Method for producing silicon carbide seed crystal having low through dislocation density

Abstract

The invention provides a manufacturing method of a silicon carbide seed crystal with low penetration dislocation density, and belongs to the technical field of semiconductor crystal growth, and the manufacturing method comprises the following steps: S1, cutting a silicon carbide crystal along a growth direction to obtain a first wafer; s2, processing and polishing the first wafer into a first seed crystal; s3, vertically placing the first seed crystal in a crystal growth device, and enabling the first seed crystal to grow towards two sides along the thickness direction of the first seed crystal to obtain a first crystal; and S4, cutting the first crystal along the growth direction of the first crystal to obtain a seed crystal product with a fixed thickness. According to the manufacturing method of the silicon carbide seed crystal with low penetration dislocation density, the crystal thickness required by single-sided growth is equally divided to two surfaces due to double-sided growth, so that the operability is improved, the crystal growth difficulty is reduced, and the crystal growth time is shortened; furthermore, the crystal defects of microtubules, polymorphisms and the like in the later stage of single crystal growth caused by unstable gas phase growth components in the growth cavity are reduced, and the crystal quality is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor crystal growth, and more specifically, relates to a method for manufacturing a silicon carbide seed crystal with low threading dislocation density. Background Art

[0002] Silicon carbide crystals are generally produced by physical vapor transport (PVT). The specific steps of this method are: placing silicon carbide powder at the bottom of a graphite crucible, placing a round silicon carbide seed crystal at the top of the graphite crucible, and using an induction coil to heat the graphite crucible to the silicon carbide sublimation temperature. The silicon carbide powder decomposes into gas phase components such as Si vapor, Si2C and SiC2. Under the action of the axial temperature gradient, the various components are transported to the top of the crucible and deposited as SiC single crystals on the surface of the silicon carbide seed crystal at the top. The entire thermal field structure is centrally symmetrical, and a cylindrical ingot eventually grows on the round seed crystal.

[0003] During the crystal growth process, the threading dislocations (TD) in the seed crystal will be inherited into the crystal, and the substrate processed from the crystal will have a threading dislocation (TD) density similar to that of the seed crystal. Therefore, in order to obtain a high-quality silicon carbide substrate, a seed crystal with a low threading dislocation (TD) density needs to be manufactured.

[0004] At present, the production process of seed crystals with extremely low through-dislocation (TD) density mostly adopts repeated a-plane growth method, in which the first wafer is obtained by cutting along the crystal growth direction, and then the wafer is used as a seed crystal for PVT method growth to obtain the second crystal. The second crystal is then cut along the growth direction to obtain the second wafer. Single crystal growth of the second wafer can reduce the TD in the obtained single crystal to an extremely low density.

[0005] However, the repeated a-plane growth method requires multiple changes in the crystal growth direction, multiple crystal growth steps, and each growth needs to grow to a sufficient thickness before it can be used, resulting in an extremely low utilization rate of the ingot; the polycrystalline silicon carbide raw material will gradually graphitize as it grows, resulting in a continuous change in the gas phase growth components in the growth chamber. The longer the crystal growth time, the more obvious the component changes. Therefore, it is difficult to ensure the stability of the growth components during long-term crystal growth, resulting in the appearance of microtubes, polymorphs and other crystal defects in the later stage of single crystal growth, which seriously affects the crystal quality and ultimately leads to crystal growth failure. The repeated a-plane growth method requires multiple large-thickness single crystal growths to obtain seed crystals of sufficient diameter. The process is extremely cumbersome and complicated, the cost is extremely high, and the probability of success is extremely low. Summary of the invention

[0006] The object of the present invention is to provide a method for manufacturing a silicon carbide seed crystal with a low threading dislocation density, aiming to more simply manufacture the seed crystal with a low threading dislocation density and improve the success rate of seed crystal manufacturing.

