Sic composite substrate, sic epitaxial wafer, and method for manufacturing sic epitaxial wafer

Abstract

The present invention provides an SiC composite substrate, an SiC epitaxial wafer, and a method for manufacturing an SiC epitaxial wafer with which it is possible, in a CVD process, to inhibit the occurrence of warpage caused by a stress difference and to inhibit pasted substrates from peeling off from each other. This invention includes a first layer and a second layer formed from an α-SiC single crystal and pasted together with a first main surface of the first layer. The first layer includes a first crystal part formed from an α-SiC single crystal or an α-SiC quasi-single crystal, and a second crystal part formed from β-SiC crystals. With respect to the total area of the first main surface, the area ratio of the first crystal part is 50% or more, and the area ratio of the second crystal part is 10% or less.

Description

SiC Composite Substrate, SiC Epitaxial Wafer, and Method for Manufacturing SiC Epitaxial Wafer

[0001] The present disclosure relates to a SiC composite substrate, a SiC epitaxial wafer, and a method for manufacturing a SiC epitaxial wafer.

[0002] Silicon carbide (SiC) has a breakdown electric field that is one order of magnitude larger and a bandgap that is three times larger than that of silicon (Si). In addition, silicon carbide (SiC) has properties such as a thermal conductivity that is about three times higher than that of silicon (Si). Therefore, silicon carbide (SiC) is expected to be applied to power devices, high-frequency devices, etc. In addition, devices using silicon carbide (SiC) can operate in a high temperature range of 150°C or higher. For this reason, in recent years, SiC epitaxial wafers have come to be used as substrates for semiconductor devices as described above.

[0003] A semiconductor device using SiC is referred to as a SiC device. A SiC device is fabricated using a SiC epitaxial wafer. A SiC epitaxial wafer is obtained by laminating a SiC epitaxial layer on the surface of a SiC substrate. A SiC substrate is a substrate before a SiC epitaxial layer is laminated. A SiC substrate is, for example, cut out from a SiC ingot (also referred to as a SiC boule). A SiC ingot is composed of a SiC single crystal processed into a cylindrical shape.

[0004] However, such a SiC single crystal substrate using a SiC single crystal is difficult to manufacture and has a high manufacturing cost. For this reason, in order to improve the usage efficiency of the high-cost SiC single crystal substrate, a composite substrate (bonded substrate) in which a thin SiC single crystal substrate is bonded to one side of a low-cost substrate has been studied. For example, Patent Document 1 discloses a composite substrate in which a first silicon carbide layer and a second silicon carbide layer having a higher defect density than the first silicon carbide layer are bonded together.

[0005] Japanese Unexamined Patent Application Publication No. 2023-9025

[0006] However, when multiple substrates with different compositions and crystal structures are bonded together, stress differences occur internally, leading to the composite substrate warping. Furthermore, in the CVD process for growing epitaxial layers on such composite substrates, there is a problem that the bonded substrates tend to delaminate from the bonded surface in high-temperature environments.

[0007] This disclosure has been made in view of the above-mentioned problems, and aims to provide a SiC composite substrate, a SiC epitaxial wafer, and a method for manufacturing a SiC epitaxial wafer that can suppress the occurrence of warping due to stress differences and the occurrence of delamination between bonded substrates in the CVD process.

[0008] The inventors have discovered new findings that SiC composite substrates with an α-SiC bonding surface are less prone to warping even in high-temperature environments, while SiC composite substrates with a β-SiC bonding surface are less prone to delamination even in high-temperature environments. This invention was completed based on these new findings.

[0009] This disclosure provides the following means to solve the above problems.

[0010] (1) The SiC composite substrate according to the first embodiment comprises a first layer and a second layer made of an α-SiC single crystal bonded to a first main surface of the first layer, wherein the first layer includes a first crystalline portion made of an α-SiC single crystal or an α-SiC quasi-single crystal and a second crystalline portion made of a β-SiC crystal, wherein the area ratio of the first crystalline portion to the total area of ​​the first main surface is 50% or more, and the area ratio of the second crystalline portion is 10% or less.

