A method for fabricating a silicon carbide substrate using a biased seed growth

Abstract

The present invention provides a method for fabricating a silicon carbide substrate using a biased seed crystal growth, belonging to the technical field of silicon carbide crystal growth. The method for fabricating a silicon carbide substrate using a biased seed crystal growth includes the following steps: S10: Use a seed crystal with an included angle greater than 4° as a splicing seed crystal. Take two cutting points on the outer edge of the splicing seed crystal, and use the line connecting the two cutting points as a cutting track. Cut the splicing seed crystal along the cutting track, and take the smaller part after cutting as the splicing part; S20: Take a seed crystal with an included angle of 4° as the seed crystal to be spliced, and splice the splicing part on the outer periphery of the seed crystal to be spliced as a growth seed crystal; S30: Place the growth seed crystal in a growth device for growth until an ingot grows in the axial direction of the growth seed crystal; S40: Perform a rounding process on the ingot until the facets are rolled off and it becomes cylindrical, and cut the cylindrical ingot into wafers for use as a silicon carbide substrate.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon carbide crystal growth, and particularly relates to a method for fabricating a silicon carbide substrate using a biased seed crystal growth method. Background Art

[0002] Silicon carbide single crystal substrate materials belong to wide bandgap semiconductor materials, which have advantages such as high voltage resistance, high temperature resistance, high frequency, and low loss. They are the basic materials for fabricating high-power power electronic devices. To reduce the on-resistance of silicon carbide-based power devices, the substrate material needs to have good electrical conductivity, that is, a low resistivity. The way to obtain a substrate with a low resistivity is to dope nitrogen impurities during the crystal growth process in the physical vapor transport method. At the same time, in order to maintain the crystal form of the silicon carbide homoepitaxial layer, a step-flow growth mechanism needs to be introduced, and an off-axis substrate (that is, the c-axis of the substrate is offset by 4° in the <11-20> direction relative to the normal direction of the substrate surface) is used. There are two preparation methods for the off-axis substrate:

[0003] (1) Single crystal growth is carried out using a positive seed crystal, and the surface orientation angle of the substrate is adjusted to 4° during the flat grinding or cutting process of the end face of the ingot. Due to the orientation difference between the c-axis of the substrate and the ingot, this method will cause a large waste of the single crystal thickness, and as the diameter of the single crystal increases, the wasted thickness increases;

[0004] (2) Single crystal growth is carried out using a seed crystal with a surface orientation angle of 4°, which can avoid the waste of the single crystal thickness.

[0005] When preparing a 4° off-axis substrate by the above two methods, facets will be formed on the growth surface during single crystal growth. The platform width of the growth steps in the facet region is greater than that in other regions. During the single crystal growth process, the migration distance of nitrogen impurities adsorbed on the growth interface is greater than that of carbon-containing growth components. Since nitrogen impurities generally occupy the carbon lattice positions, this results in a high nitrogen doping efficiency in the region with a larger growth step platform width, causing a large difference in resistivity between the facet region and other regions. The resistivity uniformity of the substrate has a great negative impact on the performance consistency of subsequent power devices prepared based on the substrate. Summary of the Invention

[0006] An embodiment of the present invention provides a method for fabricating a silicon carbide substrate using a biased seed crystal growth method, aiming to solve the technical problem that the current method for fabricating an off-axis substrate will cause a large difference in resistivity between the facet region and other regions, and the poor resistivity uniformity has a great negative impact on the performance consistency of subsequent power devices.

[0007] To achieve the above object, the technical solution adopted by the present invention is: to provide a method for fabricating a silicon carbide substrate using a biased seed crystal growth method, including:

[0008] S10: Use a seed crystal with an included angle greater than 4° as the splicing seed crystal. Take two cutting points on the outer edge of the splicing seed crystal, and use the line connecting the two cutting points as the cutting trajectory. The cutting trajectory does not pass through the center of the splicing seed crystal. Cut the splicing seed crystal along the cutting trajectory to separate a part of the outer peripheral surface of the splicing seed crystal, and take the smaller part after cutting as the splicing portion.

[0009] S20: Take a seed crystal with an included angle of 4° as the seed crystal to be spliced, and splice the splicing portion on the outer periphery of the seed crystal to be spliced as the growth seed crystal.

[0010] S30: Place the growth seed crystal in a growth device for growth until an ingot grows along the axial direction of the growth seed crystal, and a facet grows on the ingot at the position of the splicing portion.