[0007] To achieve the above object, the technical solution adopted by the present invention is: to provide a method for manufacturing a silicon carbide seed crystal with a low threading dislocation density, comprising the following steps: S1, cutting the silicon carbide crystal along the growth direction to obtain a first wafer; S2, processing and polishing the first wafer into a first seed crystal; S3, vertically placing the first seed crystal in a crystal growth device, and allowing the first seed crystal to grow toward both sides along its thickness direction to obtain a first crystal; S4. Cut the first crystal along its growth direction to obtain a seed crystal product with a fixed thickness.

[0008] As another embodiment of the present application, in step S2, the first wafer is processed and cut into rectangular wafers, and a group of surfaces parallel to the rectangular wafers are polished to obtain a first seed crystal.

[0009] As another embodiment of the present application, the aspect ratio of the first seed crystal is 4-8.

[0010] As another embodiment of the present application, in step S2, a group of surfaces with the largest area of ​​the rectangular wafer is selected for double-sided grinding and polishing.

[0011] As another embodiment of the present application, in step S3, the crystal growth device has two sets of symmetrical thermal fields, the first seed crystal is located between the two sets of thermal fields, and the two polished surfaces of the first seed crystal are respectively located in different thermal fields.

[0012] As another embodiment of the present application, in step S3, the crystal growth device includes a graphite crucible with a rectangular structure, and a longitudinal mounting position is provided on the center line of the graphite crucible, and the mounting position is used to fix the first seed crystal in a vertical state; a group of polished surfaces of the first seed crystal are respectively facing the two sides of the mounting position.

[0013] As another embodiment of the present application, the outside of the graphite crucible has two symmetrically arranged external heat sources, which are respectively located at both ends of the length direction of the graphite crucible. The two external heat sources are parallel to the installation position and form two sets of symmetrical heat fields in the graphite crucible.

[0014] As another embodiment of the present application, the external heat source is a surface heat source, and the projection of the graphite crucible along its length direction is located on the inner side of the external heat source.

[0015] As another embodiment of the present application, the interior of the graphite crucible has two symmetrical silicon carbide powder areas, the two silicon carbide powder areas are respectively located at the two ends of the length direction of the graphite crucible, the two silicon carbide powder areas correspond one-to-one to two external heat sources, the two silicon carbide powder areas are respectively located on both sides of the installation position, and a growth space is formed between the silicon carbide powder area and the installation position.

[0016] As another embodiment of the present application, in step S3, physical vapor transport is used for growth on both sides of the first seed crystal simultaneously, and the components generated by the decomposition of the powder on both sides are transported to the first seed crystal by utilizing the temperature gradient on both sides.

[0017] The beneficial effect of the method for manufacturing a silicon carbide seed crystal with a low threading dislocation density provided by the present invention is that: compared with the prior art, the method for manufacturing a silicon carbide seed crystal with a low threading dislocation density of the present invention grinds a wafer to form a first seed crystal, so that the first seed crystal grows toward both sides along the thickness direction, and both sides of the first seed crystal undergo normal crystal growth in a double-sided growth manner, thereby improving the crystal growth efficiency; due to the double-sided growth, the crystal thickness required for single-sided growth is equally divided into two sides, which increases operability, reduces the difficulty of crystal growth, shortens the crystal growth time, and thereby reduces crystal defects such as microtubules and polymorphs that appear in the late stage of single crystal growth due to the instability of the gas phase growth components in the growth chamber, thereby improving the crystal quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 A longitudinal cross-sectional view of a crystal growth device provided in accordance with a first embodiment of the present invention; Figure 2 A dislocation density detection effect diagram of a seed crystal product is provided for the first embodiment of the present invention; Figure 3 A longitudinal cross-sectional view of a crystal growth device provided for a comparative example of the present invention; Figure 4 This is a diagram showing the dislocation density detection effect of a seed crystal product provided in a comparative example of the present invention.

[0020] In the figure: 1. graphite crucible; 2. mounting position; 3. first seed crystal; 4. external heat source; 5. silicon carbide powder; 6. crucible body; 7. heating device; 8. round seed crystal. DETAILED DESCRIPTION

[0021] 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.

