SiC single crystal, SiC substrate, epitaxial wafer, method for manufacturing SiC substrate

Abstract

This invention provides a SiC single crystal, SiC substrate, epitaxial wafer, and a method for manufacturing a SiC substrate, all of which are primarily composed of 4H and are not converted to a 6H polytype. [Solution] A SiC single crystal containing 3C in the faceted region and 4H in the non-faceted region.

Description

Technical Field

[0001] The present invention relates to a SiC single crystal, a SiC substrate, an epitaxial wafer, and a method for manufacturing a SiC substrate.

Background Art

[0002] SiC (silicon carbide) has a breakdown electric field that is one order of magnitude larger and a bandgap that is three times larger than that of Si (silicon). Also, SiC has a thermal conductivity that is about three times higher than that of Si. Therefore, SiC is expected to be applied to power devices, high-frequency devices, high-temperature operation devices, etc.

[0003] SiC has a plurality of polytypes (polymorphs) with different crystal structures. Among these polytypes, for example, cubic 3C-SiC, hexagonal 4H-SiC, 6H-SiC, and rhombohedral 15R-SiC, etc., are particularly those with a high occurrence probability and being studied for applications. Among these, in the development of devices using SiC, substrates using 4H-SiC with high electron mobility are often used (for example, see Patent Documents 1 and 2).

[0004] Also, different partial regions are formed on the growth interface of the growing SiC single crystal. For example, in a region close to the outer peripheral surface of the SiC single crystal, a facet region having a substantially flat and smooth surface structure (surface morphology) with a very high ratio of the step depth and step width to the step height of the crystal growth step is formed.

[0005] As described above, in the growth process of a SiC single crystal, regions with different growth modes, namely a region called a facet region and a region called a non-facet region, are formed. It is known that the physical properties such as resistivity and defect density of the facet region and the non-facet region are different due to the difference in their growth modes.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2019-127415 [Patent Document 2] Japanese Patent Publication No. 2022-160660 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, conventionally, when growing 4H-SiC single crystal ingots, conversion to the 6H-SiC polytype, which is also hexagonal, is likely to occur. This polytype conversion from 4H to 6H occurs when the c-plane facets change from 4H to 6H and spread from the c-plane facets to the entire growth surface via step flow growth. At this time, micropipes are formed due to the mismatch that occurs at the 4H / 6H interface.

[0008] These micropipes are thought to be formed by the aggregation of multiple through-helical dislocations and multiple through-edge dislocations. As a result, the substrate cut from these micropipes will have micropipes throughout, failing to meet the quality requirements for SiC substrates used in semiconductor devices. Therefore, 4H-SiC single crystals that do not require conversion to 6H polytype were desired.

[0009] This invention has been made in view of the above technical background, and aims to provide a SiC single crystal, SiC substrate, epitaxial wafer, and a method for manufacturing a SiC substrate that is mainly composed of 4H and is not converted to a 6H polytype. [Means for solving the problem]

[0010] The inventors have newly discovered that by incorporating 3C polytype into the c-facets, the conversion of 4H to 6H in the subsequent crystal growth region can be suppressed. Furthermore, they have newly discovered that this incorporation of 3C polytype into the c-facets can be achieved by setting the crystal growth rate to instantaneously exceed 5 mm / h.

[0011] To solve the above problems, the following means are proposed for manufacturing a SiC single crystal, a SiC substrate, an epitaxial wafer, and a SiC substrate according to one embodiment of the present invention. (1) The SiC single crystal of embodiment 1 of the present invention contains 3C in the faceted region and 4H in the non-faceted region.

[0012] (2) Aspect 2 of the present invention is the SiC single crystal of Aspect 1, wherein the SiC single crystal is an ingot after crystal growth.

[0013] (3) A third aspect of the present invention is the SiC single crystal of the first aspect, wherein the SiC single crystal is an ingot processed into a cylindrical shape.

[0014] (4) Embodiment 4 of the present invention is a SiC single crystal of Embodiment 2 in which the facet region is located within a region with a width of 20 mm extending from the outer surface towards the center.

[0015] (5) Embodiment 5 of the present invention is a SiC single crystal according to any one of embodiments 1 to 4, wherein the facet region has through-helic dislocations.

