A growth crucible, growth device and growth method for silicon carbide crystal

Abstract

The present invention provides a growth crucible, a growth device and a growth method for silicon carbide crystals, and belongs to the field of silicon carbide crystal growth. The growth crucible includes a lower crucible, an upper crucible, a crucible cover and a graphite ring; the lower crucible is sleeved on the inner periphery of the upper crucible for placing silicon carbide raw materials; a gap is left between the lower crucible and the upper crucible for the axial sliding of the upper crucible; a seed crystal holder is equipped at the upper opening of the upper crucible for fixing the seed crystal; a groove is provided in the center of the upper surface of the crucible cover for embedding a hollow rotating rod; an annular through hole is provided on the upper surface of the crucible cover along the radial direction away from the groove; the crucible cover is an inverted U-shaped structure or a circular plate structure. The growth crucible provided by the present invention can maintain the stability of the crystal growth interface and the uniformity of the airflow from the silicon carbide raw material to the crystal, and can effectively increase the utilization rate of the raw materials, increase the crystal thickness, improve the crystal quality, and save production costs in conjunction with a heating device.

Description

Technical Field

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

[0002] 4H-SiC has wide bandgap, high breakdown electric field, high thermal conductivity and high saturated electron drift velocity. Its performance far exceeds that of silicon crystals in the manufacture of high-power, high-frequency and high-temperature semiconductor electronic devices, and it has great potential. The invention of the physical vapor transport method (PVT method) has made large-diameter silicon carbide wafers commercially available.

[0003] At present, the PVT method for growing silicon carbide crystals is the most common process in the industry. The growth crucible used is Figure 1 As shown in the figure, the seed crystal is fixed on the top of the cylindrical graphite crucible, and the silicon carbide raw material (mostly silicon carbide powder or polycrystalline silicon carbide) is placed at the bottom of the graphite crucible. There is a large distance from the top to the bottom of the graphite crucible, which is convenient for building a temperature gradient. The silicon carbide raw material at the bottom is in the high temperature area (about 2300℃), and non-stoichiometric sublimation decomposition occurs to generate the gas phase component Si m C n , and then the gas phase component Si m C n Through transportation, it goes from the bottom area with high axial temperature to the seed crystal at the low temperature end (2100-2200℃), and from the growth raw material area to the growth interface. It condenses and crystallizes on the growth interface of the seed crystal, so that the growth interface gradually advances to the silicon carbide raw material area, and finally grows silicon carbide crystals.

[0004] The interface shape control in the early stage of crystal growth is extremely important. Convex growth can effectively keep the 4H crystal form covering the entire seed crystal surface and continuously repeat the growth. When the concave surface or edge grows too fast, it is easy to cause the growth steps to collide, and polymorphs such as 6H or 15R will appear. A large number of microtubes will be generated between the interfaces, thereby reducing the crystal utilization rate. The crucible structure of the traditional PVT method for growing silicon carbide crystals adjusts the seed crystal surface temperature, usually mainly by adjusting the relative position of the crucible, the structure and quantity of the insulation cotton, etc., but the insulation effect of the insulation cotton makes this method have a small adjustment window, and the relative position of the coil or heater and the crucible is limited, and the adjustment position will also affect the axial temperature distribution.

[0005] Therefore, there is an urgent need to provide a crucible structure that can flexibly adjust the radial temperature distribution of the seed crystal surface to maintain the shape stability of the crystal growth interface and improve the crystal quality. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a growth crucible, a growth device and a growth method for silicon carbide crystals. In the growth crucible provided by the present invention, an annular through hole is provided on the upper surface of the crucible cover, which can block the heat dissipation of the edge from the side, so that the heat dissipation of the back of the seed crystal from the edge to the center gradually increases, thereby ensuring that the crystal growth interface grows in a convex shape; secondly, according to the influence of different outer diameters of the graphite ring on heat transfer, the outer diameter of the graphite ring is limited to gradually increase in the axial direction away from the crucible cover, which can effectively adjust the temperature gradient of the crystal growth zone and prevent the increase of the crystal convexity, or the support groove in the graphite ring is assembled with the support ear provided on the crucible cover, so that the coverage range of the graphite ring on the outer periphery of the upper crucible in the vertical direction increases as the thread is tightened, and the growth speed of the seed crystal is regulated by controlling its speed; therefore, with the help of the axial sliding of the upper crucible, the material surface distance can be kept unchanged as the crystal thickness increases, thereby maintaining the stability of the growth interface and the uniformity of the gas flow from the silicon carbide raw material to the crystal. In summary, the growth crucible provided by the present invention, in combination with a suitable heating device, can effectively increase the utilization rate of silicon carbide raw materials, increase crystal thickness, improve crystal quality, and save production costs.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a growth crucible for silicon carbide crystals, the growth crucible comprising a lower crucible, an upper crucible, a crucible cover and a graphite ring;

[0009] The lower crucible is sleeved on the inner periphery of the upper crucible and is used to place silicon carbide raw materials; a gap is left between the lower crucible and the upper crucible for the axial sliding of the upper crucible;

[0010] The upper opening of the upper crucible is equipped with a seed crystal holder for fixing the seed crystal;

[0011] A groove is provided at the center of the upper surface of the crucible cover for embedding the hollow rotating rod; an annular through hole is provided on the upper surface of the crucible cover along a radial direction away from the groove;

[0012] The crucible cover is an inverted U-shaped structure or a circular plate structure;

[0013] When the crucible cover is an inverted U-shaped structure, the upper part of the upper crucible is sleeved on the inner side of the lower part of the crucible cover, and the upper crucible is threadedly connected to the crucible cover; the lower outer wall of the crucible cover is threadedly connected to the graphite ring; the outer diameter of the graphite ring gradually increases along the axial direction away from the crucible cover; the lower crucible is coaxially placed on the base, and the base is connected to a displacement device for displacement requirements of the upper crucible;

[0014] When the crucible cover is a circular plate structure, a plurality of support ears distributed at intervals are arranged on the circumferential periphery of the crucible cover, a plurality of support grooves are opened on the horizontal circumference of the upper inner side of the graphite ring for assembling the support ears, and the lower inner wall of the graphite ring is threadedly connected to the upper outer wall of the upper crucible; the lower crucible is coaxially placed on the base, and the base is connected to a rotating device for synchronous rotation of the upper crucible, the graphite ring and the lower crucible.

