Silicon carbide substrates and silicon carbide epitaxial wafers

Abstract

In the SiC substrate of the present invention, when a point 10 mm inside the outer periphery is taken as the first outer periphery point in the [11-20] direction from the center, and any point within a circle with a diameter of 10 mm from the center is taken as the first center point, the tensile stress in the <1-100> direction of the circumferential direction of the aforementioned first outer periphery point is greater than the tensile stress in the <1-100> direction of the same circumferential direction as the aforementioned first center point.

Description

Technical Field

[0001] This invention relates to silicon carbide (SiC) substrates and silicon carbide (SiC) epitaxial wafers. Prior Technology

[0002] Compared to silicon (Si), silicon carbide (SiC) has an insulation breaking electric field that is one order of magnitude larger and a band gap that is three times larger. Furthermore, silicon carbide (SiC) possesses thermal conductivity that is three times higher than that of silicon (Si). Therefore, silicon carbide (SiC) is expected to be used in power devices, high-frequency devices, and high-temperature operating devices. Consequently, in recent years, SiC epitaxial wafers have been used in semiconductor devices as described above.

[0003] SiC epitaxial wafers are obtained by depositing a SiC epitaxial layer on the surface of a SiC substrate cut from a SiC ingot. Hereinafter, the substrate before the SiC epitaxial layer is deposited is referred to as the SiC substrate, and the substrate after the SiC epitaxial layer is deposited is referred to as the SiC epitaxial wafer.

[0004] SiC epitaxial wafers, due to the presence of a SiC epitaxial layer on one side, are prone to warping. This warping can negatively impact semiconductor device processes. For example, warping can cause focus shifts in lithography. Furthermore, it can reduce wafer positioning accuracy during transport. Moreover, significant warping can occur in SiC epitaxial wafers due to oxide film deposition or ion implantation during semiconductor processes.

[0005] On the other hand, since the SiC substrate before the SiC epitaxial layer is deposited is flat, it is difficult to predict the warpage of the SiC epitaxial wafer or warpage during the semiconductor process while the SiC substrate is in its current state. For example, Patent Document 1 describes a method for predicting the warpage value of a SiC single-crystal wafer after the polishing process is completed by using the difference in the wavenumber shift of Raman scattered light before the polishing process is finished. Patent Document 2 discloses a substrate with reduced stress distribution in the thickness direction by measuring the Raman spectrum in the thickness direction of the substrate. Furthermore, Patent Document 3, for example, describes a method for reducing the warpage of the SiC substrate by mitigating crystallographic fatigue. [Previous Technical Documents] [Patent Literature]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2015-59073 [Patent Document 2] International Publication No. 2019 / 111507 [Patent Document 3] U.S. Patent Application Publication No. 2021 / 0198804 [Patent Document 4] Japanese Patent Application Publication No. 2007-290880 Summary of the Invention

[0007] [The problem the invention aims to solve] In Patent Documents 1 and 2, although Raman displacement is used to evaluate the internal stress of the substrate, Raman displacement does not include directional information. Furthermore, Patent Documents 1-3 describe methods for reducing stress, but simply reducing stress is insufficient to suppress warping of the SiC epitaxial wafer. Also, Patent Document 4 describes suppressing ingot cracking by increasing the circumferential compressive stress of the ingot, but this is also insufficient to suppress warping of the SiC epitaxial wafer.

[0008] The present invention was made in view of the above-mentioned problems, and aims to provide a SiC substrate capable of suppressing warping after surface treatments such as ion implantation of laminated SiC epitaxial layers and laminated oxide films. [Methods for solving problems]

[0009] The inventors have discovered that by making the tensile stress in the circumferential direction near the outer periphery greater than the tensile stress in the circumferential direction near the center, warping after surface treatments such as laminated SiC epitaxial layers can be suppressed. In other words, the present invention provides the following means to solve the above-mentioned problems.

[0010] (1) Regarding the SiC substrate of the first form, if the point 10 mm inside the outer periphery from the center is taken as the first outer periphery point, and any point within a circle with a diameter of 10 mm from the center is taken as the first center point, the tensile stress in the <1-100> direction of the circumferential direction of the aforementioned first outer periphery point is greater than the tensile stress in the <1-100> direction of the same circumferential direction as the aforementioned first center point.

[0011] (2) Regarding the SiC substrate of the above-mentioned form, when the point 10 mm inside the outer periphery from the center in the [-1100] direction is taken as the second outer periphery point, the tensile stress in the <11-20> direction, which is the same as the circumferential direction of the aforementioned second outer periphery point, can be greater than the tensile stress in the <11-20> direction, which is the same as the circumferential direction of the aforementioned second outer periphery point, which is the same as the circumferential direction of the aforementioned first center point.

