SiC crystal with facet only at edge, wafer thereof and semiconductor device

Abstract

The invention provides a SiC crystal with facets only at edges, a wafer thereof and a semiconductor device, and relates to the technical field of silicon carbide wafers. The SiC crystal is obtained through direct growth by adopting a PVT method and is not subjected to subsequent processing, and the SiC crystal contains a facet area and a non-facet area; the facet region is located on the outer circumferential end face of the SiC crystal, and the properties of the facet region in the whole area range meet any one or two of the following items a-b: a, the doping concentration change rate of the facet region is more than 1.5 times of the doping concentration change rate of the non-facet region; and b, the carrier concentration change rate of the facet region is more than five times the carrier concentration change rate of the non-facet region. The production cost of the silicon carbide crystals is reduced, and meanwhile, the silicon carbide crystals with few defects and high uniformity are obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon carbide wafers, and in particular to a SiC crystal having small faces only at its edge, a wafer thereof and a semiconductor device. Background Art

[0002] At present, the large-scale application of silicon carbide crystal industry faces two main problems: 1. Quality problems, which affect the yield, performance and reliability of silicon carbide devices; 2. Cost problems, which affect the application of silicon carbide in the terminal. Among them, the loss of material and device yield caused by material quality is also the main reason for the high cost and difficulty in application of silicon carbide.

[0003] There are two types of quality problems in silicon carbide: one is explicit quality problems such as material quality and yield caused by defect problems; the other is reliability problems such as material yield and device performance caused by consistency problems. Among them, small faces are an inherent property of SiC crystals prepared by the sublimation method. Such small faces exist on SiC crystals and wafers prepared by conventional physical vapor transport (PVT). The small face area has a higher doping concentration than other areas. Therefore, the carrier concentration and resistivity of the small face area are significantly different from those of other areas, resulting in abnormal quality problems in the electrical properties and defect states of the small face area.

[0004] Among them, the small facet is commonly known in the art as “growth characteristic facet”, “growth small facet”, “characteristic growth facet”, etc., and the corresponding English word is “facet”. In the present invention, the small facet does not refer to the growth interface.

[0005] Improving quality and reducing costs are the goals of the sustainable development of silicon carbide crystal materials. Especially at the stage where the silicon carbide industry is rapidly entering large-scale production and application, the stability, consistency and reliability of the performance of silicon carbide materials will play a vital role in the development of the industry. The present invention aims to solve the problems of uneven quality and abnormal quality of silicon carbide caused by the inherent small facets during the growth of silicon carbide crystals. Summary of the invention

[0006] The inventors have found that when preparing SiC crystals by physical vapor transport, a {0001} facet will appear at different positions in the silicon carbide crystal depending on the angle of the seed crystal used along the <11-20> direction. Usually, when using an on-axis seed crystal to grow a silicon carbide crystal, the {0001} facet will appear at the center of the silicon carbide crystal; when the off-cut angle (off-cut) of the seed crystal along the <11-20> direction increases, the position of the {0001} facet will appear at the edge of the silicon carbide crystal and gradually migrate toward the center as the silicon carbide crystal grows. Since the doping concentration at the facet is higher than that in other areas, the transmittance at the facet is low, the resistivity distribution is uneven, and the carrier concentration change rate is uneven, which may lead to the generation of defects such as dislocations and stacking faults in this area, and may also cause quality problems such as stacking fault expansion that seriously threaten the reliability of the device during subsequent use. Reference Figure 1 As shown, the position and shape of the small facet on the silicon carbide wafer can be directly observed from the appearance, and black spots similar to "birthmarks" visible to the naked eye can be directly observed in the silicon carbide wafer containing the small facet.

[0007] In order to solve the above problems, the first aspect of the present invention provides a SiC crystal having only small faces at the edge, wherein the SiC crystal is directly grown by a PVT method without subsequent processing, and the SiC crystal contains a small face region and a non-small face region; the small face region is located on the outer circumferential end face of the SiC crystal, and the properties within the full area of ​​the small face region satisfy any one or two of the following a to b:

[0008] a. The doping concentration change rate of the facet area is more than 1.5 times that of the non-facet area;

[0009] b. The carrier concentration change rate in the small face area is more than 5 times that in the non-small face area.

