ ) ２ O ３ Preferably, x<1 in the layer.

[0021] The thickness of the buffer layer 3 is determined by the thickness of the sapphire substrate 2 and the thickness of the β-Ga ２ O ３ The thickness of the buffer layer 3 is thinner than that of the layer 4. The thickness of the buffer layer 3 is, for example, 200 nm to 500 nm, but may be thicker than 500 nm.

[0022] β-Ga ２ O ３ The thickness of the layer 4 is, for example, 0.2 μm or more and 3 μm or less. ２ O ３ The crystal structure of the single crystal is monoclinic. ２ O ３ The primary surface 41 of the layer 4 is, for example, β-Ga ２ O ３ The (010) or (001) plane of a single crystal is, but is not limited to, the (010) or (001) plane. The (010) and (001) planes are crystal planes expressed by Miller indices, where three indices are enclosed in parentheses. ２ O ３ The primary surface 41 of the layer 4 is β-Ga ２ O ３ It may be a crystal plane having an off-angle relative to the (010) or (001) plane of the single crystal.

[0023] (2) β-Ga ２ O ３ The method for manufacturing an epitaxial wafer will be described below. ２ O ３ A method for manufacturing the epitaxial wafer 1 will be described with reference to FIGS. 4A to 4C.

[0024] β-Ga ２ O ３ The method for manufacturing the epitaxial wafer 1 includes a substrate preparation step, a buffer layer formation step, and an epitaxial growth step.

[0025] In the substrate preparation step, a sapphire substrate 2 is prepared, which has a first main surface 21 and a second main surface 22 opposite to the first main surface 21 (see FIG. 4A ). The first main surface 21 of the sapphire substrate 2 is an m-plane, but is not limited to an m-plane and may be an r-plane, a crystal plane having an off-angle of 30 degrees or less with respect to the m-plane, or a crystal plane having an off-angle of 30 degrees or less with respect to the r-plane.

[0026] In the buffer layer forming step, a buffer layer 3 is formed on the first main surface 21 of the sapphire substrate 2 (see FIG. 4B). ｘ Ga １－ｘ ) ２ O ３ layer (where 0.2≦x<1). In the buffer layer formation step, the buffer layer 3 is formed on the first main surface 21 of the sapphire substrate 2 by, for example, mist CVD (Chemical Vapor Deposition). The growth temperature of the buffer layer 3 is, for example, 600° C. or higher and lower than 700° C. In the buffer layer formation step, instead of the mist CVD method, for example, MOCVD (Metalorganic Chemical Vapor Deposition) method or MBE (Molecular Beam Epitaxy) method may be used.

[0027] In the epitaxial growth step, as shown in FIG. 4C, β-Ga is grown on the buffer layer 3. ２ O ３The layer 4 is epitaxially grown (heteroepitaxially grown). More specifically, in this embodiment, a β-Ga GaN layer is epitaxially grown on the buffer layer 3 by mist CVD. ２ O ３ The growth temperature of the layer 4 is, for example, 700° C. or higher and 900° C. or lower.

[0028] In the epitaxial growth step, a mist CVD apparatus is used as the epitaxial growth apparatus. Note that in the epitaxial growth step, for example, MOCVD or MBE may be used instead of the mist CVD method.

[0029] (3) Advantages of the β-Ga according to the first embodiment ２ O ３ The epitaxial wafer 1 includes a sapphire substrate 2, a buffer layer 3, and a β-Ga ２ O ３ The sapphire substrate 2 has a first main surface 21 and a second main surface 22 opposite to the first main surface 21. The buffer layer 3 is formed on the first main surface 21 of the sapphire substrate 2. ２ O ３ The layer 4 is formed on the buffer layer 3. The first main surface 21 of the sapphire substrate 2 is an m-plane, an r-plane, a crystal plane having an off-angle of 30 degrees or less with respect to the m-plane, or a crystal plane having an off-angle of 30 degrees or less with respect to the r-plane. The buffer layer 3 contains O and at least one element selected from the group consisting of Ga, Al, and In.

