阅读说明：本技术 一种低成本、高产率SiC单晶的生长方法 (Low-cost and high-yield SiC single crystal growth method ) 是由 谢雪健 徐现刚 彭燕 陈秀芳 杨祥龙 胡小波 于 2021-06-17 设计创作，主要内容包括：本发明涉及一种低成本、高产率SiC单晶的生长方法,该方法采用双侧生长坩埚进行,所述的双侧生长坩埚包括坩埚体,坩埚体内设置有两个纵向间隔的多孔石墨片,多孔石墨片将坩埚体的内腔分割成左夹层、生长腔和右夹层,本发明的生长方法采用双侧生长坩埚进行,在坩埚的两个夹层放置SiC粉料,使SiC籽晶的两个面均存在一定浓度的SiC生长气相组分,有效避免了晶体高温生长时籽晶分解的现象,降低大直径SiC籽晶粘接不良导致的SiC单晶合格率低的问题,大大提高了SiC单晶的制备效率,降低了SiC单晶成本。制备的SiC单晶质量优于或相当于现有技术制备的SiC单晶质量,能够用于新能源汽车、光伏发电、5G通讯等领域。(The invention relates to a low-cost high-yield SiC single crystal growth method, which is carried out by adopting a bilateral growth crucible, wherein the bilateral growth crucible comprises a crucible body, two porous graphite sheets which are longitudinally spaced are arranged in the crucible body, and the inner cavity of the crucible body is divided into a left interlayer, a growth cavity and a right interlayer by the porous graphite sheets. The quality of the prepared SiC single crystal is superior to or equal to that of the SiC single crystal prepared in the prior art, and the SiC single crystal can be used in the fields of new energy automobiles, photovoltaic power generation, 5G communication and the like.)

1. A low-cost and high-yield SiC single crystal growth method is carried out by adopting a bilateral growth crucible, wherein the bilateral growth crucible comprises a crucible body, two porous graphite sheets which are longitudinally spaced are arranged in the crucible body, the inner cavity of the crucible body is divided into a left interlayer, a growth cavity and a right interlayer by the porous graphite sheets, a clamping groove a is arranged on the top wall of the growth cavity, a clamping groove b which is opposite to the clamping groove a is arranged at the bottom of the growth cavity, and SiC seed crystals are arranged between the clamping groove a and the clamping groove b;

the growth method comprises the following steps:

1) SiC powder is filled in the left interlayer and the right interlayer, SiC seed crystals are fixed between the clamping grooves a and the clamping grooves b, guide plates inclined with the seed crystals are fixed at two ends of growth surfaces at the left side and the right side of the SiC seed crystals,

2) placing the crucible with the two sides growing after being charged in a single crystal furnace, and vacuumizing a growth chamber of the single crystal furnace;

3) introducing carrier gas into the growth chamber, starting a power supply, heating the double-side growth crucible, slowly raising the temperature and reducing the pressure, constructing a temperature gradient in the growth chamber, keeping a certain temperature and pressure in the growth chamber, sublimating the SiC powder, and transmitting gas components to SiC seed crystals through the porous graphite sheets to perform crystal growth;

4) after the crystal growth is finished, slowly reducing the temperature to room temperature, and simultaneously introducing carrier gas into the single crystal furnace to atmospheric pressure to obtain two SiC single crystals.

2. The growing method according to claim 1, wherein the porous graphite sheet has a pore size of 0.03 to 1mm and a porosity of 20 to 80%; a left interlayer: the volume ratio of the right interlayer is 1: 1-3: 1; during charging, selecting double-side growth crucibles with interlayers of different specifications according to the growth thickness of crystals on two expected sides, preferably, selecting a left interlayer: the volume ratio of the right interlayer is 1: 1-1.5-1.

3. The growth method according to claim 1, wherein the grooves a and b are width-adjustable grooves, the width of the groove is 0.01-0.1 mm wider than the thickness of the SiC seed crystal, and the height of the groove a and the groove b is 0.5-5 mm; further preferably, the height of the clamping grooves a and b is 1-3 mm.

4. The growing method according to claim 1, wherein the SiC seed crystal is at a distance of 30 to 100mm from the porous graphite sheet, preferably, the SiC seed crystal is at a distance of 40 to 80mm from the porous graphite sheet; the thickness of the SiC seed crystal wafer is 0.5-3 mm, and the diameter of the SiC seed crystal is 2-8 inches.