[0011] S40: Perform a rounding process on the ingot until the facet is rolled off and the ingot becomes cylindrical. After cutting the cylindrical ingot into wafers, use it as a silicon carbide substrate.

[0012] In a possible implementation, the cutting trajectory is a straight line and parallel to the radial direction of the splicing seed crystal.

[0013] In a possible implementation, the specific steps for splicing the splicing portion on the outer periphery of the seed crystal to be spliced are as follows:

[0014] Cut the outer periphery of the seed crystal to be spliced to form a splicing surface equal to the surface corresponding to the cutting trajectory of the splicing portion.

[0015] Splice the splicing portion on the splicing surface, and the outer peripheral surface of the splicing portion is continuous and tangent to the outer peripheral surface of the seed crystal to be spliced.

[0016] In a possible implementation, the splicing portion is cut using a wire saw.

[0017] In a possible implementation, the cutting trajectory is an arc, and the surface of the splicing portion corresponding to the cutting trajectory fits the outer peripheral surface of the seed crystal to be spliced.

[0018] In a possible implementation, after cutting the splicing portion, it is rounded using a diamond grinding wheel to make the surface of the splicing portion corresponding to the cutting trajectory consistent with the outer peripheral surface of the seed crystal to be spliced.

[0019] In a possible implementation, the splicing portion is cut using a laser.

[0020] In a possible implementation, the ingot is rounded by means of eccentric rolling.

[0021] In a possible implementation, the convexity of the ingot is 3 - 7 mm.

[0022] In a possible implementation, the larger the deflection angle of the spliced seed crystal, the smaller the width of the splicing part.

[0023] Compared with the prior art, the solution shown in the embodiments of the present application uses a seed crystal with a deflection angle greater than 4°. As the angle between the C-axis and the normal vector of the seed crystal surface increases, the position of the facet will be closer to the edge and the moving speed towards the center of the seed crystal will slow down under the same growth interface condition. Therefore, during the later rounding process of the ingot, the facet can be completely removed, so that the obtained wafer does not contain a facet, the resistivity distribution of the wafer is relatively uniform, and the performance consistency of the manufactured device is better. Description of the Drawings

[0024] Figure 1 It is a three-dimensional structure schematic diagram of a silicon carbide structure;

[0025] Figure 2 It is a cross-sectional schematic diagram of a growth seed crystal adopted in an embodiment of the present invention;

[0026] Figure 3 It is a cross-sectional schematic diagram of a growth seed crystal adopted in another embodiment of the present invention;

[0027] Figure 4 It is a process diagram of traditional seed crystal growth;

[0028] Figure 5 It is a schematic flow chart of a method for manufacturing a silicon carbide substrate by using a biased seed crystal growth provided by an embodiment of the present invention.

[0029] Description of the Reference Numerals:

[0030] 10 - splicing part; 11 - cutting track;

[0031] 20 - spliced seed crystal;

[0032] 30 - ingot;

[0033] 40 - wafer;

[0034] 50 - facet;

[0035] 60 - growth seed crystal. Detailed Embodiments

[0036] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] In the claims, the description and the above-mentioned drawings of the present invention, unless otherwise clearly defined, when using the terms "fixed connection" or "fixedly connected", it should be understood in a broad sense, that is, any connection method without displacement relationship and relative rotation relationship between the two, that is, including non-detachable fixed connection, detachable fixed connection, being integrated as a whole, and being fixedly connected through other devices or elements.

[0038] In the claims, the description and the above-mentioned drawings of the present invention, when using the terms "comprising", "having" and their variants, are intended to mean "including but not limited to".

[0039] See Figure 1 , for the description of common terms in the silicon carbide structure, where:

[0040] The C-axis is the axis perpendicular to the crystal plane {0001};

[0041] The main edge of the seed crystal is the edge within the {1-100} plane and parallel to the <11-20> direction;

[0042] The secondary edge of the seed crystal is the edge within the {11-20} plane and parallel to the <1-100> direction. When the silicon surface of the silicon carbide substrate faces upward, the secondary edge is on the left side of the main edge and forms a 90° angle with the main edge;

[0043] The main opposite of the seed crystal is the directly opposite side of the main edge of the seed crystal;

[0044] The secondary opposite of the seed crystal is the directly opposite side of the secondary edge of the seed crystal, and the secondary opposite area of the seed crystal is the area where the facet 50 is formed;

[0045] The silicon carbide substrate with a 4° deviation, that is, the normal direction of the substrate surface deviates towards <11-20> and the angle with <0001> is 4°. The meaning of a larger deviation angle is the same as that here.