[0011] (2) The SiC composite substrate according to the second embodiment comprises a first layer and a second layer made of an α-SiC single crystal bonded to the first main surface of the first layer, wherein the first layer is composed of a first crystalline portion made of an α-SiC quasi-single crystal.

[0012] (3) In the SiC composite substrate according to the above embodiment, the area ratio occupied by the second crystal portion on the first main surface of the first layer is 0.001% or more and 10% or less of the total area of ​​the first main surface.

[0013] (4) In the SiC composite substrate according to the above embodiment, the first crystal portion of the first layer contains at least two types of SiC polytypes from among 4H, 6H, and 15R.

[0014] (5) In the SiC composite substrate according to the above embodiment, on the first main surface of the first layer, the area ratio occupied by one polytype of α-SiC quasi-single crystal constituting the first crystal portion is 30% or more of the total area of ​​the first crystal portion.

[0015] (6) In the SiC composite substrate according to the above embodiment, on the first main surface of the first layer, the c-axis orientation of the α-SiC quasi-single crystals constituting the first crystal portion is aligned to the same direction for 90% or more of the time.

[0016] (7) In the SiC composite substrate according to the above embodiment, the orientation difference between the c-axis orientation of the α-SiC quasi-single crystal constituting the first crystal portion and the c-axis orientation of the α-SiC single crystal constituting the second layer on the first main surface of the first layer is 12° or less.

[0017] (8) In the SiC composite substrate according to the above embodiment, the second crystal portion includes a facet region containing 3C.

[0018] (9) In the SiC composite substrate according to the above embodiment, the diameter is 145 mm or more.

[0019] (10) In the SiC composite substrate according to the above embodiment, the diameter is 195 mm or more.

[0020] (11) A SiC epitaxial wafer according to the ninth embodiment comprises a SiC composite substrate according to the above embodiment and a SiC epitaxial layer, wherein the SiC epitaxial layer is laminated on the second layer.

[0021] (12) A method for manufacturing a SiC epitaxial wafer according to the tenth embodiment involves preparing a SiC composite substrate according to the above embodiment and forming a SiC epitaxial layer on the second layer of the SiC composite substrate.

[0022] According to this disclosure, it becomes possible to provide a SiC composite substrate, a SiC epitaxial wafer, and a method for manufacturing a SiC epitaxial wafer that can suppress the occurrence of warping due to stress differences and the occurrence of delamination between bonded substrates in the CVD process.

[0023] This is a schematic cross-sectional view of the SiC composite substrate along the Z direction according to this embodiment. This is an example of the crystal arrangement of the first crystal portion when the first main surface of the SiC composite substrate is viewed vertically from above. This is a schematic cross-sectional view of the SiC epitaxial wafer along the Z direction according to this embodiment. This is a schematic diagram showing the method for evaluating the shape (warpage) of the SiC composite substrate using Warp.

[0024] This embodiment will now be described in detail with reference to the drawings as appropriate. The drawings used in the following description may be enlarged for convenience to clearly illustrate the features of this embodiment, and the dimensional ratios of each component may differ from those of the actual components. The materials, dimensions, ratios, etc., exemplified in the following description are examples only, and this disclosure is not limited thereto. It is possible to modify and implement these examples as appropriate without altering the essence of the invention.

[0025] In this specification, individual orientations are indicated by [], collective orientations by <>, individual planes by (), and collective planes by {}. While crystallography dictates that negative exponents are represented by a "-" (bar) directly above the number, in this specification, the negative sign is placed before the number.

[0026] First, let's define the direction using 4H-SiC as an example. The thickness direction of the SiC substrate is defined as the Z direction. The Z direction may be the <0001> direction of the SiC substrate, or it may be tilted by an offset angle relative to the <0001> direction. One direction of the plane perpendicular to the Z direction is defined as the X direction. Also, on the plane perpendicular to the Z direction, the direction perpendicular to the X direction is defined as the Y direction. The X direction is, for example, the <11-20> direction of the SiC substrate. The Y direction is, for example, the <1-100> direction of the SiC substrate.

