Silicon carbide single crystal near-free-state growth device and growth method

Abstract

The invention discloses a silicon carbide single crystal near-free-state growth device and growth method. The silicon carbide single crystal near-free-state growth device comprises a crucible cover, a crucible barrel, a neck bush and a seed crystal support, the crucible cover is positioned at the upper end of the crucible barrel and is matched with a barrel opening of the crucible barrel; the seed crystal support is positioned at the lower end of the crucible cover and is parallel to the crucible cover, the vertical section of the seed crystal support is of a transverse bow-shaped structure, and the middle position of the bow-shaped structure is sunken downwards; the vertical section of the neck bush is of an inverted-T-shaped opening structure, and the opening position at the upper end is matched with the lower end of the middle sunken position of the seed crystal support. The seed crystal support shaped like the Chinese character'gong 'can drain growth components on the edge of the crystal into a cavity on the back of the seed crystal, the edge of the crystal is in an unsaturated state, silicon carbide polycrystals cannot nucleate and grow on the edge of the crystal and the inner wall of the lining cylinder, and generation of the silicon carbide polycrystals is avoided. The near-free-state growth method ensures the stability of a growth interface, no defect proliferation occurs in the growth process, and the thickness of the silicon carbide single crystal is effectively increased.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor materials, and in particular relates to a silicon carbide single crystal near-free-state growth device and a growth method. Background Art

[0002] With the rapid development of modern science and technology, the demand for high-performance semiconductor materials is growing. Silicon carbide single crystals have shown great application potential in electronic devices under extreme environments such as high temperature, high frequency, and high power due to their excellent physical and chemical properties, such as high hardness, high thermal conductivity, high breakdown electric field strength, and good chemical stability.

[0003] The physical vapor transport (PVT) method is one of the most commonly used methods for growing silicon carbide single crystals. During the PVT growth process, the silicon carbide raw material is placed in a high temperature zone. Under certain temperature gradient and pressure conditions, the silicon carbide source material sublimates and decomposes, and the generated gaseous substances recrystallize in the low temperature zone to form silicon carbide single crystals. The advantage of this method is that it can grow large-sized, high-quality silicon carbide single crystals with good crystal integrity. However, the PVT method also has some limitations, such as a relatively low growth rate and extremely strict control requirements on parameters such as temperature and pressure during the growth process.

[0004] The difficulty of existing silicon carbide single crystal growth technology is how to maintain a stable growth interface to ensure that the silicon carbide crystal continues to grow thick and high quality. During the growth of silicon carbide crystals, the morphology of the growth interface and the shape of the growth surface are changing with the growth, and the migration of the growth center and the edge boundary conditions are undergoing complex changes, making it difficult to maintain the crystal growth interface, and thus difficult to ensure the integrity of the subsequent growth of silicon carbide single crystals, and it is impossible to grow thicker, high-quality single crystal ingots.

[0005] From the perspective of crystal growth, the growth quality of single crystals is best in a free growth system after crystal nucleation. This is because in a free growth system, there is no binding effect, and the crystals are arranged in a complete and repeated periodic arrangement according to the single crystal structure unit. According to the periodic bond chain (PBC) theory, during the crystal growth process, the time required to form a bond on the growth interface decreases with the increase of bonding energy, so the normal growth rate of the growth interface increases with the increase of bonding energy. Since the size of the bonding energy determines the normal growth rate of the growth interface, the size of the bonding energy also determines the growth morphology of the crystal. Therefore, in a free growth system, the growth rate ratio of each crystal face is constant, and the single crystal presents a regular geometric polyhedron. However, in the actual single crystal growth process, it is difficult to achieve the conditions of a free growth system. By controlling the single crystal growth device and growth conditions, the nearly free growth of the single crystal can be achieved, even if some crystal faces in the single crystal growth process follow the conditions of the free growth system, especially the crystal faces of the required growth interface and the crystal faces adjacent to them. How to achieve nearly free growth of silicon carbide single crystals is still an urgent problem to be solved in this field. So far, there has been no report on the nearly free-state growth method of silicon carbide single crystals. Summary of the invention

[0006] In view of the problems in the prior art of lack of a near-free-state growth method for silicon carbide single crystals and a lack of high-quality single crystal ingots, the present invention provides a near-free-state growth device and a growth method for silicon carbide single crystals, which can significantly increase the growth thickness of the silicon carbide single crystal, improve the growth yield, reduce the dislocation defect density, and optimize the crystal quality.