5. The growth method according to claim 1, wherein the SiC seed crystal is one seed crystal or two closely attached seed crystals, and the seed crystal is a 4H-SiC wafer or/and a 6H-SiC wafer.

6. The growth method according to claim 5, wherein the SiC seed crystal is a single seed crystal, and when the 4H-SiC single crystal and the 6H-SiC single crystal are grown simultaneously, the seed crystal is selected from 1 4H-SiC wafer or 1 6H-SiC wafer, and the carbon surface of the seed crystal faces the 4H-SiC single crystal growth cavity or the silicon surface of the seed crystal faces the 6H-SiC single crystal growth cavity.

7. The growth method according to claim 5, wherein when the SiC seed crystals are two seed crystals, two SiC wafers are tightly attached and placed in the clamping grooves a and b for fixation; when two 4H-SiC single crystals grow, two 4H-SiC wafers are selected as seed crystals, the silicon surfaces of the two wafers are attached to one wafer, and the carbon surfaces of the two wafers face to the growth cavity respectively; when two 6H-SiC single crystals grow, two 6H-SiC wafers are selected as seed crystals, the carbon surfaces of the two wafers are attached to one wafer, and the silicon surfaces of the two wafers face to the growth cavity respectively; when 1 piece of 4H-SiC and 1 piece of 6H-SiC single crystal are grown, 1 piece of 4H-SiC and 1 piece of 6H-SiC wafer are selected as seed crystals, the silicon surface of the 4H-SiC seed crystal and the carbon surface of the 6H-SiC seed crystal are attached to one piece, and the carbon surface of the 4H-SiC seed crystal and the silicon surface of the 6H-SiC seed crystal face the 4H-SiC single crystal and the 6H-SiC single crystal growth cavity respectively.

8. The growth method as claimed in claim 1, wherein the guide plates inclined to the seed crystal are arranged at the positions close to the clamping grooves a and b at the two ends of the seed crystal, and the distance between the two guide plates at the same side close to the growth surface of the seed crystal is smaller than the distance between the two guide plates far away from the growth surface of the seed crystal.

9. The growth method according to claim 1, wherein the pressure in the growth chamber of the single crystal furnace is 10 or less during the evacuation in step 2)^-2Pa, preferably, the pressure in the growth chamber of the single crystal furnace is 10 or less^-4Pa; the purpose is toRemoving air and residual water vapor in the growth system; the carrier gas is high-purity argon, high-purity helium, high-purity hydrogen or a mixed gas of the high-purity argon, the high-purity helium and the high-purity hydrogen.

10. The growth method according to claim 1, wherein in step 3), a temperature gradient is established in such a way that a positive temperature gradient pointing from the SiC seed crystal to the SiC powder exists in the horizontal direction in the growth cavity by adjusting heating, and the temperature gradient between the SiC powder and the SiC seed crystal is 20-50 ℃/cm; a positive temperature gradient exists in the vertical direction, wherein the center of the seed crystal points to the edge of the seed crystal, and the temperature gradient between the center of the seed crystal and the edge of the seed crystal is 5-10 ℃/cm;

the heating rate is 30-150 ℃/h and the pressure reduction rate is 10-500 mbar/h before the crystal grows in a heat preservation way;

the temperature for the crystal to grow is 2100-plus-2350 ℃, the growth pressure is 1-50 mbar, and the temperature-keeping time is 40-150 h.

Technical Field

The invention relates to a low-cost and high-yield SiC single crystal growth method, and belongs to the technical field of crystal growth.

Background

As a typical representative of the third-generation semiconductor material, the SiC material has excellent properties such as a large forbidden band width, a high thermal conductivity, a small critical breakdown field strength, a high carrier saturation mobility rate, a small dielectric constant, and a strong radiation resistance. Therefore, the SiC material is particularly suitable for 5G radio frequency devices and high voltage power devices. SiC-based devices have superior performance compared to devices made of the first generation semiconductor Si. For example, compared with a Si-based IGBT, a SiC MOS power device represented by a SiC MOS can have a lower on-resistance, and is embodied in a product, for example, the size is reduced, so that the size is reduced, the switching speed is high, and the power consumption is greatly reduced compared with a conventional power device. In the field of electric vehicles, the power consumption can be reduced and the volume can be reduced when the SiC device is used; meanwhile, the charging time can be greatly shortened by applying SiC in the high-voltage direct-current charging pile, and great social benefits are brought.

