Apparatus and method for liquid phase method growth of silicon carbide crystals

Abstract

The application provides a device for growing silicon carbide crystal by liquid phase method. The thread of the lower end of the seed crystal rod is right-handed or left-handed, which is the same as the thread of the inner part of the seed crystal holder. The thread of the inner part of the locking nut is left-handed or right-handed, which is the same as the thread of the outer part of the seed crystal holder. The thread of the inner part of the locking nut is opposite to the thread of the lower end of the seed crystal rod. Thus, the device of the application can realize self-locking function. The application also provides a method for preparing silicon carbide crystal, which uses the device for growing silicon carbide crystal by liquid phase method. The device of the application can conveniently and reliably realize high-speed forward and reverse rotation of the seed crystal holder, introduce forced convection in the melt, promote uniformity of the melt composition and accelerate solute transport, and improve the quality and speed of growing silicon carbide crystal by liquid phase method. The method of the application can prepare silicon carbide crystal with excellent quality.

Description

TECHNICAL FIELD

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

[0002] Silicon carbide (SiC) is one of the widely concerned wide bandgap semiconductor materials, which has the advantages of low density, large bandgap (3.2 eV at room temperature for 4H-SiC), high breakdown field strength (about 10 times that of Si), high saturated electron mobility (about 2 times that of Si), high thermal conductivity (3 times that of Si and 10 times that of GaAs), and good chemical stability, etc. It is an ideal substrate material for making high-frequency, high-voltage, high-power devices and blue light emitting diodes. It has important application potential in the fields of electric vehicles, rail transit, high-voltage power transmission and transformation, photovoltaic, 5G communication, etc.

[0003] The main growth method of SiC at present is physical vapor phase transmission method, but it has the problems of high defect density, difficult expansion and p-type doping. The liquid phase method has low growth temperature, relatively stable growth environment, and the growth process is close to the thermodynamic equilibrium condition, so the crystal quality is good, and it has good prospects in expansion and p-type doping, etc. In recent years, it has been widely concerned by the academic and industrial circles.

[0004] In the liquid phase method, the raw material supply is divided into two parts: Si is provided by Si-containing metal raw material, and C is dissolved into the melt from the inner wall and bottom of the graphite crucible. Si and C are transported to the seed crystal by diffusion and convection to realize the growth of SiC crystal. Therefore, in the growth of SiC crystal by liquid phase method, the dissolution and transportation of C are crucial, which directly determines the quality and speed of the crystal. If the solute supply is insufficient during the growth process, not only will the growth rate decrease, but also macroscopic defects such as grooves and inclusions will be produced. In addition, due to factors such as asymmetric temperature field of the growth system and uneven material of the crucible, the solute distribution will be uneven, which will affect the crystal quality.

[0005] The use of high-speed reversing rotation of the seed crystal holder can introduce forced convection in the melt, thereby improving the solute transport speed and the composition uniformity of the melt.

[0006] The existing technology generally uses threaded connection to fix the seed crystal rod and the seed crystal holder, for example, Chinese patent (CN 216809016U) uses external threads on the seed crystal rod and internal threads on the seed crystal holder to fix them. However, this fixing method is only suitable for unidirectional rotation.

[0007] There are also people who fill the gap inside the screw thread with glue or insert a plug to achieve the purpose of not loosening in forward and reverse rotation, but these methods are more complex to implement and do not have high reliability, and there is still a great possibility of loosening when rotating at high speed. In addition, the use of adhesion will introduce additional impurities into the growth system.

[0008] Therefore, there is an urgent need for a device that can improve the solute transport speed and the composition uniformity of the melt in liquid phase method for growing silicon carbide crystals, thereby improving the quality of the crystals. SUMMARY

[0009] The purpose of the present application is to provide a device for growing silicon carbide crystals by liquid phase method. The device of the present application can conveniently and reliably achieve high-speed forward and reverse rotation of the seed crystal holder, introduce forced convection in the melt, promote the uniformity of the melt composition and accelerate solute transport, and improve the quality and speed of liquid phase method for growing silicon carbide crystals.