[0007] The present invention is achieved through the following technical solutions: A silicon carbide single crystal near-free state growth device, characterized in that it comprises a crucible cover, a crucible barrel, an inner liner, and a seed crystal holder; The crucible cover is located at the upper end of the crucible barrel and matches the barrel opening of the crucible barrel; The seed crystal holder is located at the lower end of the crucible cover, parallel to the crucible cover, and has a vertical cross section of a horizontal "bow"-shaped structure, with the middle of the "bow" shape concave downwards; The vertical cross section of the inner sleeve is a "convex" shaped opening structure, and the opening position at the upper end matches the lower end of the recessed position in the middle of the seed crystal holder.

[0008] Furthermore, the crucible cover, seed crystal holder and inner liner are detachable structures, and the maximum outline dimensions of the seed crystal holder and the inner liner match the crucible barrel and can be fixed on the inner wall of the crucible barrel.

[0009] Furthermore, the highest end of the "convex" shape of the inner sleeve is 2-5 mm higher than the lowest end of the recessed position of the seed crystal holder, and there is a gap between the inner sleeve and the recessed position of the seed crystal holder, and the size of the gap is 0.3-2 mm.

[0010] Furthermore, the distance between the uppermost end of the seed crystal holder and the crucible barrel is 5 to 15 mm; and the inner lining sleeve is fixed above the 1 / 2 position of the crucible barrel (2).

[0011] Furthermore, the thickness of the seed crystal holder is 3-10 mm, and the roughness of the middle concave surface is 1-25 μm.

[0012] Furthermore, the single crystal silicon near-free state growth device is made of graphite.

[0013] The present invention discloses a method for growing single crystal silicon in a near-free state by using a silicon carbide single crystal near-free state growth device, comprising the following steps: 1) Bond the silicon carbide single crystal seed crystal to the concave surface in the middle of the "bow" shape of the seed crystal holder; 2) The silicon carbide powder is placed in the crucible barrel, and the inner liner and the seed crystal holder with the seed crystal bonded in the step are fixed in the crucible barrel in sequence, located on the upper end of the silicon carbide powder, and then the crucible cover is installed to complete the assembly of the crucible; 3) Place the assembled crucible in the induction heating furnace, seal the furnace cavity, and evacuate the induction heating furnace to a vacuum degree of 0.1~10×10 -4 Pa, heating to 1050~1450℃, expelling moisture and impurity gases adsorbed on the furnace chamber wall and crucible wall; 4) Introduce argon gas, continue to raise the temperature to 2100~2350℃, keep warm for 100~300h, and complete the growth of silicon carbide single crystal; 5) After the growth is completed, stop introducing argon gas and cool to room temperature to obtain a silicon carbide single crystal.

[0014] Furthermore, in step 1), the diameter of the silicon carbide single crystal seed crystal is 6-12 inches, which is 5-15 mm larger than the diameter of the growing single crystal; the orientation of the silicon carbide single crystal seed crystal is 4±0.2° from the

[0001] crystal direction to the <11-20> crystal direction.

[0015] Furthermore, in step 2), the amount of silicon carbide powder added reaches 1 / 2 to 2 / 3 of the height of the crucible barrel, and the purity of the silicon carbide powder is higher than 99.999%; in step 4), the purity of argon gas is higher than 99.999%, and the flow rate is 0.05 to 0.3 L / min; Furthermore, in step 5), the cooling rate is 0.25-2°C / min; the silicon carbide single crystal is rounded, cut, ground, and polished to obtain a silicon carbide single crystal wafer with a roughness Ra < 0.5 nm.