One of the bottlenecks that currently limit the development of the SiC industry lies in: the cost of the SiC substrate is high, and the cost of the SiC substrate is about 4 to 5 times that of Si. The SiC single crystal is usually obtained by a physical vapor transport method, in the method, SiC seed crystal and SiC powder are respectively arranged at the top and the bottom of an isostatic pressure graphite crucible, a medium-frequency induction heating power supply is adopted to heat the SiC seed crystal and the SiC powder to more than 2000 ℃, a temperature gradient is established in the SiC crucible, and the SiC powder is sublimated and then recrystallized on the SiC seed crystal to realize the growth of the SiC single crystal. When the method is adopted to grow the SiC single crystal, the back of the SiC seed crystal needs to be adhered to the top of the crucible. The SiC seed crystal bonding has higher requirements on environment and technicians, and particularly, the SiC seed crystal bonding difficulty is increased along with the increase of the diameter of the SiC seed crystal, so that the seed crystal bonding qualification rate is lower. Poor seed crystal adhesion can cause high-temperature decomposition of SiC seed crystals in the growth process of the SiC crystals due to the fact that the back of the SiC seed crystals are not protected by SiC growth gas phase components, so that defects such as micropipes and cavities appear in the crystals, and the grown crystals are directly scrapped and cannot be used for preparing devices. In addition, when the method is adopted, one SiC seed crystal is consumed for growing one SiC single crystal, so that the SiC single crystal is high in growth cost and low in yield.

Chinese patent document CN206244927U discloses an apparatus for growing silicon carbide single crystals of different crystal structures. In the device, a plurality of screw threads are arranged on the inner surface of the upper cover of the graphite crucible and the side wall above the lug boss, the same lug bosses are arranged on the side wall of the graphite crucible at intervals, the graphite annular support is positioned on the lug boss at intervals, seed crystals are fixed on the lug boss, and a plurality of seed crystals are adopted to simultaneously grow silicon carbide single crystals with different crystal structures in the same production equipment. When the device grows the silicon carbide single crystal, the growth gas phase component can only be transmitted to the surface of the seed crystal through the air hole on the plane of the boss, namely the growth gas component is not opposite to the growth surface of the seed crystal, so the growth rate is low and the efficiency is not high. In addition, the temperature of the seed crystal close to the surface of the material is high, which easily causes the decomposition of the seed crystal, thereby easily causing the deterioration of the crystal quality.

Therefore, how to improve the crystal growth efficiency of SiC and reduce the preparation cost of SiC becomes a technical problem which needs to be solved in the field.

Disclosure of Invention

Aiming at the technical problems of low yield and high cost of SiC single crystals in the prior art, the invention provides a low-cost and high-yield SiC single crystal growth method.

The technical scheme of the invention is as follows:

a low-cost and high-yield SiC single crystal growth method is carried out by adopting a bilateral growth crucible, wherein the bilateral growth crucible comprises a crucible body, two porous graphite sheets which are longitudinally spaced are arranged in the crucible body, the inner cavity of the crucible body is divided into a left interlayer, a growth cavity and a right interlayer by the porous graphite sheets, a clamping groove a is arranged on the top wall of the growth cavity, a clamping groove b which is opposite to the clamping groove a is arranged at the bottom of the growth cavity, and SiC seed crystals are arranged between the clamping groove a and the clamping groove b;

the growth method comprises the following steps:

1) SiC powder is filled in the left interlayer and the right interlayer, SiC seed crystals are fixed between the clamping grooves a and the clamping grooves b, and guide plates inclined to the seed crystals are fixed at two ends of growth surfaces on the left side and the right side of the SiC seed crystals;

2) placing the crucible with the two sides growing after being charged in a single crystal furnace, and vacuumizing a growth chamber of the single crystal furnace;

3) introducing carrier gas into the growth chamber, starting a power supply, heating the double-side growth crucible, slowly raising the temperature and reducing the pressure, constructing a temperature gradient in the growth chamber, keeping a certain temperature and pressure in the growth chamber, sublimating the SiC powder, and transmitting gas components to SiC seed crystals through the porous graphite sheets to perform crystal growth;

4) after the crystal growth is finished, slowly reducing the temperature to room temperature, and simultaneously introducing carrier gas into the single crystal furnace to atmospheric pressure to obtain two SiC single crystals.