[0010] A second aspect of the present invention provides a SiC wafer, which is obtained by cutting the SiC crystal having only small faces at the edge by removing the small face area, and the SiC wafer does not contain any one or more of the small faces, high doping areas and defect aggregation areas within the entire area.

[0011] A third aspect of the present invention provides a semiconductor device, wherein the semiconductor device comprises the above-mentioned SiC wafer.

[0012] Compared with the prior art, the present invention achieves at least one of the following beneficial effects:

[0013] (1) In the present invention, the SiC crystal with only small faces at the edge directly fixes the small face region on the outer circumferential end face of the SiC crystal during the PVT growth process, and removes the small face region during the subsequent processing of the crystal, thereby achieving a low cutting loss rate, without the small face region on the entire crystal and the wafer processed therefrom, reducing the production cost of the silicon carbide crystal, while ensuring that the silicon carbide crystal with few defects and high uniformity is obtained.

[0014] (2) The silicon carbide wafer of the present invention has a high degree of uniformity, for example, doping uniformity, carrier uniformity, etc. In addition, the silicon carbide wafer of the present invention has no facets visible to the naked eye.

[0015] (3) The silicon carbide wafer of the present invention has higher yield, performance and reliability at the device end. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0017] Figure 1 An exemplary embodiment of a schematic diagram of a silicon carbide wafer structure containing facets visible to the naked eye is shown;

[0018] Figure 2 An exemplary embodiment of a schematic diagram of a facet growth process of the present invention is shown;

[0019] Figure 3 An exemplary embodiment of a schematic diagram of a silicon carbide crystal growth structure of the present invention is shown;

[0020] Figure 4 An exemplary embodiment of a schematic diagram of a facetless silicon carbide wafer structure is shown. DETAILED DESCRIPTION

[0021] In order to more clearly illustrate the overall concept of the present invention, a detailed description is given below in an exemplary manner in conjunction with the accompanying drawings.

[0022] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and therefore, the scope of protection of the present invention is not limited by the specific embodiments disclosed below. In the description of this specification, the description of reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily have to be directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0023] In an exemplary embodiment of the present invention, a SiC crystal having only facets at the edge is directly grown by a PVT method without subsequent processing, and the SiC crystal contains a facet region and a non-facet region; the facet region is located at the outer circumferential end face of the SiC crystal, and the properties within the full area of ​​the facet region satisfy any one or two of the following a to b:

[0024] a. The doping concentration change rate of the facet area is more than 1.5 times that of the non-facet area;

[0025] b. The carrier concentration change rate in the small face area is more than 5 times that in the non-small face area.

[0026] The outer circumferential end face refers to the edge position of the lateral growth of the crystal, or is called the edge position of the crystal.

[0027] Optionally, the distance between the edge of the small face region away from the outer circumferential end face and the outer circumferential end face does not exceed 3% of the diameter of the SiC crystal. Preferably, the distance between the edge of the small face region away from the outer circumferential end face and the outer circumferential end face does not exceed 2% of the diameter of the SiC crystal. The edge of the small face region away from the outer circumferential end face refers to an end of the small face region close to the center of the silicon carbide crystal.

[0028] Optionally, the maximum cross-sectional area of ​​the facet region accounts for less than 10% of the cross-sectional area of ​​the crystal along the diameter direction;

[0029] And / or the volume of the facet region accounts for less than 2% of the volume of the entire crystal. For example, the facet region may be located at the edge of an upper or lower oblique corner of the crystal.

[0030] Optionally, the maximum cross-sectional area of ​​the facet region accounts for less than 5% of the cross-sectional area of ​​the crystal along the diameter direction;

[0031] The volume of the facet region accounts for less than 0.6% of the total crystal volume. The overall shape of the facet region can be triangular, conical, spherical, ellipsoidal or rhombus. The cross section of the facet region along the diameter direction can be elliptical, crescent-shaped or circular, etc., however, the present invention is not limited thereto.

[0032] Optionally, the TDV of the small facet area is more than 6 times the TDV of the non-small facet area; or the TDV of the small facet area is more than 10 times the TDV of the non-small facet area.