[0016] The high-quality silicon carbide single crystal prepared by the present invention using a near-free state growth method has low overall stress, few edge defects, and large thickness. The total density of one-dimensional dislocation defects of the silicon carbide single crystal wafer prepared by the present invention is less than 1500 / cm 2 , the total dislocation density is better than 1000 / cm 2 , even the total dislocation density is less than 500 / cm 2 In summary, the method of the present invention successfully grows high-quality, low-stress, and low-dislocation-density semiconductor silicon carbide single crystal materials, which can be better used in the preparation of high-voltage and ultra-high-voltage power devices.

[0017] Beneficial Effects (1) The present invention can effectively improve the edge quality of silicon carbide single crystals. By introducing a "bow"-shaped seed crystal holder, the growth components at the edge of the crystal can be drained into the cavity on the back of the seed crystal, so that the edge of the crystal is in an unsaturated state, and silicon carbide polycrystals cannot nucleate and grow on the edge of the crystal and the inner wall of the liner tube, thereby eliminating the generation of parasitic silicon carbide polycrystals, and the edge maintains a bright surface of the single crystal. The presence of parasitic polycrystals at the edge of the crystal will cause stacking faults and dislocation defects to proliferate, thereby increasing the internal stress at the edge of the single crystal. Too much parasitic polycrystals will directly cause the silicon carbide single crystal to crack.

[0018] (2) The present invention can significantly increase the available thickness of the grown silicon carbide single crystal. The near-free state growth method is used to make the interface of the silicon carbide single crystal growth similar to the surface grown in a free system, so that in addition to the (000-1) crystal plane, other crystal planes such as {10-1n} are also exposed. This can ensure the stability of the growth interface, so that defects will not proliferate during the long-term growth process, which is an effective method for increasing the thickness of the silicon carbide single crystal. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of a near-free state growth device for silicon carbide single crystal, wherein 1 is a crucible cover, 2 is a graphite crucible barrel, 3 is an inner liner, 4 is silicon carbide powder, 5 is a silicon carbide single crystal, 6 is a silicon carbide seed crystal, 7 is a seed crystal holder, 8. Silicon carbide polycrystal; Figure 2 Figure 5 is a diagram of a silicon carbide single crystal ingot grown in a nearly free state by the method of the present invention, wherein 51a is a growth facet and 51b is a {10-1n} crystal face; Figure 3 This is a photo of the silicon carbide single crystal prepared in Example 1; Figure 4 This is a stress distribution diagram of the silicon carbide single crystal wafer prepared in Example 1; Figure 5 A one-dimensional dislocation distribution diagram of the silicon carbide single crystal wafer prepared in Example 1; Figure 6 Schematic diagram of a silicon carbide growth device of Comparative Example 1, wherein 1 is a crucible cover, 2 is a graphite crucible barrel, 3 is an inner liner, 4 is silicon carbide powder, 5 is a silicon carbide single crystal, and 6 is a silicon carbide seed crystal; Figure 7 This is a diagram of a silicon carbide single crystal ingot grown by the method of Comparative Example 1, wherein 52a is a growth facet and 52b is an edge polycrystalline; Figure 8 This is the stress distribution diagram of the silicon carbide single crystal wafer prepared in Comparative Example 1. DETAILED DESCRIPTION

[0020] The present invention is further explained below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent modifications of the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0021] High-purity argon: purity is above 99.999%; High-purity silicon carbide (powder): refers to silicon carbide single crystal material with a purity of more than 99.999%; Silicon carbide single crystal seed crystal: The diameter of the silicon carbide single crystal seed crystal is 6~12 inches, which is 5~15mm larger than the diameter of the growing single crystal, and the orientation is

[0001] crystal direction biased towards <11-20> crystal direction 4±0.2; Facet: The growth surface dominated by the spiral growth center that appears in the growth of silicon carbide single crystal; Near-free growth: During the growth of a single crystal, some regular crystal planes of the single crystal appear at the interface and around the main growth direction. This is different from the growth of a single crystal in a free system, which can show all regular crystal planes.