[0015] In the growth crucible provided by the present invention, an annular through hole is provided on the upper surface of the crucible cover, which can block the heat dissipation of the edge from the side, so that the heat dissipation of the back of the seed crystal from the edge to the center is gradually accelerated, thereby ensuring that the crystal growth interface grows in a convex shape; secondly, according to the influence of different outer diameter sizes of the graphite ring on heat transfer, the outer diameter size of the graphite ring is limited to gradually increase in the axial direction away from the crucible cover, which can effectively adjust the temperature gradient in the crystal growth zone and prevent the convexity of the crystal from increasing, or the support groove in the graphite ring is assembled with the support ear provided on the crucible cover, so that the coverage range of the graphite ring on the outer periphery of the upper crucible in the vertical direction increases as the thread is tightened, and the growth speed of the seed crystal is regulated by controlling its speed; therefore, with the help of the axial sliding of the upper crucible, the material surface distance can be kept unchanged as the crystal thickness increases, thereby maintaining the stability of the growth interface and the uniformity of the air flow from the silicon carbide raw material to the crystal.

[0016] In summary, the growth crucible provided by the present invention can adjust the material surface distance during the growth process, so as to keep the shape of the growth interface within a small range during the crystal growth process, and can effectively avoid the situation of uneven air flow transmission due to the reduction of the material surface distance, without the need for a separate flow guide device. It can effectively increase the utilization rate of silicon carbide raw materials, increase crystal thickness, improve crystal quality, and save production costs when combined with a suitable heating device.

[0017] Preferably, the upper opening of the lower crucible is in an inverted L shape, and the lower opening of the lower crucible is in an inverted L shape, and the two are adapted up and down. This design can prevent the crucible from falling due to accidental

[0018] Preferably, the seed crystal holder is made of graphite.

[0019] Preferably, the center of the annular through hole is distributed at 1 / 3-2 / 3 of the radial direction of the crucible cover, for example, it can be 1 / 3, 1 / 2, etc.

[0020] In the present invention, if the radial length of the center of the annular through hole from the groove is too small, the heat dissipation in the central area is too fast and the convexity of the crystal is too large; if the radial length of the center of the annular through hole from the groove is too large, the heat dissipation in the edge area is accelerated and the crystal is prone to warping.

[0021] Preferably, the diameter of the annular through hole is 1 / 5-1 / 7 of the diameter of the upper surface of the crucible cover, for example, it may be 1 / 5, 1 / 6 or 1 / 7.

[0022] In the present invention, if the diameter of the annular through hole is too small, the heat dissipation effect is poor, it is difficult to increase the axial gradient, and the crystal growth rate is slow; if the diameter of the annular through hole is too large, the heat dissipation is fast, the axial temperature difference increases, the crystal growth rate is easy to be too fast, resulting in an increase in crystal defects.

[0023] Preferably, the crucible cover is threadedly connected to the hollow rotating rod; the upper part of the hollow rotating rod is connected to a lifting device and a temperature measuring device.

[0024] Preferably, when the crucible cover is an inverted U-shaped structure, the difference between the maximum outer diameter and the minimum outer diameter of the graphite ring is 5-30 mm, for example, it can be 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 25 mm or 30 mm; the thickness of the graphite ring is 5-15 mm, for example, it can be 5 mm, 10 mm or 15 mm.

[0025] In the present invention, the design of the graphite ring helps to improve the insulating heating effect of the crucible, so that the temperature distribution of the seed crystal along the radial direction is uniform, avoiding the obvious uneven growth rate due to the large temperature difference between the center and the edge of the seed crystal, so as to adjust the shape of the crystal growth interface.

[0026] Preferably, when the crucible cover is a circular plate structure, a first annular region and a second annular region are sequentially arranged on the inner side of the graphite ring from top to bottom along the vertical direction, and the supporting groove is opened in the second annular region.

[0027] Preferably, a cross-sectional diameter of the first annular region in the horizontal direction is d1, a cross-sectional diameter of the second annular region in the horizontal direction is d2, a cross-sectional diameter of the support groove in the horizontal direction is d3, and d1≥d3≥d2.

[0028] In the present invention, d1≥d3≥d2 is defined, which can be used as a nested structure of the crucible cover.

[0029] Preferably, each of the support grooves is correspondingly provided with an opening in the vertical direction for the support ear to enter the corresponding support groove; and adjacent support grooves are not connected.

[0030] Preferably, the outer contour of the supporting ear is arc-shaped; with the horizontal center of the crucible cover as the center, the diameter of the circle where the outer contour of the supporting ear lies is d4, the diameter of the crucible cover is d5, and d1≥d3≥d4>d2≥d5.

[0031] In the present invention, by defining d1≥d3≥d4>d2≥d5, the supporting ear can be embedded in the graphite ring and connected to the graphite ring by rotating the crucible cover.

[0032] In a second aspect, the present invention provides a growth device for silicon carbide crystals, the growth device comprising a heating device and the growth crucible as described in the first aspect, wherein the heating device is arranged outside the growth crucible.

[0033] Preferably, the growth device further comprises a pressure control system.

