Apparatus for growing silicon carbide single crystal by PVT method and method for growing silicon carbide single crystal

Abstract

The present application belongs to the technical field of silicon carbide single crystal material, and particularly relates to a device for growing silicon carbide single crystal by PVT method and a method for growing silicon carbide single crystal, wherein the device for growing silicon carbide single crystal by PVT method comprises a crucible, a heat preservation layer wrapping the crucible and an external heating system, the top of the heat preservation layer is provided with a central heat dissipation zone and at least three auxiliary heat dissipation zones distributed in a circumferential direction, and the heat conduction efficiency of the auxiliary heat dissipation zones is lower than that of the central heat dissipation zone. The present application is designed by the difference in heat conduction efficiency between the central heat dissipation zone and the auxiliary heat dissipation zone at the top of the heat preservation layer, and the segmented pressure regulation process is coordinated, so that a stable radial heat barrier is constructed in the initial stage of crystal growth to inhibit edge polycrystalline defects (deeply compressed to sub-millimeter level), while the axial temperature gradient is strengthened to drive high-speed growth, so that the crystal thickness breaks through the industry bottleneck of 18 mm and the dislocation density is reduced by one order of magnitude, and finally the breakthrough of large-size silicon carbide single crystal "low-defect thick growth" is realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of silicon carbide single crystal materials, and particularly relates to a device for growing silicon carbide single crystals by a PVT method and a method for growing silicon carbide single crystals. BACKGROUND

[0002] As the third generation semiconductor, silicon carbide has excellent properties such as wide band gap, high critical breakdown electric field, high carrier mobility, high thermal conductivity, etc., so the silicon carbide devices prepared have characteristics such as high voltage resistance, high temperature resistance, low power consumption, small size, etc. Silicon carbide devices are mainly used as radio frequency electronic devices and power electronic devices, and have great application prospects in the energy field and the automobile industry. Under the strong demand of the new energy industry, the global SiC industry has entered a period of rapid growth, increasing the demand for SiC substrate capacity. At present, the size of commercial SiC substrates is still mainly 6 inches, and expanding the size of SiC substrates is one of the important ways to increase the supply of capacity and reduce costs. Therefore, preparing high-quality large-size (8 inches and above) silicon carbide substrates is a technical problem at present.

[0003] At present, the method widely used in the commercial field for growing silicon carbide single crystals is the PVT (physical vapor transport) method. The method is mainly that a graphite crucible is heated by an induction coil, silicon carbide powder in the crucible sublimates into a gas at low pressure and high temperature, and the gas is transported to the surface of a seed crystal at a lower temperature to crystallize. In the process of crystal growth, factors such as the structure of the crucible, the position of the induction coil, the temperature, and the pressure will affect the process of crystal growth. The crucible temperature field formed by a variety of factors is considered to be an important factor affecting the crystallization of silicon carbide. Among them, the temperature difference between the silicon carbide powder and the seed crystal at the crystal growth interface is called the axial temperature difference.

[0004] In addition, there is also a radial temperature difference at the growth interface of the seed crystal surface, which affects the shape of the crystal growth interface. Under the condition of keeping the crystal growth surface as a convex interface, the radial temperature gradient of the surface should be as small as possible, and a small radial temperature gradient is beneficial to improving the quality of the single crystal. At the same time, the radial temperature gradient of the polycrystalline growth region at the edge of the single crystal should be as large as possible, so as to inhibit the polycrystalline growth and ensure the expansion of the single crystal region.

[0005] When the size of the crystal increases, the radial temperature difference of the seed crystal surface also increases, making it difficult to ensure the quality of the crystal growth. Limited by the increase of thermal stress, defect control becomes more difficult, especially the control of dislocation defects. During the growth process, as the silicon carbide crystal grows, the growth surface of the crystal continuously extends downward, and the thermal field environment continuously changes. When the crystal grows to a certain extent, the growth surface is close to the powder source surface, the temperature difference becomes small, and the growth rate decreases. The change of the crystal growth rate makes the quality of the grown silicon carbide crystal uneven, and also makes it difficult to grow a relatively thick silicon carbide crystal. SUMMARY

[0006] The present application is to overcome the contradiction between the thermal field gradient and the growth kinetics in the PVT growth process of large-size silicon carbide single crystals, which leads to high defect density of the obtained silicon carbide crystals, and polycrystalline growth defects exist in the edge of the silicon carbide crystal, and therefore a device for growing silicon carbide single crystals by PVT method and a method for growing silicon carbide single crystals are provided.