[0027] "SiC Composite Substrate: First Embodiment" Figure 1 is a schematic cross-sectional view of the SiC composite substrate according to this embodiment, along the Z direction. The SiC composite substrate 10 has at least a first layer 11 and a second layer 12 bonded to the first layer 11. The diameter of the SiC composite substrate 10 in this embodiment is, for example, 6 inches or more, preferably 8 inches or more, more preferably 10 inches or more, and even more preferably 12 inches or more.

[0028] The diameter of the SiC composite substrate 10 is, for example, 145 mm or more, preferably 149 mm or more. The diameter of the SiC composite substrate 10 is, for example, 155 mm or less, preferably 151 mm or less. The diameter of the SiC composite substrate 10 is, for example, 195 mm or more, preferably 199 mm or more. The diameter of the SiC composite substrate 10 is, for example, 205 mm or less, preferably 201 mm or less. The diameter of the SiC composite substrate 10 is, for example, 245 mm or more, preferably 249 mm or more. The diameter of the SiC composite substrate 10 is, for example, 255 mm or less, preferably 251 mm or less. The diameter of the SiC composite substrate 10 is, for example, 295 mm or more, preferably 299 mm or more. The diameter of the SiC composite substrate 10 is, for example, 305 mm or less, preferably 301 mm or less.

[0029] The thickness of the SiC composite substrate 10 along the Z direction is, for example, 100 μm or more and 1 mm or less. Preferably, the thickness of the SiC composite substrate 10 is 200 μm or more and 800 μm or less, and more preferably 300 μm or more and 600 μm or less. The thickness of the SiC composite substrate 10 may be, for example, the average value of the thickness of 10 different points in the plane measured with a thickness gauge or the like.

[0030] The first layer 11 has a first main surface 11A and a second main surface 11B. The first main surface 11A and the second main surface 11B are surfaces perpendicular to the Z direction. The first main surface 11A faces the second main surface 11B.

[0031] Of these, the first layer 11 has a first main surface 11A which serves as the bonding surface to the SiC composite substrate 10, and is bonded to the second main surface 12B of the second layer 12, which will be described later.

[0032] Such a first layer 11 can be a thin circular plate with a thickness along the Z direction of, for example, about 100 μm to 500 μm and a diameter of about 100 mm to 300 mm. In this embodiment, the first layer 11 is a circular plate with a thickness of 300 μm and a diameter of 200 mm.

[0033] The first layer 11 includes a first crystalline portion Q1 made of an α-SiC single crystal or an α-SiC quasi-single crystal, and a second crystalline portion Q2 made of a β-SiC crystal. The α-SiC is a hexagonal SiC with a P63mc or P63m space group, approximating the crystal structure of wurtzite. Such α-SiC includes polytypes such as 4H-SiC, 6H-SiC, and 15R-SiC.

[0034] Typically, crystals with inconsistent crystal orientations, such as sintered SiC, are called polycrystalline SiC. On the other hand, among the α-SiC types mentioned above, polytypes such as 4H-SiC, 6H-SiC, and 15R-SiC usually have crystal orientations that are misaligned from one another. However, by using a special manufacturing method, it is possible to bring the crystal orientations within a predetermined range and give them uniformity.

[0035] For example, by sublimation growth using a SiC single crystal seed, a mixed crystal of 4H-SiC, 6H-SiC, and 15R-SiC, all sharing the same c-axis orientation, can be produced. Such a mixed crystal differs from polycrystalline materials like sintered bodies because it has a unified crystal orientation, while also differing from a single-type single crystal due to the presence of multiple polytypes.

[0036] Therefore, in this invention, α-SiC crystals composed of multiple polytypes with identical crystal orientations are referred to as "α-SiC quasi-single crystals." As an example, in this embodiment, the c-axis orientations of α-SiC quasi-single crystals composed of multiple polytypes are aligned to the same direction for more than 90% of the crystals. Here, "identical orientation" means that minute orientation deviations caused by dislocations, small-angle grain boundaries, residual stresses, etc., are acceptable. Specifically, crystal orientations within a range of ±1° within the substrate plane are considered to be identical.