[0030] According to the above configuration, β-Ga ２ O ３ It is possible to improve the crystallinity of the layer 4. ２ O ３ β-Ga manufactured using epitaxial wafer 1 ２ O ３ This makes it possible to improve the characteristics of β-Ga-based devices and increase manufacturing yields. ２ O ３ is an oxide semiconductor with a wider band gap than Si, and β-Ga ２ O ３β-Ga based devices can achieve higher breakdown voltage and higher efficiency (lower loss) compared to Si based devices. ２ O ３ Examples of such devices include metal semiconductor field effect transistors (MESFETs), metal-oxide-semiconductor field effect transistors (MOSFETs), high electron mobility transistors (HEMTs), and Schottky barrier diodes.

[0031] In the epitaxial wafer 1 according to the first embodiment, the buffer layer 3 is made of α-(Al ｘ Ga １－ｘ ) ２ O ３ The α-(Al ｘ Ga １－ｘ ) ２ O ３ In the layer, 0.2≦x<1.

[0032] According to the above configuration, the β-Ga heteroepitaxially grown on the buffer layer 3 ２ O ３ This makes it possible to improve the crystallinity of the layer 4 .

[0033] In addition, the β-Ga according to the first embodiment ２ O ３ The method for manufacturing the epitaxial wafer 1 includes a substrate preparation step, a buffer layer formation step, and an epitaxial growth step. In the substrate preparation step, a sapphire substrate 2 having a first main surface 21 and a second main surface 22 opposite to the first main surface 21 is prepared. In the buffer layer formation step, a buffer layer 3 is formed on the first main surface 21 of the sapphire substrate 2. In the epitaxial growth step, a β-Ga ２ O ３ The buffer layer 3 is epitaxially grown on the sapphire substrate 2. The first main surface 21 of the sapphire substrate 2 is an m-plane, an r-plane, a crystal plane having an off-angle of 30 degrees or less with respect to the m-plane, or a crystal plane having an off-angle of 30 degrees or less with respect to the r-plane. The buffer layer 3 contains O and at least one element selected from the group consisting of Ga, Al, and In.

[0034] According to the above configuration, β-Ga ２ O ３ This makes it possible to improve the crystallinity of the layer 4 .

[0035] In the method for manufacturing the epitaxial wafer 1 according to the first embodiment, the buffer layer 3 is formed of α-(Al ｘ Ga １－ｘ ) ２ O ３ The α-(Al ｘ Ga １－ｘ ) ２ O ３ In the layer, 0.2≦x<1.

[0036] According to the above configuration, the β-Ga heteroepitaxially grown on the buffer layer 3 ２ O ３ This makes it possible to improve the crystallinity of the layer 4 .

[0037] (Embodiment 2) Hereinafter, β-Ga according to embodiment 2 will be described. ２ O ３ The epitaxial wafer 1A and its manufacturing method will be described with reference to FIGS. 5, 6A to 6D, 7, and 8. ２ O ３ Regarding the epitaxial wafer 1A, the β-Ga ２ O ３ The same components as those in the epitaxial wafer 1 are denoted by the same reference numerals and the description thereof will be omitted as appropriate.

[0038] (1) β-Ga ２ O ３ Epitaxial wafer β-Ga according to embodiment 2 ２ O ３ As shown in FIG. 5, the epitaxial wafer 1A includes a sapphire substrate 2, a buffer layer 3A, and a β-Ga ２ O ３ The sapphire substrate 2 has a first main surface 21 and a second main surface 22 opposite to the first main surface 21. The buffer layer 3A is formed on the first main surface 21 of the sapphire substrate 2. ２ O ３The layer 4A is formed on the buffer layer 3A.

[0039] β-Ga ２ O ３ The epitaxial wafer 1A has a buffer layer 3A formed on a sapphire substrate 2, and a β-Ga ２ O ３ The epitaxial wafer is formed by epitaxially growing the layer 4A. When viewed from the thickness direction D1 of the sapphire substrate 2 (see FIG. 5), the β-Ga ２ O ３ The epitaxial wafer 1A has a substantially circular shape.