[0016] (6) The method for manufacturing a SiC substrate according to embodiment 1 of the present invention is a method for manufacturing a SiC substrate using a SiC single crystal as described in embodiment 1 or 2, wherein the outer peripheral region is removed by any width from the outer peripheral surface toward the center to form a SiC substrate of any diameter.

[0017] (7) In the SiC single crystal of embodiment 7 of the present invention, the number of through-helical dislocations present in the facet region and the region outside it is greater than the number of through-helical dislocations present closer to the center than the facet region.

[0018] (8) In the SiC epitaxial wafer of embodiment 8 of the present invention, an epitaxial layer is formed on one main surface of a SiC substrate in which the number of through-helical dislocations present in the facet region and the region outside of it is greater than the number of through-helical dislocations present closer to the center than the facet region.

[0019] (9) In the SiC single crystal of Aspect 9 of the present invention, the number of through screw dislocations existing in the facet region is larger than the number of through screw dislocations existing outside the facet region.

[0020] (10) The SiC epitaxial wafer of Aspect 10 of the present invention has an epitaxial layer formed on one main surface of a SiC substrate in which the number of through screw dislocations existing in the facet region is larger than the number of through screw dislocations existing outside the facet region.

[0021] (11) Aspect 11 of the present invention is, in the SiC single crystal of Aspect 7 or 9, the SiC single crystal is an ingot processed into a cylindrical shape.

[0022] (12) Aspect 12 of the present invention is, in the SiC single crystal of Aspect 7 or 9, the SiC single crystal is a substrate.

[0023] (13) The SiC substrate of Aspect 13 of the present invention has polycrystals having 3C or a regular orientation in an edge exclusion region on the outer peripheral side, and contains 4H on the center side rather than the edge exclusion region.

[0024] (14) The SiC epitaxial wafer of Aspect 14 of the present invention has polycrystals having 3C or a regular orientation in an edge exclusion region on the outer peripheral side, and has an epitaxial layer formed on one main surface of a SiC substrate containing 4H on the center side rather than the edge exclusion region.

Advantages of the Invention

[0025] According to one embodiment of the present invention, it is possible to provide a 4H-based SiC single crystal, SiC substrate, epitaxial wafer, and method for manufacturing a SiC substrate that are not converted into the 6H polytype.

Brief Description of the Drawings

[0026] [Figure 1] It is an explanatory diagram in which an end portion in the x direction of a SiC single crystal ingot is enlarged. [Figure 2]This is an explanatory diagram showing the difference in crystal growth between the c-plane facet F and other parts. [Figure 3] This is a schematic cross-sectional view of the SiC single crystal of this embodiment, including the facet region. [Figure 4] This is a schematic cross-sectional view showing the occurrence of through-helical dislocations in the facet region. [Figure 5] This is a schematic cross-sectional view showing the in-plane position of facet regions in a SiC single crystal. [Figure 6] This is a schematic cross-sectional view showing the in-plane position of another embodiment of a facet region in a SiC single crystal. [Figure 7] This is a schematic graph illustrating an example of controlling the growth rate for forming 3C-SiC. [Modes for carrying out the invention]

[0027] Embodiments of the present invention will be described in detail below with reference to the drawings. Note that, for the sake of clarity, the drawings used in the following description may show enlarged versions of key features, and the dimensional ratios of each component may not be the same as those in reality. Furthermore, the materials, dimensions, etc., exemplified in the following description are merely examples, and the present invention is not necessarily limited to them. It can be implemented with appropriate modifications without altering its effects.

[0028] A SiC single crystal relating to one embodiment of the present invention will be described. In one embodiment of the present invention, a SiC single crystal contains cubic 3C-SiC in the faceted region, which includes the c-plane facets, and hexagonal 4H-SiC in the non-faceted region, which is the region outside of this faceted region.