[0037] On the other hand, β-SiC is a cubic SiC, and 3C-SiC is one example of its polytype. Polycrystalline forms are easily produced from this type of 3C-SiC.

[0038] The first crystalline portion Q1 may be an α-SiC single crystal or an α-SiC quasi-single crystal, and the α-SiC quasi-single crystal may contain two or more of the SiC polytypes. For example, it may be composed of two or more of 4H-SiC, 6H-SiC, and 15R-SiC.

[0039] Furthermore, when the α-SiC quasi-single crystal is composed of the three polytypes described above, it is preferable that two of these polytypes are present in an area ratio of at least 33% or more of the total area of ​​the first crystal portion.

[0040] The second crystalline portion Q2 may be composed of either a β-SiC single crystal or a β-SiC polycrystalline material, or both. The β-SiC crystal (single crystal or polycrystalline) may also contain 3C-SiC. For example, the second crystalline portion Q2 may include a facet region containing 3C-SiC.

[0041] In this embodiment, the first layer 11 of the SiC composite substrate 10 is bonded to the second main surface 12B of the second layer 12, and the area ratio occupied by the first crystal portion Q1 is 50% or more of the total area of ​​the first main surface 11A.

[0042] More specifically, the area ratio of the total area of ​​the first crystal portion Q1 on the first main surface 11A should be 50% or more of the total area of ​​the first main surface 11A, and the remaining area should be the total area of ​​the second crystal portion Q2 and the area of ​​the α-SiC polycrystalline region on the first main surface 11A. The area ratio of the second crystal portion Q2 should be at most 10% or less of the total area of ​​the first main surface 11A.

[0043] The area ratio of each crystal on the first main surface 11A of the first layer 11 of the SiC composite substrate 10 can be determined, for example, by analyzing the Kikuchi pattern obtained by electron backscatter diffraction (EBSD).

[0044] The Kikuchi pattern is obtained by the following procedure. Using an electron backscatter diffraction apparatus (EBSD apparatus) equipped with a vacuum chamber (chamber), an electron beam irradiation mechanism, and a screen composed of a CCD sensor, a SiC sample is set in the vacuum chamber. When an electron beam is irradiated onto the surface of this sample, diffracted electrons based on Bragg's law (λ = 2d sin θ) are generated from the sample surface. By receiving these diffracted electrons with a screen composed of a CCD sensor, an image unique to the crystal surface can be obtained. This image is referred to as the Kikuchi pattern.

[0045] When measuring the area ratio of each crystal on the first main surface 11A of the SiC composite substrate 10 in which the first layer 11 and the second layer 12 are bonded together, for example, the second layer 12 can be removed by using surface grinding or the like to expose the first layer 11. Thereafter, when grinding damage is removed by polishing, ion milling, or the like, analysis by EBSD becomes possible.

[0046] The existence states of the first crystal portion Q1 and the second crystal portion Q2 on the first main surface 11A include, for example, a form in which a circular second crystal portion Q2 exists at the center of the first main surface 11A, or a form in which a ring-shaped second crystal portion Q2 exists at the outer edge of the first main surface 11A, and the other regions are occupied by the first crystal portion Q1.

[0047] In addition to this, there may also be a form in which island-shaped small-area first crystal portions Q1 and second crystal portions Q2 that are sufficiently small with respect to the total area of the first main surface 11A are mixed, or a form in which one or a plurality of second crystal portions Q2 are formed at an arbitrary portion and the first crystal portion Q1 is formed so as to surround this.

[0048] The existence states of the first crystal portion Q1 and the second crystal portion Q2 on the first main surface 11A are not limited to the forms described above, and any form is acceptable as long as the first crystal portion Q1 and the second crystal portion Q2 with an arbitrary area are formed at an arbitrary number at an arbitrary position.

[0049] Furthermore, in the first crystal portion Q1, it is sufficient that two or more types of SiC polytypes, such as 4H-SiC, 6H-SiC, and 15R-SiC, exist on the first main surface 11A in any shape, any area, and any number.