[0046] Among them, {} represents a plane and <> represents a direction.

[0047] Please refer to Figures 2 to 4 together, and now a method for manufacturing a silicon carbide substrate using a biased seed crystal growth provided by the present invention will be described.

[0048] The method for manufacturing a silicon carbide substrate using a biased seed crystal growth includes the following steps:

[0049] S10: Use a seed crystal with a deviation angle greater than 4° as a splicing seed crystal. Take two cutting points on the outer edge of the splicing seed crystal, and use the connection line of the two cutting points as the cutting track 11. The cutting track 11 does not pass through the center of the splicing seed crystal. Cut the splicing seed crystal along the cutting track 11 to separate a part of the outer peripheral surface of the splicing seed crystal, and take the smaller part after cutting as the splicing part 10;

[0050] S20: Take a seed crystal with a tilt angle of 4° as the seed crystal 20 to be spliced, and splice the splicing part 10 around the seed crystal 20 to be spliced as the growing seed crystal 60;

[0051] S30: Place the growing seed crystal 60 in a growth device for growth until an ingot 30 grows along the axial direction of the growing seed crystal 60, and a facet 50 grows on the ingot 30 at the splicing part 10;

[0052] S40: Round the ingot 30 until the facet 50 is rolled off and becomes cylindrical, and cut the cylindrical ingot 30 into wafers 40 for use as a silicon carbide substrate.

[0053] It should be noted that one or more splicing parts 10 can be cut from one splicing seed crystal.

[0054] In the traditional process of growing silicon carbide single crystals, a certain radial temperature gradient is required to achieve a convex growth interface. Since the seed crystal usually has a flat surface, during the single crystal growth process (especially in the initial stage of single crystal growth), there is a process in which the growth interface gradually becomes convex. The facet 50 is usually formed at the position where the normal vector of the growth interface surface is parallel to the C-axis. Therefore, during the single crystal growth process, the facet 50 will gradually move from the edge to the center of the single crystal.

[0055] Compared with the prior art, in the method for growing a silicon carbide substrate using a tilted seed crystal provided in this embodiment, since a seed crystal with a tilt angle greater than 4° is used, the angle between the C-axis and the normal vector of the seed crystal surface increases. Under the same growth interface conditions, the position of the facet 50 will be closer to the edge and the speed of moving towards the center of the seed crystal will slow down. Therefore, during the subsequent rounding process of the ingot 30, the facet 50 can be completely removed, so that the obtained wafer 40 does not contain the facet 50. The resistivity distribution of the wafer 40 is relatively uniform, and the performance consistency of the fabricated devices is better.

[0056] The two specific implementation manners of the above cutting trajectory 11 are as follows:

[0057] (1) Refer to Figure 2 , the cutting trajectory 11 is a straight line and parallel to the radial direction of the splicing seed crystal. The spliced part 10 formed by cutting is close to a semi-ellipse. For the spliced part 10 obtained by using this step, the outer periphery of the seed crystal 20 to be spliced needs to be cut to form a splicing surface equal to the surface corresponding to the cutting trajectory 11 of the spliced part 10, and then the spliced part 10 is spliced on the splicing surface. The outer peripheral surface of the spliced part 10 is continuous and tangent to the outer peripheral surface of the seed crystal 20 to be spliced.

[0058] In this embodiment, after the spliced part 10 and the seed crystal 20 to be spliced are spliced, a normal circular growing seed crystal 60 is formed.

[0059] (2) Refer to Figure 3, the cutting trajectory 11 is an arc, and the spliced part 10 formed after cutting is crescent-shaped. The surface of the spliced part 10 corresponding to the cutting trajectory 11 fits with the outer peripheral surface of the spliced seed crystal 20.

[0060] In this embodiment, there is no need to reprocess the spliced seed crystal 20. The growth seed crystal 60 formed after splicing the spliced part 10 and the spliced seed crystal 20 is no longer circular.

[0061] Among the above two cutting trajectories 11, the straight cutting trajectory 11 is more convenient to operate when cutting the spliced part 10. The spliced part 10 can be cut by a diamond wire cutting method. After cutting, the spliced seed crystal 20 needs to be processed before splicing; the arc cutting trajectory 11 is not easy to master the cutting trajectory 11 during cutting. Therefore, it is easy to not fit with the outer peripheral surface of the spliced seed crystal 20 after cutting. The spliced part 10 can be rounded by a diamond grinding wheel after cutting, so that the surface of the spliced part 10 corresponding to the cutting accumulation is consistent with the outer peripheral surface of the spliced seed crystal 20. The two cutting methods can be selected according to actual needs.