[0040] The sapphire substrate 2 has a substantially circular shape when viewed from a thickness direction D1 (see FIG. 5) of the sapphire substrate 2.

[0041] The first main surface 21 of the sapphire substrate 2 is an m-plane, an r-plane, a crystal plane having an off-angle of 30 degrees or less relative to the m-plane, or a crystal plane having an off-angle of 30 degrees or less relative to the r-plane.

[0042] The buffer layer 3A is made of β-Ga ２ O ３ The buffer layer 3A is an α-Ga layer formed on the first main surface 21 of the sapphire substrate 2. ２ O ３ layer 30 (see FIG. 6B), and ２ O ３ The layer 30 is formed by annealing the β-Ga ２ O ３ The crystal structure of the single crystal is monoclinic. ２ O ３ The (010) or (001) plane of the single crystal is used, but is not limited to the (010) or (001) plane, and may be, for example, the (-201) plane. Each of the (010), (001), and (-201) planes is a crystal plane according to Miller indices, where the three indices are written in parentheses. The primary surface 31A of the buffer layer 3A is a β-Ga ２ O ３ It may be a crystal plane having an off-angle relative to the (010), (001) or (-201) plane of the single crystal.

[0043] The thickness of the buffer layer 3A is determined by the thickness of the sapphire substrate 2 and the thickness of the β-Ga ２ O ３ The thickness of the buffer layer 3A is thinner than that of the layer 4A. The thickness of the buffer layer 3A is, for example, 200 nm to 500 nm, but may be thicker than 500 nm.

[0044] β-Ga ２ O ３ The thickness of the layer 4A is, for example, 0.2 μm or more and 3 μm or less. ２ O ３ The crystal structure of the single crystal is monoclinic. ２ O ３ The primary surface 41A of the layer 4A is, for example, β-Ga ２ O ３ The (010) or (001) plane of the single crystal is not limited to the (010) or (001) plane, but may be, for example, the (-201) plane. Each of the (010), (001) and (-201) planes is a crystal plane expressed by Miller indices, where three indices are placed in parentheses. ２ O ３ The primary surface 41A of the layer 4A is β-Ga ２ O ３ It may be a crystal plane having an off-angle relative to the (010), (001) or (-201) plane of the single crystal.

[0045] (2) β-Ga ２ O ３ Epitaxial wafer manufacturing method β-Ga ２ O ３ The method for manufacturing the epitaxial wafer 1A includes a substrate preparation step, a buffer layer formation step, and an epitaxial growth step.

[0046] In the substrate preparation step, a sapphire substrate 2 is prepared, which has a first main surface 21 and a second main surface 22 opposite to the first main surface 21 (see FIG. 6A ). The first main surface 21 of the sapphire substrate 2 is an m-plane, but is not limited to an m-plane and may be an r-plane, a crystal plane having an off-angle of 30 degrees or less with respect to the m-plane, or a crystal plane having an off-angle of 30 degrees or less with respect to the r-plane.

[0047] In the buffer layer formation step, α-Ga is deposited on the first main surface 21 of the sapphire substrate 2. ２ O３ The layer 30 is heteroepitaxially grown by mist CVD (see FIG. 6B). In the buffer layer formation step, the α-Ga layer 30 is grown on the first main surface 21 of the sapphire substrate 2 by, for example, MOCVD or MBE, instead of the mist CVD method. ２ O ３ Layer 30 may be grown heteroepitaxially. ２ O ３ The growth temperature of the layer 30 is, for example, 600°C or higher and lower than 700°C.