According to the invention, the pore diameter of the porous graphite sheet is preferably 0.03-1 mm, and the porosity is preferably 20-80%.

Preferably according to the invention, the left interlayer: the volume ratio of the right interlayer is 1: 1-3: 1. During charging, the double-side growth crucibles with different specifications of interlayers are selected according to the growth thickness of crystals on two expected sides.

Further preferably, the left interlayer: the volume ratio of the right interlayer is 1: 1-1.5-1.

According to the invention, the clamping grooves a and b are both adjustable-width clamping grooves, and the width of each clamping groove is 0.01-0.1 mm wider than the thickness of the SiC seed crystal.

The width of the clamping groove is too wide, the SiC seed crystal is not firmly fixed, and when the width of the clamping groove is too narrow, the clamping groove can generate certain mechanical stress on the SiC seed crystal, so that the growth of high-quality SiC single crystals is not facilitated.

The height of the clamping grooves at the bottom and the top of the crucible has a great influence on the quality of the crystal. When the height of the clamping groove is too high, too many contact parts of the clamping groove and the seed crystal can be caused, the edge of the seed crystal is decomposed, and the edge quality of the crystal is influenced; when the height of the clamping groove is too low, the seed crystal is not firmly fixed. Therefore, the height of the clamping groove a and the clamping groove b is preferably 0.5-5 mm; further preferably, the height of the clamping grooves a and b is 1-3 mm.

According to the invention, the distance between the SiC seed crystal and the porous graphite sheet is preferably 30-100 mm, and the distance between the SiC seed crystal and the porous graphite sheet is further preferably 40-80 mm.

According to the invention, the thickness of the SiC seed crystal wafer is 0.5-3 mm, and the diameter of the SiC seed crystal is 2-8 inches.

Preferably, the SiC seed crystal is one seed crystal or two closely attached seed crystals, and the seed crystal is a 4H-SiC wafer or/and a 6H-SiC wafer.

Preferably, the SiC seed crystal is a piece of seed crystal, when the 4H-SiC single crystal and the 6H-SiC single crystal are grown simultaneously, the seed crystal adopts 1 piece of 4H-SiC wafer or 1 piece of 6H-SiC wafer, and the carbon surface of the seed crystal faces the 4H-SiC single crystal growth cavity or the silicon surface of the seed crystal faces the 6H-SiC single crystal growth cavity.

Preferably, when the SiC seed crystal is two seed crystals, two SiC wafers are adopted to be tightly attached and are placed in the clamping groove a and the clamping groove b for fixing, when two 4H-SiC single crystals grow, the two 4H-SiC wafers are selected as the seed crystals, the silicon surfaces of the two wafers are attached to one wafer, and the carbon surfaces of the two wafers face the growth cavity respectively; when two 6H-SiC single crystals grow, two 6H-SiC wafers are selected as seed crystals, the carbon surfaces of the two wafers are attached to one wafer, and the silicon surfaces of the two wafers face to the growth cavity respectively; when 1 piece of 4H-SiC and 1 piece of 6H-SiC single crystal are grown, 1 piece of 4H-SiC and 1 piece of 6H-SiC wafer are selected as seed crystals, the silicon surface of the 4H-SiC seed crystal and the carbon surface of the 6H-SiC seed crystal are attached to one piece, and the carbon surface of the 4H-SiC seed crystal and the silicon surface of the 6H-SiC seed crystal face the 4H-SiC single crystal growth cavity and the 6H-SiC single crystal growth cavity respectively.

The close bonding of the SiC wafer can be achieved by setting the widths of the chucking grooves a, b.

According to the invention, the guide plates inclined with the seed crystal are arranged at the positions, close to the clamping grooves a and b, of the two ends of the seed crystal, and the distance between the two guide plates on the same side and the growth surface of the seed crystal is smaller than the distance between the two guide plates on the same side and the growth surface of the seed crystal.

The guide plate of the invention is used for guiding the component transmission of the SiC growth gas. The distance between the two guide plates on the same side and close to the growth surface of the seed crystal is related to the height of the clamping groove. The distance between the two guide plates on the same side and the growth surface of the seed crystal is (SiC seed crystal diameter-groove height: 2-0.5) to (SiC seed crystal diameter-groove height: 2-3). The method is mainly used for preventing the growing crystal quality of the contact part of the seed crystal and the clamping groove from being low, and the growing crystal needs to be expanded once by means of the guide plate, so that the high quality of the edge part of the growing crystal is ensured.

