A growth method for reducing stress in silicon carbide crystals

Abstract

The present invention discloses a growth method for reducing stress of silicon carbide crystals. A crucible liner ring is made of hard graphite and porous graphite and is placed between a seed crystal and a graphite crucible. The thickness, shape and combination form of the hard graphite and the porous graphite are adjusted by computational simulation so that during the crystal growth process, the silicon atmosphere is effectively discharged at the initial growth stage to reduce the negative impact on the nucleation of silicon carbide. While maintaining the crystal shape of equal diameter or expanded diameter growth, the pores of the porous graphite can be compressed to release thermal stress, reduce the occurrence of cracks and cracks in the crystal ingot, reduce the density of microtubes, grain boundaries and dislocation defects, and obtain a high-quality crystal ingot.

Description

Technical Field

[0001] The invention belongs to the technical field of silicon carbide growth, relates to the growth of silicon carbide crystals, and in particular to a growth method for reducing the stress of silicon carbide crystals. Background Art

[0002] The development and progress of semiconductor materials are core key technologies. As one of the important representatives of the third generation of semiconductor materials, silicon carbide single crystal materials have become a hot semiconductor material in the future due to their large bandgap, high saturated electron mobility, strong breakdown field, and high thermal conductivity. A good silicon carbide single crystal growth thermal field is the key to obtaining high-quality silicon carbide wafers and directly affects the performance of silicon carbide devices. The structural design of the growth thermal field will directly affect the quality of ingot growth (such as defect density, grain boundaries, and microtubes, etc.). Therefore, the structure of the silicon carbide growth thermal field required for growing crystals has also become an important part of ensuring the quality of single crystal growth.

[0003] At present, the mainstream silicon carbide thermal field material uses graphite, but in the process of crystal growth, due to the difference in thermal expansion coefficients between graphite and silicon carbide materials, thermal mismatch occurs between the contact surfaces of the two, which directly affects the stress magnitude and stress release of the crystal during growth, resulting in a large number of microtubes, grain boundaries, dislocations and other defects in the crystal during growth or out of the furnace. More seriously, it even causes a large number of cracks and cracks in the crystal; in the early stage of crystal growth, excessive partial pressure of silicon atmosphere will affect the initial nucleation of silicon carbide on the seed crystal, causing more defects in the subsequent growth; as the silicon carbide crystal continues to grow, the powder will gradually carbonize, and the carbon powder will adhere to the crystal surface to form carbon inclusions, reducing the effective thickness and utilization rate of the ingot, causing waste of resources and increasing production costs. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a growth method for reducing the stress of silicon carbide crystals. The present invention uses hard graphite and porous graphite to make a crucible liner ring, which is placed between the seed crystal and the graphite crucible. The thickness, shape, and combination form of the hard graphite and the porous graphite are adjusted through computational simulation, so that during the crystal growth process, the silicon atmosphere can be effectively discharged in the early growth stage to reduce the negative impact on the nucleation of silicon carbide. While maintaining the crystal shape of equal diameter or expanded diameter growth, the pores of the porous graphite can be compressed to achieve the effect of releasing thermal stress, thereby reducing the occurrence of cracks and cracks in the ingot, reducing the density of microtubes, grain boundaries and dislocation defects, and obtaining high-quality ingots.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A growth method for reducing stress of silicon carbide crystals, the growth method comprising the following steps:

[0007] S1: Place silicon carbide powder in a crucible and control the density of the powder through an oscillating platform;

[0008] S2: Fix the crucible liner ring between the seed crystal and the crucible;

[0009] S3: placing the crucible in step S2 in a heating chamber of a growth furnace to perform the next growth operation;

[0010] S4: evacuate the heating chamber of the growth furnace to maintain a vacuum at 0 Pa and increase the temperature;

[0011] S5: After reaching the set temperature, argon gas is introduced into the heating chamber to raise the pressure of the heating chamber of the growth furnace to 600 mbar, and the silicon atmosphere that has been generated is discharged through the pores of the porous graphite of the crucible liner ring, and then the heating chamber is evacuated to 0 Pa, and the above operation is repeated to complete the complete discharge of the silicon atmosphere;

[0012] S6: After the pressure rises to 600 mbar again, the pressure is controlled within the growth pressure range by stepwise depressurization and maintained for 3 h;

[0013] S7: Under the condition of stable pressure, the temperature is raised to the growth temperature to stabilize the growth;

[0014] S8: After the growth is completed, the pressure is raised to 600 mbar, and the temperature of the heating chamber of the growth furnace is lowered to reduce the heating power to 0, and the growth atmosphere is continued to be introduced to allow the temperature in the growth furnace to naturally cool to room temperature;

[0015] S9: After the temperature of the heating chamber of the growth furnace reaches room temperature, the used crucible liner ring is removed, the grown crystal ingot is taken out, and the crystal furnace is opened;

[0016] The crucible liner ring comprises a detachable inner ring and an outer ring, the inner ring is made of porous graphite material, and the outer ring is made of hard graphite material.