[0048] Then, α-Ga ２ O ３ The layer 30 is annealed at an annealing temperature of 700° C. to 900° C. to form α-Ga ２ O ３ The layer 30 is made of β-Ga ２ O ３ The buffer layer 3A is formed by converting the α-Ga ２ O ３ The phase structure of the layer 30 is changed to β-Ga ２ O ３ The buffer layer 3A is formed from an α-Ga layer. ２ O ３ The thickness of the layer 30 is, for example, 200 nm to 500 nm, but may be thicker than 500 nm.

[0049] In the epitaxial growth step, as shown in FIG. 6D, β-Ga is grown on the buffer layer 3A. ２ O ３ The layer 4A is epitaxially grown (homoepitaxially grown). More specifically, in this embodiment, a β-Ga ２ O ３ The layer 4A is epitaxially grown by mist CVD (Chemical Vapor Deposition). In the epitaxial growth step, α-Ga is grown on the buffer layer 3A. ２ O ３ The β-Ga layer is grown on the buffer layer 3A by mist CVD at a higher growth temperature than when the layer is epitaxially grown by mist CVD. ２ O ３The layer 4A is epitaxially grown. ２ O ３ The growth temperature of the layer 4A is set to 1000 K. ２ O ３ The temperature is higher than the growth temperature of the layer 30, for example, 700°C or higher and 900°C or lower.

[0050] In the epitaxial growth step, a mist CVD apparatus is used as the epitaxial growth apparatus. Note that in the epitaxial growth step, for example, MOCVD or MBE may be used instead of the mist CVD method.

[0051] In the annealing process of the buffer layer formation process, α-Ga is heated by microwave heating. ２ O ３ The annealing process uses, for example, a microwave heating device 5 as shown in FIG. 7. The microwave heating device 5 includes a microwave power source 6, a sapphire substrate 2, and an α-Ga ２ O ３ The laminated body with the layer 30 is accommodated, and the α-Ga ２ O ３ The heating vessel 7 for heating the layer 30, a heat insulating member 8, and a shield case 9 are provided.

[0052] The frequency of the microwaves output from the microwave power supply 6 is, for example, 2.47 GHz, and the power of the microwaves is, for example, 250 W. The microwave irradiation time is, for example, 1 hour.

[0053] The heating vessel 7 is made of, for example, silicon carbide (SiC). SiC generates heat by absorbing microwaves output from the microwave power supply 6. In the example of Fig. 7, the heating vessel 7 is composed of a crucible 71 made of SiC and a lid 72 made of SiC.

[0054] In the microwave heating method, microwaves directly vibrate molecules, so in addition to simple high-temperature annealing, it can also vibrate dipolar molecules, making it possible to convert metastable (α-phase) crystals into more stable crystals (β-phase crystals).

[0055] (3) Crystallinity of the Buffer Layer Figure 8 shows an X-ray rocking curve obtained by ω scan (2θ-ω scan) of X-ray diffraction of the first sample consisting of a laminate of the sapphire substrate 2 and the buffer layer 3A. The first sample consisting of a laminate of the sapphire substrate 2 and the buffer layer 3A has an α-Ga layer deposited on the sapphire substrate 2 whose first main surface 21 is an m-plane. ２ O ３ This is a sample in which the layer 30 is formed by mist CVD and then subjected to high-temperature annealing using the microwave heating device 5 shown in FIG. 7, thereby forming a buffer layer 3A on the sapphire substrate 2.

[0056] 9 shows an X-ray rocking curve obtained by ω scan (2θ-ω scan) of X-ray diffraction of a second sample made of a laminate of a comparative example. The laminate of the comparative example is an α-Ga layer formed on a sapphire substrate whose first main surface is a c-plane. ２ O ３ The layer was formed by mist CVD and then annealed at high temperature using the microwave heating device 5 shown in FIG. 7 to form a buffer layer on the sapphire substrate. ２ O ３ The layer growth conditions were: α-Ga ２ O ３ The growth conditions are the same as for layer 30 .