According to the invention, the pressure of the growth chamber of the single crystal furnace is preferably less than or equal to 10 during the evacuation^-2Pa, further preferably, the pressure of the growth chamber of the single crystal furnaceForce less than or equal to 10^-4Pa. The aim is to remove air and residual water vapor in the growth system;

preferably, the carrier gas is high purity argon, high purity helium, high purity hydrogen or a mixture thereof.

According to the invention, the heating mode is preferably medium-frequency induction heating or resistance heating.

Preferably, in the step 3), a temperature gradient is constructed in such a way that a positive temperature gradient pointing to the SiC powder from the SiC seed crystal exists in the horizontal direction in the growth cavity by adjusting and heating, and the temperature gradient between the SiC powder and the SiC seed crystal is 20-50 ℃/cm; and a positive temperature gradient exists in the vertical direction, wherein the center of the seed crystal points to the edge of the seed crystal, and the temperature gradient between the center of the seed crystal and the edge of the seed crystal is 5-10 ℃/cm.

According to the invention, through designing the temperature field, the high-temperature area in the SiC powder is positioned in the upper and lower areas of the two interlayers, and the residual materials can be accumulated in the middle area of the interlayers after the crystal growth is finished.

Preferably, in the step 3), the heating rate is 30-150 ℃/h and the pressure reduction rate is 10-500 mbar/h before the crystal grows in a heat preservation way.

According to the invention, in the step 3), the heat preservation growth temperature of the crystal is 2100-2350 ℃, the growth pressure is 1-50 mbar, and the heat preservation time is 40-150 h.

According to the invention, the method can be used for preparing n-type, p-type, unintended doping, doping semi-insulating or high-purity semi-insulating crystals, and the crystal deflection angle is that the c axis deviates 0-8 degrees along the <11-20> direction; and SiC single crystals of other crystal forms such as 3C-SiC, 15R-SiC and the like can also be prepared.

According to the invention, after the crystal growth is finished, the grown 2 crystals are separated by a wire cutting machine or a grinding wheel sawing machine according to the position of the seed crystal. And cutting, grinding and polishing the 2 prepared single crystals to obtain the SiC substrate. The details of the present invention which are not limited in detail are in accordance with the prior art.

The obtained SiC substrate is subjected to test characterization such as microtube density, crystal form and X-ray rocking curve, the test results are shown in figures 3-6, and it can be seen from figures 3-6 that the quality of the SiC single crystal prepared by the method of the invention is equivalent to the quality of the seed crystal, and is equivalent to or better than the quality of the SiC single crystal prepared by the physical vapor transport method in the prior art, and two SiC single crystals can be prepared at one time.

The crucible structure of the invention realizes that 2 SiC single crystals can be grown simultaneously in one crucible, simultaneously saves SiC seed crystal bonding process, saves manpower and material resources, simultaneously reduces the problem of low qualified rate of SiC single crystals caused by poor bonding of large-diameter SiC seed crystals, greatly improves the preparation efficiency of SiC single crystals and reduces the cost of SiC single crystals. The quality of the prepared SiC single crystal is superior to or equal to that of the SiC single crystal prepared in the prior art, and the SiC single crystal can be used in the fields of new energy automobiles, photovoltaic power generation, 5G communication and the like.

Compared with the prior art, the invention has the following remarkable and excellent effects:

1. the growth method of the invention is carried out by adopting the crucibles with double-side growth, and the SiC powder is placed in the two interlayers of the crucibles, so that SiC growth gas-phase components with certain concentration are respectively arranged on the two surfaces of the SiC seed crystal, and the phenomenon of seed crystal decomposition during the high-temperature growth of the crystal is effectively avoided, therefore, the cleaned SiC wafer can be directly adopted as the SiC seed crystal, the bonding treatment of the seed crystal is not needed, and a large amount of manpower and material resources are saved.