[0034] In a third aspect, the present invention provides a method for growing a silicon carbide crystal, wherein the method adopts the growth device as described in the second aspect for growth, and the method comprises the following steps:

[0035] S1, evacuating the growth device, and then introducing a protective gas and a doping gas into the growth chamber of the growth device at a first set temperature;

[0036] S2, heating to a second set temperature, then heating to a third set temperature for stepwise decompression, and then growing under low pressure conditions, while making the upper crucible slide upward along the axial direction of the lower crucible to control the growth rate of the seed crystal;

[0037] S3, after cooling and returning the pressure of the growth device, taking out the grown silicon carbide crystal.

[0038] The growth method provided by the invention can effectively ensure the stability of the crystal growth environment and is simple to operate.

[0039] Preferably, the upper crucible slides upward along the axial direction of the lower crucible in method 1 or method 2;

[0040] The first method is the upper crucible pulling method;

[0041] The second method includes:

[0042] The base drives the graphite ring to rotate to a corresponding angle, and then transmits it vertically upward, so that the supporting ears arranged on the crucible cover vertically enter the interior of the supporting groove through the opening provided on the graphite ring; when the horizontal height of the supporting ears is aligned with the supporting groove, the base drives the graphite ring to rotate synchronously, and at this time the supporting ears slide relatively inside the supporting groove; when the supporting ears contact the horizontal side ends of the corresponding supporting grooves, the graphite ring stops rotating synchronously with the base, and at this time the upper crucible continues to rotate synchronously driven by the lower crucible, thereby tightening the threads between the upper crucible and the graphite ring, and at the same time, due to the tightening of the threads, the upper crucible slides upward along the axial direction of the lower crucible.

[0043] Preferably, the first set temperature is 1500-1700°C, for example, 1500°C, 1600°C or 1700°C.

[0044] Preferably, the protective gas includes an inert gas, and the doping gas includes nitrogen.

[0045] Preferably, the inert gas comprises argon.

[0046] Preferably, the flow rate of the protective gas is 100-200 mL / min, for example, 100 mL / min, 150 mL / min or 200 mL / min, and the flow rate of the doping gas is 5-10 mL / min, for example, 5 mL / min, 6 mL / min, 7 mL / min, 8 mL / min, 9 mL / min or 10 mL / min, etc.

[0047] Preferably, the pressure of the growth chamber at the first set temperature is 200-400 mbar, for example, 200 mbar, 250 mbar, 300 mbar, 350 mbar or 400 mbar.

[0048] Preferably, the second set temperature is 1900-2000°C, such as 1900°C, 1950°C or 2000°C, etc., and the growth chamber pressure at the second set temperature is 100-200mbar, such as 100mbar, 150mbar or 200mbar, etc.

[0049] Preferably, the heating time of the second set temperature is 2-4 hours, for example, it can be 2 hours, 3 hours or 4 hours.

[0050] Preferably, the third set temperature includes an upper temperature located on the seed crystal holder and a lower temperature located on the bottom of the lower crucible, the upper temperature is 2100-2200°C, for example, it can be 2100°C, 2150°C or 2200°C, etc., the lower temperature is 2200-2300°C, for example, it can be 2200°C, 2250°C or 2300°C, etc.

[0051] Preferably, the step-by-step pressure reduction process includes one stage pressure reduction, two stages pressure reduction and three stages pressure reduction. The pressure after the first stage pressure reduction is 50-100 mbar, for example, it can be 50 mbar, 60 mbar, 70 mbar, 80 mbar, 90 mbar or 100 mbar, etc., the pressure after the second stage pressure reduction is 25-50 mbar, for example, it can be 25 mbar, 30 mbar, 35 mbar, 40 mbar, 45 mbar or 50 mbar, etc., and the pressure after the third stage pressure reduction is 5-10 mbar, for example, it can be 5 mbar, 6 mbar, 7 mbar, 8 mbar, 9 mbar or 10 mbar, etc.

[0052] Preferably, the growth time is 80-150 h, for example, 80 h, 100 h, 125 h or 150 h.

[0053] Preferably, in the upper crucible pulling method, the pulling speed of the upper crucible is 0.1-0.5 mm / h, for example, 0.1 mm / h, 0.2 mm / h, 0.3 mm / h, 0.4 mm / h or 0.5 mm / h.

[0054] Preferably, the growth method comprises the following steps:

[0055] (1) Pre-evacuate the growth device. When the pressure in the growth chamber is 0.5-5 Pa (for example, 0.5 Pa, 1 Pa, 2 Pa, 3 Pa, 4 Pa ​​or 5 Pa, etc.), start the molecular pump to further evacuate to 5×10 -3 -5×10 -2 Pa (for example, it can be 5×10 -3 Pa, 8×10 -3 Pa, 1×10 -2 Pa, 2×10 -2 Pa or 5×10 -2 Pa, etc.);

[0056] (2) turning on the heating device, raising the temperature of the growth crucible to 1100-1200° C. (e.g., 1100° C., 1150° C., or 1200° C.) at a heating rate of 6-7° C. / min (e.g., 6° C. / min, 6.5° C. / min, or 7° C. / min, etc.), then turning off the molecular pump, and maintaining the vacuum by the mechanical pump;

[0057] (3) heating the chamber to a first set temperature of 1500-1700° C. at a heating rate of 2-3° C. / min (e.g., 2° C. / min, 2.5° C. / min, or 3° C. / min, etc.), and then introducing a protective gas at a flow rate of 100-200 mL / min and a doping gas at a flow rate of 5-10 mL / min into the growth chamber, and setting the pressure to 200-400 mbar;

[0058] (4) heating to a second set temperature, wherein the second set temperature is 1900-2200° C., the heating time is 2-4 hours, and the pressure is set to 100-200 mbar;

