Method for manufacturing silicon carbide substrate by using bias seed crystal growth

Abstract

The invention provides a method for manufacturing a silicon carbide substrate by using bias seed crystal growth, and belongs to the technical field of silicon carbide crystal growth, the method for manufacturing the silicon carbide substrate by using bias seed crystal growth comprises the following steps: S10, using a seed crystal with a deflection angle greater than 4 degrees as a spliced seed crystal, taking two cutting points on the outer edge of the spliced seed crystal, taking a connecting line of the two cutting points as a cutting track, cutting the spliced seed crystal along the cutting track, and taking a part with a smaller volume after cutting as a splicing part; s20, taking a seed crystal with a deflection angle of 4 degrees as a spliced seed crystal, and splicing the splicing part at the periphery of the spliced seed crystal as a growth 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 S40, carrying out rolling treatment on the crystal ingot until the small surface is rolled off and the crystal ingot is cylindrical, cutting the cylindrical crystal ingot into a wafer, and using the wafer as the silicon carbide substrate.

Description

Technical Field

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

[0002] Silicon carbide single crystal substrate material belongs to wide bandgap semiconductor material, which has the advantages of high voltage resistance, high temperature, high frequency, low loss, etc. It is the basic material for making high-power power electronic devices. In order to reduce the on-resistance of silicon carbide-based power devices, the substrate material needs to have good conductivity, that is, low resistivity. The way to obtain a low-resistivity substrate 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, it is necessary to introduce a step flow growth mechanism and use an off-axis substrate (that is, the substrate c-axis is 4° offset from the substrate surface normal direction to the <11-20> direction). There are two ways to prepare an off-axis substrate: (1) Using forward seed crystals for single crystal growth, the substrate surface orientation angle is adjusted to 4° during the end surface grinding or cutting of the ingot. Due to the difference in c-axis orientation between the substrate and the ingot, this method will result in a large waste of single crystal thickness, and the waste thickness increases with the increase in the diameter of the single crystal; (2) Using seed crystals with a surface orientation angle of 4° for single crystal growth can avoid wasting single crystal thickness.

[0003] When the above two methods are used to prepare a 4° off-axis substrate, small faces will be formed on the growth surface during single crystal growth. The platform width of the growth step in the small face area is greater than that in other areas. During the single crystal growth process, the migration distance of nitrogen impurities adsorbed on the growth interface is greater than the migration distance of the carbon-containing growth component. Since nitrogen impurities generally occupy carbon lattice positions, this leads to high nitrogen doping efficiency in areas with larger growth step platform widths, resulting in a large difference in resistivity between the small face area and other areas. The resistivity uniformity of the substrate has a significant negative impact on the performance consistency of subsequent power devices prepared based on the substrate. Summary of the invention

[0004] An embodiment of the present invention provides a method for manufacturing a silicon carbide substrate using biased seed crystal growth, aiming to solve the technical problem that the current method of manufacturing off-axis substrates will lead to a large difference in resistivity between the small face area and other areas, and the poor resistivity uniformity has a significant negative impact on the performance consistency of subsequent power devices.

[0005] To achieve the above object, the technical solution adopted by the present invention is: to provide a method for manufacturing a silicon carbide substrate using biased seed crystal growth, comprising: 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 rounding treatment on the crystal ingot until the small surface is rolled off and the crystal ingot becomes cylindrical, and cutting the cylindrical crystal ingot into wafers for use as silicon carbide substrates.

[0006] In a possible implementation, the cutting trajectory is a straight line and parallel to the radial direction of the spliced ​​seed crystal.

[0007] In a possible implementation, the specific steps of splicing the splicing portion on 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.

[0008] In a possible implementation, the splicing portion is cut using diamond wire.

[0009] In a possible implementation, the cutting track is an arc, and the surface of the splicing portion corresponding to the cutting track fits with the outer peripheral surface of the spliced ​​seed crystal.

[0010] In a possible implementation, the spliced ​​portion is rounded using a diamond grinding wheel after cutting, so that the surface of the spliced ​​portion corresponding to the cutting track is consistent with the outer peripheral surface of the spliced ​​seed crystal.

[0011] In a possible implementation, the joint portion is cut using laser.

[0012] In a possible implementation, the crystal ingot is rounded by using an eccentric rolling method.

[0013] In a possible implementation, the convexity of the crystal ingot is 3-7 mm.

[0014] In a possible implementation, the larger the deflection angle of the spliced ​​seed crystal is, the smaller the width of the spliced ​​portion is.