[0022] The schematic diagram of the silicon carbide single crystal near-free state growth device in the present invention is as follows Figure 1 As shown by Figure 1 It can be known that the near-free-state growth device of silicon carbide single crystal includes a crucible cover 1, a crucible barrel 2, an inner liner 3, and a seed crystal holder 7; the crucible cover 1 is located at the upper end of the crucible barrel 2, and matches with the barrel mouth of the crucible barrel 2; the seed crystal holder 7 is located at the lower end of the crucible cover 2, parallel to the position of the crucible cover 2, and has a vertical cross-section of a horizontal "bow"-shaped structure, and the middle position of the "bow" is concave downward; the vertical cross-section of the inner liner 3 is a "convex"-shaped opening structure, and the opening position at the upper end matches the lower end of the concave position in the middle of the seed crystal holder 7; The crucible cover 1, seed crystal holder 7 and inner liner 3 are detachable structures, the maximum outline dimensions of the seed crystal holder 7 and the inner liner 3 match the crucible barrel 2, and can be fixed on the inner wall of the crucible barrel 2; the highest end of the "convex" shape of the inner liner 3 is 2~5mm higher than the lowest end of the recessed position of the seed crystal holder 7, and there is a gap between the inner liner 3 and the recessed position of the seed crystal holder 7, and the gap size is 0.3~2mm; the distance between the upper end of the seed crystal holder 7 and the crucible barrel 2 is 5~15mm; the inner liner 3 is fixed above the 1 / 2 position of the crucible barrel 2; the thickness of the seed crystal holder 7 is 5mm, and the roughness of the middle recessed surface is 15μm; the single crystal silicon near-free state growth device is made of graphite.

[0023] The silicon carbide single crystal ingot grown by the silicon carbide single crystal near-free state growth device of the present invention is shown in FIG. Figure 2 As shown, 51a is the growth facet and 51b is the {10-1n} crystal plane.

[0024] Example 1 (1) A 6-inch silicon carbide single crystal seed crystal 6 with a diameter of 155 mm is bonded to the concave surface (the surface facing the growth space) in the middle of the "bow" shape of the seed crystal holder 7 by means of an adhesive; (2) placing silicon carbide powder 4 in the crucible barrel 2, the amount of silicon carbide powder 4 added reaching 1 / 2 of the height of the crucible barrel 2, fixing the inner liner 3 and the seed crystal holder 7 bonded with the seed crystal in step (1) in the crucible barrel 2 in sequence, located on the upper end of the silicon carbide powder 4, the installed inner liner 3 covers the concave part between the silicon carbide seed crystal 6 and the seed crystal holder 7, and is 2 mm higher than the lower end of the seed crystal holder 7, and there is a gap between the inner liner 3 and the seed crystal holder 7, the gap size is 0.3 mm, installing the crucible cover, the distance between the lower surface of the crucible cover and the highest point of the seed crystal holder is 5 mm, and the assembly of the crucible is completed; (3) Place the assembled crucible in an induction heating furnace, seal the furnace cavity, and evacuate the induction heating furnace to a vacuum degree of 1×10 -4 Pa, heating to 1100°C, expelling moisture and impurity gases adsorbed on the furnace chamber wall and crucible wall; (4) High-purity argon gas is introduced at a flow rate of 0.2 L / min, and the temperature is continued to rise to 2100-2150°C and kept at this temperature for 100 h to complete the growth of silicon carbide single crystals. The silicon carbide single crystals grow on the seed crystal holder 7, and silicon carbide polycrystals grow in the gap 8 between the seed crystal holder 7 and the inner sleeve 3; (5) After the growth is completed, stop introducing argon gas and maintain the cooling rate at 0.25~1℃ / min. Cool to room temperature to obtain a silicon carbide single crystal. The silicon carbide single crystal is rounded, cut, ground, and polished to obtain a silicon carbide single crystal wafer with a roughness Ra=0.2nm.