[0059] (5) heating to a third set temperature, wherein the third set temperature includes an upper temperature at the seed crystal holder and a lower temperature at the bottom of the lower crucible, wherein the upper temperature is 2100-2200° C., the lower temperature is 2200-2300° C., and the heating time is 5-15 h (for example, 5 h, 10 h, or 15 h, etc.);

[0060] (6) performing step-by-step pressure reduction at a third set temperature, wherein the step-by-step pressure reduction process includes a first-stage pressure reduction, a second-stage pressure reduction, and a third-stage pressure reduction, wherein the pressure after the first-stage pressure reduction is 50-100 mbar, the pressure after the second-stage pressure reduction is 25-50 mbar, and the pressure after the third-stage pressure reduction is 5-10 mbar, and after the pressure reduction is completed, growth is performed for 80-150 hours, and at the same time, the upper crucible is made to slide upward along the axial direction of the lower crucible by adopting method one or method two, thereby controlling the growth rate of the seed crystal;

[0061] The first method is the upper crucible pulling method;

[0062] The second method includes: the base drives the graphite ring to rotate to a corresponding angle, and then transmits it vertically upward, so that the support ear provided on the crucible cover vertically enters the support groove through the opening provided on the graphite ring; when the horizontal height of the support ear is aligned with the support groove, the base drives the graphite ring to rotate synchronously, and the support ear slides relatively inside the support groove; when the support ear contacts the horizontal side end of the corresponding support groove, the graphite ring stops rotating synchronously with the base, and the upper crucible continues to rotate synchronously driven by the lower crucible, thereby tightening the thread between the upper crucible and the graphite ring, and at the same time, due to the tightening of the thread, the upper crucible slides upward along the axial direction of the lower crucible;

[0063] (7) After the growth is completed, the temperature is lowered to room temperature within 10-20 hours (for example, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours or 20 hours, etc.), and the pressure is returned at the same time. After the temperature is lowered, the grown silicon carbide crystal is taken out.

[0064] It should be noted that the present invention does not limit the specific temperature of room temperature. For example, it can be 25±5°C, such as 20°C, 25°C or 30°C.

[0065] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] (1) In the growth crucible provided by the present invention, an annular through hole is provided on the upper surface of the crucible cover, which can block the heat dissipation at the edge from the side, so that the heat dissipation at the back of the seed crystal from the edge to the center gradually increases, thereby ensuring that the crystal growth interface grows in a convex shape; secondly, according to the influence of different outer diameters of the graphite ring on heat transfer, the outer diameter of the graphite ring is limited to gradually increase in the axial direction away from the crucible cover, which can effectively adjust the temperature gradient in the crystal growth zone and prevent the convexity of the crystal from increasing, or the support groove in the graphite ring is assembled with the support ear provided on the crucible cover, so that the coverage range of the graphite ring on the outer periphery of the upper crucible in the vertical direction increases as the thread is tightened, and the growth rate of the seed crystal is regulated by controlling its speed; therefore, with the help of the axial sliding of the upper crucible, the material surface distance can be kept unchanged as the crystal thickness increases, thereby maintaining the stability of the growth interface and the uniformity of the gas flow from the silicon carbide raw material to the crystal.

[0068] (2) The growth crucible provided by the present invention, when combined with a suitable heating device, can effectively increase the utilization rate of silicon carbide raw materials, increase crystal thickness, improve crystal quality, and save production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 Schematic diagram of a growth crucible used in the prior art.

[0070] Figure 2 This is a schematic diagram of the growth crucible structure provided in Example 1 of the present invention.

[0071] Figure 3 FIG. 1 is a top view of the crucible cover in Example 1 of the present invention.

[0072] Figure 4 This is a schematic diagram of the growth crucible structure provided in Example 2 of the present invention.

[0073] Figure 5 This is a schematic structural diagram of the crucible cover provided in Example 2 of the present invention.

[0074] Figure 6 This is a schematic diagram of the structure of the graphite ring provided in Example 2 of the present invention.

[0075] Figure 7 This is a schematic diagram of the assembly of the graphite ring and the crucible cover provided in Example 2 of the present invention.

[0076] Figure 8 This is a cross-sectional view of the assembly of a graphite ring and a crucible cover provided in Example 2 of the present invention.

[0077] Fig. 9 A schematic diagram of the growth crucible structure after the upper crucible is pulled in the growth method provided in Application Example 1 of the present invention;

[0078] Fig.10This is a schematic diagram of the growth crucible structure after the upper crucible slides upward along the axial direction of the lower crucible in the growth method provided in Application Example 2 of the present invention.

[0079] Among them, 1-crucible cover; 2-graphite ring; 3-upper crucible; 4-lower crucible; 5-silicon carbide raw material; 6-base; 7-seed crystal holder; 8-seed crystal; 9-hollow rotating rod; 10-annular through hole; 11-support ear; 12-support groove. DETAILED DESCRIPTION

[0080] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0081] It should be noted that the room temperature below refers to 25°C.