[0012] (3) Regarding the second type of SiC substrate, it is from the center... [-1100] In the direction of the second outer peripheral point, the point 10 mm inside the outer peripheral point is taken as the second outer peripheral point, and any point within a circle with a diameter of 10 mm from the center is taken as the first center point. The tensile stress in the <11-20> direction of the circumferential direction of the second outer peripheral point is greater than the tensile stress in the <11-20> direction of the first center point, which is the same as the circumferential direction of the second outer peripheral point.

[0013] (4) Regarding the SiC substrate of the above-mentioned form, when the point 10 mm inside the outer periphery from the center in the [11-20] direction is taken as the first outer periphery point, the tensile stress in the <1-100> direction, which is the same as the circumferential direction of the first outer periphery point, can be greater than the tensile stress in the <1-100> direction, which is the same as the circumferential direction of the first outer periphery point, which is the same as the circumferential direction of the first center point.

[0014] (5) In the SiC substrate of the above configuration, the tensile stress in the circumferential direction at the first outer peripheral point can be at least 10 MPa greater than the tensile stress acting in the same direction as the first outer peripheral point at the first center point. Furthermore, the tensile stress in the circumferential direction at the second outer peripheral point can be at least 10 MPa greater than the tensile stress acting in the same direction as the second outer peripheral point at the first center point.

[0015] (6) In the SiC substrate of the above configuration, the tensile stress in the circumferential direction at the first outer peripheral point is at least 30 MPa greater than the tensile stress acting in the same direction as the first outer peripheral point at the first center point. Furthermore, the tensile stress in the circumferential direction at the second outer peripheral point is at least 30 MPa greater than the tensile stress acting in the same direction as the second outer peripheral point at the first center point.

[0016] (7) The diameter of the SiC substrate system with the above-mentioned shape is also 145 mm or more.

[0017] (8) The diameter of the SiC substrate system with the above-mentioned shape is also 195 mm or more.

[0018] (9) The surface roughness (Ra) of the first surface of the SiC substrate with the above-mentioned morphology can be less than 1 nm.

[0019] (10) The warp of the SiC substrate with the above-mentioned morphology is also acceptable to be less than 50 μm.

[0020] (11) Regarding the SiC substrate of the above form, the bow of the support body located at the position of overlapping the inner circumference of 7.5 mm from the outermost periphery on the first surface and the surface connecting the overlapping part when viewed from the thickness direction are taken as the reference surface, can be 30 μm or less.

[0021] (12) The SiC epitaxial wafer system of the third type has a SiC substrate of the above type and a SiC epitaxial layer deposited on one side of the aforementioned SiC substrate.

[0022] (13) The warp of the SiC epitaxial wafer system with the above-mentioned morphology is also acceptable if it is less than 50 μm.

[0023] (14) Regarding the SiC epitaxial wafer of the above-mentioned form, the curvature (Bow) of the support body located at the position of overlapping the circumference of the inner side of 7.5 mm from the outermost periphery and the surface connecting the overlapping part when viewed from the thickness direction is taken as the reference surface, can be less than 30 μm. [Invention Effects]

[0024] The SiC substrate with the above-mentioned structure can suppress warping after surface treatment such as the deposition of SiC epitaxial layers. Simple Explanation of the Diagram

[0025] [Figure 1] A schematic diagram illustrating the warping of SiC epitaxial wafers. [Figure 2] Plan view of the SiC substrate of this embodiment. [Figure 3] A schematic diagram illustrating the method for measuring the tensile stress in the circumferential direction at the first outer circumference point. [Figure 4] A schematic diagram illustrating the method for measuring the tensile stress in the circumferential direction at the second outer circumference point. [Figure 5] is a schematic diagram of the evaluation method for the shape of the SiC substrate formed by Warp. [Figure 6] is a diagram illustrating the evaluation method for the shape of a SiC substrate formed by Bow. [Figure 7] A schematic diagram illustrating a sublimation method of an example of a SiC ingot manufacturing apparatus. Implementation

[0026] Hereinafter, the SiC substrate and the like of this embodiment will be described in detail with appropriate reference to the accompanying drawings. In the drawings used in the following description, for ease of understanding of the features of this embodiment and to facilitate the enlargement of characteristic parts, the dimensions and ratios of each component may differ from the actual dimensions. The materials, dimensions, etc., illustrated in the following description are merely examples, and the present invention is not limited thereto; appropriate modifications can be made without changing its spirit.

[0027] First, the warpage of the SiC epitaxial wafer 20 will be explained. Figure 1 is a schematic diagram illustrating the warpage of the SiC epitaxial wafer 20. The SiC epitaxial wafer 20 is obtained by depositing a SiC epitaxial layer 11 on the first surface 10a of the SiC substrate 10. The SiC epitaxial wafer 20 has a SiC substrate 10 and a SiC epitaxial layer 11.

[0028] The SiC substrate 10 has no significant warping and is generally flat. By "generally flat," we mean that when placed on a flat surface, there is no significant upward movement.