2. According to the growth method, the seed crystals are not required to be bonded, so that the crystal rejection probability caused by the defects of high microtubule density, multiple cavities, even polycrystal and the like caused by the bonding problem of the seed crystals can be effectively avoided, and the growth qualification rate of the SiC single crystals is greatly improved to a certain extent;

3. the crucible structure of the invention realizes that one crucible can simultaneously grow 2 SiC single crystals, 2 SiC single crystal growth chambers are constructed in one crucible, SiC powder faces the SiC seed crystal growth surface, the growth rate is ensured, and simultaneously, 2 SiC single crystals can be grown at one time, thereby greatly improving the yield of the SiC single crystals and effectively reducing the preparation cost of the SiC single crystals.

4. In the growth method, two surfaces of the SiC seed crystal can be used as growth surfaces, the utilization rate of the seed crystal is improved by 2 times, the high-quality SiC seed crystal is fully utilized, the cost of the SiC seed crystal is greatly reduced, and the preparation cost of the SiC single crystal is further effectively reduced.

5. The SiC single crystal growth technology is compatible with the existing single crystal growth technology and equipment, and is convenient to popularize and apply.

Drawings

FIG. 1 is a schematic diagram showing the growth of a SiC single crystal in example 1 of the present invention;

1 is a graphite crucible, 2 is SiC powder, 3 is SiC seed crystal, 4 is a guide plate, and 5A and 5B are respectively grown 4H-SiC and 6H-SiC single crystals; 6 is a clamping groove, and 7 is a porous graphite sheet.

FIG. 2 is a schematic diagram showing the growth of a SiC single crystal in example 2 of the present invention;

1 is a graphite crucible, 2 is SiC powder, 3 is SiC seed crystal, 4 is a guide plate, and 5A and 5B are 2 grown 4H-SiC single crystals; 6 is a clamping groove, and 7 is a porous graphite sheet.

FIG. 3 is a stress test chart of a 4H-SiC single crystal substrate prepared in example 1;

FIG. 4 is a distribution diagram of a 4H-SiC single crystal substrate microtube prepared in example 1;

FIG. 5 shows Raman mapping results of a 4H-SiC single crystal substrate grown in example 1;

FIG. 6 is the results of the half-value width mapping of the X-ray (004) plane rocking curve of the 4H-SiC single crystal substrate grown in example 1.

Detailed Description

The present invention is further illustrated by, but not limited to, the following examples.

Example 1

A method for simultaneously preparing 1 4-inch 4H-SiC monocrystal and 1 4-inch 6H-SiC monocrystal is carried out by adopting a bilateral growth crucible as shown in figure 1, wherein the bilateral growth crucible comprises a crucible body, two porous graphite sheets 7 which are longitudinally spaced are arranged in the crucible body, an inner cavity of the crucible body is divided into a left interlayer, a growth cavity and a right interlayer by the porous graphite sheets 7, a clamping groove a is arranged on the top wall of the growth cavity, and a clamping groove b opposite to the clamping groove a is arranged at the bottom of the growth cavity;

the preparation method comprises the following steps:

(1) charging: placing 2kg of SiC powder and 2kg of SiC powder in a left interlayer and a right interlayer of a crucible with two growth sides respectively, wherein the left interlayer comprises the following steps: the volume ratio of the right interlayer is 1:1, the aperture of the porous graphite sheet 7 is 0.03mm, and the porosity is 20%;

(2) seed crystal and guide plate placement: selecting 1 sheet with thickness of 500um and density of 0 pieces/cm^-2The 4-inch 4H-SiC wafer is used as a seed crystal and is placed in the clamping groove a and the clamping groove b for fixing. The width of the clamping groove a and the clamping groove b is 0.51mm, the height of the clamping groove a and the clamping groove b is 1mm, the distance between the SiC seed crystal and the porous graphite sheet is 30mm, guide plates 4 inclined with the seed crystal are arranged at the positions, close to the clamping groove a and the clamping groove b, of the two ends of the seed crystal, and the distance between the two guide plates on the same side and the growth surface of the seed crystal is smaller than the distance between the two guide plates on the same side and the growth surface of the seed crystal; the distance between the two guide plates and the growth surface of the seed crystal is 97.5 mm;

(3) vacuumizing: placing the crucible with the charged two-side growth in a single crystal furnace, and vacuumizing the growth chamber of the single crystal furnace to 10 DEG^-2Pa；