[0022] See also Figures 1 to 4Now, the method for manufacturing a silicon carbide seed crystal with low threading dislocation density provided by the present invention is described. The method for manufacturing a silicon carbide seed crystal with low threading dislocation density comprises the following steps: S1, cutting the silicon carbide crystal along the growth direction to obtain a first wafer; S2, processing and polishing the first wafer into a first seed crystal 3; S3, vertically placing the first seed crystal 3 in a crystal growth device, so that the first seed crystal 3 grows toward both sides along its thickness direction, to obtain a first crystal; S4. Cut the first crystal along its growth direction to obtain a seed crystal product with a fixed thickness.

[0023] The method for manufacturing a silicon carbide seed crystal with a low through-dislocation density provided by the present invention, compared with the prior art, grinds a wafer to form a first seed crystal 3, so that the first seed crystal 3 grows toward both sides along the thickness direction, and both sides of the first seed crystal 3 undergo normal crystal growth by double-sided growth, thereby improving the crystal growth efficiency; due to the double-sided growth, the crystal thickness required for single-sided growth is equally divided into two sides, which increases operability, reduces the difficulty of crystal growth, shortens the crystal growth time, and thus reduces the occurrence of micro-tubes, polymorphs and other crystal defects in the late stage of single crystal growth caused by the instability of the gas phase growth components in the growth chamber, thereby improving the crystal quality. In addition, multiple cutting is not required during the crystal growth process and the growth size is reduced, which reduces the difficulty of crystal cultivation, thereby improving the crystal quality and crystal growth efficiency.

[0024] In step S2, the first wafer is processed and cut into rectangular wafers, and a group of surfaces parallel to the rectangular wafers are polished to obtain the first seed crystal 3. The first wafer obtained by cutting is cut into a rectangular wafer by longitudinal cutting of the ingot, and the rectangular wafer is polished to form the first seed crystal 3 with two smooth sides. Compared with the large-sized round or square seed crystals used in the conventional growth method, the rectangular seed crystal is less difficult to obtain, and the rectangular seed crystal can be obtained by normal longitudinal cutting of the ingot, which is simple and convenient to operate and has a high success rate.

[0025] Optionally, the aspect ratio of the first seed crystal 3 is 4-8, and its thickness value can be selected according to actual conditions. The length of the first seed crystal 3 is 4-8 times the width, and a group of surfaces with the largest area of ​​the rectangular wafer is selected for double-sided grinding and polishing. This group of surfaces is used as the growth surface and is placed in a crystal growth device for double-sided growth. During growth, both sides of the growth surface grow outward, and the first crystal grown is a structure that approximates a rectangular parallelepiped.

[0026] The volume of the crystal obtained by growing the first seed crystal 3 is smaller than that of the crystal obtained by growing the circular seed crystal 8 , which can save silicon carbide powder 5 , reduce powder waste, and reduce the difficulty of placing the silicon carbide powder 5 .

[0027] In step S2, in addition to polishing the growth surface, conventional operations may be performed on other surfaces of the first seed crystal 3 according to actual conditions.

[0028] After the first wafer is polished to become the first seed crystal 3, the first seed crystal 3 is placed in the crystal growth device in step S3, which is used to cultivate the double-sided growth of the first seed crystal 3. In step S3, the crystal growth device has two sets of symmetrical thermal fields, the first seed crystal 3 is located between the two sets of thermal fields, and the two polished surfaces of the first seed crystal 3 are respectively located in different thermal fields. In order to adapt to the rectangular first seed crystal 3, its thermal field is selected to be rectangular, thereby ensuring that the crystal grows uniformly along the thickness direction of the first seed crystal 3.

[0029] The two sets of thermal fields formed in the crystal growth device are respectively oriented toward the two growth surfaces of the first seed crystal 3, and the thermal fields form temperature gradients in the growth space in both growth directions of the first seed crystal 3. The temperature gradient is used to achieve directional transport of silicon carbide components to achieve double-sided growth of the first seed crystal 3.