[0033] Optionally, the doping concentration change rate of the small face area is more than 5 times that of the non-small face area; and / or the carrier concentration change rate of the small face area is more than 10 times that of the non-small face area.

[0034] In the present invention, in a SiC crystal with only small faces at the edge, the small face region is directly fixed at the edge of the crystal during the PVT growth process, thereby reducing the subsequent cutting loss rate of the silicon carbide crystal and reducing the production cost.

[0035] In another exemplary embodiment of the present invention, a SiC wafer is obtained by cutting the SiC crystal having only small faces at the edge by removing the small face area, and the entire area of ​​the SiC wafer does not contain any one or more of the small faces, high doping areas and defect aggregation areas.

[0036] Among them, the high-doped area refers to the black spots similar to "birthmarks" visible to the naked eye in the silicon carbide wafer, where the doping concentration is greater than the doping concentration in the non-small face area; the defect aggregation area refers to the black spots similar to "birthmarks" visible to the naked eye in the silicon carbide wafer, where the defect density is greater than the defect density in the non-small face area.

[0037] Optionally, the SiC wafer has an in-plane doping concentration variation rate of less than 10%; and / or an in-plane carrier concentration variation rate of less than 5%.

[0038] Preferably, the SiC wafer has an in-plane doping concentration variation rate of less than 8%; and / or an in-plane carrier concentration variation rate of less than 3%.

[0039] Optionally, the SiC wafer TDV density is less than 100 cm -2 Preferably, the TDV density of the silicon carbide wafer is less than 10 cm -2 .

[0040] The total density variation (TDV) is defined as: a number of squares with a specific area are divided in the wafer, such as n squares with an area of ​​1mmx1mm, 2mmx2mm, 5mmx5mm, and 10mmx10mm, and the edge dislocation (TED) or screw dislocation (TSD) density in the square is d1, d2, d3...dn. TDV is the difference between the maximum TED / TSD density and the minimum TED / TSD density dmax-dmin. Due to the elimination of small faces, TDV is improved, eliminating the problem of low overall defect density and high local density.

[0041] Optionally, the SiC wafer is a silicon carbide wafer of any thickness, for example, the thickness of the SiC wafer is not less than 200 μm; or the thickness of the silicon carbide wafer is not less than 300 μm; or the thickness of the silicon carbide wafer is not less than 400 μm.

[0042] Optionally, the SiC wafer can be N2-doped or co-doped with any other element. Specifically, nitrogen can be co-doped with any one or more of P, As, Ge, Sn, B, and Al, and the prepared silicon carbide wafer is conductive.

[0043] Optionally, the wafer size may be 4 inches, 6 inches, 8 inches, 10 inches or 12 inches.

[0044] Optionally, the total density variation of the silicon carbide wafer basal plane dislocation (BPD) is less than 50 cm -2 Preferably, the total BPD density variation of the silicon carbide wafer is less than 20 cm -2 More preferably, the total BPD density of the silicon carbide wafer varies by less than 10 cm -2 Among them, the total BPD density change is "the maximum BPD density within the silicon carbide wafer surface - the minimum BPD density within the silicon carbide wafer surface".

[0045] Specifically, the processing method of the SiC crystal with only small faces at the edge includes the following steps:

[0046] S1: A discontinuous temperature gradient distribution is set in the radial direction of the crystal growth surface. A positive temperature gradient much larger than that in other areas is set within 5 mm from the crystal growth edge. The temperature gradient value is ≥5°C / cm, so as to ensure that the crystal edge has sufficient lateral growth driving force and the continuous diameter expansion growth ability of the crystal edge.

[0047] S2: Use a seed crystal with an off-angle of >0° along <11-20> or <1-100> or any other crystal direction parallel to the c-plane direction.

[0048] S3: The angle α of the crystal growth graphite ring parallel to the crystal growth direction is greater than 0°, thereby ensuring that the radial growth caused by the lateral growth of the crystal has sufficient expansion space.

