Method for manufacturing a silicon carbide seed crystal with a low threading dislocation density

Abstract

The present invention provides a method for manufacturing a silicon carbide seed crystal with a low threading dislocation density, belonging to the technical field of semiconductor crystal growth, and comprising the following steps: S1, cutting a 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 enabling the first seed crystal to grow towards both sides along its thickness direction to obtain a first crystal; S4, cutting the first crystal along its growth direction to obtain a seed crystal product with a fixed thickness. The method for manufacturing a silicon carbide seed crystal with a low threading dislocation density provided by the present invention divides the crystal thickness required for single-sided growth into two surfaces due to double-sided growth, increases the operability, reduces the crystal growth difficulty, shortens the crystal growth time, and further reduces crystallization defects such as microtubes and polytypes that occur in the later stage of single crystal growth due to unstable gas-phase growth components in the growth chamber, thereby improving the crystal quality.

Description

Technical Field

[0001] The present 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 a low threading dislocation density. Background Art

[0002] Silicon carbide crystals are generally grown by physical vapor transport (PVT). The specific steps of this method are as follows: place silicon carbide powder at the bottom of a graphite crucible, place a circular silicon carbide seed crystal on top of the graphite crucible, heat the graphite crucible to the sublimation temperature of silicon carbide using an induction coil, then the silicon carbide powder decomposes into gaseous components such as Si vapor, Si2C, and SiC2. Under the action of the axial temperature gradient, 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 centrosymmetric, and a cylindrical ingot is finally grown on the circular seed crystal.

[0003] During the crystal growth process, the threading dislocations (TDs) in the seed crystal will be inherited into the crystal, and the substrate processed from this 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, it is necessary to manufacture a seed crystal with a low threading dislocation (TD) density.

[0004] Currently, the production process of seed crystals with an extremely low threading dislocation (TD) density mostly adopts the repeated a-plane growth method. The first wafer is obtained by cutting along the crystal growth direction, and then this wafer is used as a seed crystal for PVT growth to obtain the second crystal. Then, the second crystal is cut along the growth direction to obtain the second wafer, and 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 changing the crystal growth direction multiple times, has many crystal growth steps, and each growth needs to grow to a sufficient thickness before it can be used, resulting in extremely low utilization rate of the ingot; the polycrystalline silicon carbide raw material will gradually graphitize during the growth process, resulting in continuous changes in the gaseous growth components in the growth chamber. The longer the growth time, the more obvious the component change. Therefore, it is difficult to ensure the stability of the growth components during long-term crystal growth, which leads to crystallization defects such as microtubes and polytypes in the later stage of single crystal growth, seriously affecting the crystal quality and ultimately resulting in crystal growth failure. The repeated a-plane growth method requires multiple single crystal growths with large thicknesses to obtain a seed crystal with a sufficient diameter. The process is extremely cumbersome and complex, with extremely high costs and a very low success probability. Summary of the Invention

[0006] The purpose 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 a 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 manufacturing method of a silicon carbide seed crystal with a low threading dislocation density, comprising the following steps:

[0008] S1. Cut the silicon carbide crystal along the growth direction to obtain a first wafer;

[0009] S2. Process and polish the first wafer into a first seed crystal;

[0010] S3. Vertically place the first seed crystal in a crystal growth device, and make the first seed crystal grow towards both sides along its thickness direction to obtain a first crystal;

[0011] S4. Cut the first crystal along its growth direction to obtain a seed crystal product with a fixed thickness.

[0012] As another embodiment of the present application, in step S2, the first wafer is processed and cut into a rectangular wafer, and a set of surfaces parallel to the rectangular wafer are ground and polished to obtain the first seed crystal.

[0013] As another embodiment of the present application, the aspect ratio of the first seed crystal is 4-8.

[0014] As another embodiment of the present application, in step S2, a set of surfaces with the largest area of the rectangular wafer are selected for double-sided grinding and polishing.

[0015] As another embodiment of the present application, in step S3, the crystal growth device has two sets of symmetric 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.

[0016] As another embodiment of the present application, in step S3, the crystal growth device includes a graphite crucible with a cuboid structure. A longitudinal installation position is provided on the center line of the graphite crucible, and the installation position is used to fix the first seed crystal in a vertical state; a set of polished surfaces of the first seed crystal face both sides of the installation position respectively.

[0017] As another embodiment of the present application, two symmetrically arranged external heat sources are provided outside the graphite crucible. The two external heat sources are respectively located at both ends of the length direction of the graphite crucible, and both external heat sources are parallel to the installation position and form two sets of symmetric thermal fields in the graphite crucible.

[0018] 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 inside the external heat source.