[0029] First, let's explain the c-plane facets and facet regions. Figure 1 is an enlarged diagram illustrating the x-direction end of a SiC single crystal ingot. The SiC single crystal 20 is grown on a seed crystal 10. The crystal planes CS of the seed crystal 10 and the single crystal 20 are inclined in the x-direction with respect to the first plane 10A at an offset angle θ. The crystal growth plane 20A of the SiC single crystal 20 is formed convex in the z-direction. When the crystal growth plane 20A is convex in the z-direction, a portion of the crystal growth plane 20A becomes parallel to the crystal plane CS.

[0030] On this crystal growth surface 20A, the plane parallel to the crystal plane CS is the c-plane facet F, and since these c-plane facets F are parallel to the crystal plane CS, it can be said that the c-plane ((0001) plane) is exposed. Within the single crystal 20, the positions where the c-plane facets are formed can be identified as trajectories 21, and the inner region demarcated by these trajectories 21 is defined as the facet region FE. Furthermore, the area outside of this facet region FE is defined as the non-facet region NF.

[0031] The crystal growth behavior of the c-facet F differs from that of the other parts of the crystal growth surface 20A. Figure 2 is an explanatory diagram illustrating the difference in crystal growth between the c-facet F and the other parts. Figure 2(a) shows crystal growth in the step-flow growth area, and Figure 2(b) shows crystal growth on the c-facet F.

[0032] As shown in Figure 2(a), step flow growth occurs on crystal growth planes 20A other than the c-plane facet F. Step flow growth involves crystal growth in the a-plane direction (<11-20> direction). The SiC single crystal 20 grows in the z-direction as a whole due to crystal growth in the a-plane direction. Step flow growth involves crystal growth that inherits information from the a-plane.

[0033] SiC has many polytypes, such as 3C-SiC, 4H-SiC, 6H-SiC, and 15R-SiC. These polytypes are oriented in the c-plane direction. <0001> There is no difference in the outermost surface structure when viewed from the direction (<11-20>), but the structure when viewed from the a-plane direction (<11-20> direction) is different. Step flow growth is less likely to produce polytypes because the crystal grows in the a-plane direction.

[0034] In contrast, as shown in Figure 2(b), the c-plane facet F has an exposed c-plane. In the c-plane facet F, crystals grow in an island-like manner in the c-plane direction. As mentioned above, the polytype of SiC cannot be distinguished in the c-plane direction, and it is not determined which crystal structure will be formed when the crystal grows in the c-plane direction. Therefore, polytypes are more likely to occur in the c-plane facet F.

[0035] Figure 3 is a schematic cross-sectional view of the SiC single crystal of this embodiment, including the facet region. In this embodiment, the SiC single crystal intentionally generates cubic 3C-SiC in the facet region FE, which includes the c-plane facet F. A polycrystalline region PE is formed in the facet region FE, starting from this 3C-SiC. The presence of 3C-SiC and the polycrystalline region originating from it in the c-plane facet F suppresses the conversion of 4H-SiC to 6H-SiC during subsequent crystal growth.

[0036] Because 3C-SiC has a coefficient of thermal expansion that is about 30% lower than that of 4H-SiC, stress is generated around the 3C-SiC in 4H-SiC that contains 3C-SiC during the cooling process after crystal growth. At temperatures above 1100°C, SiC undergoes plastic deformation, and these stresses are relieved by becoming basal plane dislocations. As a result, stress relaxation proceeds more excessively during the cooling process compared to crystals without 3C-SiC, less stress remains in the 4H-SiC portion, making it possible to obtain a substrate that is less prone to cracking and warping during post-processing.

[0037] Figure 4 is a schematic cross-sectional view showing the occurrence of through-helical dislocations in the facet region. The suppression of conversion to 6H-SiC, as described above, is due to the suppression of polytype formation by the overlap of c-plane facets F and through-spirular dislocations (TSDs) SD. Through-spirular dislocations SD are spiral defects. When you go around a spiral dislocation, the lattice plane either moves up or down by one lattice plane, like a spiral staircase. Steps are observed on the surface near exposed through-spirular dislocations. Crystals grow in a spiral manner near through-spirular dislocations. Spiral growth makes polytype formation less likely because the crystal grows in the a-plane direction.