[0025] The photo of the silicon carbide single crystal prepared in Example 1 is as follows Figure 3 As shown, from Figure 3 In the figure, six symmetrical and regular {10-1n} crystal planes can be clearly seen, and the thickness of the single crystal is 23mm. After being processed into a silicon carbide single crystal wafer, its stress is tested. The stress distribution diagram of the silicon carbide single crystal wafer is shown in the figure below. Figure 4 As shown in the figure, it can be seen that the overall stress distribution of the wafer is uniform and the stress value is low, and there is no stress concentration area at the edge. The processed silicon carbide single crystal wafer is corroded and its one-dimensional dislocation density is measured. The results are shown in Figure 5 As shown, the total dislocation density is 1143 / cm 2 , proving that the quality of silicon carbide single crystals grown in a nearly free state is better.

[0026] Example 2 Different from Example 1, in step (1) of Example 2, the silicon carbide seed crystal 6 is an 8-inch seed crystal with a diameter of 205 mm, and the remaining steps and conditions are the same as those of Example 1. The grown 8-inch silicon carbide single crystal shows six symmetrical and regular {10-1n} crystal planes, the single crystal thickness is 21 mm, the overall stress distribution is uniform and the stress value is low, and the dislocation defect is 1205 / cm 2 .

[0027] Example 3 Different from Example 1, the gap between the inner sleeve 3 and the seed crystal holder 7 in step (3) of Example 3 is 0.5 mm, and the remaining steps and conditions are the same as those of Example 1. The grown silicon carbide single crystal shows six larger symmetrical and regular {10-1n} crystal planes, the single crystal thickness is 22 mm, the overall stress distribution is uniform and the stress value is low, and the dislocation defect is 954 / cm 2 .

[0028] Example 4 Different from Example 1, in step (5) of Example 4, the temperature is further increased to 2200-2250°C, and the remaining steps and conditions are the same as those of Example 1. The grown silicon carbide single crystal shows six symmetrical and regular {10-1n} crystal planes, the single crystal thickness is 36 mm, the overall stress distribution is uniform and the stress value is low, and the dislocation defect is 1450 / cm 2 .

[0029] Example 5 Different from Example 1, the holding time in step (5) of Example 5 is 200h, and the other steps and conditions are the same as those of Example 1. The grown silicon carbide single crystal showed six symmetrical and regular {10-1n} crystal planes, the single crystal thickness was 45mm, the overall stress distribution was uniform and the stress value was low, and the dislocation defect was 678 / cm 2 .

[0030] Comparative Example 1 Different from Example 1, the overall assembly diagram of the silicon carbide single crystal grown in Comparative Example 1 is as follows: Figure 6 As shown, there is no step (1) of gluing the seed crystal to the "bow"-shaped seed crystal holder, but the seed crystal is directly glued to the graphite crucible cover 1, and in step (3), the graphite crucible cover and the liner ring glued with the seed crystal are directly installed on the upper part of the graphite barrel filled with the material; the remaining steps and conditions are the same as those in Example 1; The structure of the silicon carbide single crystal grown in Comparative Example 1 is shown in FIG. Figure 7 As shown in Figure 1, polycrystalline exists at the edge and irregular {10-1n} crystal planes appear. The stress distribution of the processed wafer is shown in Figure 1. Figure 8 As shown in the figure, it can be seen from the cross-sectional stress that the stress at the edge increases sharply, proving that there are a large number of defects at the edge of the crystal.

[0031] Comparative Example 2 Different from Example 1, the overall assembly diagram of the grown silicon carbide single crystal in Comparative Example 2 is as follows: Figure 6 As shown, there is no step (1) of gluing the seed crystal to the "bow"-shaped graphite holder, but the seed crystal is directly glued to the graphite crucible cover 1, in step (3), the graphite crucible cover and the inner liner with the seed crystal glued are directly installed on the upper part of the graphite barrel filled with the material, and the insulation time in step (5) is 150h, and the remaining steps and conditions are the same as those in Example 1; There are a lot of polycrystals at the edge of the silicon carbide single crystal grown in Comparative Example 2, and the silicon carbide single crystal cracks after the growth is completed.