[0017] As a preferred embodiment of the present invention, in S4, the temperature is raised from room temperature to 1300° C. for 3 h, and then raised to 1800° C. for 5 h.

[0018] As a preferred embodiment of the present invention, in S6, the growth pressure ranges from 1 to 30 mbar.

[0019] As a preferred embodiment of the present invention, in S7, the growth temperature is 1900-2300° C., and the growth time is 60-150 hours.

[0020] As a preferred embodiment of the present invention, in S7, the growth temperature is 2200-2300° C., and the growth time is 60-150 h.

[0021] As a preferred solution of the present invention, the upper and lower parts of the inner ring are of equal or unequal thickness, and the outer ring is matched with the inner ring.

[0022] As a preferred solution of the present invention, the inner ring and the outer ring form a cylindrical ring structure.

[0023] As a preferred solution of the present invention, the thickness of the inner ring is 0-30 cm.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1) The present invention can effectively solve the stress problem in the growth process of silicon carbide (SiC) single crystal, thereby greatly improving the quality of silicon carbide ingots.

[0026] 2) Effectively reduce the thermal stress of the ingot. The crucible liner ring is designed and prepared by combining porous graphite materials and hard graphite materials. The shape and structure of porous graphite and hard graphite are flexibly designed according to the thermal field conditions. During the high-temperature growth of the ingot, the elasticity and compressibility of porous graphite are used to effectively reduce the thermal stress caused by thermal mismatch, reduce defects such as microtubes, grain boundaries and dislocations, and improve the growth quality of silicon carbide.

[0027] 3) It is conducive to the initial nucleation of silicon carbide crystals. By changing the vacuum degree during the growth process, the pore channels of the porous graphite in the crucible liner can be effectively used to discharge the initial silicon atmosphere, reducing its influence on the nucleation of silicon carbide seed crystals, thereby improving the growth quality of the ingot in the nucleation stage.

[0028] 4) Reduce the negative impact of impurities during growth. During the growth process, by continuously introducing protective gas into the growth chamber and pumping to maintain vacuum, impurities in the growth atmosphere can be effectively extracted from the crucible through the porous graphite pores of the crucible liner ring, reducing the defects caused by impurities in the ingot during the growth process, thereby improving the overall quality of the ingot.

[0029] 5) Reduce carbon inclusions in the later stage of the ingot and increase the effective thickness and utilization rate of the ingot. As the silicon carbide crystal grows, the silicon carbide powder will gradually carbonize. In the later growth, the carbon powder will form carbon inclusions on the surface of the ingot, reducing the utilization rate of the ingot. The method of this patent uses the pore channels of porous graphite in conjunction with the gas flow in the crucible to remove the carbon powder from the growth crucible, reducing the probability of it forming inclusions on the surface of the ingot, increasing the effective thickness of the ingot, and thus improving the utilization rate.

[0030] 6) Improve the growth rate of silicon carbide crystals and the utilization rate of powder. By using the porous graphite channels in the crucible liner, the proportion of the growth atmosphere can be adjusted in the growth crucible to form a new stable state, promote the sublimation of powder, form an atmosphere ratio more suitable for crystal growth on the crystal surface, and increase the growth rate of the ingot; and reduce the waste of silicon carbide raw powder caused by insufficient sublimation, and improve the utilization efficiency of powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the structure inside the crystal growth crucible of the present invention.

[0032] Figure 2 It is a schematic structural diagram of the crucible liner ring of the present invention.

[0033] Figure 3 This is a dislocation identification picture of the crystal obtained in Example 1 after being corroded by molten KOH.

[0034] Figure 4 This is a dislocation identification picture of the crystal obtained in Example 2 after being corroded by molten KOH.