[0038] Because atomic mismatches occur at the boundaries between different polytypes, through-helical dislocations (SD) also occur around the area where 3C-SiC is generated. Through-helical dislocations (SD) exposed on the c-plane facet F become a persistent step source, forming hills (growth hills) with the helical dislocations as apex. Since the atomic arrangement of 4H-SiC is always present in these steps, crystal growth is possible while maintaining the atomic arrangement of 4H-SiC without conversion to 6H-SiC.

[0039] Figure 5 is a schematic cross-sectional view showing the in-plane position of facet regions in a SiC single crystal. Facet regions FE, including 3C-SiC and through-helic dislocations (SD), can be located at any position within the plane of a SiC single crystal. The in-plane position of facet regions FE can be controlled by adjusting known parameters such as the crystal growth plane shape and off-angle. For example, convex growth shifts the formation position of facet regions FE towards the center of the plane, while flat growth shifts it towards the edges. Similarly, low off-angle growth moves facet regions FE towards the center of the plane, while high off-angle growth shifts them towards the edges.

[0040] Since the conversion to 3C-SiC only occurs within the facet region FE, which includes the c-plane facet F, controlling the in-plane position of the facet region FE to be, for example, closer to the edge makes it possible to cut out a product-ready SiC wafer from the inside of that region, which consists only of 4H-SiC and does not contain 6H-SiC. For this reason, it is preferable to use a seed crystal that is slightly larger than the size of the product wafer.

[0041] Furthermore, as shown in Figure 6, by growing a SiC single crystal with a large diameter and setting the in-plane position of the facet region FE near the center, it is possible to efficiently cut out product SiC wafers by using the areas on both sides as productable regions.

[0042] One method for forming 3C-SiC within the facet region FE is a sublimation method in which a raw material gas obtained by sublimating raw material SiC is recrystallized on the surface of a SiC seed crystal to grow a SiC single crystal. This can be achieved by temporarily performing high-speed growth exceeding 5 mm / h, as shown in the schematic graph in Figure 7, while performing low-speed growth of 5 mm / h or less for the majority of the rest.

[0043] By rapidly increasing the temperature, 3C-SiC can be generated within the faceted region. Subsequently, by lowering the temperature to achieve a stable growth rate, stable growth of 4H-SiC becomes possible in the non-faceted region. When growing long SiC single crystals, the position of the faceted region may change, or through-helix dislocations may coalesce and disappear. Therefore, it is preferable to generate 3C-SiC by rapidly increasing the temperature multiple times during the growth of the SiC single crystal.

[0044] Furthermore, methods for forming 3C-SiC within these facet regions FE include rapidly changing the pressure or pre-embedding 3C-SiC in the SiC seed crystal.

[0045] As described above, the SiC single crystal of this embodiment contains cubic 3C-SiC in the faceted region, which includes the c-plane facets. This generates through-helic dislocations around the 3C-SiC, and these through-helic dislocations act as step sources, ensuring the constant presence of 4H-SiC atomic arrangements and preventing conversion to 6H-SiC. Therefore, the non-faceted region outside the faceted region can be composed of 4H-SiC, and by cutting a product SiC wafer from this non-faceted region, a high-quality product SiC wafer composed solely of 4H-SiC and free of 6H-SiC can be obtained.

[0046] The SiC single crystal in this embodiment may be any as-grown SiC single crystal ingot that has not undergone any shape processing after crystal growth. Alternatively, it may be a cylindrical ingot obtained by removing a predetermined width from the outer periphery of such an as-grown SiC single crystal ingot. By processing a SiC single crystal into, for example, a cylindrical shape with a nearly constant diameter, the number of facet regions FE containing 3C-SiC and through-helic dislocations can be reduced.

[0047] In the case of a cylindrical ingot from which the outer region has been removed by a predetermined width, for example, by controlling the growth conditions so that the facet region FE forms within a 20 mm wide region extending from the outer surface towards the center, and then removing the 20 mm wide outer region, a SiC single crystal ingot composed solely of 4H-SiC can be obtained, which is free from the facet region FE containing 3C-SiC and through-helic dislocations.

[0048] Because the presence of through-helical dislocations suppresses the conversion from 4H-SiC to 6H-SiC, in another embodiment of the present invention, the SiC single crystal has more through-helical dislocations in the facet region and the region outside of it than in the number of through-helical dislocations located closer to the center than the facet region.