[0049] S4: Recombined silicon carbide powder is arranged between the inner wall of the crystal growth chamber and the crystal growth graphite ring, so as to ensure that the SiC crystal has a recombined reaction atmosphere for lateral growth and a chemical environment for continuous lateral growth of the SiC crystal. Figure 3 As shown, by arranging a graphite support component on the upper part of the SiC crucible, SiC powder is loaded between the graphite support component and the wall of the SiC crucible as a source of material for lateral growth, thereby ensuring that the radial growth caused by the lateral growth of the crystal has sufficient diameter expansion space. However, the present invention is not limited to this, and other design methods can also be used.

[0050] Through the above scheme, the positive temperature gradient at the edge of the SiC crystal drives the SiC crystal to continue to grow laterally, and ensures that its growth rate is greater than the rate at which the small face moves toward the center of the crystal due to the temperature gradient in the center of the crystal, so that the small face grows and is fixed in the edge area of ​​the crystal. Figure 2 When the crystal and wafer are processed to the standard diameter, the small face can be completely removed, and a high-quality silicon carbide wafer without small face area can be obtained with a low cutting loss rate. Figure 4 As shown. This scheme can ensure a small radial temperature gradient and stress in the central area during crystal growth, thereby effectively controlling the generation of stress and defects in the crystal. At the same time, by designing the edge temperature gradient and the lateral growth mode of the crystal, the small face is driven to move to the outer area of ​​the crystal target diameter, which not only ensures the overall stress and defect control of the crystal, but also achieves the purpose of eliminating the small face. The final silicon carbide wafer has a high degree of uniformity, for example, doping uniformity, carrier uniformity, etc.

[0051] Examples 1-7

[0052] According to the processing method in Table 1, the processing method of the SiC crystal with only small faces at the edge of Examples 1-7 includes the following steps:

[0053] S1: A discontinuous temperature gradient distribution is set in the radial direction of the crystal growth surface. A positive temperature gradient much larger than that in other areas is set within 5 mm from the crystal growth edge. The temperature gradient value is ≥5°C / cm, so as to ensure that the crystal edge has sufficient lateral growth driving force and the continuous diameter expansion growth ability of the crystal edge.

[0054] S2: Use a seed crystal with a deviation angle of >0° along the <11-20> crystal direction.

[0055] S3: The angle α of the crystal growth graphite ring parallel to the crystal growth direction is greater than 0°, ensuring that the radial growth caused by the lateral growth of the crystal has sufficient expansion space.

[0056] S4: Recombined silicon carbide powder is placed between the inner wall of the crystal growth chamber and the crystal growth graphite ring to ensure that the SiC crystal has a recombined reaction atmosphere for lateral growth and a chemical environment for continuous lateral growth of the SiC crystal. This method will also be applicable to the production of 10-inch and 12-inch silicon carbide wafers in the future.

[0057] Comparative Example 1

[0058] Based on Example 2, the main difference is that the conventional continuous positive radial temperature distribution design is adopted in step S1.

[0059] Comparative Example 2

[0060] Based on Example 2, the difference is that a positive temperature gradient smaller than that in other areas is set within 5 mm from the crystal growth edge, and the temperature gradient value is ≥5°C / cm.

[0061] Specifically, the processing parameters of Examples 1-7 are shown in Table 1.

[0062] Table 1 Processing method parameters

[0063]

[0064] Experimental example

[0065] The SiC crystal prepared by the above method has only small faces at the edge, and the position test of the small face region in the crystal is shown in Table 2. Among them, the volume of the small face region can be calculated by calculus or modeling.

[0066] Table 2 Position test table of small facet area in crystal

[0067]

[0068] As shown in Table 2, it can be seen that in the present application, the SiC crystal with only small faces at the edge directly controls the small face area to be away from the outer circumferential end face of the crystal during the PVT production process, and drives the small face to move to the outer area of ​​the crystal target diameter. In the subsequent crystal processing process, the small face area can be removed at a lower cutting loss rate, thereby obtaining a SiC crystal with fewer defects. In Comparative Examples 1 and 2, the small face area is in the middle position, which is within the range of the crystal target diameter, resulting in a lower yield, performance and reliability of the device end obtained by subsequent processing.