[0050] The first crystalline portion Q1 may be an α-SiC single crystal or an α-SiC quasi-single crystal, and the α-SiC quasi-single crystal may contain two or more of the SiC polytypes. For example, it may be composed of two or more of 4H-SiC, 6H-SiC, and 15R-SiC.

[0051] As an example, Figure 2 shows an example of the crystal arrangement of the first crystal portion Q1 on the first main surface 11A of the SiC composite substrate 10. In this embodiment, a second crystal portion Q2 made of a β-SiC polycrystal centered on 3C-SiC is arranged at the center of the first main surface 11A of the SiC composite substrate 10, and a first crystal portion Q1 made of an α-SiC quasi-monocrystal containing 4H-SiC and 6H-SiC is arranged surrounding this second crystal portion Q2.

[0052] Furthermore, the area ratio of the first crystal portion Q1 to the total area of ​​the first main surface 11A is set to 90%, and the area ratio of the second crystal portion Q2 is set to 10%.

[0053] The second layer 12 has a first main surface 12A and a second main surface 12B. The first main surface 12A and the second main surface 12B are surfaces perpendicular to the Z direction. The first main surface 12A faces the second main surface 12B.

[0054] Of these, the second layer 12 has a second main surface 12B which serves as the bonding surface to the SiC composite substrate 10, and is bonded with the first main surface 11A of the first layer 11 having the above-described configuration.

[0055] The second layer 12 can be, for example, a circular thin film with a thickness of about 10 μm to 100 μm along the Z direction and a diameter of about 100 mm to 300 mm. In this embodiment, the second layer 12 is a thin film with a thickness of 50 μm and a diameter of 200 mm, the same as the first layer.

[0056] This second layer 12 is made of an α-SiC single crystal. The α-SiC single crystal can be any of the polytypes: 4H-SiC, 6H-SiC, or 15R-SiC.

[0057] In the SiC composite substrate 10 of this embodiment, the orientation difference between the c-axis orientation of the α-SiC quasi-single crystal constituting the first crystalline portion Q1 and the c-axis orientation of the α-SiC single crystal constituting the second layer 12 on the first main surface 11A of the first layer 11 may be 12° or less. This orientation difference is preferably 10° or less, and more preferably 8° or less.

[0058] According to the SiC composite substrate 10 of this embodiment with the above configuration, by including both a first crystal portion Q1 made of an α-SiC single crystal or an α-SiC quasi-single crystal and a second crystal portion Q2 made of a β-SiC crystal in the first main surface 11A of the first layer 11, which is the surface bonded to the second layer 12, it becomes possible to prevent delamination between the first layer 11 and the second layer 12 and to prevent warping of the SiC composite substrate 10 even in high-temperature environments such as during epitaxial growth.

[0059] In particular, by setting the area ratio of the first crystal portion Q1 to 50% or more and the area ratio of the second crystal portion Q2 to 10% or less relative to the total area of ​​the first main surface 11A of the first layer 11, it becomes possible to reliably prevent both delamination and warping of the SiC composite substrate 10.

[0060] Furthermore, Warp can be used as one method for evaluating the warpage of the SiC composite substrate 10. Warp is the difference between the maximum and minimum values ​​of the deviation from the reference plane, and in this embodiment, it is measured as follows.

[0061] Figure 4 is a schematic diagram showing a method for evaluating the shape (warpage) of a SiC composite substrate 10 using Warp. Warp is the distance in the thickness direction between the highest point hp on the first main surface 12A of the second layer of the SiC composite substrate 10 and the lowest point lp on the second main surface 11B of the first layer. The larger the Warp, the more deformed the SiC composite substrate 10 is judged to be. First, the SiC composite substrate 10 is placed on three support points set on a flat surface F. A virtual surface Slp is determined that passes through the lowest point lp on the second main surface 11B of the first layer and is parallel to the flat surface F, and a virtual surface Shp is determined that passes through the highest point hp on the first main surface 12A of the second layer and is parallel to the flat surface F. Warp is determined as the distance in the height direction between the virtual surface Slp and the virtual surface Shp. The height direction is perpendicular to the flat surface F and away from the flat surface F.