[0057] 8 and 9, the crystal corresponding to each peak and its plane orientation are shown together with Miller indices. From the X-ray rocking curves in each of FIGS. 8 and 9, it can be seen that the buffer layer of the comparative example shows multiple peaks of crystalline structures, whereas the buffer layer 3A shows only peaks of β-Ga. ２ O ３ This shows that the (020) plane is dominant. In other words, the crystallinity of the buffer layer 3A is improved compared to the buffer layer of the comparative example.

[0058] (4) Advantages of the β-Ga according to the second embodiment ２ O ３ The epitaxial wafer 1A includes a sapphire substrate 2, a buffer layer 3A, and a β-Ga ２ O ３The sapphire substrate 2 has a first main surface 21 and a second main surface 22 opposite to the first main surface 21. The buffer layer 3A is formed on the first main surface 21 of the sapphire substrate 2. ２ O ３ Layer 4A is formed on buffer layer 3A. First main surface 21 of sapphire substrate 2 is an m-plane, an r-plane, a crystal plane having an off-angle of 30 degrees or less with respect to the m-plane, or a crystal plane having an off-angle of 30 degrees or less with respect to the r-plane. Buffer layer 3A contains O and at least one element selected from the group consisting of Ga, Al, and In.

[0059] According to the above configuration, β-Ga ２ O ３ This makes it possible to improve the crystallinity of the layer 4A.

[0060] In addition, β-Ga according to the second embodiment ２ O ３ In the epitaxial wafer 1A, the buffer layer 3A is made of β-Ga ２ O ３ It is a layer.

[0061] According to the above configuration, β-Ga ２ O ３ This makes it possible to improve the crystallinity of the layer 4A.

[0062] β-Ga according to embodiment 2 ２ O ３ The method for manufacturing the epitaxial wafer 1A includes a substrate preparation step, a buffer layer formation step, and an epitaxial growth step. In the substrate preparation step, a sapphire substrate 2 having a first main surface 21 and a second main surface 22 opposite to the first main surface 21 is prepared. In the buffer layer formation step, a buffer layer 3A is formed on the first main surface 21 of the sapphire substrate 2. In the epitaxial growth step, a β-Ga ２ O ３ The layer 4A is epitaxially grown. The first main surface 21 of the sapphire substrate 2 is an m-plane, an r-plane, a crystal plane having an off-angle of 30 degrees or less with respect to the m-plane, or a crystal plane having an off-angle of 30 degrees or less with respect to the r-plane. The buffer layer 3A contains O and at least one element selected from the group consisting of Ga, Al, and In.

[0063] According to the above configuration, β-Ga ２ O ３ This makes it possible to improve the crystallinity of the layer 4A.

[0064] In addition, β-Ga according to the second embodiment ２ O ３ In the method for producing the epitaxial wafer 1A, in the epitaxial growth step, β-Ga ２ O ３ The layer 4A is epitaxially grown by mist CVD, MOCVD or MBE.

[0065] According to the above configuration, β-Ga ２ O ３ This makes it possible to improve the crystallinity of the layer 4A.

[0066] In addition, β-Ga according to the second embodiment ２ O ３ In the manufacturing method of the epitaxial wafer 1A, in the buffer layer forming step, α-Ga is formed on the first main surface 21 of the sapphire substrate 2. ２ O ３ The layer 30 is heteroepitaxially grown by mist CVD, MOCVD, or MBE, and then α-Ga ２ O ３ The layer 30 is annealed at an annealing temperature of 700° C. to 900° C. to form α-Ga ２ O ３ The layer 30 is made of β-Ga ２ O ３ The layer is converted into a buffer layer 3A.

[0067] According to the above configuration, β-Ga ２ O ３ Layer 4A can be homoepitaxially grown on buffer layer 3A, and β-Ga ２ O ３ This makes it possible to improve the crystallinity of the layer 4A.

[0068] In addition, β-Ga according to the second embodiment ２ O ３ The method for producing the epitaxial wafer 1A is as follows: in the annealing process, α-Ga is grown by microwave heating. ２ O ３ Layer 30 is heated.