[0010] Another purpose of the present application is to provide a method for preparing silicon carbide crystals. The method of the present application produces silicon carbide crystals with excellent quality.

[0011] The above purposes of the present application are achieved by the following technical solutions.

[0012] In one aspect, the present application provides a device for growing silicon carbide crystals by liquid phase method, comprising a seed crystal rod, a seed crystal holder and a locking nut;

[0013] The seed crystal rod comprises a first section, a second section and a third section in the axial direction, wherein the diameter of the second section is greater than the diameter of the first section and the diameter of the third section to form a boss on the seed crystal rod; the third section is provided with external threads;

[0014] The seed crystal holder comprises a base plate and a first cylindrical section extending circumferentially along one side of the base plate; the first cylindrical section is provided with internal threads and external threads;

[0015] The locking nut comprises a second cylindrical section and a third cylindrical section in the circumferential direction, the inner diameter of the second cylindrical section is smaller than the inner diameter of the third cylindrical section; the third cylindrical section is provided with internal threads;

[0016] The diameter of the second section is greater than the inner diameter of the second cylindrical section and less than or equal to the inner diameter of the third cylindrical section;

[0017] The outer thread on the third section and the inner thread on the first cylindrical section of the seed holder are of the same hand, so that the third section of the seed rod can be threadedly connected with the first cylindrical section of the seed holder; the outer thread on the first cylindrical section and the inner thread on the third cylindrical section of the locking nut are of the same hand, so that the third cylindrical section of the locking nut can be threadedly connected with the first cylindrical section of the seed holder and, after being connected, the second cylindrical section is pressed against the boss; and the outer thread on the third section and the inner thread on the third cylindrical section are of opposite hands.

[0018] Preferably, in the device for growing silicon carbide crystals by liquid phase method according to the present application, the axial length of the third section of the seed rod is greater than the axial length of the first cylindrical section of the seed holder, so that, after the third section of the seed rod is threadedly connected with the first cylindrical section of the seed holder, there is a spacing distance between the boss and the first cylindrical section of the seed holder.

[0019] Preferably, in the device for growing silicon carbide crystals by liquid phase method according to the present application, the axial length of the third section of the seed rod is 1-4 mm greater than the axial length of the first cylindrical section of the seed holder, so that, after the third section of the seed rod is threadedly connected with the first cylindrical section of the seed holder, there is a spacing distance of 1-4 mm between the boss and the first cylindrical section of the seed holder.

[0020] Preferably, in the device for growing silicon carbide crystals by liquid phase method according to the present application, the axial length of the third cylindrical section of the locking nut is less than the sum of the axial lengths of the second section and the third section of the seed rod, so that, after the third cylindrical section of the locking nut is threadedly connected with the first cylindrical section of the seed holder, there is a spacing distance between the third cylindrical section of the locking nut and the base plate of the seed holder, thereby ensuring that the locking nut is tightly fitted against the boss after being screwed.

[0021] Preferably, in the device for growing silicon carbide crystals by liquid phase method according to the present application, the axial length of the third cylindrical section of the locking nut is less than the sum of the axial lengths of the second section and the third section of the seed rod, so that, after the third cylindrical section of the locking nut is threadedly connected with the first cylindrical section of the seed holder, there is a spacing distance of 1-4 mm between the third cylindrical section of the locking nut and the base plate of the seed holder, thereby ensuring that the locking nut is tightly fitted against the boss after being screwed.

[0022] Preferably, in the device for growing silicon carbide crystals by liquid phase method according to the present application, the first cylindrical section of the seed holder is provided with a tool withdrawal groove on the side close to the base plate, so as to ensure that, after the seed rod is screwed with the seed holder, the third section of the seed rod can be tightly fitted against the bottom of the threaded hole of the seed holder.

[0023] Preferably, in the device for growing silicon carbide crystal by liquid phase method of the present application, the length of the external thread on the third section of the seed rod is 1-4 mm longer than the length of the internal thread on the first cylindrical section of the seed holder.