[0019] As another embodiment of the present application, the interior of the graphite crucible has two symmetric silicon carbide powder regions, which are respectively located at both ends of the graphite crucible in the length direction. The two silicon carbide powder regions correspond to two external heat sources one by one. The two silicon carbide powder regions are respectively located on both sides of the installation position, and a growth space is formed between the silicon carbide powder region and the installation position.

[0020] As another embodiment of the present application, in step S3, physical vapor transport method is used for growth on both sides of the first seed crystal simultaneously, and the components decomposed from the powders on both sides are transported to the first seed crystal by using the temperature gradients on both sides.

[0021] The beneficial effects of the manufacturing method of the silicon carbide seed crystal with low threading dislocation density provided by the present invention are as follows: compared with the prior art, in the manufacturing method of the silicon carbide seed crystal with low threading dislocation density of the present invention, the wafer is polished to form the first seed crystal, and the first seed crystal grows towards both sides in the thickness direction. Through the double-sided growth method, normal crystal growth is carried out on both surfaces of the first seed crystal, improving the crystal growth efficiency; because the double-sided growth divides the crystal thickness required for single-sided growth equally onto two surfaces, the operability is increased, the crystal growth difficulty is reduced, the crystal growth time is shortened, and further, the crystallization defects such as microtubes and polytypes that appear in the later stage of single crystal growth due to unstable gas-phase growth components in the growth cavity are reduced, improving the crystal quality. Description of the Drawings

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0023] Figure 1 It is a longitudinal sectional view of the crystal growth device provided by the first embodiment of the present invention;

[0024] Figure 2 It is an effect diagram of the dislocation density detection of the seed crystal product provided by the first embodiment of the present invention;

[0025] Figure 3 It is a longitudinal sectional view of the crystal growth device provided by the comparative example of the present invention;

[0026] Figure 4 It is an effect diagram of the dislocation density detection of the seed crystal product provided by the comparative example of the present invention.

[0027] In the figure: 1. Graphite crucible; 2. Installation position; 3. First seed crystal; 4. External heat source; 5. Silicon carbide powder; 6. Crucible body; 7. Heating device; 8. Circular seed crystal. Detailed Embodiments

[0028] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clear and understandable, the present invention will be further described in detail below with reference to 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 used to limit the present invention.

[0029] Please refer to Figures 1 to 4 , and a method for manufacturing a silicon carbide seed crystal with a low threading dislocation density provided by the present invention will be described. The method for manufacturing a silicon carbide seed crystal with a low threading dislocation density includes the following steps:

[0030] S1. Cut the silicon carbide crystal along the growth direction to obtain a first wafer;

[0031] S2. Process and polish the first wafer into a first seed crystal 3;

[0032] S3. Vertically place the first seed crystal 3 in a crystal growth device, and make the first seed crystal 3 grow towards both sides along its thickness direction to obtain a first crystal;

[0033] S4. Cut the first crystal along its growth direction to obtain a seed crystal product with a fixed thickness.

[0034] Compared with the prior art, the method for manufacturing a silicon carbide seed crystal with a low threading dislocation density provided by the present invention grinds the wafer to form a first seed crystal 3, and makes the first seed crystal 3 grow towards both sides along the thickness direction. Through the double-sided growth method, normal crystal growth is carried out on both surfaces of the first seed crystal 3, improving the crystal growth efficiency; because the double-sided growth divides the crystal thickness required for single-sided growth equally on two surfaces, the operability is increased, the crystal growth difficulty is reduced, the crystal growth time is shortened, and further, crystallization defects such as microtubes and polytypes that appear in the later stage of single crystal growth due to unstable gas-phase growth components in the growth chamber are reduced, improving the crystal quality. In addition, during the crystal growth process, it is not necessary to cut multiple times and the growth size is reduced, reducing the difficulty of crystal cultivation, and thus improving the crystal quality and crystal growth efficiency.

[0035] In step S2, the first wafer is processed and cut into a rectangular wafer, and a set of surfaces parallel to the rectangular wafer are ground and polished to obtain the first seed crystal 3. That is, the first wafer obtained by cutting is longitudinally cut through the ingot to obtain a rectangular wafer, and then the rectangular wafer is polished to form a first seed crystal 3 with two smooth side surfaces. Compared with the large-sized circular or square seed crystals used in the conventional growth method, the rectangular seed crystal is easier to obtain, and the rectangular seed crystal can be obtained by normal longitudinal cutting of the ingot, with simple and convenient operation and a high success rate.

[0036] Optionally, the aspect ratio of the first seed crystal 3 is 4-8, and its thickness value can be selected according to the actual situation. The length of the first seed crystal 3 is 4-8 times its width. The two surfaces with the largest rectangular wafer area are selected for double-sided grinding and polishing, and these two surfaces are used as the growth surfaces and placed in the crystal growth device for double-sided growth. During growth, both sides of the growth surface grow outward, and the first crystal grown is approximately a cuboid structure.