[0029] To obtain high-quality SiC for a movable device, a SiC epitaxial layer 11 is deposited on the SiC substrate 10. However, before depositing the SiC epitaxial layer 11, mechanical processing such as grinding is usually performed. At this time, a processing-modified layer is formed on the first surface 10a of the SiC substrate 10. When the SiC epitaxial layer 11 is deposited on one side of the SiC substrate 10, or when a processing-modified layer is formed, the SiC epitaxial wafer 20 may warp.

[0030] "First Implementation Form" Figure 2 shows the SiC substrate 10 of this embodiment. The SiC substrate 10 is made of SiC. The crystal form of the SiC substrate 10 is not particularly limited and can be any of 2H, 3C, 4H, and 6H. For example, the SiC substrate 10 is 4H-SiC.

[0031] The SiC substrate 10 has a slightly circular shape when viewed from above. The SiC substrate 10 may have an orientation plane (OF) or notch for controlling the direction of the crystal axis. The diameter of the SiC substrate 10 is, for example, 145 mm or more, preferably 195 mm or more. The larger the diameter of the SiC substrate 10, the greater the absolute amount of warpage, even with the same curvature. Large warpage in SiC epitaxial wafers has a significant impact on subsequent processing procedures, requiring the ability to suppress warpage. In other words, the more applicable the present invention is to a larger diameter SiC substrate 10, the more effective it will be.

[0032] Regarding the SiC substrate 10 of this embodiment, the tensile stress in the <1-100> direction of the circumference of the first outer peripheral point 1 is greater than the tensile stress in the <1-100> direction of the first center point 2, which is in the same circumference direction as the first outer peripheral point 1. It is preferable that the tensile stress in the circumference direction of the first outer peripheral point 1 is at least 10 MPa greater than the tensile stress acting in the same circumference direction as the first outer peripheral point 2, and more preferably at least 30 MPa greater.

[0033] The first outer peripheral point 1 is located on the outer peripheral portion 5 at a distance of 10 mm from the outer peripheral end of the SiC substrate 10. The first outer peripheral point 1 is a point in the outer peripheral portion 5 located in the direction from the center of the SiC substrate 10 toward [11-20]. The first center point 2 is any point within the center portion 6. The center portion 6 is a region within a circle with a diameter of 10 mm starting from the center of the SiC substrate 10. The first center point 2 is, for example, aligned with the center of the SiC substrate 10.

[0034] Here, the notation for parentheses indicating the direction of the Miller index is <> or []. <1-100> is included due to the symmetry of the crystallographic direction. [-1100]. The <11-20> series contains [11-20] due to the symmetry of the crystallization direction.

[0035] Tensile stress is calculated as the product of strain ε and Young's modulus. Strain ε is obtained as (a0-a) / a0. a0 is the reference lattice constant. a0 is approximately 3.08 Å for 4H-SiC. a is the lattice constant obtained by X-ray diffraction (XRD). The direction of stress is determined by the direction of the incident X-rays diffracted by X-ray diffraction. In this invention, tension is treated as a positive value and compression as a negative value. When discussing the magnitude of stress, the absolute value is used. The smaller the lattice constant a is than the reference lattice constant a0, the larger the strain ε becomes, and consequently, the larger the tensile stress.

[0036] Figure 3 is a schematic diagram illustrating the method for measuring the tensile stress in the circumferential direction at the first outer peripheral point 1. The circumferential direction of the first outer peripheral point 1 is the direction orthogonal to the line segment connecting the center of the SiC substrate 10 and the first outer peripheral point 1 (hereinafter referred to as the first direction). The first direction is the <1-100> direction. When measuring the tensile stress in the circumferential direction at the first outer peripheral point 1, X-rays are irradiated from the first direction. By incident X-rays onto the SiC substrate 10 from this circumferential direction, the lattice constant a in the circumferential direction of the first outer peripheral point 1 is determined. Then, using this lattice constant a, the stress in the circumferential direction of the first outer peripheral point 1 is calculated using the above formula. However, the smaller the measured lattice constant a is than the reference lattice constant a0, the more likely tensile stress is to be applied.

[0037] The tensile stress acting at the first center point 2 in the same direction as the circumferential direction of the first outer perimeter point 1 is determined by incident X-rays onto the first center point 2 using the same method as for the first outer perimeter point 1. The direction in the same direction as the circumferential direction of the first outer perimeter point 1 is the aforementioned first direction. The first outer perimeter point 1 and the first center point 2 are compared to determine the magnitude of the tensile stress acting in the same direction (the first direction).

[0038] When the tensile stress in the circumferential direction at the first outer peripheral point 1 is greater than the tensile stress acting in the same direction as the first outer peripheral point 1 at the first center point 2, the SiC epitaxial wafer 20 is less likely to warp after the SiC epitaxial layer 11 is deposited. This is because the stronger tensile stress applied in the circumferential direction at the first outer peripheral point 1 causes the SiC epitaxial wafer 20 to expand outward, acting on the SiC epitaxial wafer 20.