[0035] In the figure, 1. crucible; 2. seed crystal; 3. crucible lining ring; 4. silicon carbide powder; 5. inner ring; 6. outer ring. DETAILED DESCRIPTION

[0036] In order to make the technical means, creative features, purpose and efficacy of the present invention easy to understand, the present invention is further described below in conjunction with specific embodiments, but the following embodiments are only preferred embodiments of the present invention, not all. Based on the embodiments in the implementation mode, other embodiments obtained by those skilled in the art without creative work all belong to the protection scope of the present invention. The experimental methods in the following embodiments, unless otherwise specified, are conventional methods, and the materials, reagents, etc. used in the following embodiments, unless otherwise specified, can all be obtained from commercial channels.

[0037] See also Figure 1 and Figure 2 The present invention provides a growth method for reducing stress of silicon carbide crystals, comprising:

[0038] Step S1: Place silicon carbide powder 4 on Figure 1 In the component crucible 1, the filling height of the silicon carbide powder 4 from the seed crystal 2 is 10-30 cm, so that the surface of the silicon carbide powder 4 remains flat, and the density of the silicon carbide powder 4 is controlled by the oscillation platform to maintain a uniform distribution of the pores of the entire silicon carbide powder 4.

[0039] Step S2: Figure 2The crucible lining ring 3 shown is fixed between the seed crystal 2 and the crucible 1 to prevent the crucible lining ring 3 from falling due to high temperature during the heating process.

[0040] Among them, the inner ring 5 of the crucible liner ring 3 is a porous graphite material, and its thickness can be adjusted between 0 and 30 cm. The upper and lower parts can be designed to have equal thickness or unequal thickness structures, and can also be designed to have regular or irregular shapes; the outer ring 6 of the crucible liner ring 3 is a hard graphite material, and its thickness and shape are adjusted and adapted accordingly according to the adjustment of the porous graphite material, and are jointly prepared into a cylindrical ring structure.

[0041] Step S3: placing the crucible 1 in step S2 in the heating chamber of the growth furnace to perform the next growth operation.

[0042] Step S4: The heating chamber of the growth furnace is evacuated and maintained at 0 Pa, and then heated to raise the temperature from room temperature to 1300° C. in 3 h, and then to 1800° C. in 5 h.

[0043] Step S5: After the temperature rises to 1800°C, argon gas is introduced into the heating chamber to increase the pressure of the heating chamber of the growth furnace to 600 mbar, and the silicon atmosphere that has been generated is discharged through the pores of the porous graphite of the crucible liner ring, and then the heating chamber is evacuated to 0 Pa. The above operation is repeated to complete the complete discharge of the silicon atmosphere.

[0044] Step S6: After the pressure rises to 600 mbar, the pressure is controlled within the growth pressure range of 1-30 mbar by stepwise depressurization and maintained for 3 hours;

[0045] Step S7: Under the condition of stable pressure, the temperature is increased to a growth temperature of 1900-2300° C. and the growth is stabilized for 60-150 hours.

[0046] Step S8: After the growth is completed, the pressure is increased to 600 mbar, and the temperature of the heating chamber of the growth furnace is reduced to reduce the heating power to 0, and the growth atmosphere is continued to be introduced to allow the temperature in the growth furnace to naturally cool to room temperature.

[0047] Step S9: After the temperature of the heating chamber of the growth furnace reaches room temperature, the used crucible liner ring 3 is removed, and the grown crystal ingot is taken out, thus completing the crystal furnace opening.

[0048] In the present invention, the structure and shape of the crucible liner ring 3 can be flexibly designed according to different thermal fields. The new thermal field component is suitable for the growth process of ingots of different sizes. The use of a more suitable crucible liner ring can effectively improve the crystal quality.

[0049] By combining porous graphite materials and hard graphite materials, a new thermal field structure is proposed to improve the defect problems caused by factors such as stress and impurities during the crystal growth process.

[0050] In the design and preparation of the crucible liner ring, the thickness, shape and height of the porous graphite material and the hard graphite material can be more adjusted with the changes in the thermal field structure or growth conditions, and have a wider applicability.

[0051] The application of porous graphite plays an important role in reducing stress and eliminating negative components. The preparation process is simple and easy to obtain. Proper design can also increase the service life of hard graphite, while improving crystal quality and reducing production costs.

[0052] The invention relates to synthetic reaction conditions: 1900-2300° C., pressure controlled to be 1-30 mbar, under which the reaction conditions are maintained for 60-150 hours, having a wider adjustment window and being able to improve the growth rate of the crystal. Example 1

[0053] This embodiment discloses a growth method for reducing stress of silicon carbide crystals, and the specific implementation steps are as follows.