[0007] To achieve the above-mentioned application purposes, the present application is realized by the following technical solutions:

[0008] In the first aspect, the present application first provides a device for growing silicon carbide single crystals by PVT method, which comprises a crucible, a heat preservation layer wrapping the crucible and an external heating system,

[0009] The top of the heat preservation layer is provided with a central heat dissipation zone and at least three circumferentially distributed auxiliary heat dissipation zones.

[0010] The heat conduction efficiency of the auxiliary heat dissipation zone is lower than that of the central heat dissipation zone.

[0011] In the field of silicon carbide single crystal preparation, PVT method has long faced a structural contradiction: as the size of the crystal increases, the difficulty of thermal field management increases exponentially. The traditional device regulates the axial temperature gradient through a single large temperature measuring hole, which can maintain the convex profile of the crystal growth interface, but inevitably aggravates the imbalance of radial temperature distribution, that is, the severe heat dissipation in the central region leads to heat accumulation in the edge region, thereby inducing a triple chain reaction: first, the insufficient radial temperature difference at the edge of the growth interface promotes the growth of polycrystalline disorder, which erodes the integrity of the single crystal region; second, dislocation defects proliferate densely along the temperature steep region, especially BPD (basal plane dislocation) extends to the interior of the crystal under the action of thermal stress; third, when the crystal grows to the middle and later stages, the distance between the powder source and the seed crystal is shortened, resulting in the decay of the axial temperature difference, and the growth rate drops sharply, forcing the process to terminate prematurely.

[0012] The prior art has tried to optimize the heat preservation layer with the goal of uniformizing the thermal field, but this has weakened the axial driving force; in addition, there are schemes to expand the central heat dissipation zone, which temporarily improves the growth rate, but at the expense of the quality of the crystal. Therefore, these improvements are always stuck in the impasse of "axial temperature difference and radial gradient cannot be compatible".

[0013] The essence of the scheme in the present application is not to pursue uniformity, but to construct a temperature gradient distribution for directional induction. The device in the present application realizes precise shunting of heat field energy by setting a "central heat dissipation area + circumferential auxiliary heat dissipation area" composite structure on the top of the heat preservation layer, wherein the central heat dissipation area serves as a main channel to maintain high-intensity heat dissipation, which can guarantee the growth energy driven by the axial temperature difference; and the auxiliary heat dissipation area distributed around it can act as a control valve, thereby effectively enhancing the heat conduction efficiency and forming a local heat dissipation channel. Therefore, when the heat spreads from the inside of the crucible to the top, the heat dissipation channel formed by the auxiliary heat dissipation area forces the heat to dissipate uniformly in the central area, thereby forming a gentle axial temperature drop (accelerating gas phase transmission) in the central area of the growth interface, and at the same time, an abrupt radial temperature platform is established in the edge area to effectively suppress polycrystal nucleation. More importantly, the auxiliary heat dissipation area continuously maintains the powder source temperature in the later stage of crystal growth by enhancing heat dissipation, effectively offsetting the temperature difference decay caused by the shortening of the distance.

[0014] In the present application, a dynamic equilibrium temperature distribution is generated at the crystal growth interface through the difference in heat conduction efficiency between the central heat dissipation area and the auxiliary heat dissipation area. That is, the axial temperature difference in the central area remains high, driving high-speed transmission of gas phase substances, and the crystal growth rate is increased by more than 20%; while the radial temperature difference in the edge area is compressed below the critical point, and polycrystal growth is limited to a sub-millimeter depth, allowing the single crystal area to expand steadily to the edge.

[0015] In addition, through the differential design of heat conduction efficiency in the present application, the phenomenon of heat stress concentration can be eliminated from the source, and the initiation and expansion of dislocation defects are significantly inhibited, with TSD (threading screw dislocation) density reduced to less than 1 / 4 of that of the traditional process, and BPD (basal plane dislocation) showing an order of magnitude decrease. The synergistic effect of "axial driving reinforcement" and "radial stability improvement" directly promotes the quality breakthrough of 8-inch and larger size silicon carbide single crystals, allowing the crystal thickness to break through 18 mm while the uniformity of dislocation defect distribution is improved by 60%, thereby changing the cognition that "thick crystals must have defects".