[0039] Furthermore, in this embodiment, it is preferable that the tensile stress in the circumferential direction of the SiC substrate 10 at the second outer peripheral point 3 is greater than the tensile stress acting in the same direction as the circumferential direction of the second outer peripheral point 3 at the first center point 2. Moreover, it is preferable that the tensile stress in the circumferential direction of the second outer peripheral point 3 is at least 10 MPa greater than the tensile stress acting in the same direction as the circumferential direction of the second outer peripheral point 3 at the first center point 2, and more preferably at least 30 MPa greater.

[0040] The second outer peripheral point 3 is located on the outer peripheral portion 5, 10 mm inside the outer peripheral end of the SiC substrate 10. The second outer peripheral point 3 is located in the outer peripheral portion 5 in the direction from the center of the SiC substrate 10 toward [-1100].

[0041] Figure 4 is a schematic diagram illustrating the method for measuring the tensile stress in the circumferential direction at the second outer peripheral point 3. The circumferential direction of the second outer peripheral point 3 is the direction orthogonal to the line segment connecting the center of the SiC substrate 10 and the second outer peripheral point 3 (hereinafter referred to as the second direction). The second direction is the <11-20> direction. When measuring the tensile stress in the circumferential direction at the second outer peripheral point 3, X-rays are irradiated from the second direction. By incident X-rays onto the SiC substrate 10 from this circumferential direction, the lattice constant 'a' in the circumferential direction of the second outer peripheral point 3 is determined. Then, using this lattice constant 'a', the tensile stress in the circumferential direction of the second outer peripheral point 3 is determined by the above formula.

[0042] When comparing the tensile stress in the circumferential direction at the second outer perimeter point 3 with the tensile stress acting in the same direction as the circumferential direction at the first center point 2, the tensile stress in the direction <11-20> of the direction in the first center point 2 that is in the same direction as the circumferential direction at the second outer perimeter point 3 is determined. The tensile stress acting in the first center point 2 in the direction in the same direction as the circumferential direction at the second outer perimeter point 3 is determined by incident X-rays onto the first center point 2 using the same method as at the second outer perimeter point 3. The direction in the direction in the same direction as the circumferential direction at the second outer perimeter point 3 is the second direction mentioned above.

[0043] When the tensile stress in the circumferential direction at the second outer perimeter point 3 is greater than the tensile stress acting in the same direction as the circumferential direction at the second outer perimeter point 3 at the first center point 2, the SiC epitaxial wafer 20 is less prone to warping after the SiC epitaxial layer 11 is deposited. This is believed to be due to the force extending the SiC epitaxial wafer 20 outwards acting in different directions within the plane of the SiC epitaxial wafer 20.

[0044] Furthermore, in this embodiment, it is preferable that the tensile stress in the circumferential direction at any position on the outer periphery 5 of the SiC substrate 10 is greater than the tensile stress at the first center point 2. Here, the tensile stress at the first center point 2 is the tensile stress acting in the same direction as the circumferential direction of the measurement point. Also, it is preferable that the average tensile stress applied to the area outside the outer periphery 5 is greater than the average tensile stress applied to the center portion 6. Here, the average tensile stress is, for example, the average of the tensile stresses measured at five different points within that area.

[0045] It is preferable that the surface of the SiC substrate 10 is polished. The surface roughness (Ra) of the first surface 10a of the SiC substrate 10 is preferably below 1 nm, for example. The first surface 10a is, for example, the side surface of the deposited SiC epitaxial layer 11.

[0046] It is preferable that both the first surface 10a and the second surface 10b of the SiC substrate 10 are polished. The first surface 10a is, for example, the Si surface, and the second surface 10b is, for example, the C surface. The relationship between the first surface 10a and the second surface 10b can also be reversed. Both the first surface 10a and the second surface 10b can be mirror surfaces with residual scratches, etc., or they can be CMP (Chemical Mechanical Polishing) treated surfaces. The degree of polishing can also be different for the first surface 10a and the second surface 10b. A processing-modified layer is formed on the mirror surface with residual scratches, etc., while almost no processing-modified layer is formed on the CMP treated surface. The processing-modified layer is the part damaged by processing, which is the part where the crystal structure has collapsed.

[0047] For example, when the first surface 10a is mirror-polished and the second surface 10b is CMP-treated, the difference in surface conditions between the two surfaces generates a Trewmann effect on the SiC substrate 10. The Trewmann effect is a phenomenon where a force compensates for the difference in residual stress between the two surfaces of the substrate. The Trewmann effect can cause warping of the SiC epitaxial wafer 20. Therefore, the more applicable this invention is to SiC substrates 10 with different surface conditions of the first surface 10a and the second surface 10b, the more effective it is.