[0024] Preferably, in the device for growing silicon carbide crystal by liquid phase method of the present application, the diameter of the second section is 4-10 mm larger than the inner diameter of the second cylindrical section.

[0025] Preferably, in the device for growing silicon carbide crystal by liquid phase method of the present application, the material of the seed rod, the seed holder and the locking nut is high-purity graphite or molybdenum.

[0026] In another aspect, the present application provides a method for preparing silicon carbide crystal, which uses the device for growing silicon carbide crystal by liquid phase method of the present application, comprising the following steps:

[0027] (1) placing the growth raw material in the crucible, heating the crucible by the induction heating device to melt the growth raw material into a melt, and controlling the seed rod to rotate unidirectionally at a first speed;

[0028] (2) controlling the seed rod to rotate unidirectionally at the first speed while lowering the seed holder to make the silicon carbide seed fixed on the seed holder contact the melt;

[0029] (3) after the seed contacts the melt, controlling the seed rod to rotate periodically at a second speed: after rotating at the second speed for a certain period of time, slowing down to zero, accelerating to the second speed in the opposite direction, maintaining for a certain period of time, slowing down to zero, accelerating to the second speed in the opposite direction, and repeating the cycle until the growth is completed;

[0030] (4) after the growth is completed, controlling the seed rod to rotate unidirectionally at the first speed while lifting the seed holder until the seed is separated from the melt, and obtaining the silicon carbide single crystal after cooling with the furnace;

[0031] The first speed is 0 or 1-30 rpm; and the second speed is 100-300 rpm.

[0032] In the present application, the seed rod does not rotate or rotates unidirectionally at a low speed during the heating and the lowering of the silicon carbide seed. When the temperature field is very uniform, the seed rod does not rotate can also uniformly increase the temperature. When the temperature field is not very uniform, the low-speed rotation can weaken the adverse effects (such as thermal stress and seed ablation caused by uneven heating) caused by the non-uniform temperature field. However, if the rotation speed is too fast at this stage, the liquid surface will shake and the melt will splash in the moment of contacting the liquid surface, which will affect the subsequent crystal growth.

[0033] In the present application, after the seed rod is reversed, the seed rod is controlled to rotate at the second speed, then slowly decelerated to 0 rpm, and then accelerated to the second speed in the opposite direction. When the speed is low, forced convection is not obvious, and the promotion of solute transport is not obvious. When the speed is high, the melt surface is unstable, and high requirements are put forward for the mechanical precision of the growth furnace and the strength of the graphite part, because if the round runout of the seed rod is too large, the radial component brought by high-speed rotation will make the seed holder swing, and in severe cases, the seed rod will be broken. The selection of acceleration and deceleration time and holding time is also based on this principle.

[0034] Preferably, in the method of the present application, the step (3) of controlling the seed rod to rotate periodically at the second speed is carried out in a method comprising the following steps:

[0035] After rotating at the second speed for 30-60 min, slowly decelerate to zero, then accelerate to the second speed in the opposite direction, keep for 30-60 min, then slowly decelerate to zero, then accelerate to the second speed in the opposite direction, and repeat the cycle until the growth is completed; wherein the total acceleration and deceleration time is 1-15 min.

[0036] Preferably, in the method of the present application, the crucible is a graphite crucible; more preferably, the purity of the graphite crucible is not less than 99.95%, the inner diameter of the graphite crucible is 10-150 mm larger than the diameter of the seed ingot, the wall thickness of the graphite crucible is not less than 10 mm, and the density of the graphite crucible is 1.7-2.0 g / cm 3 .