[0082] Example 1

[0083] This embodiment provides a crucible for growing silicon carbide crystals, and its structural schematic diagram is shown in FIG. Figure 2 As shown, the growth crucible includes a lower crucible 4, an upper crucible 3, a crucible cover 1 and a graphite ring 2;

[0084] The lower crucible 4 is sleeved on the inner periphery of the upper crucible 3 and is used to place the silicon carbide raw material 5; a gap is left between the lower crucible 4 and the upper crucible 3 for the axial sliding of the upper crucible 3;

[0085] The upper opening of the upper crucible 3 is equipped with a seed crystal holder 7 for fixing a seed crystal 8;

[0086] Figure 3 The top view of the crucible cover 1 is shown. As can be seen from the figure, a groove is provided at the center of the upper surface of the crucible cover 1 for threaded connection with the hollow rotating rod 9; an annular through hole 10 is provided on the upper surface of the crucible cover 1 in a radial direction away from the groove;

[0087] The crucible cover 1 is an inverted U-shaped structure, the upper part of the upper crucible 3 is sleeved on the inner side of the lower part of the crucible cover 1, and the upper crucible 3 is threadedly connected to the crucible cover 1; the lower outer wall of the crucible cover 1 is threadedly connected to the graphite ring 2; the lower crucible 4 is coaxially placed on the base 6, and the base 6 is connected to a displacement device for displacement requirements of the upper crucible 3;

[0088] The outer diameter of the graphite ring 2 gradually increases along the axial direction away from the crucible cover 1, the minimum outer diameter of the graphite ring 2 is 210 mm, the maximum outer diameter is 230 mm, and the thickness of the graphite ring 2 is 10 mm;

[0089] The upper opening of the lower crucible 4 is in an inverted L shape, and the lower opening of the lower crucible 4 is in an inverted L shape, and the two are adapted up and down;

[0090] The seed crystal holder 7 is made of graphite;

[0091] The center of the annular through hole 10 is located at 1 / 4 of the radial direction of the crucible cover 1; the diameter of the annular through hole 10 is 1 / 6 of the diameter of the upper surface of the crucible cover 1;

[0092] The upper part of the hollow rotary rod 9 is connected to a lifting device and a temperature measuring device.

[0093] This embodiment also provides a growth device for silicon carbide crystals, the growth device comprising a heating device, a heat preservation layer, a pressure control system and the growth crucible as described above;

[0094] The heating device is a resistive heater, which is arranged outside the growth crucible and is used to provide heating to the silicon carbide raw material 5 inside the growth crucible to achieve the growth of silicon carbide crystals;

[0095] The heat-insulating layer is arranged on the outside of the heating device, and is used to provide heat-insulating effect to the silicon carbide growth crucible, so as to ensure the temperature stability of the environment in which the silicon carbide growth crucible is located;

[0096] The pressure control system is used to control the pressure of a growth chamber in a growth crucible with a heating device on the outside.

[0097] Example 2

[0098] This embodiment provides a crucible for growing silicon carbide crystals, and its structural schematic diagram is shown in FIG. Figure 4 As shown, the growth crucible includes a lower crucible 4, an upper crucible 3, a crucible cover 1 and a graphite ring 2;

[0099] The lower crucible 4 is sleeved on the inner periphery of the upper crucible 3 and is used to place the silicon carbide raw material 5; a gap is left between the lower crucible 4 and the upper crucible 3 for the axial sliding of the upper crucible 3;

[0100] The upper opening of the upper crucible 3 is equipped with a seed crystal holder 7 for fixing a seed crystal 8;

[0101] Figure 5 The schematic diagram of the structure of the crucible cover 1 is shown. As can be seen from the figure, a groove is provided at the center of the upper surface of the crucible cover 1 for threaded connection with a hollow rotating rod 9; an annular through hole 10 is provided on the upper surface of the crucible cover 1 in a radial direction away from the groove; the crucible cover 1 is a circular plate structure, and two supporting ears 11 are relatively distributed on the circumferential periphery of the crucible cover 1; the outer contour of the supporting ears 11 is arc-shaped;

[0102] Figure 6shows a schematic structural diagram of the graphite ring 2, Figure 7 and Figure 8 The figure shows the assembly schematic diagram and the assembly cross-sectional diagram of the graphite ring 2 and the crucible cover 1, respectively. It can be seen from the figure that two support grooves 12 are provided on the horizontal circumferential direction of the upper inner side of the graphite ring 2 for assembling the support ears 11, and the lower inner wall of the graphite ring 2 is threadedly connected with the upper outer wall of the upper crucible 3; the inner side of the graphite ring 2 is provided with a first annular area and a second annular area in sequence from top to bottom along the vertical direction, and the support groove 12 is provided in the second annular area; each of the support grooves 12 is correspondingly provided with an opening in the vertical direction for the support ears 11 to enter the corresponding support groove 12; the adjacent support grooves 12 are not connected;

[0103] The cross-sectional diameter of the first annular area in the horizontal direction is d1, the cross-sectional diameter of the second annular area in the horizontal direction is d2, the cross-sectional diameter of the support groove 12 in the horizontal direction is d3, the diameter of the circle where the outer periphery of the support ear 11 is located with the horizontal center of the crucible cover 1 as the center of the circle is d4, the diameter of the crucible cover 1 is d5, d1≥d3≥d4>d2≥d5.

[0104] The upper opening of the lower crucible 4 is in an inverted L shape, and the lower opening of the lower crucible 4 is in an inverted L shape, and the two are adapted up and down;

[0105] The seed crystal holder 7 is made of graphite;

[0106] The center of the annular through hole 10 is located at 1 / 4 of the radial direction of the crucible cover 1; the diameter of the annular through hole 10 is 1 / 6 of the diameter of the upper surface of the crucible cover 1;

[0107] The upper part of the hollow rotating rod 9 is connected to a lifting device and a temperature measuring device;

[0108] The lower crucible 4 is coaxially placed on a base 6 , and the base 6 is connected to a rotating device for synchronously rotating the upper crucible 3 , the graphite ring 2 and the lower crucible 4 .

[0109] This embodiment also provides a growth device for silicon carbide crystals, the growth device comprising a heating device, a heat preservation layer, a pressure control system and the growth crucible as described above;

[0110] The heat-insulating layer is arranged on the outer side of the growth crucible, and is used to provide heat-insulating effect to the silicon carbide growth crucible, so as to ensure the temperature stability of the environment where the silicon carbide growth crucible is located;

[0111] The heating device is a resistive heater, which is arranged outside the insulation layer and is used to provide heating to the silicon carbide raw material 5 inside the growth crucible to achieve the growth of silicon carbide crystals;

[0112] The pressure control system is used to control the pressure of a growth chamber in a growth crucible with a heating device on the outside.