[0048] In this embodiment, the SiC substrate 10 preferably has a warp of 50 μm or less, and more preferably a warp of 30 μm or less. Using a SiC substrate 10 with a warp of 50 μm or less that satisfies the aforementioned tensile stress relationship can significantly reduce the warpage of the SiC epitaxial wafer 20. Therefore, it is possible to avoid a decrease in the accuracy of the SiC epitaxial wafer 20 during transport, and even in fine lithography processes, proper focus alignment can be achieved.

[0049] Figure 5 shows a schematic diagram of the evaluation method for the shape (deformation) of a SiC substrate formed by warp. Warp is the distance in the thickness direction between the highest point hp and the lowest point lp of the first surface 10a. The larger the warp, the more likely the SiC substrate 10 is deformed. First, the SiC substrate 10 is placed on three support points on the flat plane F. The imaginary surface Slp, parallel to the flat plane F, is obtained through the lowest point lp of the first surface 10a, and the imaginary surface Shp, parallel to the flat plane F, is obtained through the highest point hp of the first surface 10a. Warp is calculated as the distance in the height direction between the imaginary surfaces Slp and Shp. The height direction is orthogonal to the flat plane F and is the direction away from the flat plane F.

[0050] In this embodiment, it is preferable that the bow size of the SiC substrate 10 is 30 μm or less, and more preferably 10 μm or less. Furthermore, a bow size of -30 μm or more is preferred. When a SiC substrate 10 with an absolute bow size of 30 μm or less that satisfies the above-mentioned tensile stress relationship is used, the warpage of the SiC epitaxial wafer 20 can be sufficiently reduced. Therefore, it is possible to avoid a decrease in accuracy during the transport of the SiC epitaxial wafer 20, and even in fine lithography processes, proper focus alignment can be achieved.

[0051] Figure 6 is a schematic diagram illustrating the evaluation method for the shape (deformation) of a SiC substrate formed by Bow. Bow refers to the position of the SiC substrate 10 in the height direction relative to the center c of the reference plane Sr. In other words, Bow is the signed distance from the center c of the SiC substrate 10 to the reference plane Sr. The reference plane Sr is the plane connecting the points sp that overlap with the plurality of supports when viewed from the thickness direction in the first surface 10a. The plurality of supports are arranged, for example, at positions that overlap with the circumference from the outer periphery of the SiC substrate 10 to the inner side of 7.5 mm. For example, the SiC substrate 10 is supported by three supports. Each of the three supports is located at a position symmetrical to the center of the SiC substrate 10 supported by the support, three times. The reference plane Sr is, for example, a three-point reference plane. The larger the absolute value of Bow, the more likely the SiC substrate 10 is to be deformed. First, the SiC substrate 10 is placed on the three support points on the flat surface F. Viewed from the thickness direction, the reference plane Sr is determined by connecting the three points sp of the first face 10a at the support point. Then, the reference plane Sr is set to 0, and the direction away from the flat surface F with reference plane Sr as the reference is defined as +, and the direction approaching the flat surface F with reference plane Sr as the reference is defined as -. Bow is determined as the position of the center c of the first face 10a relative to the reference plane Sr in the height direction. In other words, Bow is determined as the signed distance from the center c of the first face 10a to the reference plane Sr.

[0052] Furthermore, after the epitaxial layer 11 is deposited, the SiC epitaxial wafer 20 preferably has a warp of 50 μm or less, more preferably a warp of 30 μm or less. Also, after the epitaxial layer 11 is deposited, the SiC epitaxial wafer preferably has a bow of 30 μm or less, more preferably a bow of 10 μm or less, and preferably a bow of -30 μm or more. The reference plane for measuring the bow of the SiC epitaxial wafer 20 is the plane connecting the points overlapping with the plurality of supports, viewed from the thickness direction on the surface of the epitaxial layer 11. The positions of the plurality of supports are the same as the positions for measuring the bow of the SiC substrate 10. First, the SiC epitaxial wafer 20 is placed on three support points on the flat surface F. By connecting the three points on the surface of the epitaxial layer 11 located at the support points as viewed from the thickness direction, the reference plane for measuring the bow of the SiC epitaxial wafer 20 is determined. Bow is determined by the position of the center of the surface of epitaxial layer 11 in the height direction relative to the reference plane. In other words, Bow is determined by the signed distance of the reference plane relative to the center of the surface of epitaxial layer 11.

[0053] Next, an example of a method for manufacturing the SiC substrate 10 of this embodiment will be described. The SiC substrate 10 is obtained by slicing a SiC ingot. The SiC ingot is obtained, for example, by sublimation.