[0037] In a specific embodiment of the present application, the device comprises a seed rod, a seed holder, and a locking nut; the lower end of the seed rod is right-handed thread, and above the thread there is a boss; the inside of the locking nut is left-handed thread, and the upper inner diameter is smaller, which can be fitted with the boss after being screwed. The seed holder is provided with right-handed internal thread and left-handed external thread, and the right-handed internal thread is connected with the right-handed thread on the seed rod, and the left-handed external thread is connected with the left-handed thread inside the locking nut. In use, the seed rod is screwed into the threaded hole on the seed holder until the bottom of the hole, and then the locking nut is sleeved from the upper end of the seed rod and connected with the external thread on the seed holder. The effect achieved by the device is that during the growth process, when the rotation direction of the seed holder is consistent with the thread rotation direction of the seed rod, the resistance received by the seed holder will tighten the seed rod and the seed holder, and the seed rod and the seed holder are tightly fitted at the bottom of the threaded hole and will not loosen. When the rotation direction changes, i.e. is consistent with the thread rotation direction of the locking nut, the resistance received by the seed holder will tighten the locking nut and the seed holder, and the locking nut will have a tendency to move downward, but due to the obstruction of the boss on the seed rod, the locking nut will press the seed rod and the seed holder tightly, ensuring that the seed rod and the seed holder are tightly connected.

[0038] In the specific embodiment of the present application, the thread direction of the lower end of the seed crystal rod is the same as that of the inner thread of the seed crystal holder, being right-handed or left-handed thread, the thread direction of the inner thread of the locking nut is the same as that of the outer thread of the seed crystal holder, being left-handed or right-handed thread, and the thread direction of the inner thread of the locking nut is opposite to that of the lower end of the seed crystal rod.

[0039] In the specific embodiment of the present application, the thread length of the seed crystal rod is greater than the length of the thread hole of the seed crystal holder by 1-4 mm, and a tool withdrawal groove with a length of 1-2 mm is arranged at the bottom of the thread hole of the seed crystal holder, so that the lower end of the seed crystal rod can be tightly fitted with the bottom of the thread hole of the seed crystal holder after the seed crystal rod is screwed with the seed crystal holder; the length from the lower end of the seed crystal rod to the lower end of the boss is greater than the depth of the inner thread hole of the seed crystal holder by 1-4 mm, so that there is a gap of 1-4 mm between the boss and the seed crystal holder after the seed crystal rod is screwed with the seed crystal holder; the inner diameter of the upper part of the locking nut is smaller than the diameter of the upper boss of the seed crystal rod by 4-10 mm, and the length of the locking nut is appropriate, so that there is a gap of 1-4 mm between the lower end of the locking nut and the seed crystal holder after the locking nut is screwed, so as to ensure that the locking nut is tightly fitted with the boss after being screwed. The effect achieved by the device is that, during the growth process, when the rotation direction is consistent with the thread direction of the seed crystal rod, the resistance of the seed crystal holder causes the seed crystal rod to be screwed with the seed crystal holder, and the seed crystal rod is tightly fitted with the bottom of the thread hole of the seed crystal holder, so that the seed crystal rod will not be loosened. When the rotation direction is changed, i.e. is consistent with the thread direction of the locking nut, the resistance of the seed crystal holder causes the locking nut to be screwed with the seed crystal holder, and the locking nut has a downward movement tendency, but the locking nut will press the seed crystal rod and the seed crystal holder tightly due to the obstruction of the boss on the seed crystal rod, so as to ensure that the seed crystal rod and the seed crystal holder are not loosened.

[0040] In the specific embodiment of the present application, the diameter of the seed crystal rod is 5-40 mm, the diameter of the seed crystal holder is the same as or 1-4 mm smaller than the diameter of the selected seed crystal, the inner diameter of the graphite crucible is 10-150 mm greater than the diameter of the selected seed crystal, and the wall thickness is not less than 10 mm. The density of the graphite crucible is 1.7-2.0 g / cm 3 .

[0041] In the specific embodiment of the present application, the seed crystal is a conductive type (n-type or p-type) or semi-insulating type silicon carbide seed crystal, and the size is 1-8 inches.

[0042] In the specific embodiment of the present application, the materials of the seed crystal rod, the seed crystal holder and the locking nut are high-purity graphite or molybdenum, the crucible is a graphite crucible, and the purity of the graphite crucible is not less than 99.95%.

[0043] In the specific embodiment of the present application, the heating cylinder is a heating cylinder made of graphite soft felt or graphite hard felt, and the purity of the graphite felt is not less than 99.9%.