[0069] According to the above configuration, α-Ga ２ O ３ Layer 30 is then recrystallized to form a more uniform β-Ga ２ O ３ It is possible to convert the layer into a buffer layer 3A consisting of layers.

[0070] (5) Modification Example β-Ga according to the second embodiment ２ O ３ In the method for manufacturing the epitaxial wafer 1A, a microwave heating apparatus 5A shown in Fig. 10 may be used in the annealing process. The configuration of the microwave heating apparatus 5A is substantially the same as that of the microwave heating apparatus 5 shown in Fig. 7, but differs from the microwave heating apparatus 5 in that the heating container 7 has an opening 70.

[0071] That is, in the annealing treatment of the modified example, the sapphire substrate 2 and the α-Ga ２ O ３ The laminate with the layer 30 is converted into α-Ga by absorbing microwaves. ２ O ３ The layer 30 is placed in a heating vessel 7 for heating, and a part of the microwave is irradiated through an opening 70 of the heating vessel 7 to form an α-Ga ２ O ３ Layer 30 is irradiated.

[0072] In the microwave heating device 5A shown in FIG. ２ O ３ Since the layer 30 is also irradiated, α-Ga ２ O ３ The layer 30 can be grown in a shorter time, more uniformly throughout the layer, and with stable β-Ga ２ O ３ It can be converted into layer 4A.

[0073] (Other Modifications) The first and second embodiments are merely examples of various embodiments of the present disclosure. The first and second embodiments can be modified in various ways depending on the design and the like as long as the object of the present disclosure can be achieved.

[0074] For example, the buffer layer 3 is made of α-(Al ｘ Ga １－ｘ ) ２ O ３ Not limited to the β-(Al ｚ Ga１－ｚ ) ２ O ３ In this case, 0<z<1.

[0075] The buffer layer 3 is made of α-(In ｙ Al ｘ Ga １－ｘ－ｙ ) ２ O ３ (Here, 0<x≦1, 0≦y<1, 0<x+y≦1) is not limited to this, and β-(In ｙ Al ｘ Ga １－ｘ－ｙ ) ２ O ３ (where 0<x≦1, 0≦y<1, 0<x+y≦1).

[0076] In addition, β-Ga ２ O ３ The layers 4 and 4A may contain n-type impurities (for example, Sn, Si, or Ge). ２ O ３ Layer 4 is n-type β-Ga ２ O ３ It is a layer. ２ O ３ The layers 4 and 4A may contain Fe or Al as impurities.

[0077] (Aspects) The following aspects are disclosed in this specification.

[0078] β-Ga according to the first aspect ２ O ３ The epitaxial wafer (1; 1A) includes a sapphire substrate (2), a buffer layer (3; 3A), and a β-Ga ２ O ３ The sapphire substrate (2) has a first main surface (21) and a second main surface (22) opposite to the first main surface (21). The buffer layer (3; 3A) is formed on the first main surface (21) of the sapphire substrate (2). ２ O ３The layer (4; 4A) is formed on the buffer layer (3; 3A). The first main surface (21) of the sapphire substrate (2) is an m-plane, an r-plane, a crystal plane having an off-angle of 30 degrees or less with respect to the m-plane, or a crystal plane having an off-angle of 30 degrees or less with respect to the r-plane. The buffer layer (3; 3A) contains O and at least one element selected from the group consisting of Ga, Al, and In.

[0079] According to this aspect, β-Ga ２ O ３ This makes it possible to improve the crystallinity of the layer (4; 4A).

[0080] β-Ga according to the second aspect ２ O ３ In the epitaxial wafer (1), in a first embodiment, the buffer layer (3) is α-(Al ｘ Ga １－ｘ ) ２ O ３ The α-(Al ｘ Ga １－ｘ ) ２ O ３ In the layer, 0.2≦x<1.

[0081] According to this embodiment, the β-Ga heteroepitaxially grown on the buffer layer (3) ２ O ３ This makes it possible to improve the crystallinity of the layer (4).