[0030] Specifically, the crystal growth device in step S3 includes a graphite crucible 1 with a rectangular structure, and a longitudinal mounting position 2 is provided on the midline of the graphite crucible 1, and the mounting position 2 is used to fix the first seed crystal 3 in a vertical state; a group of polished surfaces of the first seed crystal 3 are respectively facing the two sides of the mounting position 2.

[0031] The first cuboid seed crystal 3 polished and formed in the above step S2 needs to be placed in a cuboid graphite crucible 1 for double-sided growth. A mounting position 2 is set on the center line of the cuboid graphite crucible 1, and a through hole for fixing the first seed crystal 3 is opened on the mounting position 2, and the through hole is used to allow the first seed crystal 3 to pass through and limit the first seed crystal 3.

[0032] The mounting position 2 is a plate-like structure, and the plane where the mounting position 2 is located is perpendicular to the length direction of the graphite crucible 1. A through hole is provided in the middle of the mounting position 2, and the through hole is used to install the first seed crystal 3. The first seed crystal 3 is fixed in the through hole, and the thickness of the first seed crystal 3 extending out of the through hole is consistent on both sides, so as to ensure that the growth speed and growth effect of both sides of the first seed crystal 3 are consistent.

[0033] In order to improve the growth stability of the first seed crystal 3, the outside of the graphite crucible 1 has two symmetrically arranged external heat sources 4, which are respectively located at both ends of the length direction of the graphite crucible 1. The two external heat sources 4 are parallel to the mounting position 2 and form two sets of symmetrical heat fields in the graphite crucible 1. The external heat source 4 is a surface heat source, and the projection of the graphite crucible 1 along its length direction is located on the inner side of the external heat source 4.

[0034] The external heat source 4 can be a resistance heater. Compared with the induction heating method, the heating is more uniform, which can ensure that the temperature difference between the bottom and the top of the powder is smaller, so as to achieve the purpose of uniform sublimation of the powder. And the surface heat source can cover the end surface of the graphite crucible 1 to ensure the temperature gradient of the growth chamber of the graphite crucible 1.

[0035] In step S3, the interior of the graphite crucible 1 has two symmetrical silicon carbide powder 5 areas, the two silicon carbide powder 5 areas are respectively located at the two ends of the length direction of the graphite crucible 1, the two silicon carbide powder 5 areas correspond one to one with the two external heat sources 4, the two silicon carbide powder 5 areas are respectively located on both sides of the installation position 2, and a growth space is formed between the silicon carbide powder 5 areas and the installation position 2.

[0036] Different from the conventional bottom loading and side ring loading, the double side loading method enables the silicon carbide powder 5 to be located at two parallel ends of the external heat source 4. This loading method can ensure a better sublimation effect of the powder while maintaining a stable transport of components from the powder to the seed crystal.

[0037] The double-sided heating method is combined with double-sided loading to establish a temperature gradient from both sides toward the center, realizing the transport of components from the silicon carbide powder area 5 to the seed crystal area. The double-sided heating method is better matched with the double-sided loading method, realizing the lateral growth of the crystal, realizing the establishment of a temperature gradient from the powder to the seed crystal growth surface, and relying on the temperature gradient to achieve directional transport of carbon and silicon components, thereby realizing the double-sided growth of the seed crystal; the obtained silicon carbide seed crystal has a much lower through-dislocation density than the existing seed crystal.

[0038] In step S3, physical vapor transport is used for growth on both sides of the first seed crystal 3 at the same time, and the components generated by the decomposition of the powder on both sides are transported to the first seed crystal 3 by utilizing the temperature gradient on both sides. Physical vapor transport growth is to transport the components generated by the decomposition of the powder to the middle seed crystal position through the temperature gradient from both sides to the center.