[0062] Furthermore, a bonding layer (intermediate layer) may be formed between the first layer 11 and the second layer 12 as described above. The bonding layer is located between the first layer 11 and the second layer 12 and is, for example, a layer whose main components are elements contained in at least one of the first layer 11 and the second layer 12. The bonding layer may be, for example, amorphous. The bonding layer is a layer formed by bonding the first layer 11 and the second layer 12 together. The bonding layer may contain, for example, Si and C. The bonding layer may also contain Ar.

[0063] Such junction layers can sometimes be confirmed using a transmission electron microscope (TEM). If the junction layer contains Ar, the presence of Ar can be confirmed by secondary ion mass spectrometry (SIMS). The thickness of the junction layer should, for example, be between 0.25 nm and 10 nm. The thickness of the junction layer can sometimes be measured with a transmission electron microscope (TEM). However, the resolution of the transmission electron microscope must be considered.

[0064] Next, an example of a method for forming a first crystalline portion Q1 made of α-SiC quasi-single crystal and a second crystalline portion Q2 made of β-SiC crystal in the first layer 11 of the SiC composite substrate 10 described above will be explained.

[0065] One example of a method for forming 3C-SiC within a facet region including a second crystal portion Q2 that exists together with a first crystal portion Q1 made of α-SiC quasi-single crystal constituting the first layer 11 is a sublimation method in which a SiC single crystal is grown by recrystallizing a source gas obtained by sublimating raw material SiC on the surface of a SiC seed crystal. This can be achieved, for example, by temporarily performing high-speed growth exceeding 5 mm / h, and performing low-speed growth of 5 mm / h or less for the majority of the rest.

[0066] Thus, by rapidly increasing the temperature and then decreasing it to achieve a stable crystal growth rate, the amount of 3C-SiC inclusion decreases. However, if the amount of 3C-SiC inclusion becomes too high, warping is more likely to occur. Therefore, by appropriately adjusting the temperature conditions, it is possible to control the amount of 3C-SiC inclusion to an optimal level.

[0067] Furthermore, methods for forming 3C-SiC within these facet regions include rapidly changing the pressure or pre-embedding 3C-SiC in the SiC seed crystal.

[0068] Furthermore, the facet region containing 3C-SiC can be located at any position within the plane of the first main surface 11A of the first layer 11. The in-plane position of the facet region can be controlled by adjusting known parameters such as the crystal growth plane shape and the off-angle.

[0069] For example, convex growth shifts the formation location of the facet region towards the center of the plane, while flat growth shifts it towards the edges. Similarly, low off-angle growth shifts the facet region towards the center of the plane, while high off-angle growth shifts it towards the edges.

[0070] By growing it in a convex shape and forming a facet containing 3C-SiC in the center of the plane, when forming an epitaxial layer on the first main surface 12A of the second layer 12 by epitaxial growth, delamination between the first layer 11 and the second layer 12 is less likely to occur, especially in the center of the plane, and a SiC composite substrate 10 with suppressed warping can be realized.

[0071] Furthermore, by growing it in an M-shape and forming facets containing 3C-SiC at the outer edge of the plane, when forming an epitaxial layer on the first main surface 12A of the second layer 12 by epitaxial growth, delamination between the first layer 11 and the second layer 12 is less likely to occur, especially at the outer edge of the plane, and a SiC composite substrate 10 with suppressed warping can be realized.

[0072] The method for bonding the second layer 12 to the first main surface 11A of the first layer 11 obtained in this way can be carried out based on a known method for manufacturing a bonded substrate.

[0073] "SiC Composite Substrate: Second Embodiment" The SiC composite substrate of the second embodiment of the present invention is a SiC composite substrate having a first layer and a second layer bonded to the first main surface of the first layer, wherein the first layer is composed of a first crystalline portion made of α-SiC quasi-single crystal, and the second layer is made of α-SiC single crystal.

[0074] When the first layer contains α-SiC polycrystalline material, the crystal orientations of the particles constituting the α-SiC polycrystalline material differ, which makes it easy for an in-plane distribution of expansion coefficients to occur at a fine level.