[0044] Compared with the prior art, the present application has at least the following beneficial effects:

[0045] (1) The present application provides a seed holder high-speed positive and reverse rotation device and method capable of introducing forced convection in the process of growing silicon carbide crystal by liquid phase method, which can enhance solute transport during the growth process, improve solute distribution uniformity, and improve the quality and speed of liquid phase growth of silicon carbide crystal.

[0046] (2) The present application provides a device capable of conveniently and reliably achieving high-speed positive and reverse rotation of the seed holder during the process of growing silicon carbide crystal by liquid phase method, which is essentially a self-locking device used to prevent the seed holder and seed rod from loosening during the reversing rotation, especially when the acceleration and deceleration are relatively fast. The device described in the present application can conveniently, quickly and reliably achieve locking to prevent the seed holder and seed rod from loosening during the growth process. In addition, the seed rod and locking nut described in the present application can be reused, reducing costs. BRIEF DESCRIPTION OF DRAWINGS

[0047] Hereinafter, embodiments of the present application will be described in detail with reference to the accompanying drawings, in which:

[0048] Figure 1 is a schematic diagram of the device of one specific embodiment of the present application;

[0049] Figure 2 is a schematic diagram of the self-locking structure of the device of one specific embodiment of the present application;

[0050] Figure 3 is a physical diagram of the self-locking structure of the device of one specific embodiment of the present application;

[0051] Figure 4 is a shape diagram of the silicon carbide crystal obtained in Example 1 of the present application;

[0052] Figure 5 is a rocking curve data diagram of the silicon carbide crystal obtained in Example 1 of the present application;

[0053] Figure 6 is a shape diagram of the silicon carbide crystal obtained in Example 2 of the present application;

[0054] Figure 7 is a rocking curve data diagram of the silicon carbide crystal obtained in Example 2 of the present application;

[0055] Figure 8 is a shape diagram of the silicon carbide crystal obtained in Comparative Example 1 of the present application;

[0056] Figure 9 is a rocking curve data diagram of the silicon carbide crystal obtained in Comparative Example 1 of the present application;

[0057] In the drawings, the reference signs are as follows:

[0058] 1 - water-cooled rod; 2 - seed rod; 3 - heating cylinder; 4 - crucible; 5 - raw material; 6 - induction coil; 7 - crucible tray; 8 - locking nut; 9 - boss; 10 - locking nut left-hand internal thread; 11 - seed holder left-hand external thread; 12 - seed rod right-hand external thread; 13 - seed holder right-hand internal thread; 14 - relief groove; 15 - seed holder; 16 - seed; 17 - first section; 18 - second section; 19 - third section; 20 - first cylindrical section; 21 - second cylindrical section; 22 - third cylindrical section. DETAILED DESCRIPTION

[0059] The application will be further described in details below with reference to specific embodiments, and the examples given are only for illustrating the application, but not for limiting the scope of the application.

[0060] Reference Figures 1 to 4 , the application provides a device for growing silicon carbide crystal by liquid phase method, which comprises a seed rod (2), a seed holder (15) and a locking nut (8); the seed rod (2) comprises a cylindrical first section (17), a second section (18) and a third section (19) along the axial direction of the seed rod (2), wherein the diameter of the second section (18) is greater than the diameter of the first section (17) and the diameter of the third section (19) to form a boss (9) on the seed rod; the third section (19) is provided with external thread, i.e. the seed rod right-hand external thread (12). The seed holder (15) comprises a base plate and a first cylindrical section (20) extending circumferentially along one side of the base plate; the first cylindrical section (20) is provided with internal thread and external thread, i.e. the seed holder right-hand internal thread (13) and the seed holder left-hand external thread (11) respectively; the locking nut (8) comprises a second cylindrical section (21) and a third cylindrical section (22) along the circumferential direction of the locking nut (8), the inner diameter of the second cylindrical section (21) is smaller than the inner diameter of the third cylindrical section (22); the third cylindrical section (22) is provided with internal thread, i.e. the locking nut left-hand internal thread (10); the diameter of the second section (18) is greater than the inner diameter of the second cylindrical section (21) and less than or equal to the inner diameter of the third cylindrical section (22); the external thread on the third section (19) and the internal thread on the first cylindrical section (20) are of the same direction, so that the third section (19) of the seed rod and the first cylindrical section (20) of the seed holder can be threadedly connected; the external thread on the first cylindrical section (20) and the internal thread on the third cylindrical section (22) are of the same direction, so that the third cylindrical section (22) of the locking nut and the first cylindrical section (20) of the seed holder can be threadedly connected and after the connection, the second cylindrical section (21) is pressed against the boss (9); and the external thread on the third section (19) and the internal thread on the third cylindrical section (22) are of opposite directions.