(4) Crystal growth: introducing argon into the growth chamber to 1000mbar, turning on a heating power supply, keeping the heating rate at 150 ℃/h and the pressure reduction rate at 500mbar/h, adjusting the heating to ensure that a positive temperature gradient pointing to the SiC powder from the SiC seed crystal exists in the horizontal direction in the growth chamber, and the temperature gradient between the SiC powder and the SiC seed crystal is 20-50 ℃/cm; a positive temperature gradient exists in the vertical direction, wherein the center of the seed crystal points to the edge of the seed crystal, and the temperature gradient between the center of the seed crystal and the edge of the seed crystal is 5-10 ℃/cm; keeping the temperature at 2200 ℃ and 50mbar for 150h, and carrying out crystal growth;

(5) taking crystals: after the crystal growth is finished, slowly reducing the temperature to room temperature, simultaneously introducing carrier gas into the single crystal furnace to atmospheric pressure, and taking out to prepare other 2 crystals.

And separating the grown 4H-SiC crystal from the 6H-SiC crystal by using a grinding wheel saw. And respectively carrying out cutting, grinding and polishing treatment on the 2 prepared single crystals to obtain the SiC substrate. The obtained SiC substrate is subjected to test characterization such as micropipe density, crystal form and X-ray rocking curve, the stress test of the prepared 4H-SiC monocrystal substrate has no obvious stress stripe, and the micropipe density is 0/cm^-2The crystal form of 4H-SiC is 100 percent, and the full half-peak width of an X-ray rocking curve test (004) is smallAt 30 arc seconds (results are shown in FIGS. 3-6); the stress test of the prepared 6H-SiC single crystal substrate has no obvious stress stripe, and the density of the micropipe is 0/cm^-2The 6H-SiC crystal form is 100%, and the half-peak width of the X-ray rocking curve test (006) is less than 40 arcsec. The 2 SiC single crystals prepared by the method have higher quality.

Example 2

A method for simultaneously preparing 2 6-inch 4H-SiC single crystals is carried out by adopting a bilateral growth crucible which is shown in figure 2, the bilateral growth crucible comprises a crucible body, two porous graphite sheets 7 which are longitudinally spaced are arranged in the crucible body, the inner cavity of the crucible body is divided into a left interlayer, a growth cavity and a right interlayer by the porous graphite sheets 7, a clamping groove a is arranged on the top wall of the growth cavity, and a clamping groove b which is opposite to the clamping groove a is arranged at the bottom of the growth cavity;

the preparation method comprises the following steps:

(1) charging: 3kg of SiC powder and 1kg of SiC powder are respectively placed in a left interlayer and a right interlayer of a crucible with two growth sides, wherein the left interlayer comprises the following components in parts by weight: the volume ratio of the right interlayer is 3:1, the aperture of the porous graphite sheet is 1.0mm, and the porosity is 60%;

(2) seed crystal and guide plate placement: 2 pieces of micro-tube with the thickness of 800um and the density of 3.2 pieces/cm are selected²The 6-inch 4H-SiC wafer is used as seed crystal, the silicon surfaces of the two seed crystals are tightly attached to one seed crystal, and the carbon surfaces of the two wafers respectively face the two growth cavities; and the clamping grooves are arranged in the clamping grooves a and the clamping grooves b for fixing. The width of the clamping groove a and the clamping groove b is 0.90mm, the height of the clamping groove a and the clamping groove b is 0.5mm, the distance between the SiC seed crystal and the porous graphite sheet is 40mm and 80mm respectively, guide plates 4 inclined with the seed crystal are arranged at the positions, close to the clamping groove a and the clamping groove b, of the two ends of the seed crystal, and the distance between the two guide plates on the same side and the growth surface of the seed crystal is smaller than the distance between the two guide plates on the same side and the growth surface of the seed crystal; the distance between the two guide plates and the seed crystal growth surface is 147 mm;

(3) vacuumizing: placing the crucible with the charged two-side growth in a single crystal furnace, and vacuumizing the growth chamber of the single crystal furnace to 10 DEG^-2Pa；

(4) Crystal growth: introducing argon into the growth chamber to 1000mbar, turning on a heating power supply, keeping the heating rate at 50 ℃/h and the pressure reduction rate at 100mbar/h, adjusting the heating to ensure that a positive temperature gradient pointing to the SiC powder from the SiC seed crystal exists in the horizontal direction in the growth chamber, and the temperature gradient between the SiC powder and the SiC seed crystal is 20-50 ℃/cm; a positive temperature gradient exists in the vertical direction, wherein the center of the seed crystal points to the edge of the seed crystal, and the temperature gradient between the center of the seed crystal and the edge of the seed crystal is 5-10 ℃/cm; keeping the temperature at 2100 ℃ for 40h at 1mbar for crystal growth;

(5) taking crystals: after the crystal growth is finished, slowly reducing the temperature to room temperature, simultaneously introducing carrier gas into the single crystal furnace to atmospheric pressure, and taking out to prepare other 2 crystals.