[0037] 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 the silicon carbide powder 5, reduce the waste of the powder, and reduce the difficulty of placing the silicon carbide powder 5.

[0038] In step S2, in addition to polishing the growth surface, other surfaces of the first seed crystal 3 can be subjected to conventional operations according to the actual situation.

[0039] 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, and this crystal growth device 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 symmetric 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. To adapt to the rectangular first seed crystal 3, a rectangular thermal field is selected, so as to ensure uniform growth of the crystal along the thickness direction of the first seed crystal 3.

[0040] The two sets of thermal fields formed in the crystal growth device are respectively directed towards the two growth surfaces of the first seed crystal 3, and temperature gradients are formed in the growth spaces in the two growth directions of the first seed crystal 3. With this temperature gradient, the directional transport of the silicon carbide component is realized to achieve the double-sided growth of the first seed crystal 3.

[0041] Specifically, the crystal growth device in step S3 includes a graphite crucible 1 with a cuboid structure. There is a longitudinal installation position 2 on the center line of the graphite crucible 1, and the installation position 2 is used to fix the first seed crystal 3 in a vertical state; the two polished surfaces of the first seed crystal 3 are respectively directed towards both sides of the installation position 2.

[0042] The rectangular first seed crystal 3 polished in the above step S2 needs to be placed in the graphite crucible 1 with a cuboid structure for double-sided growth. An installation position 2 is provided on the center line of the graphite crucible 1 with a cuboid structure, and a through hole for fixing the first seed crystal 3 is opened on the installation position 2, and this through hole is used to allow the first seed crystal 3 to pass through and limit the first seed crystal 3.

[0043] 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 formed in the middle of the mounting position 2, and the through hole is used for mounting the first seed crystal 3. The first seed crystal 3 is fixed in the through hole, and the thicknesses of the two sides of the first seed crystal 3 extending out of the through hole are the same, so as to ensure that the growth rates and growth effects of the two sides of the first seed crystal 3 are the same.

[0044] To improve the growth stability of the first seed crystal 3, there are two symmetrically arranged external heat sources 4 on the outer side of the graphite crucible 1. The two external heat sources 4 are respectively located at both ends of the length direction of the graphite crucible 1. The two external heat sources 4 are both parallel to the mounting position 2 and form two 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 inside the external heat source 4.

[0045] The external heat source 4 can be a resistance heater. Compared with the induction heating method, its heating is more uniform, which can ensure that the temperature difference between the bottom and the top of the powder is smaller, achieving the purpose of uniform sublimation of the powder. And the surface heat source can cover the end face of the graphite crucible 1 to ensure the temperature gradient of the growth cavity of the graphite crucible 1.

[0046] In step S3, there are two symmetric silicon carbide powder 5 regions inside the graphite crucible 1. The two silicon carbide powder 5 regions are respectively located at both ends of the length direction of the graphite crucible 1. The two silicon carbide powder 5 regions correspond to the two external heat sources 4 one by one. The two silicon carbide powder 5 regions are respectively located on both sides of the mounting position 2, and a growth space is formed between the silicon carbide powder 5 region and the mounting position 2.

[0047] Different from the traditional bottom loading and side annular loading methods, the double-side loading method makes the silicon carbide powder 5 located at the two ends parallel to the external heat source 4. This loading method can ensure better sublimation effect of the powder and maintain the stable transport of components from the powder to the seed crystal at the same time.

[0048] The double-side side heating method is combined with the double-side loading to establish a temperature gradient from both sides to the center, realizing the transport of components from the silicon carbide powder 5 region to the seed crystal region. The double-side side heating method fits better with the double-side loading method, realizing the lateral growth of the crystal, establishing the temperature gradient of the powder to the seed crystal growth surface, relying on the temperature gradient to realize the directional transport of carbon and silicon components, so as to realize the double-side growth of the seed crystal; the through dislocation density of the obtained silicon carbide seed crystal is greatly reduced compared with the existing seed crystal.

[0049] In step S3, physical vapor transport method is used for growth on both sides of the first seed crystal 3 at the same time. By using the temperature gradients on both sides, the components decomposed from the powder on both sides are transported to the first seed crystal 3. The physical vapor transport method for growth is to transport the components decomposed from the powder to the middle seed crystal position through the temperature gradient from both sides to the center.

[0050] Example 1:

[0051] 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, and then the two surfaces with the largest area are double-sided polished to obtain a smooth first seed crystal 3. The first seed crystal 3 is placed in the crystal growth device as shown in Figure 1 . The graphite crucible 1 in the crystal growth device is charged on both sides with a charging thickness of 120 mm. Physical vapor transport growth is carried out with a single-sided growth thickness of 75 mm and a total growth distance of 150 mm to obtain a first crystal grown along the thickness direction of the first seed crystal 3. The obtained first crystal is cut along the thickness direction of the first crystal to obtain a wafer with a thickness of 0.5 mm, and after polishing, a seed crystal product for conventional use is obtained. This seed crystal has an extremely low threading dislocation (TD) density, and the detection result of its dislocation density is as shown in Figure 2 .