[0113] Example 3

[0114] The difference between this embodiment and the first embodiment is that the center of the annular through hole 10 is distributed at 3 / 4 of the radial direction of the crucible cover 1 .

[0115] The remaining structures and parameters remain the same as those in Example 1.

[0116] Example 4

[0117] The difference between this embodiment and the first embodiment is that the center of the annular through hole 10 is distributed at 1 / 6 of the radial direction of the crucible cover 1 .

[0118] The remaining structures and parameters remain the same as those in Example 1.

[0119] Comparative Example 1

[0120] The difference between this comparative example and Example 1 is that the upper surface of the crucible cover 1 is not provided with an annular through hole 10 .

[0121] The remaining structures and parameters remain the same as those in Example 1.

[0122] Comparative Example 2

[0123] The difference between this comparative example and Example 1 is that the outer diameter of the graphite ring 2 remains constant.

[0124] The remaining structures and parameters remain the same as those in Example 1.

[0125] Application Example 1

[0126] This application example provides a method for growing a silicon carbide crystal. The growth method uses the growth device described in Example 1. The growth method includes the following steps:

[0127] (1) Pre-evacuate the growth device. When the pressure in the growth chamber is 5 Pa, turn on the molecular pump to further evacuate to 5×10 -3 Pa;

[0128] (2) Turn on the heating device and raise the temperature of the growth crucible to 1100°C at a heating rate of 6°C / min, then turn off the molecular pump and keep the gas pumped by the mechanical pump;

[0129] (3) heating the chamber to a first set temperature of 1600° C. at a heating rate of 2° C. / min, and then introducing argon gas at a flow rate of 150 mL / min and doping gas nitrogen at a flow rate of 10 mL / min into the growth chamber, with the pressure set to 300 mbar;

[0130] (4) heating to a second set temperature of 2000° C., heating time of 3 h, and pressure of 150 mbar;

[0131] (5) heating to a third set temperature, wherein the third set temperature includes an upper temperature at the seed crystal holder and a lower temperature at the bottom of the lower crucible, wherein the upper temperature is 2100° C., the lower temperature is 2300° C., and the heating time is 10 h;

[0132] (6) Stepwise depressurization is performed at a third set temperature, wherein the stepwise depressurization process includes one stage depressurization, two stages depressurization and three stages depressurization, wherein the pressure after the first stage depressurization is 75 mbar, the pressure after the second stage depressurization is 35 mbar, and the pressure after the third stage depressurization is 10 mbar. After the depressurization is completed, growth is performed for 100 hours, and at the same time, the upper crucible 3 is pulled up by the upper crucible 3 so that the upper crucible 3 slides upward along the axial direction of the lower crucible 4, thereby controlling the growth rate of the seed crystal 8. The schematic diagram of the growth crucible structure after the upper crucible 3 is pulled up is shown in FIG. Fig. 9 As shown;

[0133] (7) After the growth is completed, the temperature is lowered to room temperature within 15 hours while the pressure is returned. After the temperature is lowered, the grown silicon carbide crystal is taken out.

[0134] Application Example 2

[0135] This application example provides a method for growing a silicon carbide crystal. The growth method uses the growth device described in Example 2. The growth method includes the following steps:

[0136] (1) Pre-evacuate the growth device. When the pressure in the growth chamber is 5 Pa, turn on the molecular pump to further evacuate to 5×10 -3 Pa;

[0137] (2) Turn on the heating device and raise the temperature of the growth crucible to 1100°C at a heating rate of 6°C / min, then turn off the molecular pump and keep the gas pumped by the mechanical pump;

[0138] (3) heating the chamber to a first set temperature of 1600° C. at a heating rate of 2° C. / min, and then introducing argon gas at a flow rate of 150 mL / min and doping gas nitrogen at a flow rate of 10 mL / min into the growth chamber, with the pressure set to 300 mbar;

[0139] (4) heating to a second set temperature of 2000° C., heating time of 3 h, and pressure of 150 mbar;

[0140] (5) heating to a third set temperature, wherein the third set temperature includes an upper temperature at the seed crystal holder and a lower temperature at the bottom of the lower crucible, wherein the upper temperature is 2100° C., the lower temperature is 2300° C., and the heating time is 10 h;

[0141] (6) performing step-by-step pressure reduction at a third set temperature, wherein the step-by-step pressure reduction process includes a first stage pressure reduction, a second stage pressure reduction, and a third stage pressure reduction, wherein the pressure after the first stage pressure reduction is 75 mbar, the pressure after the second stage pressure reduction is 35 mbar, and the pressure after the third stage pressure reduction is 10 mbar. After the pressure reduction is completed, growth is performed for 100 hours, and at the same time, the upper crucible 3 is made to slide axially upward along the lower crucible 4 in the following manner, thereby controlling the growth rate of the seed crystal 8. The schematic diagram of the growth crucible structure after the upper crucible 3 slides axially upward along the lower crucible 4 is shown in FIG. Fig.10 As shown, the specific steps include:

[0142] The base 6 drives the graphite ring 2 to rotate to a corresponding angle, and then transmits it vertically upward, so that the support ear 11 provided on the crucible cover 1 vertically enters the inside of the support groove 12 through the opening provided on the graphite ring 2; when the horizontal height of the support ear 11 is aligned with the support groove 12, the base 6 drives the graphite ring 2 to rotate synchronously, and at this time, the support ear 11 slides relatively inside the support groove 12; when the support ear 11 contacts the horizontal side end of the corresponding support groove 12, the graphite ring 2 stops rotating synchronously with the base 6, and at this time, the upper crucible 3 continues to rotate synchronously driven by the lower crucible 4, thereby tightening the thread between the upper crucible 3 and the graphite ring 2, and at the same time, due to the tightening of the thread, the upper crucible 3 slides upward along the axial direction of the lower crucible 4;

[0143] (7) After the growth is completed, the temperature is lowered to room temperature within 15 hours while the pressure is returned. After the temperature is lowered, the grown silicon carbide crystal is taken out.