The grown 2 6 inch 4H-SiC crystals were separated using a wire saw. And respectively carrying out cutting, grinding and polishing treatment on the 2 prepared single crystals to obtain the SiC substrate. The obtained SiC substrate is subjected to test characterization such as micropipe density, crystal form and X-ray rocking curve, the stress test of the prepared 2 4H-SiC single crystal substrates has no obvious stress stripes, and the density of the micropipes is 3.7/cm^-2The crystal form of 4H-SiC is 100%, and the half-peak width of X-ray rocking curve test (004) is less than 45 arcsec. The 2 SiC single crystals prepared by the method have higher quality.

Example 3

The method for simultaneously preparing 2 8-inch 6H-SiC single crystals adopts a crucible with double growth sides,

the preparation method comprises the following steps:

(1) charging: placing 4kg of SiC powder and 4kg of SiC powder in a left interlayer and a right interlayer of a crucible with two growth sides respectively, wherein the left interlayer comprises the following steps: the volume ratio of the right interlayer is 1:1, the aperture of the porous graphite sheet is 1.0mm, and the porosity is 80%;

(2) seed crystal and guide plate placement: 2 pieces of the micro-tube with the thickness of 3000um and the density of 5.5 pieces/cm are selected²The 8-inch 6H-SiC wafer is used as seed crystal, the silicon surfaces of the two seed crystals are tightly attached to one seed crystal, and the carbon surfaces of the two wafers respectively face the two growth cavities; and the clamping grooves are arranged in the clamping grooves a and the clamping grooves b for fixing. The width of the clamping groove a and the clamping groove b is 3.05mm, the height of the clamping groove a and the clamping groove b is 3.0mm, the distance between the SiC seed crystal and the interlayer porous graphite sheet at the two sides is 40mm, and the positions, close to the clamping groove a and the clamping groove b, at the two ends of the seed crystal are provided with the seed crystal which inclinesThe distance between the two guide plates close to the seed crystal growth surface on the same side is smaller than that between the two guide plates far away from the seed crystal growth surface; the distance between the two guide plates and the seed crystal growth surface is 193 mm;

(3) vacuumizing: placing the crucible with the charged two-side growth in a single crystal furnace, and vacuumizing the growth chamber of the single crystal furnace to 10 DEG^-4Pa；

(4) Crystal growth: introducing argon into the growth chamber to 1000mbar, turning on a heating power supply, keeping the temperature rising rate at 30 ℃/h and the pressure reduction rate at 10mbar/h, adjusting the heating to ensure that a positive temperature gradient pointing to the SiC powder from the SiC seed crystal exists in the horizontal direction in the growth chamber, wherein the temperature gradient between the SiC powder and the SiC seed crystal is 20-50 ℃/cm; a positive temperature gradient exists in the vertical direction, wherein the center of the seed crystal points to the edge of the seed crystal, and the temperature gradient between the center of the seed crystal and the edge of the seed crystal is 5-10 ℃/cm; maintaining at 2350 deg.C and 50mbar for 100 hr for crystal growth;

(5) taking crystals: after the crystal growth is finished, slowly reducing the temperature to room temperature, simultaneously introducing carrier gas into the single crystal furnace to atmospheric pressure, and taking out to prepare other 2 crystals.

The grown 2 8 inch 6H-SiC crystals were separated using a wire saw. And respectively carrying out cutting, grinding and polishing treatment on the 2 prepared single crystals to obtain the SiC substrate. The obtained SiC substrate is subjected to test characterization such as micropipe density, crystal form and X-ray rocking curve, the stress test of the prepared 2 4H-SiC single crystal substrates has no obvious stress stripes, and the density of the micropipes is 5.5/cm^-2The 6H-SiC crystal form is 100%, and the half-peak width of the X-ray rocking curve test (006) is less than 50 arcsec. The 2 pieces of 6H-SiC single crystals prepared by the method are high in quality.