[0062] When actually cutting the spliced part 10, laser cutting can also be used. Laser cutting can cut strictly according to the cutting trajectory 11. The contour error of the spliced part 10 after cutting is small, which can facilitate the splicing operation of the spliced part 10 and the spliced seed crystal 20 and reduce the labor intensity.

[0063] Specifically, the width of the spliced part 10 can be determined according to the specific deflection angle of the spliced seed crystal, and is also related to the thermal field structure and the requirements of the convexity of the crystal (the central thickness difference between the spherical crown surface after crystal growth and the flat surface after crystal grinding). For example, the width of the spliced part 10 corresponding to an 8° spliced seed crystal can be about 10 mm. That is, after growing the ingot 30 from the growth seed crystal 60 and rounding off 10 mm, the wafer 40 without the small facet 50 can be obtained. The diameter of the rounded ingot 30 can fully meet the product requirements. If the deflection angle of the spliced seed crystal is larger, the width of the spliced part 10 can be smaller.

[0064] It should be noted that the convexity of the ingot 30 is 3 - 7 mm, and 5 mm can be specifically selected.

[0065] A specific rounding method of the above ingot 30 is: the ingot 30 is rounded by a partial rolling method. Since the spliced part 10 is mainly located in a part of the outer periphery of the spliced seed crystal 20, after growing the ingot 30, the small facet 50 is also only located in a part of the ingot 30. Therefore, when rounding, focus on rolling off the side with the small facet 50, and ensure that the ingot 30 is cylindrical, which can avoid waste of the effective part of the ingot 30 and produce more wafers 40.

[0066] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for producing a silicon carbide substrate using biased seed growth, characterized in that: The steps include: S10: using a seed crystal with a deflection angle greater than 4° as a splicing seed crystal, taking two cutting points at the outer edge of the splicing seed crystal, taking the line connecting the two cutting points as a cutting trajectory, the cutting trajectory not passing through the center of the splicing seed crystal, cutting the splicing seed crystal along the cutting trajectory, separating part of the outer circumference of the splicing seed crystal, and taking the part with a smaller volume after cutting as the splicing part; S20: taking a seed crystal with a deviation angle of 4° as a spliced ​​seed crystal, and splicing the spliced ​​portion to the periphery of the spliced ​​seed crystal as a growing seed crystal; S30: placing the growth seed crystal in a growth device for growth, until a crystal ingot grows in the axial direction of the growth seed crystal, and a small facet grows on the crystal ingot from the splicing portion; S40: performing a rounding process on the crystal ingot until the small face is rolled off and the crystal ingot becomes cylindrical, and cutting the cylindrical crystal ingot into wafers for use as silicon carbide substrates; The cutting trajectory is a straight line and parallel to the radial direction of the spliced ​​seed crystal; The specific steps of splicing the splicing part to the periphery of the spliced ​​seed crystal are: Cutting the periphery of the spliced ​​seed crystals to form a splicing surface equal to the surface of the splicing portion corresponding to the cutting track; The splicing portion is spliced ​​onto the splicing surface, and the outer peripheral surface of the splicing portion is continuous and tangent to the outer peripheral surface of the spliced ​​seed crystal.

2. The method for manufacturing a silicon carbide substrate using biased seed growth according to claim 1, characterized in that: The splicing portion is cut using diamond wire.

3. The method for manufacturing a silicon carbide substrate using biased seed growth according to claim 1, characterized in that: The cutting trajectory is an arc, and the surface of the splicing part corresponding to the cutting trajectory is in contact with the outer peripheral surface of the spliced ​​seed crystal; after the splicing part is cut, it is rounded using a diamond grinding wheel to make the surface of the splicing part corresponding to the cutting trajectory consistent with the outer peripheral surface of the spliced ​​seed crystal.

4. The method for manufacturing a silicon carbide substrate using biased seed growth according to claim 1, characterized in that: The splicing portion is cut using laser.

5. The method for manufacturing a silicon carbide substrate using biased seed growth according to claim 1, characterized in that: The crystal ingot is rounded by using an eccentric rolling method.

6. The method for manufacturing a silicon carbide substrate using biased seed growth according to claim 1, characterized in that: The convexity of the ingot is 3-7 mm.

7. The method for manufacturing a silicon carbide substrate using biased seed growth according to claim 1, characterized in that: The larger the off-angle of the spliced ​​seed crystal is, the smaller the width of the spliced ​​portion is.

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