[0052] Example 2:

[0053] 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, and then the two surfaces with the largest area are double-sided polished to obtain a smooth first seed crystal 3. The first seed crystal 3 is placed in the crystal growth device as shown in Figure 1 . The graphite crucible 1 in the crystal growth device is charged on both sides with a charging thickness of 80 mm. Physical vapor transport growth is carried out with a single-sided growth thickness of 50 mm and a total growth distance of 100 mm to obtain a first crystal grown along the thickness direction of the first seed crystal 3. The obtained first crystal is cut along its growth direction to obtain a wafer with a thickness of 1 mm, and after polishing, a seed crystal product for conventional use is obtained.

[0054] The crystal growth devices in Example 1 and Example 2 are both the above-mentioned graphite crucible 1. The graphite crucible 1 has a cuboid structure, and its inner cavity is a cuboid cavity. An installation position 2 is fixed in the graphite crucible 1. The installation position 2 is longitudinally arranged and perpendicular to the length direction of the graphite crucible 1. The installation position 2 is longitudinally located at the center of the inner cavity of the graphite crucible 1, and the distances from its two ends in the length direction of the graphite crucible 1 are the same. The installation position 2 can adopt a plate-like structure and is fixedly connected to the side wall of the graphite crucible 1. A through hole is opened at the center of the installation position 2 for installing the first seed crystal 3. The through hole at the center of the installation position 2 is a rectangular hole with a height greater than the width, and the first seed crystal 3 is longitudinally placed in the through hole of the installation position 2. The installation position 2 and the first seed crystal 3 can be fixed by bonding, clamping and other methods.

[0055] Optionally, the thickness of the installation position 2 is the same as that of the first seed crystal 3. When the thicknesses are the same, when the first seed crystal 3 is fixed in the installation position 2, the two side surfaces of the first seed crystal 3 are flush with the two side surfaces of the installation position 2. The installation position 2 can be made of graphite material.

[0056] 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 symmetrically arranged, and the distances from the two external heat sources 4 to the growth surfaces of the corresponding first seed crystals 3 are the same. The external heat source 4 is selected to have a plate-like structure, and the distances between the two external heat sources 4 and the end face of the graphite crucible 1 are the same.

[0057] At the two ends of the graphite crucible 1 in the length direction are the placement areas for the silicon carbide powder 5. The silicon carbide powder 5 is arranged in the two placement areas as raw materials.

[0058] Comparative Example:

[0059] Directly use the seed crystal to grow PVT crystals along its thickness direction. The crystal growth device is shown in Figure 3 , the crystal growth device includes a crucible body 6. At the bottom of the crucible body 6 is the silicon carbide powder 5. At the top of the crucible body 6 is a circular seed crystal 8. A heating device 7 is provided in a circumferential ring around the crucible body 6. The heating device 7 is used to heat the crucible. The seed crystal grows in the crucible body 6 to obtain a comparative crystal. The comparative crystal is cut, ground, and polished to obtain a comparative seed crystal product. The dislocation density of the comparative seed crystal product is as Figure 4 shown. The comparative seed crystal product is an existing seed crystal. The heating device 7 can adopt a circular heating coil.

[0060] From the comparison of the above-mentioned Example 1, 2 and the comparative example, it can be learned that the through dislocation density of the seed crystal product obtained by the manufacturing method of the silicon carbide seed crystal with a low through dislocation density is greatly reduced compared with the existing seed crystal.

[0061] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall 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, cutting the first crystal along its growth direction to obtain a seed crystal product with a fixed thickness; In step S2, the first wafer is processed and cut into rectangular wafers, and a group of surfaces parallel to the rectangular wafer are polished to obtain a first seed crystal; The crystal growth device in step S3 includes a graphite crucible with a rectangular structure, a longitudinal mounting position is provided on the midline of the graphite crucible, a through hole is provided in the middle of the mounting position, and the through hole is used to mount the first seed crystal; and the first seed crystal has a uniform thickness on both sides extending out of the through hole; The outside of the graphite crucible has two symmetrically arranged external heat sources, which are respectively located at the two 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; 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.

2. The method for manufacturing a silicon carbide seed crystal with a low threading dislocation density according to claim 1, characterized in that: The aspect ratio of the first seed crystal is 4-8.

3. 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, a group of surfaces with the largest area of ​​the rectangular wafer is selected for double-sided grinding and polishing.

4. The method for manufacturing a silicon carbide seed crystal with a low threading dislocation density according to claim 3, 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.

5. The method for manufacturing a silicon carbide seed crystal with a low threading dislocation density according to claim 1, 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.

6. 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.

Images