[0054] Figure 7 is a schematic diagram illustrating an example of the sublimation method of the SiC ingot manufacturing apparatus 30. In Figure 7, the direction orthogonal to the surface of the stage 32 is designated as the z-direction, the direction orthogonal to the z-direction is designated as the x-direction, and the direction orthogonal to both the z-direction and the x-direction is designated as the y-direction.

[0055] The sublimation method involves placing a seed crystal 33, formed from a single crystal of SiC, on a pedestal 32 within a graphite crucible 31. By heating the crucible 31, sublimation gas from the sublimation of the raw material powder 34 within the crucible 31 is supplied to the seed crystal 33, causing the seed crystal 33 to grow into a larger SiC ingot 35. The crucible 31 is heated, for example, by a coil 36.

[0056] By controlling the crystal growth conditions in the sublimation process, the tensile stress applied inside the SiC substrate 10 obtained from the SiC ingot 35 can be controlled.

[0057] For example, when growing a SiC ingot with the 35 c-plane, the temperature of the center and the temperature of the outer periphery of the crystal growth plane are controlled. The crystal growth plane is the surface on which the crystal growth process takes place. For example, when growing a SiC ingot with the 35 c-plane, the temperature of the outer periphery is lower than the temperature of the center of the crystal growth plane. Furthermore, crystal growth is carried out with a growth rate difference between the center and the outer periphery within the xy-plane of 0.001 mm / h or more and 0.05 mm / h or less. Here, the growth rate at the center within the xy-plane is slower than the growth rate at the outer periphery. The growth rate is varied by changing the temperature of the crystal growth plane.

[0058] The temperature of the crystal growth surface can be adjusted by controlling the position of the control coil 36 relative to the heating center of the crucible 31 in the z-direction. For example, the position of the heating center of the crucible 31 in the z-direction can be changed by altering the position of the coil 36 in the z-direction. The position of the heating center of the crucible 31 in the z-direction and the position of the crystal growth surface in the z-direction are controlled to move at a rate of 0.5 mm / h. Here, the position of the heating center of the crucible 31 in the z-direction is controlled so that it is positioned below (towards the raw material powder 34) relative to the position of the crystal growth surface in the z-direction.

[0059] Next, the SiC ingot produced under these conditions is processed into a SiC substrate 10. In general processing methods, the stress applied to the single crystal changes between the state of the SiC ingot and the state of the SiC substrate. For example, in the molding process, when processing a SiC ingot with a diameter of 180 mm into a SiC substrate with a diameter of 150 mm, the diameter needs to be reduced. Also, for example, in the multi-wire cutting process, surface ripples are generated, and these ripples need to be removed. Through such processes, for example, the stress-high portion of the SiC ingot is removed or the shape of the lattice plane changes, and the stress in the state of the SiC ingot is opened in the state of the SiC substrate, so a SiC substrate with high tensile stress cannot be obtained at the outer periphery. In order to obtain a SiC substrate with high tensile stress at the outer periphery, it is necessary to process it so that the stress of the single crystal applied to the ingot state is inherited to the state of the substrate.

[0060] For example, after performing non-destructive processing on one side of a SiC ingot, it is cut off with a single-wire saw, and the non-destructive-processed side is then adhered to the cut surface for further non-destructive processing. By performing non-destructive processing on both sides of the SiC substrate 10, a portion of the tensile stress generated in the state of the SiC ingot is also inherited by the substrate. The non-destructive processing method is, for example, CMP processing. Thus, by processing the substrate in a lattice-shaped manner with the residual SiC ingot state, it is possible to produce a SiC substrate 10 with high tensile stress because the stress of the SiC ingot is not released. Then, by performing a forming process to adjust the diameter, a SiC substrate 10 with high tensile stress can be obtained.

[0061] As described above, the SiC substrate 10 of the first embodiment is not prone to warping even after the SiC epitaxial layer 11 is deposited. This is achieved by intentionally increasing the tensile stress in the circumferential direction on the outer side of the SiC substrate 10, thereby exerting a force that extends the SiC epitaxial wafer 20 outward.

[0062] "Second Implementation Form" Regarding the SiC substrate 10 of the second embodiment, the tensile stress in the <11-20> direction of the circumferential direction at the second outer peripheral point 3 is greater than the tensile stress in the <11-20> direction acting on the first center point 2 in the same circumferential direction as the second outer peripheral point 3. The SiC substrate 10 in the second embodiment is the same as the SiC substrate 10 in the first embodiment, except for the location used to measure the state of the SiC substrate 10. For example, the preferred ranges for warp, bow, diameter, surface roughness, etc., of the SiC substrate 10 in the second embodiment are the same as those of the SiC substrate 10 in the first embodiment.

[0063] The tensile stress in the circumferential direction of the second outer peripheral point 3 is preferably 10 MPa greater than the tensile stress acting in the same direction as the circumferential direction of the second outer peripheral point 3 of the first center point 2, and more preferably 30 MPa greater.