[0039] Embodiment 1: A 6-inch silicon carbide crystal is cut along the growth direction to obtain a first wafer with a thickness of 0.5 mm. The first wafer is processed into a cuboid with a length of 150 mm and a width of 20 mm. Then, a group of surfaces with the largest area are double-sided polished to obtain a first seed crystal 3 with a smooth surface. The first seed crystal 3 is placed in a Figure 1In the crystal growth device shown, the graphite crucible 1 in the crystal growth device is loaded on both sides, and the loading thickness is 120mm. Physical vapor transport growth is performed, and the single-side growth thickness is 75mm, and the total growth distance is 150mm, and the first crystal grown along the thickness direction of the first seed crystal 3 is obtained. The first crystal obtained above is cut along the thickness direction of the first crystal to obtain a wafer with a thickness of 0.5mm, and the seed crystal product for conventional use is obtained after grinding and polishing. The seed crystal has an extremely low through-dislocation (TD) density, and its dislocation density detection result is as shown in FIG. Figure 2 .

[0040] Embodiment 2: A 4-inch silicon carbide crystal is cut along its growth direction to obtain a first wafer with a thickness of 1 mm. The first wafer is processed into a cuboid with a length of 100 mm and a width of 20 mm. Then, a group of surfaces with the largest area are double-sided polished to obtain a first seed crystal 3 with a smooth surface. The first seed crystal 3 is placed in a Figure 1 In the crystal growth device shown, the graphite crucible 1 in the crystal growth device is loaded on both sides, and the loading thickness is 80 mm. Physical vapor transport growth is performed, and the single-side growth thickness is 50 mm, and the total growth distance is 100 mm, and a first crystal grown along the thickness direction of the first seed crystal 3 is obtained. The first crystal obtained above is cut along its growth direction to obtain a wafer with a thickness of 1 mm, and after grinding and polishing, a seed crystal product for conventional use is obtained.

[0041] The crystal growth devices in Example 1 and Example 2 are both the above-mentioned graphite crucible 1. The graphite crucible 1 is a rectangular parallelepiped structure, and its inner cavity is a rectangular parallelepiped cavity. A mounting position 2 is fixed in the graphite crucible 1, and the mounting position 2 is longitudinally arranged and perpendicular to the length direction of the graphite crucible 1. The mounting position 2 is longitudinally located at the center of the inner cavity of the graphite crucible 1, and its distance from the two ends of the length direction of the graphite crucible 1 is consistent. The mounting position 2 can adopt a plate-like structure, which is fixedly connected to the side wall of the graphite crucible 1. A through hole is opened in the center of the mounting position 2, and the through hole is used to install the first seed crystal 3. The through hole in the center of the mounting position 2 is a rectangular hole, and its height is greater than its width. The first seed crystal 3 is longitudinally placed in the through hole of the mounting position 2. The mounting position 2 and the first seed crystal 3 can be fixed by bonding, clamping, etc.

[0042] Optionally, the thickness of the mounting position 2 is consistent with the thickness of the first seed crystal 3. When the thicknesses of the two are consistent, when the first seed crystal 3 is fixed in the mounting position 2, two side surfaces of the first seed crystal 3 are flush with two side surfaces of the mounting position 2. The mounting position 2 can be made of graphite.

[0043] An external heat source 4 is arranged outside the graphite crucible 1. The external heat source 4 is a surface heat source. Two external heat sources 4 are arranged symmetrically, and the distances between the two external heat sources 4 and the growth surfaces of the corresponding first seed crystals 3 are consistent. The external heat source 4 is a plate-like structure, and the distances between the two external heat sources 4 and the end surfaces of the graphite crucible 1 are consistent.

[0044] The two ends of the graphite crucible 1 in the length direction serve as placement areas for the silicon carbide powder 5 , and the silicon carbide powder 5 is arranged in the two placement areas as a raw material.