[0054] 1) A crucible liner ring made entirely of hard graphite material was processed according to the thermal field structure design and placed in the thermal field to complete the crystal growth; the parameters of the hard graphite material refer to Table 1.

[0055] 2) Place silicon carbide powder in the growth crucible, with the filling height 20 cm away from the seed crystal, so that the surface of the powder remains flat, and the density of the powder is controlled by the oscillation platform to maintain the uniform distribution of the overall powder pores. Fix the self-designed crucible liner ring between the seed crystal and the crucible. Place the crucible in the heating chamber of the growth furnace. Evacuate the heating chamber of the growth furnace and keep it at 0 Pa, and use 8 h to raise the temperature to 1800℃. After the temperature rises to 1800℃, introduce argon into the heating chamber to increase the pressure of the heating chamber of the growth furnace to 600 mbar, and then evacuate the heating chamber to 0 Pa, and repeat the above operation. After the pressure rises to 600 mbar, control the pressure within the growth pressure range of 30 mbar through staged decompression and maintain it for 3 hours; under the condition of stable pressure, increase the temperature to the growth temperature of 2200~2300℃, and grow stably for 150 hours. After the growth is completed, the pressure is raised to 600 mbar, and the temperature of the growth furnace heating chamber is reduced to 0, and the growth atmosphere is continued to be introduced to allow the temperature in the growth furnace to cool naturally to room temperature. After the temperature of the growth furnace heating chamber reaches room temperature, the used crucible liner ring is removed, and the grown ingot is taken out to complete the crystal furnace opening.

[0056] 3) Process the crystal into wafers, take a piece from the middle of the ingot and etch it, and identify defects such as dislocations on the wafer after molten KOH etching to determine the quality of the crystal. Figure 3The number of dislocations in the wafer can be obtained, where the total number is 26805, the TSD is 2537, the TED is 22316, and the BPD is 1952. Example 2

[0057] This embodiment discloses a growth method for reducing stress of silicon carbide crystals, and the specific implementation steps are as follows:

[0058] 1) According to the thermal field structure design, crucible liners made of porous graphite and hard graphite materials were processed, in which the porous graphite had an equal width structure from top to bottom and the same thickness as the hard graphite. The parameters of the porous graphite and hard graphite materials are shown in Table 1; they were placed in the thermal field to complete the crystal growth.

[0059] 2) Place silicon carbide powder in the growth crucible, with the filling height 20 cm away from the seed crystal, so that the surface of the powder remains flat, and the density of the powder is controlled by the oscillation platform to maintain a uniform distribution of the overall powder pores. Fix the self-designed crucible liner ring between the seed crystal and the crucible to prevent the crucible liner ring from falling due to high temperature during the heating process. Place the crucible in the heating chamber of the growth furnace. Evacuate the heating chamber of the growth furnace and keep it at 0 Pa, then heat it, raise the temperature from room temperature to 1300℃ in 3h, and then raise the temperature to 1800℃ in 5h. After the temperature rises to 1800℃, introduce argon gas into the heating chamber, so that the pressure of the heating chamber of the growth furnace is raised to 600 mbar, and the silicon atmosphere that has been generated is discharged through the pores of the porous graphite of the crucible liner ring, and then evacuate the heating chamber to 0 Pa, repeat the above operation, and complete the complete discharge of the silicon atmosphere. After the pressure rises to 600 mbar, the pressure is controlled within the growth pressure range of 30 mbar through staged pressure reduction and maintained for 3 hours; under the condition of stable pressure, the temperature is raised to the growth temperature of 2200~2300℃ and stable growth is carried out for 150 hours. After the growth is completed, the pressure is raised to 600 mbar, and the temperature of the heating chamber of the growth furnace is lowered to reduce the heating power to 0, and the growth atmosphere is continued to be introduced to allow the temperature in the growth furnace to cool naturally to room temperature. After the temperature of the heating chamber of the growth furnace reaches room temperature, the used crucible liner ring is removed, and the grown ingot is taken out to complete the crystal furnace opening.

[0060] 3) Process the crystal into wafers, take a piece of the middle of the crystal for etching, and identify defects such as dislocations on the wafer after molten KOH etching to determine the quality of the crystal. Figure 4 The number of dislocations in the wafer can be obtained, where the total number is 5195, the TSD is 1351, the TED is 2662, and the BPD is 1182.