[0064] Furthermore, it is preferable that the tensile stress in the <1-100> direction of the circumference of the first outer peripheral point 1 is greater than the tensile stress in the <1-100> direction of the same circumference as the first center point 2. It is preferable that the tensile stress in the circumference of the first outer peripheral point 1 is at least 10 MPa greater than the tensile stress acting in the same circumference as the first outer peripheral point 2, and more preferably at least 30 MPa greater.

[0065] The SiC substrate 10 of the second embodiment has the same effect as the SiC substrate 10 of the first embodiment.

[0066] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to a specific embodiment. Various modifications and alterations can be made within the scope of the spirit of the present invention as described in the patent claims.

[0067] (Example 1) The warpage of SiC epitaxial layers during deposition on the surface of a SiC substrate was determined through simulation. The simulation was performed using the finite element method (FEM) in ANSYS. Furthermore, the simulation results using ANSYS with the FEM method were confirmed to be consistent with those of the actual fabricated product.

[0068] The simulation was conducted according to the following steps. First, the physical properties of the SiC substrate and the surface layer with different stresses were set. The set physical properties were the SiC substrate thickness, surface layer thickness, Young's modulus, and Brosson's ratio. The SiC substrate thickness was 350 μm. The SiC substrate diameter was 150 mm. The SiC substrate warp was 0 μm. The SiC substrate Young's modulus was 480 GPa, and the Brosson's ratio was 0.20. The surface layer thickness was 10 μm. Here, considering the case where the surface layer is stressed by ion implantation, the Young's modulus and Brosson's ratio of the surface layer were the same as those of the SiC substrate.

[0069] Next, the stress distribution of the SiC substrate and the stress of the surface layer are set. The tensile stress at the first outer perimeter point 1 of the SiC substrate is set to be 40 MPa greater than the tensile stress at the first center point 2. That is, the stress difference between the first outer perimeter point 1 and the first center point 2 is set to 40 MPa, with the first outer perimeter point 1 being stronger than the first center point, and a tensile stress is applied. A stress of 60 MPa is applied to the entire surface layer.

[0070] Simulations were performed under the above conditions to determine the warpage of the SiC substrate with the surface layer. Warpage was evaluated using the warp value. The warpage in Example 1 was 47 μm. The warpage of the SiC substrate with the surface layer was determined by considering the surface layer as an epitaxial layer, which can be viewed as the warpage of the epitaxial wafer. While the warpage varies depending on the stress difference related to the film thickness and impurity concentration difference of the epitaxial layer when the surface layer is an epitaxial layer, it is confirmed to be related to the determined warpage of the SiC substrate with the surface layer.

[0071] (Example 2) Example 2 differs from Example 1 in that the tensile stress at the first outer peripheral point 1 of the SiC substrate is set to be 20 MPa greater than the tensile stress at the first center point 2. That is, the stress difference between the first outer peripheral point 1 and the first center point 2 is set to 20 MPa, with the first outer peripheral point 1 being stronger than the first center point, and tensile stress is applied accordingly. Other parameters are the same as in Example 1. Similarly, the warp of the SiC substrate with the surface layer is calculated through simulation. The warp of Example 2 is 78 μm.

[0072] (Comparative Example 1) The difference between Comparative Example 1 and Example 1 is that the tensile stress at the first outer peripheral point 1 of the SiC substrate was set to be the same as the tensile stress at the first center point 2. That is, the stress difference between the first outer peripheral point 1 and the first center point 2 was set to 0 MPa, and the same stress was applied to the first outer peripheral point 1 as to the first center point 2. Other parameters were the same as in Example 1, and as in Example 1, the warp of the SiC substrate with the surface layer was determined by simulation. The warp of Comparative Example 1 was 116 μm.

[0073] (Comparative Example 2) The difference between Comparative Example 2 and Example 1 is that the tensile stress at the first center point 2 of the SiC substrate is set to be 20 MPa greater than the tensile stress at the first outer perimeter point 1. That is, the stress difference between the first outer perimeter point 1 and the first center point 2 is set to... -20 MPa was set to apply a stronger tensile stress to the first center point 2 than to the first outer perimeter point 1. That is, the first outer perimeter point 1 was subjected to a compressive stress compared to the first center point 2. Other parameters were the same as in Example 1. As in Example 1, the warp of the SiC substrate with the surface layer was determined by simulation. The warp of Comparative Example 2 was 189 μm.

[0074] The results of Examples 1 and 2 and Comparative Examples 1 and 2 are summarized in Table 1.

[0075]

[0076] Compared to the central portion, Examples 1 and 2, which experience greater tensile stress on the outer periphery, exhibit less warpage in the SiC substrate with the surface layer compared to Comparative Example 1 (where no tensile stress is applied to the outer periphery) and Comparative Example 2 (where compressive stress is applied to the outer periphery). In other words, among substrates with tensile stress on the outer periphery compared to the central portion, compared to SiC substrates without tensile stress on the outer periphery compared to the central portion and SiC substrates with compressive stress on the outer periphery as described in previous literature, warpage in epitaxial wafers and semiconductor processes can be reduced.