[0045] Comparative Example: Use seed crystal to directly grow PVT crystal along its thickness direction. See the crystal growth device for details. Figure 3 The crystal growth device includes a crucible body 6, a silicon carbide powder 5 is provided at the bottom of the crucible body 6, a round seed crystal 8 is provided at the top of the crucible body 6, and a heating device 7 is provided around the crucible body 6, and the heating device 7 is used to heat the crucible. The seed crystal grows in the crucible body 6 to obtain a comparison crystal, and the comparison crystal is cut, ground and polished to obtain a comparison seed crystal product. The dislocation density of the comparison seed crystal product is as follows: Figure 4 As shown. The comparative seed crystal product is the existing seed crystal. The heating device 7 can adopt a ring-shaped heating coil.

[0046] By comparing the above-mentioned Examples 1 and 2 with the comparative example, it can be understood that the seed crystal product obtained by the method for manufacturing a silicon carbide seed crystal with a low threading dislocation density has a threading dislocation density that is much lower than that of the existing seed crystal.

[0047] 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 seed crystal having a low threading dislocation density, characterized in that: The following steps are involved: S1, cutting the silicon carbide crystal along the growth direction to obtain a first wafer; S2, processing and polishing the first wafer into a first seed crystal; S3, vertically placing the first seed crystal in a crystal growth device, and allowing the first seed crystal to grow toward both sides along its thickness direction to obtain a first crystal; S4. Cut the first crystal along its growth direction to obtain a seed crystal product with a fixed thickness.

2. The method for manufacturing a silicon carbide seed crystal with a low threading dislocation density according to claim 1, characterized in that: In step S2, the first wafer is processed and cut into rectangular wafers, and a group of surfaces parallel to the rectangular wafers are ground and polished to obtain a first seed crystal.

3. The method for manufacturing a silicon carbide seed crystal with a low threading dislocation density according to claim 2, characterized in that: The aspect ratio of the first seed crystal is 4-8.

4. The method for manufacturing a silicon carbide seed crystal with a low threading dislocation density according to claim 2, characterized in that: In step S2, a group of surfaces with the largest area of ​​the rectangular wafer is selected for double-sided grinding and polishing.

5. The method for manufacturing a silicon carbide seed crystal with a low threading dislocation density according to claim 4, characterized in that: In step S3, the crystal growth device has two sets of symmetrical thermal fields, the first seed crystal is located between the two sets of thermal fields, and the two polished surfaces of the first seed crystal are located in different thermal fields respectively.

6. The method for manufacturing a silicon carbide seed crystal with a low threading dislocation density according to claim 4, characterized in that: In step S3, the crystal growth device includes a cuboid graphite crucible, the center line of the graphite crucible has a longitudinal mounting position, the mounting position is used to fix the first seed crystal in a vertical state; a group of polished surfaces of the first seed crystal are respectively facing the two sides of the mounting position.

7. The method for manufacturing a silicon carbide seed crystal with a low threading dislocation density according to claim 6, characterized in that: The outside of the graphite crucible is provided with two symmetrically arranged external heat sources, which are respectively located at two ends of the length direction of the graphite crucible. Both external heat sources are parallel to the installation position and form two sets of symmetrical heat fields in the graphite crucible.

8. The method for manufacturing a silicon carbide seed crystal with a low threading dislocation density according to claim 7, characterized in that: The external heat source is a surface heat source, and the projection of the graphite crucible along its length direction is located on the inner side of the external heat source.

9. The method for manufacturing a silicon carbide seed crystal with a low threading dislocation density according to claim 7, characterized in that: The inside of the graphite crucible has two symmetrical silicon carbide powder areas, which are respectively located at the two ends of the length direction of the graphite crucible. The two silicon carbide powder areas correspond one to one with two external heat sources. The two silicon carbide powder areas are respectively located on both sides of the installation position, and a growth space is formed between the silicon carbide powder area and the installation position.

10. The method for manufacturing a silicon carbide seed crystal with a low threading dislocation density according to claim 1, characterized in that: In step S3, physical vapor transport is used to grow on both sides of the first seed crystal simultaneously, and the components generated by decomposition of the powder on both sides are transported to the first seed crystal by utilizing the temperature gradient on both sides.

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