[0049] In this way, by increasing the number of through-helical dislocations in the outer region where the facet region exists compared to the central region, the central part of the SiC single crystal can be composed solely of 4H-SiC, resulting in a region with fewer through-helical dislocations.

[0050] Furthermore, by controlling the number of through-helical dislocations and removing the outer periphery region of the ingot after crystal growth of a SiC single crystal, it is possible to obtain a high-quality SiC single crystal ingot composed solely of 4H-SiC with a low number of through-helical dislocations. Additionally, by slicing such a SiC single crystal ingot, a high-quality SiC substrate can be obtained.

[0051] Another SiC substrate of the present invention is a SiC substrate having 3C-SiC or polycrystalline material with a regular orientation in the edge exclusion region on the outer periphery, and containing 4H-SiC closer to the center than this edge exclusion region.

[0052] When evaluating the crystal structure of a SiC substrate after polishing, the area around the periphery of the substrate that is excluded from consideration is the edge exclusion region. This is because the polishing speed fluctuates significantly in this area, and therefore it is excluded from the crystal evaluation. The width of the edge exclusion region is usually about 2 mm to 3 mm from the periphery.

[0053] If the presence of 3C-SiC or polycrystals with regular orientation is excluded up to the edge exclusion region, the removal width of the outer peripheral region of the substrate becomes large, making it difficult to obtain a large-diameter SiC substrate. However, as in this embodiment, by allowing the presence of 3C-SiC or polycrystals with regular orientation in the edge exclusion region, 4H-SiC is easily obtained in the device formation region inside the edge exclusion region, and a large-diameter SiC substrate can be easily obtained.

[0054] Alternatively, the configuration may involve forming an epitaxial layer on one main surface of a SiC substrate having the SiC single crystal structure described above. By forming an epitaxial layer on a SiC substrate having the SiC single crystal structure described above by epitaxial growth, the epitaxial wafer of this embodiment can be obtained.

[0055] Although one embodiment of the present invention has been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be carried out in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

Claims

1. A SiC single crystal containing 3C in the faceted region and 4H in the non-faceted region.

2. The SiC single crystal according to claim 1, wherein the SiC single crystal is an ingot after crystal growth.

3. The SiC single crystal according to claim 1, wherein the SiC single crystal is an ingot processed into a cylindrical shape.

4. The SiC single crystal according to claim 2, wherein the facet region is located within a region with a width of 20 mm extending from the outer surface towards the center.

5. The SiC single crystal according to any one of claims 1 to 4, wherein the facet region has through-helic dislocations.

6. A method for manufacturing a SiC substrate using a SiC single crystal according to claim 1 or 2, A method for manufacturing a SiC substrate, comprising removing an outer region of any width from the outer surface toward the center to form a SiC substrate of any diameter.

7. A SiC single crystal in which the number of through-helical dislocations in the facet region and the region outside of it is greater than the number of through-helical dislocations located closer to the center than the facet region.

8. A SiC epitaxial wafer in which an epitaxial layer is formed on one main surface of a SiC substrate in which the number of through-helical dislocations present in the facet region and the region outside of it is greater than the number of through-helical dislocations present closer to the center than the facet region.

9. A SiC single crystal in which the number of through-helical dislocations in the facet region is greater than the number of through-helical dislocations outside the facet region.

10. A SiC epitaxial wafer in which an epitaxial layer is formed on one main surface of a SiC substrate where the number of through-helical dislocations in the facet region is greater than the number of through-helical dislocations outside the facet region.

11. The SiC single crystal according to claim 7 or 9, wherein the SiC single crystal is an ingot processed into a cylindrical shape.

12. The SiC single crystal is a substrate, according to claim 7 or 9.

13. A SiC substrate having polycrystalline material with 3C or regular orientation in the edge exclusion region on the outer periphery, and containing 4H on the central side of the edge exclusion region.

14. A SiC epitaxial wafer having polycrystalline material with 3C or regular orientation in the outer edge exclusion region, and an epitaxial layer formed on one main surface of a SiC substrate containing 4H on the central side of the edge exclusion region.

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