Claims

1. A silicon carbide single crystal near-free state growth device, characterized in that: It comprises a crucible cover (1), a crucible barrel (2), an inner liner (3), and a seed crystal holder (7); The crucible cover (1) is located at the upper end of the crucible barrel (2) and matches the barrel opening of the crucible barrel (2); The seed crystal holder (7) is located at the lower end of the crucible cover (1), parallel to the crucible cover (1), and has a vertical cross-section of a horizontal "bow"-shaped structure, with the middle of the "bow" shape being concave downwards; The vertical cross-section of the inner liner (3) is a "convex"-shaped opening structure, and the opening position at the upper end matches the lower end of the middle recessed position of the seed crystal holder (7).

2. The silicon carbide single crystal near-free state growth device according to claim 1, characterized in that: The crucible cover (1), seed crystal holder (7) and inner lining (3) are detachable structures; the maximum outline dimensions of the seed crystal holder (7) and the inner lining (3) match the crucible barrel (2) and can be fixed on the inner wall of the crucible barrel (2).

3. The silicon carbide single crystal near-free state growth device according to claim 1, characterized in that: The highest end of the "convex" shape of the inner liner (3) is 2 to 5 mm higher than the lowest end of the recessed position of the seed crystal holder (7), and there is a gap between the inner liner (3) and the recessed position of the seed crystal holder (7), and the size of the gap is 0.3 to 2 mm.

4. The silicon carbide single crystal near-free state growth device according to claim 1, characterized in that: The distance between the uppermost end of the seed crystal holder (7) and the crucible barrel (2) is 5 to 15 mm; and the inner lining (3) is fixed above the 1 / 2 position of the crucible barrel (2).

5. The silicon carbide single crystal near-free state growth device according to claim 1, characterized in that: The seed crystal holder (7) has a thickness of 3 to 10 mm, and a roughness of a middle concave surface of 1 to 25 μm.

6. The silicon carbide single crystal near-free state growth device according to claim 1, characterized in that: The single crystal silicon near-free state growth device is made of graphite.

7. A method for nearly free-state growth of a silicon carbide single crystal, characterized in that: The silicon carbide single crystal near-free state growth device according to any one of claims 1 to 6 comprises the following steps: 1) bonding a silicon carbide single crystal seed crystal to the concave surface in the middle of the "bow" shape of the seed crystal holder (7); 2) placing silicon carbide powder in a crucible barrel (2), fixing the inner liner (3) and the seed crystal holder (7) bonded with the seed crystal in step (1) in the crucible barrel (2) in sequence, positioned above the silicon carbide powder (4), and then installing the crucible cover (1) to complete the assembly of the crucible; 3) Place the assembled crucible in the induction heating furnace, seal the furnace cavity, and evacuate the induction heating furnace to a vacuum degree of 0.1~10×10 -4 Pa, heating to 1050~1450℃, expelling moisture and impurity gases adsorbed on the furnace chamber wall and crucible wall; 4) Introduce argon gas, continue to raise the temperature to 2100~2350℃, keep warm for 100~300h, and complete the growth of silicon carbide single crystal; 5) After the growth is completed, stop introducing argon gas and cool to room temperature to obtain a silicon carbide single crystal.

8. The method for nearly free-state growth of single crystal silicon according to claim 7, characterized in that: In step 1), the diameter of the silicon carbide single crystal seed crystal is 6 to 12 inches, which is 5 to 15 mm larger than the diameter of the growing single crystal; the orientation of the silicon carbide single crystal seed crystal is 4±0.2° from the [0001] crystal direction to the <11-20> crystal direction.

9. The method for nearly free-state growth of single crystal silicon according to claim 7, characterized in that: In step 2), the amount of silicon carbide powder added reaches 1 / 2~2 / 3 of the height of the crucible barrel, and the purity of the silicon carbide powder is higher than 99.999%; in step 4), the purity of argon gas is higher than 99.999%, and the inlet flow rate is 0.05~0.3L / min.

10. The method for nearly free-state growth of single crystal silicon according to claim 7, characterized in that: Step 5) The cooling rate is 0.25-2°C / min; the silicon carbide single crystal is rounded, cut, ground, and polished to obtain a silicon carbide single crystal wafer with a roughness Ra < 0.5 nm.

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