[0082] β-Ga according to the third aspect ２ O ３ In the epitaxial wafer (1A), in the first embodiment, the buffer layer (3A) is β-Ga ２ O ３ It is a layer.

[0083] According to this embodiment, β-Ga is homoepitaxially grown on the buffer layer (3A). ２ O ３ This makes it possible to improve the crystallinity of the layer (4A).

[0084] β-Ga according to the fourth aspect ２ O ３The method for manufacturing an epitaxial wafer (1; 1A) includes a substrate preparation step, a buffer layer formation step, and an epitaxial growth step. In the substrate preparation step, a sapphire substrate (2) having a first main surface (21) and a second main surface (22) opposite to the first main surface (21) is prepared. In the buffer layer formation step, a buffer layer (3; 3A) is formed on the first main surface (21) of the sapphire substrate (2). In the epitaxial growth step, β-Ga is grown on the buffer layer (3; 3A). ２ O ３ The first main surface (21) of the sapphire substrate (2) is an m-plane, an r-plane, a crystal plane having an off-angle of 30 degrees or less with respect to the m-plane, or a crystal plane having an off-angle of 30 degrees or less with respect to the r-plane. The buffer layer (3; 3A) contains O and at least one element selected from the group consisting of Ga, Al, and In.

[0085] According to this aspect, β-Ga ２ O ３ This makes it possible to improve the crystallinity of the layer (4; 4A).

[0086] β-Ga according to the fifth aspect ２ O ３ The method for producing an epitaxial wafer (1;1A) is based on the fourth aspect. In the epitaxial growth step, β-Ga ２ O ３ The layer (4; 4A) is epitaxially grown by mist CVD, MOCVD or MBE.

[0087] According to this aspect, β-Ga ２ O ３ This makes it possible to improve the crystallinity of the layer (4; 4A).

[0088] β-Ga according to the sixth aspect ２ O ３ In the fourth or fifth aspect of the method for producing an epitaxial wafer (1), the buffer layer (3) is an α-(Al ｘ Ga １－ｘ ) ２ O ３ layer, and α-(Al ｘ Ga １－ｘ ) ２ O ３In the layer, 0.2≦x<1.

[0089] According to this embodiment, the β-Ga epitaxially grown on the buffer layer (3) ２ O ３ This makes it possible to improve the crystallinity of the layer (4).

[0090] β-Ga according to the seventh aspect ２ O ３ The method for producing an epitaxial wafer (1A) is based on the fourth or fifth aspect. In the buffer layer formation step, α-Ga is deposited on the first main surface (21) of the sapphire substrate (2). ２ O ３ The layer (30) is heteroepitaxially grown by mist CVD, MOCVD or MBE, and then α-Ga ２ O ３ The layer (30) is annealed at an annealing temperature of 700° C. to 900° C. to form α-Ga ２ O ３ The layer (30) is made of β-Ga ２ O ３ The layer is converted into a buffer layer 3A.

[0091] According to this aspect, β-Ga ２ O ３ A layer (4A) can be homoepitaxially grown on the buffer layer (3A), and β-Ga ２ O ３ This makes it possible to improve the crystallinity of the layer (4A).

[0092] β-Ga according to the eighth aspect ２ O ３ In the seventh aspect of the method for producing an epitaxial wafer (1A), in the annealing treatment, α-Ga is grown by microwave heating. ２ O ３ The layer (30) is heated.

[0093] According to this aspect, α-Ga ２ O ３ The entire layer (30) is more uniformly β-Ga ２ O ３ Since it is possible to convert the layer into a layer, it is possible to improve the crystallinity of the buffer layer (3A).

[0094] β-Ga according to the ninth aspect ２ O ３ The method for producing the epitaxial wafer (1A) is based on the eighth aspect. In the annealing treatment, the sapphire substrate (2) and the α-Ga ２ O ３ The laminate with the layer (30) is converted into α-Ga by absorbing microwaves. ２ O ３ The layer (30) is placed in a heating vessel (7) for heating, and a part of the microwave is irradiated through an opening (70) of the heating vessel (7) to form an α-Ga ２ O ３ The layer (30) is irradiated.