[0069] The SiC crystals obtained in Examples 1-7 with only small faces at the edges were processed, and the small face areas were removed and cut to obtain SiC wafers. Comparative Examples 1 and 2 were cut to form silicon carbide wafers. The performance test of the SiC wafers is shown in Reference Table 3.

[0070] Among them, the doping concentration change rate is "the maximum value of the in-plane doping concentration - the minimum value of the in-plane doping concentration"; the carrier concentration change rate is "the maximum value of the in-plane carrier concentration - the minimum value of the in-plane carrier concentration".

[0071] Table 3 Performance test table

[0072]

[0073] As shown in Table 3, it can be seen that the silicon carbide wafer obtained in the present application has a high degree of uniformity, for example, doping uniformity, carrier uniformity, etc. In addition, the silicon carbide wafer of the present invention has no small facets visible to the naked eye.

[0074] On the basis of Examples 1-3, the SiC crystals prepared in Examples 1-3 with only small faces at the edges were directly cut to obtain silicon carbide wafers containing small faces, and the performance of the obtained silicon carbide wafers was tested, as shown in Table 4.

[0075] Table 4 Test table of silicon carbide wafers with small faces

[0076]

[0077]

[0078] Referring to Table 4, it can be seen that the doping concentration change rate of the small face area is more than 1.5 times that of the non-small face area; the carrier concentration change rate of the small face area is more than 4 times that of the non-small face area; the TDV of the small face area is more than 6 times that of the non-small face area.

[0079] In summary, in the present invention, the SiC crystal with only small faces at the edge is directly grown by the PVT method without subsequent processing, the small face area is fixed on the outer circumferential end face of the SiC crystal, and the small face area is removed during the subsequent processing of the crystal, so as to achieve a low cutting loss rate without the small face area on the entire crystal and the wafer processed therefrom, thereby reducing the production cost of the silicon carbide crystal and ensuring that the silicon carbide crystal with few defects and high uniformity is obtained.

[0080] The above description is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A SiC crystal having facets only at the edge, characterized in that: The SiC crystal is directly grown by the PVT method without subsequent processing, and the SiC crystal contains a small face region and a non-small face region; the small face region is located on the outer circumferential end face of the SiC crystal, and the properties within the full area of ​​the small face region satisfy any one or two of the following a-b: a. The doping concentration change rate of the facet area is more than 1.5 times that of the non-facet area; b. The carrier concentration change rate in the small face area is more than 5 times that in the non-small face area.

2. The SiC crystal according to claim 1, characterized in that: The distance between the edge of the small face region away from the outer circumferential end face and the outer circumferential end face does not exceed 3% of the diameter of the SiC crystal.

3. The SiC crystal according to claim 1, characterized in that: The maximum cross-sectional area of ​​the facet region accounts for less than 10% of the cross-sectional area of ​​the crystal along the diameter direction; and / or the volume of the small face region accounts for less than 2% of the total crystal volume.

4. The SiC crystal according to claim 3, characterized in that: The maximum cross-sectional area of ​​the facet region accounts for less than 5% of the cross-sectional area of ​​the crystal along the diameter direction; and / or the volume of the small face region accounts for less than 0.6% of the total crystal volume.

5. The SiC crystal according to claim 1, characterized in that: The TDV of the facet area is more than 6 times that of the non-facet area.

6. The SiC crystal according to claim 5, characterized in that: The TDV of the facet area is more than 10 times that of the non-facet area.

7. The SiC crystal according to claim 1, characterized in that: The rate of change of doping concentration in the facet region is more than 5 times that of the non-facet region; And / or the carrier concentration change rate of the small face area is more than 10 times the carrier concentration change rate of the non-small face area.

8. A SiC wafer, characterized in that: The SiC wafer is obtained by cutting the SiC crystal having only small faces at the edge according to any one of claims 1 to 7 above by removing the small face area. The SiC wafer does not contain any one or more of a small facet, a high-doping area and a defect aggregation area within the entire area.

9. The SiC wafer according to claim 8, characterized in that The SiC wafer in-plane doping concentration variation rate is less than 10%; And / or the in-plane carrier concentration change rate is less than 5%.

10. A semiconductor device, characterized in that: The semiconductor device comprises the SiC wafer according to claim 8 or 9.

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