[0016] As a preferred embodiment, the central heat dissipation area is a through hole with a diameter of 30-50 mm, and the auxiliary heat dissipation area is a through hole with a diameter of 15-25 mm.

[0017] As a preferred embodiment, the number of auxiliary heat dissipation areas is 6, which are evenly distributed in a 60° ring shape with the central heat dissipation area as the center.

[0018] As a preferred embodiment, the auxiliary heat dissipation area is embedded with a filler having a higher thermal conductivity than the base material of the heat preservation layer.

[0019] The design of embedding high thermal conductivity filler in the auxiliary heat dissipation area is essentially to precisely regulate the heat field, thereby realizing secondary calibration of the heat dissipation rate. When the heat diffuses from the inside of the crucible to the top of the insulation layer, the filler forms a controllable heat "fast channel" in the auxiliary heat dissipation area due to the higher thermal conductivity than the base material. This not only avoids excessive accumulation of heat in the auxiliary area (prevents edge polycrystallization), but more importantly, by precisely exporting excess heat, a gentle but stable radial temperature platform is built at the edge of the growth interface. Compared with the bare hole without filler (heat disorder escape) or low thermal conductivity filling (heat blockage), the design makes the heat flow realize "deceleration without stagnation" in the auxiliary area: thereby weakening the difference in heat conduction efficiency between the center area and the edge area (suppressing thermal stress concentration), and maintaining sufficient heat flow driving force to prevent the temperature of the crystal edge from dropping sharply, thereby compressing the radial temperature difference gradient of the crystal growth interface by more than 50%, and firmly limiting the polycrystalline defects to a sub-millimeter depth, while reducing the dislocation defect density by an order of magnitude.

[0020] Preferably, the filler is a hollow cylindrical graphite cylinder.

[0021] In a second aspect, the present application also provides a method for growing a silicon carbide single crystal, which uses the device described above, and comprises the following steps:

[0022] After the crucible is evacuated, a protective gas is filled;

[0023] b) continuously filling the protective gas and heating to the crystal growth temperature;

[0024] c) maintaining the crystal growth temperature and reducing the pressure in stages, thereby growing a silicon carbide crystal;

[0025] d) increasing the pressure and linearly reducing the temperature to room temperature to obtain a silicon carbide single crystal.

[0026] In the field of PVT preparation of silicon carbide single crystals, the traditional process often falls into a dilemma: if a constant low pressure environment is used to pursue the growth rate, the polycrystalline defects caused by the imbalance of the heat field will spread like weeds at the edge of the crystal; and if high pressure slow growth is maintained to suppress defects, the thickness of the crystal will be firmly locked below the industrialization threshold. The prior art has attempted to balance this contradiction by linearly reducing the pressure or controlling the pressure in stages, but the dynamic response lag of the heat field causes the pressure change to be seriously out of sync with the crystal growth stage. When the crystal is still in the initial growth which is sensitive to structure, the pressure is prematurely reduced to a very low pressure zone, causing a defect outbreak; and when the crystal enters the middle and late stages which need to be accelerated, the pressure system loses kinetic energy due to the depletion of the adjustment margin.

[0027] The creation of the method lies in the discovery that the essence of pressure regulation is to match the kinetic phase change of crystal growth. Therefore, the pressure reduction process is divided into two stages for accurate response: the first stage maintains a medium-low pressure environment of 10-50 mbar, at which time the crystal is in a sensitive period from nucleation to steady state, and the mild pressure condition wins the key time window for the self-regulation of the heat field. The auxiliary heat dissipation area at the top of the heat preservation layer completes the heat flow redistribution during this period, and directs the heat accumulated in the edge area to the center area, building a thermodynamic barrier to inhibit the growth of polycrystals in the crystal periphery. After the crystal thickness breaks through the structural stability threshold of 5-8 mm, the second stage reduces the pressure to an extremely low pressure range of 1-5 mbar, at which time the axial temperature gradient has accumulated sufficient potential energy in the heat field reconstruction, so that the crystal growth rate jumps to a new level in the low pressure environment.