[0095] According to this embodiment, it is possible to further improve the crystallinity of the buffer layer (3A).

[0096] 1, 1A epitaxial wafer 2 sapphire substrate 21 first main surface 22 second main surface 3, 3A buffer layer 30 α-Ga ２ O ３ Layers 4 and 4A β-Ga ２ O ３ Layer 7 Heating vessel 70 Opening D1 Thickness direction

Claims

1. A sapphire substrate having a first main surface and a second main surface opposite to the first main surface; a buffer layer formed on the first main surface of the sapphire substrate; and a β-Ga GaN layer formed on the buffer layer. ２ O ３ a β-Ga layer, wherein the first main surface of the sapphire substrate is an m-plane, an r-plane, a crystal plane having an off-angle of 30 degrees or less with respect to the m-plane, or a crystal plane having an off-angle of 30 degrees or less with respect to the r-plane, and the buffer layer contains at least one element selected from the group consisting of Ga, Al, and In, and O. ２ O ３ Epitaxial wafer.

2. The buffer layer is α-(Al ｘ Ga １－ｘ ) ２ O ３ layer, wherein the α-(Al ｘ Ga １－ｘ ) ２ O ３ β-Ga as claimed in claim 1, wherein 0.2≦x<1 in the layer. ２ O ３ Epitaxial wafer.

3. The buffer layer is β-Ga ２ O ３ The β-Ga layer according to claim 1 ２ O ３ Epitaxial wafer.

4. A substrate preparation step of preparing a sapphire substrate having a first main surface and a second main surface opposite to the first main surface; a buffer layer formation step of forming a buffer layer on the first main surface of the sapphire substrate; and a β-Ga GaN layer on the buffer layer. ２ O ３ and an epitaxial growth step of epitaxially growing a β-Ga layer, wherein the first main surface of the sapphire substrate is an m-plane, an r-plane, a crystal plane having an off-angle of 30 degrees or less with respect to the m-plane, or a crystal plane having an off-angle of 30 degrees or less with respect to the r-plane, and the buffer layer contains at least one element selected from the group consisting of Ga, Al, and In, and O. ２ O ３ A method for manufacturing an epitaxial wafer.

5. In the epitaxial growth step, the β-Ga ２ O ３ The β-Ga layer according to claim 4 is epitaxially grown by mist CVD, MOCVD or MBE. ２ O ３ A method for manufacturing an epitaxial wafer.

6. The buffer layer is α-(Al ｘ Ga １－ｘ ) ２ O ３ layer, wherein the α-(Al ｘ Ga １－ｘ ) ２ O ３ 6. The β-Ga GaN layer according to claim 4, wherein 0.2≦x<1. ２ O ３ A method for manufacturing an epitaxial wafer.

7. In the buffer layer forming step, α-Ga is formed on the first main surface of the sapphire substrate. ２ O ３ The α-Ga layer is heteroepitaxially grown by mist CVD, MOCVD, or MBE. ２ O ３ The α-Ga layer is annealed at an annealing temperature of 700° C. to 900° C. ２ O ３ The layer is made of β-Ga ２ O ３ β-Ga as claimed in claim 4 or 5, ２ O ３ A method for manufacturing an epitaxial wafer.

8. In the annealing process, the α-Ga is heated by microwave heating. ２ O ３ The β-Ga layer according to claim 7 is heated. ２ O ３ A method for manufacturing an epitaxial wafer.

9. In the annealing treatment, the sapphire substrate and the α-Ga ２ O ３ The laminate of the α-Ga layer and the α-Ga ２ O ３ The layer is placed in a heating vessel for heating, and a part of the microwave is irradiated through an opening of the heating vessel to the α-Ga ２ O ３ The β-Ga layer according to claim 8 is irradiated. ２ O ３ A method for manufacturing an epitaxial wafer.

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