[0144] Application Example 3-4

[0145] Application Examples 3-4 respectively provide a method for growing a silicon carbide crystal, and the growth methods respectively use the growth devices described in Examples 3-4, and the growth methods are consistent with Application Example 1.

[0146] Application Comparative Example 1-2

[0147] Application Examples 1-2 respectively provide a method for growing a silicon carbide crystal, and the growth methods respectively use the growth devices described in Comparative Examples 1-2, and the growth methods are consistent with Application Example 1.

[0148] analyze:

[0149] The silicon carbide crystals prepared in the above-mentioned application examples 1-4 and the application comparative examples 1-2 were tested.

[0150] The test results are shown in Table 1.

[0151] Table 1

[0152]

[0153] analyze:

[0154] In summary, the growth crucible provided by the present invention, in combination with a suitable heating device, can effectively increase the utilization rate of silicon carbide raw materials, increase crystal thickness, and improve crystal quality.

[0155] By comparing Application Example 1 with Application Examples 3-4, it can be seen that if the radial length of the distance between the center of the annular through hole and the groove is too large, the crystal surface will be M-shaped, which is prone to deformation and seriously reduces the quality of the crystal; if the radial length of the distance between the center of the annular through hole and the groove is too small, the heat dissipation in the central area will be accelerated, a bulge will be generated in the central area of ​​the crystal, the dislocation will increase, and the crystal quality will decrease.

[0156] By comparing Application Example 1 with Application Comparative Example 1, it can be seen that if the upper surface of the crucible cover is not provided with an annular through hole, the convexity of the circular area corresponding to the upper temperature measuring hole increases, the dislocation density increases, and the crystal quality decreases.

[0157] By comparing Application Example 1 with Application Comparative Example 2, it can be seen that if the outer diameter of the graphite ring remains constant, the overall convexity of the crystal will increase, which will increase the density of dislocations and microtubes and reduce the quality of the crystal.

[0158] The applicant declares that the present invention illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A crucible for growing silicon carbide crystals, characterized in that: The growth crucible comprises a lower crucible, an upper crucible, a crucible cover and a graphite ring; The lower crucible is sleeved on the inner periphery of the upper crucible and is used to place silicon carbide raw materials; a gap is left between the lower crucible and the upper crucible for the axial sliding of the upper crucible; The upper opening of the upper crucible is equipped with a seed crystal holder for fixing the seed crystal; A groove is provided at the center of the upper surface of the crucible cover for embedding the hollow rotating rod; an annular through hole is provided on the upper surface of the crucible cover along a radial direction away from the groove; The center of the annular through hole is distributed at 1 / 3-1 / 5 of the radial direction of the crucible cover; The diameter of the annular through hole is 1 / 5-1 / 7 of the diameter of the upper surface of the crucible cover; The crucible cover is an inverted U-shaped structure or a circular plate structure; When the crucible cover is an inverted U-shaped structure, the upper part of the upper crucible is sleeved on the inner side of the lower part of the crucible cover, and the upper crucible is threadedly connected to the crucible cover; the lower outer wall of the crucible cover is threadedly connected to the graphite ring; the outer diameter of the graphite ring gradually increases along the axial direction away from the crucible cover; the lower crucible is coaxially placed on the base, and the base is connected to a displacement device for displacement requirements of the upper crucible; The difference between the maximum outer diameter and the minimum outer diameter of the graphite ring is 5-30 mm, and the thickness of the graphite ring is 5-15 mm; When the crucible cover is a circular plate structure, a plurality of support ears distributed at intervals are arranged on the circumferential periphery of the crucible cover, a plurality of support grooves are opened on the horizontal circumference of the upper inner side of the graphite ring for assembling the support ears, and the lower inner wall of the graphite ring is threadedly connected to the upper outer wall of the upper crucible; the lower crucible is coaxially placed on the base, and the base is connected to a rotating device for synchronous rotation of the upper crucible, the graphite ring and the lower crucible.

2. The growth crucible according to claim 1, characterized in that The upper opening of the lower crucible is in an inverted L shape, and the lower opening of the lower crucible is in an inverted L shape, and the two are adapted up and down; The material of the seed crystal holder includes graphite; The crucible cover is threadedly connected to the hollow rotating rod; the upper part of the hollow rotating rod is connected to a lifting device and a temperature measuring device.

3. The growth crucible according to claim 1, characterized in that When the crucible cover is a circular plate structure, a first annular region and a second annular region are sequentially arranged on the inner side of the graphite ring from top to bottom along the vertical direction, and the supporting groove is opened in the second annular region; The cross-sectional diameter of the first annular region in the horizontal direction is d1, the cross-sectional diameter of the second annular region in the horizontal direction is d2, and the cross-sectional diameter of the supporting groove in the horizontal direction is d3, d1≥d3>d2.

4. The growth crucible according to claim 3, characterized in that Each of the support grooves is correspondingly provided with an opening in the vertical direction for the support ear to enter the corresponding support groove; adjacent support grooves are not connected; The outer contour of the support ear is arc-shaped; with the horizontal center of the crucible cover as the center of the circle, the diameter of the circle where the outer periphery of the support ear is located is d4, the diameter of the crucible cover is d5, and d1≥d3≥d4>d2≥d5.