[0061] Compared with the data in Example 1, the number of dislocations in the wafer in Example 2 is significantly reduced, indicating that the growth method for reducing the stress of silicon carbide crystals has a significant effect.

[0062] Table 1. Material parameters of porous graphite and hard graphite

[0063]

[0064] It can be seen that the present invention effectively reduces the thermal stress of the ingot. The crucible liner ring is designed and prepared by combining porous graphite material and hard graphite material. The shape structure of porous graphite and hard graphite is flexibly designed according to the thermal field conditions. During the high-temperature growth of the ingot, the elasticity and compressibility of porous graphite are utilized to effectively reduce the thermal stress problem caused by thermal mismatch, reduce defects such as microtubes, grain boundaries and dislocations, and improve the growth quality of silicon carbide. It is beneficial to the initial nucleation of silicon carbide crystals. By changing the vacuum degree during the growth process, the pore channels of the porous graphite in the crucible liner ring can be effectively utilized to discharge the initial silicon atmosphere, reduce its influence on the nucleation of the silicon carbide seed crystal, and thus improve the growth quality of the ingot in the nucleation stage.

[0065] The above is only a preferred embodiment of the present invention, and is not any formal or substantial limitation of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the method of the present invention, and these improvements and supplements should also be regarded as the protection scope of the present invention. Any technician familiar with this profession, without departing from the spirit and scope of the present invention, can make some changes, modifications and evolutions of the technical content disclosed above, which are equivalent embodiments of the present invention; at the same time, any changes, modifications and evolutions of any equivalent changes made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A growth method for reducing stress in silicon carbide crystals, characterized in that: The growth method comprises the following steps: S1: Place silicon carbide powder in a crucible and control the density of the powder through an oscillating platform; S2: Fix the crucible liner ring between the seed crystal and the crucible; S3: placing the crucible in step S2 in a heating chamber of a growth furnace to perform the next growth operation; S4: evacuate the heating chamber of the growth furnace to maintain a vacuum at 0 Pa and increase the temperature; S5: After reaching the set temperature, argon gas is introduced into the heating chamber to raise the pressure of the heating chamber of the growth furnace to 600 mbar, and the silicon atmosphere that has been generated is discharged through the pores of the porous graphite of the crucible liner ring, and then the heating chamber is evacuated to 0 Pa, and the above operation is repeated to complete the complete discharge of the silicon atmosphere; S6: After the pressure rises to 600 mbar again, the pressure is controlled within the growth pressure range by stepwise depressurization and maintained for 3 h; S7: Under the condition of stable pressure, the temperature is raised to the growth temperature to stabilize the growth; S8: After the growth is completed, the pressure is raised to 600 mbar, and the temperature of the heating chamber of the growth furnace is lowered to reduce the heating power to 0, and the growth atmosphere is continued to be introduced to allow the temperature in the growth furnace to naturally cool to room temperature; S9: After the temperature of the heating chamber of the growth furnace reaches room temperature, the used crucible liner ring is removed, the grown crystal ingot is taken out, and the crystal furnace is opened; The crucible liner ring comprises a detachable inner ring and an outer ring, the inner ring is made of porous graphite material, the thickness of the porous graphite is between 0-30 cm, and the outer ring is made of hard graphite material.

2. A method for reducing stress in silicon carbide crystal growth according to claim 1, characterized in that: In S4, the temperature is raised from room temperature to 1300°C for 3 h, and then raised to 1800°C for another 5 h.

3. A growth method for reducing stress in silicon carbide crystals according to claim 1, characterized in that: In S6, the growth pressure range is 1~30 mbar.

4. A growth method for reducing stress in silicon carbide crystals according to claim 1, characterized in that: In S7, the growth temperature is 1900~2300°C and the growth time is 60~150h.

5. A growth method for reducing stress in silicon carbide crystals according to claim 4, characterized in that: In S7, the growth temperature is 2200~2300°C and the growth time is 60~150h.

6. A growth method for reducing stress in silicon carbide crystals according to claim 1, characterized in that: The upper and lower parts of the inner ring are of equal or unequal thickness, and the outer ring is adapted to the inner ring.

7. A growth method for reducing stress in silicon carbide crystals according to claim 1 or 6, characterized in that: The inner ring and the outer ring form a cylindrical ring structure.

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