[0028] The technical effect of the method is manifested in the synergistic improvement of defect control and growth efficiency. Among them, the medium-low pressure environment of the first stage builds a "repair window" of about 10-20 hours for the crystal edge, and the auxiliary heat dissipation area suppresses the radial temperature difference within a safe threshold during this period, so that the depth of polycrystalline defects is compressed to one tenth of that of the traditional process; the dislocation defects are like precisely combed silk threads in the heat stress relief environment, and the TSD density decreases by more than 60%, especially the BPD defects which expand along the basal plane, which are reduced by an order of magnitude. When the system switches to the second stage of extremely low pressure, the axial temperature gradient has accumulated sufficient kinetic energy through heat field optimization, and the 2mbar low pressure environment pushes the gas phase transmission efficiency to the peak, and the crystal realizes a thickness breakthrough of more than 18mm in 150-200 hours, and the growth rate decay curve is more than 50% flatter than the traditional scheme.

[0029] As a preferred, the pressure in the crucible (1) is filled to 500-600 mbar in step a).

[0030] As a preferred, the crystal growth temperature in step b) is 2000-2200℃, and the holding time is 1-3h.

[0031] As a preferred, the stepwise pressure reduction in step c) includes:

[0032] The first stage is reduced to 10-50 mbar within 2-4h and maintained for 10-20h;

[0033] The second stage is reduced to 1-5 mbar within 10-20h and maintained for 150-200h.

[0034] As a preferred, the pressure in step d) is increased to 200 mbar and the cooling rate is 20-40℃ / h.

[0035] Therefore, the present application has the following beneficial effects:

[0036] The application realizes the technical effect of large-size silicon carbide single crystal "low defect thick growth" by constructing a stable radial heat barrier in the initial stage of crystal growth to inhibit edge polycrystalline defects (compressed to sub-millimeter level), while strengthening the axial temperature gradient to drive high-speed growth, so that the crystal thickness breaks through the industry bottleneck of 18mm and the dislocation density is reduced by an order of magnitude. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 It is a structure schematic diagram of the PVT method for growing silicon carbide single crystal device of the application.

[0038] Figure 2 It is a structure schematic diagram of the PVT method for growing silicon carbide single crystal device of the application. Figure 1 It is a structure schematic diagram of the PVT method for growing silicon carbide single crystal device of the application.

[0039] Figure 3 It is a dislocation density test diagram of the silicon carbide crystal prepared in Example 2.

[0040] Figure 4 It is a dislocation density test diagram of the silicon carbide crystal prepared in Comparative Example 1.

[0041] Figure 5 It is a dislocation density test diagram of the silicon carbide crystal prepared in Comparative Example 2.

[0042] Figure 6 It is a dislocation density test diagram of the silicon carbide crystal prepared in Comparative Example 3.

[0043] Figure 7 It is a dislocation density test diagram of the silicon carbide crystal prepared in Comparative Example 4.

[0044] In the figure, 1 is a crucible, 2 is a heat preservation layer, 3 is an external heating system, 11 is a hollow cavity, 12 is a seed crystal, 21 is a central heat dissipation area, 22 is an auxiliary heat dissipation area, and 221 is a filler. DETAILED DESCRIPTION

[0045] The application will be further described below in conjunction with specific embodiments. Those skilled in the art will be able to implement the application based on these descriptions. In addition, the embodiments of the application involved in the following description are generally only a part of the embodiments of the application, not all the embodiments. Therefore, based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor shall fall within the scope of protection of the application.

[0046] Example 1

[0047] As Figure 1 and Figure 2As shown, the embodiment provides a device for growing silicon carbide single crystal by PVT method, which specifically comprises a crucible 1, an inner hollow cavity 11 is arranged in the crucible 1, the bottom of the hollow cavity 11 is filled with silicon carbide powder, and the top of the hollow cavity 11 is bonded with a seed crystal 12 for depositing silicon carbide crystal. The outer part of the crucible 1 is further provided with an external heating system 3 for heating the crucible 1, which is composed of at least one group of medium frequency coils, so that the crucible 1 can be heated by magnetic induction when the external heating system 3 is started, so that the silicon carbide powder at the bottom of the hollow cavity 11 sublimates to form silicon carbide vapor, which gradually cools down during the rising process, thereby crystallizing on the surface of the seed crystal 12, thereby gradually growing the silicon carbide crystal.