5. A silicon carbide crystal growth device, characterized in that: The growth device comprises a heating device and the growth crucible according to any one of claims 1 to 4, wherein the heating device is arranged outside the growth crucible.

6. A method for growing silicon carbide crystals, characterized in that: The growth method adopts the growth device as claimed in claim 5 for growth, and the growth method comprises the following steps: S1, evacuating the growth device, and then introducing a protective gas and a doping gas into the growth chamber of the growth device at a first set temperature; S2, heating to a second set temperature, then heating to a third set temperature for stepwise decompression, and then growing under low pressure conditions, while making the upper crucible slide upward along the axial direction of the lower crucible to control the growth rate of the seed crystal; S3, after cooling and returning the pressure of the growth device, taking out the grown silicon carbide crystal.

7. The growth method according to claim 6, characterized in that: The upper crucible slides upward along the axial direction of the lower crucible in method 1 or method 2; The first method is the upper crucible pulling method; The second method includes: The base drives the graphite ring to rotate to a corresponding angle, and then transmits it vertically upward, so that the supporting ears arranged on the crucible cover vertically enter the interior of the supporting groove through the opening provided on the graphite ring; when the horizontal height of the supporting ears is aligned with the supporting groove, the base drives the graphite ring to rotate synchronously, and at this time the supporting ears slide relatively inside the supporting groove; when the supporting ears contact the horizontal side ends of the corresponding supporting grooves, the graphite ring stops rotating synchronously with the base, and at this time the upper crucible continues to rotate synchronously driven by the lower crucible, thereby tightening the threads between the upper crucible and the graphite ring, and at the same time, due to the tightening of the threads, the vertical coverage of the graphite ring on the periphery of the upper crucible increases as the threads are tightened, and the upper crucible slides upward along the axial direction of the lower crucible.

8. The growth method according to claim 6, characterized in that: The first set temperature is 1500-1700°C; The protective gas includes an inert gas, and the doping gas includes nitrogen; The flow rate of the protective gas is 100-200 mL / min, and the flow rate of the doping gas is 5-10 mL / min; The growth chamber pressure at the first set temperature is 200-400 mbar; The second set temperature is 1900-2000° C., and the growth chamber pressure at the second set temperature is 100-200 mbar; The heating time of the second set temperature is 2-4h; The third set temperature includes an upper temperature located on the seed crystal holder and a lower temperature located on the bottom of the lower crucible, the upper temperature is 2100-2200° C., and the lower temperature is 2200-2300° C.; The step-by-step pressure reduction process includes one stage pressure reduction, two stage pressure reduction and three stage pressure reduction, the pressure after the one stage pressure reduction is 50-100 mbar, the pressure after the two stage pressure reduction is 25-50 mbar, and the pressure after the three stage pressure reduction is 5-10 mbar; The growth time is 80-150h; In the upper crucible pulling method, the pulling speed of the upper crucible is 0.1-0.5 mm / h.

9. The growth method according to claim 6, characterized in that: The growth method comprises the following steps: (1) Pre-evacuate the growth device. When the pressure in the growth chamber is 0.5-5 Pa, turn on the molecular pump to further evacuate to 5×10 -3 -5×10 -2 Pa; (2) Turn on the heating device and raise the temperature of the growth crucible to 1100-1400°C at a heating rate of 6-7°C / min, then turn off the molecular pump and keep the gas pumping by the mechanical pump; (3) heating the chamber to a first set temperature of 1500-1700°C at a heating rate of 2-3°C / min, and then introducing a protective gas at a flow rate of 100-200 mL / min and a doping gas at a flow rate of 5-10 mL / min into the growth chamber, with the pressure set to 200-400 mbar; (4) Heating to a second set temperature, wherein the second set temperature is 1900-2200°C, the heating time is 2-4 hours, and the pressure is set to 100-200 mbar; (5) heating to a third set temperature, wherein the third set temperature includes an upper temperature at the seed crystal holder and a lower temperature at the bottom of the lower crucible, wherein the upper temperature is 2100-2200° C., the lower temperature is 2200-2300° C., and the heating time is 5-15 hours; (6) performing step-by-step pressure reduction at a third set temperature, wherein the step-by-step pressure reduction process includes a first stage pressure reduction, a second stage pressure reduction and a third stage pressure reduction, wherein the pressure after the first stage pressure reduction is 50-100 mbar, the pressure after the second stage pressure reduction is 25-50 mbar, and the pressure after the third stage pressure reduction is 5-10 mbar, and after the pressure reduction is completed, growth is performed for 80-150 hours, and at the same time, the upper crucible is made to slide upward along the axial direction of the lower crucible by adopting method one or method two, thereby controlling the growth rate of the seed crystal; The first method is the upper crucible pulling method; The second method includes: the base drives the graphite ring to rotate to a corresponding angle, and then transmits it vertically upward, so that the support ear provided on the crucible cover vertically enters the support groove through the opening provided on the graphite ring; when the horizontal height of the support ear is aligned with the support groove, the base drives the graphite ring to rotate synchronously, and the support ear slides relatively inside the support groove; when the support ear contacts the horizontal side end of the corresponding support groove, the graphite ring stops rotating synchronously with the base, and the upper crucible continues to rotate synchronously driven by the lower crucible, thereby tightening the thread between the upper crucible and the graphite ring, and at the same time, due to the tightening of the thread, the coverage of the graphite ring on the outer periphery of the upper crucible in the vertical direction increases as the thread is tightened, and the upper crucible slides upward along the axial direction of the lower crucible; (7) After the growth is completed, the temperature is lowered to room temperature within 10-20 hours while the pressure is returned. After the temperature is lowered, the grown silicon carbide crystal is taken out.

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