[0075] Therefore, we found that making the first layer composed of a first crystal portion made of α-SiC quasi-single crystals with uniform orientation also has the effect of suppressing delamination. In the SiC composite substrate of this embodiment, it is possible to suppress delamination between the first layer and the second layer even if the first layer does not contain a β-SiC crystal portion.

[0076] "SiC Epitaxial Wafer" Figure 3 is a schematic cross-sectional view of the SiC epitaxial wafer according to this embodiment along the Z direction. The SiC epitaxial wafer 20 of one embodiment of the present invention is obtained by laminating a SiC epitaxial layer 21 on the first main surface 12A of the second layer 12 using the SiC composite substrate 10 of the first embodiment described above.

[0077] The epitaxial growth process for forming these SiC epitaxial layers involves high-temperature processes, such as those exceeding 1000°C. This raised concerns that conventional SiC composite (bonded) substrates might experience problems such as warping of the entire composite substrate or delamination of the bonded areas.

[0078] However, in the SiC composite substrate 10 of this embodiment, a first crystal portion Q1 made of an α-SiC single crystal or α-SiC quasi-single crystal that suppresses warping even in high-temperature environments, and a second crystal portion Q2 made of a β-SiC crystal that suppresses delamination are formed on the first main surface 11A of the first layer 11, which is the bonding surface. Therefore, even in a SiC epitaxial wafer 20 in which SiC epitaxial layers 21 are stacked by an epitaxial growth process which is a high-temperature process, defects such as warping of the entire composite substrate and delamination of the bonded portion can be prevented.

[0079] Furthermore, even with a SiC epitaxial wafer using the SiC composite substrate of the second embodiment, by making the first layer of the SiC composite substrate composed of a first crystal portion made of α-SiC quasi-single crystals with uniform orientation, defects such as warping of the entire composite substrate and delamination of the bonded portions can be prevented.

[0080] Furthermore, the same Warp method used to evaluate the warp of the SiC composite substrate 10 described above can be applied to the warp of the SiC epitaxial wafer 20 in exactly the same way.

[0081] When manufacturing such SiC epitaxial wafers 20, a SiC composite substrate 10 is prepared, and SiC epitaxial layers 21 are stacked by an epitaxial growth process to produce the SiC epitaxial wafer 20. The preparation of the SiC composite substrate 10 may be done by manufacturing the SiC composite substrate 10 oneself, or by obtaining the SiC composite substrate 10 by other means (for example, by purchase).

[0082] While preferred embodiments of this disclosure have been described in detail above, this disclosure is not limited to any particular embodiment, and various modifications and changes are possible within the scope of the gist of this disclosure as described in the claims.

[0083] The effects of the present invention were verified. As an example of the present invention, a SiC composite substrate of this embodiment was fabricated by bonding a second layer of 50 μm thickness to a first layer of 200 mm (8 inches) in diameter and 300 μm thickness. After epitaxial deposition was performed on the first main surface of the second layer, delamination and warping were evaluated. The thickness of the epitaxial layer was set to 10 μm. The area ratio of α-SiC / β-SiC, the polytype ratio, and the crystal orientation in the first layer were calculated using EBSD.

[0084] On the other hand, Comparative Example 1 consisted of a single polytype (4H) and α-SiC (polycrystalline) for the first layer of α-SiC. Comparative Example 2 consisted of only α-SiC for the first layer, and no β-SiC was formed. Comparative Example 3 consisted of only β-SiC (3C-SiC) for the first layer. Comparative Example 4 consisted of only α-SiC (polycrystalline) for the first layer. The reference example also consists of α-SiC (4H) for the first layer. The verification results using each of these samples are shown in Table 1. The evaluation criteria for each are as follows.

[0085] [Delamination] The bonding area between the first and second layers was visually inspected. Delamination was observed and marked as "present," while no delamination was observed and marked as "absent." [Warping] Warp was measured as an indicator of warping. A: Warp less than 20 μm B: Warp 20 μm or more and less than 50 μm C: Warp 50 μm or more [Device Yield] The device yield of Example 5 was set as "B (Average)." Devices with a higher device yield than Example 5 were marked as "A (Good)," and devices with a lower device yield than Example 5 were marked as "C (Bad)."