[0048] In order to maintain the temperature of the crucible 1 stable during heating, the outer part of the crucible 1 is further provided with a heat preservation layer 2 wrapping the crucible 1. The heat preservation layer 2 is composed of graphite soft felt, and in order to facilitate heat dissipation and temperature measurement of the crucible 1, a hollow center heat dissipation area 21 is arranged at the top center of the heat preservation layer 2, so that there is a significant axial temperature difference in the inner part of the hollow cavity 11 of the crucible 1, thereby driving the deposition rate of the silicon carbide crystal. In addition, in order to reduce the radial temperature difference in the inner part of the hollow cavity 11, at least three auxiliary heat dissipation areas 22 are arranged around the center heat dissipation area 21 on the heat preservation layer 2, wherein the aperture size of the auxiliary heat dissipation area 22 is smaller than that of the center heat dissipation area 21, so that the heat conduction efficiency of the auxiliary heat dissipation area 22 (15-25 mm) is lower than that of the center heat dissipation area 21 (30-50 mm). Since the center heat dissipation area 21 at the center has the largest size, the heat dissipation here is the largest, the temperature at the center is the lowest, the axial temperature difference is the largest, the growth rate of the crystal is the fastest, and the growth interface presents a convex interface. The center heat dissipation area 21 around the center heat dissipation area 21 reduces the radial temperature gradient of the crystal growth surface, while relatively increases the radial temperature gradient of the edge polycrystal growth area, inhibits the polycrystal growth, expands the single crystal area, and is also beneficial to reduce the dislocation density of the crystal and improve the crystal quality.

[0049] In another preferred embodiment of the present application, the number of auxiliary heat dissipation zones 22 is six, which are evenly distributed in a 60° annular shape with the central heat dissipation zone 21 as the center. Moreover, the auxiliary heat dissipation zones 22 are embedded with filling pieces 221 having a higher thermal conductivity than the base material of the insulation layer 2. In another preferred embodiment of the present application, the filling pieces 221 are hollow graphite cylinders. Therefore, when the heat spreads from the inside of the crucible to the top of the insulation layer, the filling pieces 221 form a controllable "fast channel" for heat in the auxiliary heat dissipation zones due to their higher thermal conductivity than the base material. This not only avoids excessive heat accumulation in the auxiliary zones, which leads to the accumulation of thermal stress, but more importantly, by precisely exporting excess heat, a radial temperature platform is constructed at the growth interface, which is flat in the center but steep at the edges, preventing edge polycrystalline growth. Compared to the disordered escape of heat from the bare hole without filling pieces or the heat blockage of low thermal conductivity filling, this design enables the heat flow in the auxiliary zone to achieve an intelligent transition of "deceleration without stagnation": it weakens the difference in heat conduction efficiency between the central zone and the edge zone to inhibit the concentration of thermal stress, and at the same time, it maintains sufficient driving force for the heat flow to prevent the temperature of the crystal edge from dropping sharply. This fine balance compresses the radial temperature difference gradient at the crystal growth interface by more than 50%, tightly limits polycrystalline defects to a sub-millimeter depth, and reduces the dislocation defect density by an order of magnitude, which is equivalent to installing a stealthy flow stabilizer in the thermal field.

[0050] Example 2

[0051] A silicon carbide single crystal growth method using the device of Example 1, comprising the following steps:

[0052] a) Evacuation: evacuate the furnace to a vacuum pressure below 1E-5 mbar. This step is to evacuate the air in the crucible. Open the argon flow valve to increase the pressure in the furnace to 500-600 mbar (500 mbar in this example) at an argon flow rate of 1000 ml / min, and fill the crucible with protective gas;

[0053] b) Heating and temperature rising stage: adjust the argon flow rate to 100-200 ml / min (150 ml / min in this example), and maintain the pressure at 500 mbar. Start heating, and in 6-8 h (8 h in this example), raise the temperature of the crucible from room temperature to 2000-2200°C (measured at the upper side of the crucible) (2100°C in this example), and maintain the temperature at the target temperature for 1-3 h (2 h in this example);

[0054] c) Pressure reduction and crystal growth: the pressure was reduced from 500 mbar to 30 mbar in 2-4 h (4 h in this example), and then from 30 mbar to 10-50 mbar (30 mbar in this example) in 2-4 h (3 h in this example). At this time, the crystal started to grow slowly. The pressure was maintained at 10 mbar for 10-20 h (15 h in this example) to maintain a low growth rate in the initial growth stage. The pressure was reduced from 10 mbar to 2 mbar in 15 h to allow the crystal to enter a fast growth stage, and the pressure was maintained to continue the growth for 150-200 h (175 h in this example);

[0055] d) End of growth: the nitrogen flow was adjusted to 1000 ml / min, and the pressure was increased from 2 mbar to 200 mbar to end the growth. The temperature was linearly reduced to room temperature in 14 h, and the growth was ended.