[0015] Compared with the prior art, the solution shown in the embodiment of the present application uses a seed crystal with a deflection angle greater than 4°, which increases the angle between the C-axis and the normal vector of the seed crystal surface. Under the same growth interface conditions, the position of the small face will be closer to the edge and the speed of moving toward the center of the seed crystal will be slower. Therefore, in the later rounding process of the ingot, the small face can be completely removed, so that the obtained chip does not contain the small face, the resistivity distribution of the chip is more uniform, and the performance consistency of the manufactured device is better. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the three-dimensional structure of silicon carbide; Figure 2 A schematic cross-sectional view of a growth seed crystal used in an embodiment of the present invention; Figure 3 A schematic cross-sectional view of a growth seed crystal used in another embodiment of the present invention; Figure 4 This is a diagram of the traditional seed crystal growth process; Figure 5 A schematic flow chart of a method for manufacturing a silicon carbide substrate using biased seed growth provided in an embodiment of the present invention.

[0017] Description of reference numerals: 10-joining part; 11-cutting track; 20-spliced ​​seed crystal; 30- ingot; 40- wafer; 50-small noodles; 60-Growing seed crystal. DETAILED DESCRIPTION

[0018] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] In the claims, specification and the above drawings of the present invention, unless otherwise clearly defined, if the term "fixed connection" or "fixed connection" is used, it should be understood in a broad sense, that is, any connection method without a displacement relationship and relative rotation relationship between the two, that is to say, including non-detachable fixed connection, detachable fixed connection, integrated connection and fixed connection through other devices or elements.

[0020] In the claims, description and drawings of the present invention, if the terms "include", "have" and their variations are used, they are intended to mean "including but not limited to".

[0021] See also Figure 1, the commonly used terms in silicon carbide structure are explained, among which: The C axis is the axis perpendicular to the crystal plane {0001}; The main edge of the seed crystal is the edge in the {1-100} plane and parallel to the <11-20> direction; The secondary edge of the seed crystal is an edge in the {11-20} plane and parallel to the <1-100> direction. When the silicon surface in the silicon carbide substrate faces upward, the secondary edge is on the left side of the primary edge and forms an angle of 90° with the primary edge. The main pair of seed crystals is directly opposite to the main side of the seed crystal; The seed crystal pair is the opposite side of the seed crystal pair, and the seed crystal pair area is the area where the facet 50 is formed; The silicon carbide substrate is biased 4°, that is, the normal direction of the substrate surface is biased towards <11-20>, and <0001> The included angle is 4°, and larger deflection angles have the same meaning here.

[0022] Among them, {} represents the surface and <> represents the direction.

[0023] Please also read Figures 2 to 4 Now, the method for manufacturing a silicon carbide substrate using biased seed crystal growth provided by the present invention is described.

[0024] The method for manufacturing a silicon carbide substrate using biased seed crystal growth comprises the following steps: S10: using a seed crystal with a deflection angle greater than 4° as a splicing seed crystal, taking two cutting points on the outer edge of the splicing seed crystal, taking the line connecting the two cutting points as a cutting track 11, the cutting track 11 does not pass through the center of the splicing seed crystal, cutting the splicing seed crystal along the cutting track 11, separating part of the outer circumference of the splicing seed crystal, and taking the part with a smaller volume after cutting as the splicing portion 10; S20: taking a seed crystal with a deflection angle of 4° as the spliced ​​seed crystal 20, and splicing the splicing portion 10 to the periphery of the spliced ​​seed crystal 20 as the growing seed crystal 60; S30: placing the growth seed crystal 60 in a growth device for growth, until a crystal ingot 30 grows in the axial direction of the growth seed crystal 60 , and a small face 50 grows on the crystal ingot 30 at the splicing portion 10 ; S40: performing rounding processing on the crystal ingot 30 until the small face 50 is rolled off and becomes cylindrical, and cutting the cylindrical crystal ingot 30 into wafers 40 for use as silicon carbide substrates.

[0025] It should be noted that one or more splicing parts 10 can be cut from one splicing seed crystal.

[0026] In the traditional process of growing silicon carbide single crystals, a certain radial temperature gradient is required to achieve a convex growth interface, and the seed crystal usually has a flat surface. During the single crystal growth process (especially in the early stage of single crystal growth), there will be a process in which the growth interface gradually becomes convex. The small face 50 is usually formed at a position where the surface normal vector of the growth interface is parallel to the C-axis. Therefore, during the single crystal growth process, the small face 50 will gradually move from the edge to the center of the single crystal.

[0027] The method for producing a silicon carbide substrate using biased seed crystal growth provided in the present embodiment, compared with the prior art, uses a seed crystal with a bias angle greater than 4°, so that the angle between the C-axis and the normal vector of the seed crystal surface is increased. Under the same growth interface condition, the position of the small face 50 will be closer to the edge and the speed of moving toward the center of the seed crystal will be slower. Therefore, in the later rounding process of the ingot 30, the small face 50 can be completely removed, so that the obtained chip 40 does not contain the small face 50, the resistivity distribution of the chip 40 is more uniform, and the performance consistency of the manufactured device is better.