[0077] 1: 1st peripheral point 2: The first center point 3: 2nd peripheral point 5: Peripheral part 6: Central Section 10:SiC substrate 10a: Page 1 10b: Page 2 11: SiC epitaxial layer 20: SiC epitaxial wafer hp: highest point lp: lowest point sp: support point Shp, Slp: Imaginary surface Sr: Reference plane

Claims

1. A silicon carbide epitaxial wafer, comprising: a silicon carbide substrate; and a silicon carbide epitaxial layer deposited on one side of the silicon carbide substrate; the diameter of the silicon carbide substrate is 195 mm or more; the warp of the silicon carbide epitaxial wafer is 50 μm or less; and the warp of the silicon carbide substrate is 50 μm or less.

2. As in request item 1, the silicon carbide epitaxial wafer, wherein, On the surface of the silicon carbide epitaxial layer, the curvature (Bow) of the support located at the position where it overlaps with the inner circumference of 7.5 mm from the outermost periphery, and the surface passing through the overlapping part in the thickness direction as the reference plane, is less than 30 μm.

3. As in request item 1, the silicon carbide epitaxial wafer, wherein, The warp of this silicon carbide epitaxial wafer is less than 30 μm.

4. As in request item 2, the silicon carbide epitaxial wafer, wherein, The bend (bow) is less than 10 μm.

5. As in request item 2, the silicon carbide epitaxial wafer, wherein, The bow is greater than -30 μm.

6. As in request item 1, the silicon carbide epitaxial wafer, wherein, The thickness of the silicon carbide substrate is less than 350 μm.

7. A silicon carbide epitaxial wafer, comprising: a silicon carbide substrate; and a silicon carbide epitaxial layer deposited on one side of the silicon carbide substrate; the diameter of the silicon carbide substrate is 195 mm or more; the warp of the silicon carbide epitaxial wafer is 50 μm or less; and the value of the silicon carbide epitaxial wafer minus the warp of the silicon carbide substrate is 0 μm or more and 78 μm or less.

8. As in request item 7, the silicon carbide epitaxial wafer, wherein, The value of the warp of the silicon carbide epitaxial wafer minus the warp of the silicon carbide substrate is between 0 μm and 47 μm.

9. A silicon carbide epitaxial wafer, comprising: a silicon carbide substrate; and a silicon carbide epitaxial layer deposited on one side of the silicon carbide substrate; the diameter of the silicon carbide substrate is 195 mm or more; the thickness of the silicon carbide substrate is 350 μm or less; and the warp of the silicon carbide epitaxial wafer is 50 μm or less.

10. The silicon carbide epitaxial wafer as described in claim 7, wherein, On the surface of the silicon carbide epitaxial layer, the curvature (Bow) of the support located at the position where it overlaps with the inner circumference of 7.5 mm from the outermost periphery, and the surface passing through the overlapping part in the thickness direction as the reference plane, is less than 30 μm.

11. As in claim 9, the silicon carbide epitaxial wafer, wherein, On the surface of the silicon carbide epitaxial layer, the curvature (Bow) of the support located at the position where it overlaps with the inner circumference of 7.5 mm from the outermost periphery, and the surface passing through the overlapping part in the thickness direction as the reference plane, is less than 30 μm.

12. As in request item 10, the silicon carbide epitaxial wafer, wherein, The bend (bow) is less than 10 μm.

13. The silicon carbide epitaxial wafer as described in claim 11, wherein, The bend (bow) is less than 10 μm.

14. The silicon carbide epitaxial wafer as described in claim 10, wherein, The bow is greater than -30 μm.

15. The silicon carbide epitaxial wafer as described in claim 11, wherein, The bow is greater than -30 μm.

16. As in claim 9, the silicon carbide epitaxial wafer, wherein, The warp of this silicon carbide epitaxial wafer is less than 30 μm.

17. The silicon carbide epitaxial wafer as described in claim 1, wherein, The warp of this silicon carbide substrate is less than 30 μm.

18. The silicon carbide epitaxial wafer as described in claim 6, wherein, The warp of this silicon carbide substrate is less than 30 μm.

19. The silicon carbide epitaxial wafer as described in claim 16, wherein, The warp of this silicon carbide substrate is less than 30 μm.

20. The silicon carbide epitaxial wafer as described in claim 19, wherein, On the surface of the silicon carbide epitaxial layer, the curvature (Bow) of the support body located at the position of overlapping the circumference of the inner side of 7.5 mm from the outermost periphery, and the surface passing through the overlapping part in the thickness direction as the reference surface, is more than -30 μm and less than 10 μm.

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