[0056] Comparative Example 1

[0057] Comparative Example 1 differs from Example 1 in that the graphite soft felt with a diameter of 50 mm was used as the heat insulation layer 2.

[0058] The crystal growth process was the same as that of Example 2.

[0059] Comparative Example 2

[0060] Comparative Example 2 differs from Example 1 in that the heat insulation layer 2 used has no auxiliary heat dissipation zone 22, and only has a central heat dissipation zone 21 with a diameter of 40 mm at the top.

[0061] The crystal growth process was the same as that of Example 2.

[0062] Comparative Example 3

[0063] Comparative Example 3 differs from Example 1 in that the auxiliary heat dissipation zone 22 of the heat insulation layer 2 used has no filler 221.

[0064] The crystal growth process was the same as that of Example 2.

[0065] Comparative Example 4

[0066] Comparative Example 4 differs from Example 2 in that, in the crystal growth process, the pressure was directly reduced to 2 mbar, and the growth was maintained at 2 mbar for 175 h.

[0067] The samples prepared above were subjected to thickness measurement. The defects in the center and the edge were detected, including TSD (threading screw dislocation), TED (threading edge dislocation), and BPD (basal plane dislocation). The detection results are shown in Table 1. Figures 3-7 The results are shown in Table 1.

[0068] Table 1

[0069]

[0070] From the results of Table 1, it can be seen that by adjusting the thermal field structure of crystal growth, the TSD, TED and BPD defects in the crystal can be effectively reduced, the defects at the edge can be reduced, and the growth rate of the crystal can be increased, thereby improving the quality of the crystal.

[0071] The specific embodiments described herein are merely illustrative of the spirit of the present application. Those skilled in the art can make various modifications or supplements to the described specific embodiments or replace them with similar ways, without departing from the spirit of the present application or exceeding the scope defined by the appended claims.

Claims

1. An apparatus for growing silicon carbide single crystals by the PVT method, comprising a crucible (1), an insulation layer (2) surrounding the crucible, and an external heating system, characterized in that, The top of the insulation layer (2) is provided with a central heat dissipation area (21) and at least three circumferentially distributed auxiliary heat dissipation areas (22). The heat conduction efficiency of the auxiliary heat dissipation area (22) is lower than that of the central heat dissipation area (21). The central heat dissipation area (21) is a through hole with a diameter of 30-50mm, and the auxiliary heat dissipation area (22) is a through hole with a diameter of 15-25mm; The auxiliary heat dissipation area (22) is embedded with a filler (221) with a thermal conductivity higher than that of the insulation layer substrate. The filler (221) is a hollow cylindrical graphite cylinder.

2. The apparatus according to claim 1, characterized in that, The number of auxiliary heat dissipation areas (22) is 6, which are evenly distributed in a 60° ring with the central heat dissipation area (21) as the center.

3. A method for growing silicon carbide single crystals, using the apparatus described in claim 1 or 2, characterized in that, Includes the following steps: a) After evacuating the crucible, a protective gas is introduced to make the pressure inside the crucible (1) reach 500-600 mbar; b) Continuously fill with protective gas and heat to the crystal growth temperature, which is 2000-2200℃, and hold for 1-3 hours; c) Maintain the crystal growth temperature and reduce the pressure in stages to grow silicon carbide crystals; The phased pressure reduction includes: The first phase involves reducing the bar to 10-50 mbar within 2-4 hours and maintaining it for 10-20 hours. The second stage involves reducing the pressure to 1-5 mbar within 10-20 hours and maintaining it for 150-200 hours; d) Increase the pressure to 200 mbar and linearly decrease the temperature to room temperature at a rate of 20-40 °C / h to obtain silicon carbide single crystals.

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