[0086]

[0087] According to the results shown in Table 1, Examples 1 to 5 of the present invention showed "no" delamination, warpage of "A", and device yields of "A" to "B". On the other hand, Comparative Examples 1 to 4 showed "present" delamination or warpage of "C", and device yields of "C".

[0088] Therefore, it has been confirmed that the SiC composite substrate of this embodiment can be realized in which both warping and delamination can be prevented even after undergoing high-temperature processes such as epitaxial film deposition.

[0089] The SiC composite substrate of the present invention makes it possible to prevent both warping and delamination, even when a composite substrate is formed by bonding a thin SiC single crystal substrate to one side of a low-cost substrate, and even after undergoing high-temperature processes such as epitaxial deposition. This makes it possible to manufacture high-precision semiconductor devices using SiC at low cost. Therefore, the present invention has industrial applicability.

[0090] 10...SiC composite substrate 11...First layer 11A...First main surface (first layer) 11B...Second main surface (first layer) 12...Second layer 12A...First main surface (second layer) 12B...Second main surface (second layer) 20...SiC epitaxial wafer 21...SiC epitaxial layer Q1...First crystal portion Q2...Second crystal portion

Claims

1. A SiC composite substrate comprising a first layer and a second layer made of an α-SiC single crystal bonded to a first main surface of the first layer, wherein the first layer includes a first crystalline portion made of an α-SiC single crystal or an α-SiC quasi-single crystal and a second crystalline portion made of a β-SiC crystal, and the area ratio of the first crystalline portion to the total area of ​​the first main surface is 50% or more, and the area ratio of the second crystalline portion is 10% or less.

2. A SiC composite substrate comprising a first layer and a second layer made of an α-SiC single crystal bonded to the first main surface of the first layer, wherein the first layer is composed of a first crystalline portion made of an α-SiC quasi-single crystal.

3. The SiC composite substrate according to claim 1, wherein the area ratio occupied by the second crystal portion on the first main surface of the first layer is 0.001% or more and 10% or less of the total area of ​​the first main surface.

4. The SiC composite substrate according to claim 1 or 2, wherein the first crystalline portion of the first layer contains at least two types of SiC polytypes from among 4H, 6H, and 15R.

5. The SiC composite substrate according to claim 1 or 2, wherein, on the first main surface of the first layer, the area ratio occupied by one polytype of α-SiC quasi-single crystal constituting the first crystal portion is 30% or more of the total area of ​​the first crystal portion.

6. The SiC composite substrate according to claim 1 or 2, wherein in the first main surface of the first layer, the c-axis orientation of α-SiC quasi-single crystals constituting the first crystalline portion is aligned to the same direction for 90% or more of the time.

7. The SiC composite substrate according to claim 1 or 2, wherein the orientation difference between the c-axis orientation of the α-SiC quasi-single crystal constituting the first crystalline portion and the c-axis orientation of the α-SiC single crystal constituting the second layer on the first main surface of the first layer is 12° or less.

8. The SiC composite substrate according to claim 1, wherein the second crystalline portion includes a facet region containing 3C.

9. The SiC composite substrate according to claim 1 or 2, wherein the diameter is 145 mm or more.

10. The SiC composite substrate according to claim 1 or 2, wherein the diameter is 195 mm or more.

11. A SiC epitaxial wafer comprising the SiC composite substrate described in claim 1 and a SiC epitaxial layer, wherein the SiC epitaxial layer is laminated on the second layer.

12. A SiC epitaxial wafer comprising the SiC composite substrate described in claim 2 and a SiC epitaxial layer, wherein the SiC epitaxial layer is laminated on the second layer.

13. A method for manufacturing a SiC epitaxial wafer, comprising preparing a SiC composite substrate as described in claim 1, and forming a SiC epitaxial layer on the second layer of the SiC composite substrate.

14. A method for manufacturing a SiC epitaxial wafer, comprising preparing a SiC composite substrate according to claim 2, and forming a SiC epitaxial layer on the second layer of the SiC composite substrate.

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