[0028] Two specific implementations of the above-mentioned cutting track 11 are: (1) See Figure 2 The cutting track 11 is a straight line and parallel to the radial direction of the splicing seed crystal. The splicing portion 10 formed by cutting is close to a semi-ellipse. The splicing portion 10 obtained by this step needs to be cut on the periphery of the spliced ​​seed crystal 20 to form a splicing surface equal to the surface of the splicing portion 10 corresponding to the cutting track 11, and then the splicing portion 10 is spliced ​​on the splicing surface. The outer peripheral surface of the splicing portion 10 is continuous and tangent to the outer peripheral surface of the spliced ​​seed crystal 20.

[0029] In this embodiment, the splicing portion 10 and the spliced ​​seed crystal 20 are spliced ​​to form a normal circular growing seed crystal 60 .

[0030] (2) See Figure 3 The cutting track 11 is an arc, and the splicing portion 10 formed after cutting is crescent-shaped. The surface of the splicing portion 10 corresponding to the cutting track 11 fits with the outer peripheral surface of the spliced ​​seed crystal 20.

[0031] In this embodiment, the spliced ​​seed crystal 20 does not need to be reprocessed, and the growing seed crystal 60 formed by splicing the splicing portion 10 and the spliced ​​seed crystal 20 is no longer circular.

[0032] Of the two cutting trajectories 11 mentioned above, the straight cutting trajectory 11 is more convenient to operate when cutting the splicing part 10. The splicing part 10 can be cut by diamond wire cutting. After cutting, the spliced ​​seed crystal 20 needs to be processed before it can be spliced; the arc cutting trajectory 11 is not convenient to control the cutting trajectory 11 during cutting, so it is easy to fail to fit the outer peripheral surface of the spliced ​​seed crystal 20 after cutting. After the splicing part 10 is cut, a diamond grinding wheel can be used to round it so that the surface of the splicing 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.

[0033] When actually cutting the splicing part 10, laser cutting can also be used. Laser cutting can be performed strictly according to the cutting track 11. The contour error of the splicing part 10 after cutting is small, which can facilitate the splicing operation of the splicing part 10 and the spliced ​​seed crystal 20 and reduce labor intensity.

[0034] Specifically, the width of the splicing portion 10 can be determined according to the specific deflection angle of the splicing seed crystal, and is also related to the thermal field structure and the convexity of the crystal (the center thickness difference between the spherical crown surface after the crystal grows and the plane of the crystal after grinding). For example, the width of the splicing portion 10 corresponding to the 8° splicing seed crystal can be about 10 mm, that is, by growing the seed crystal 60 into the ingot 30 and then rounding it off by 10 mm, a chip 40 without small faces 50 can be obtained. The diameter of the ingot 30 after rounding can fully meet the product requirements. If the deflection angle of the splicing seed crystal is larger, the width of the splicing portion 10 can be even smaller.

[0035] It should be noted that the convexity of the crystal ingot 30 is 3-7 mm, and specifically 5 mm.

[0036] A specific rounding method of the above-mentioned ingot 30 is: the ingot 30 is rounded by eccentric rolling. Since the splicing portion 10 is mainly located at a part of the periphery of the spliced ​​seed crystal 20, after the ingot 30 is grown, the small face 50 is also only located at a part of the ingot 30. Therefore, when rolling, the side with the small face 50 is rolled off, and the ingot 30 is ensured to be cylindrical, which can avoid the waste of the effective part of the ingot 30 and produce more wafers 40.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in 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 rounding treatment on the crystal ingot until the small surface is rolled off and the crystal ingot becomes cylindrical, and cutting the cylindrical crystal ingot into wafers for use as silicon carbide substrates.

2. The method for manufacturing a silicon carbide substrate using biased seed growth according to claim 1, characterized in that: The cutting track is a straight line and parallel to the radial direction of the spliced ​​seed crystal.

3. The method for manufacturing a silicon carbide substrate using biased seed growth according to claim 2, characterized in that: 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.

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

5. The method for manufacturing a silicon carbide substrate using biased seed growth according to claim 1, characterized in that: The cutting track is an arc, and the surface of the splicing portion corresponding to the cutting track is in contact with the outer peripheral surface of the spliced ​​seed crystal.

6. The method for manufacturing a silicon carbide substrate using biased seed growth according to claim 5, characterized in that: After the splicing part is cut, the splicing part is rounded using a diamond grinding wheel so that the surface of the splicing part corresponding to the cutting track is consistent with the outer peripheral surface of the spliced ​​seed crystal.

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

8. 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.

9. 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.

10. 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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