[0061] In one specific embodiment of the present application, the axial length of the third section (19) of the seed rod (2) is greater than the axial length of the first cylindrical section (20) of the seed holder (15), so that after the third section (19) of the seed rod (2) is screwed with the first cylindrical section (20) of the seed holder (15), there is a spacing distance between the boss (9) and the first cylindrical section (20) of the seed holder (15).

[0062] In one specific embodiment of the present application, the axial length of the third section (19) of the seed rod (2) is greater than the axial length of the first cylindrical section (20) of the seed holder (15) by 1-4 mm, so that after the third section (19) of the seed rod (2) is screwed with the first cylindrical section (20) of the seed holder (15), there is a spacing distance of 1-4 mm between the boss (9) and the first cylindrical section (20) of the seed holder (15).

[0063] In one specific embodiment of the present application, the axial length of the third cylindrical section (22) of the locking nut is less than the sum of the axial lengths of the second section (18) and the third section (19) of the seed rod (2), so that after the third cylindrical section (22) of the locking nut is screwed with the first cylindrical section (20) of the seed holder (15), there is a spacing distance between the third cylindrical section (22) of the locking nut and the base plate of the seed holder (15), so as to ensure that the locking nut is tightly fitted with the boss (9) after being screwed.

[0064] In one specific embodiment of the present application, the axial length of the third cylindrical section (22) of the locking nut (8) is less than the sum of the axial lengths of the second section (18) and the third section (19) of the seed rod (2), so that after the third cylindrical section (22) of the locking nut (8) is screwed with the first cylindrical section (20) of the seed holder (15), there is a spacing distance of 1-4 mm between the third cylindrical section (22) of the locking nut (8) and the base plate of the seed holder (15), so as to ensure that the locking nut (8) is tightly fitted with the boss (9) after being screwed.

[0065] In one specific embodiment of the present application, the first cylindrical section (20) of the seed holder (15) is provided with a tool withdrawal groove (14) on the side close to the base plate, so as to ensure that the third section (19) of the seed rod (2) is tightly fitted with the bottom of the threaded hole of the seed holder (15) after the seed rod (2) is screwed with the seed holder (15).

[0066] In one specific embodiment of the present application, the length of the external thread on the third section (19) of the seed rod (2) is greater than the length of the internal thread on the first cylindrical section (20) of the seed holder (15) by 1-4 mm.

[0067] In one specific embodiment of the present application, the diameter of the second section (18) is 4-10 mm larger than the inner diameter of the second cylindrical section (21).

[0068] In one specific embodiment of the present application, the material of the seed rod (2), the seed holder (15) and the locking nut (8) is high-purity graphite or molybdenum.

[0069] In one specific embodiment of the present application, the lower end of the seed rod is right-handed thread, and a boss is provided above the thread, the seed holder is provided with right-handed internal thread and left-handed external thread, and the locking nut is internally provided with left-handed thread. In use, the seed rod is screwed into the threaded hole of the seed holder until the bottom of the hole, and then the locking nut is sleeved onto the upper end of the seed rod and screwed into the left-handed external thread of the seed holder. The length of the thread of the seed rod is 13 mm, the depth of the threaded hole of the seed holder is 11 mm, and the depth of the thread relief groove of the seed holder is 2 mm. The diameter of the boss of the seed rod is 26 mm, and the length from the lower end of the seed rod to the lower end of the boss is 13 mm. The length of the locking nut is 17 mm, and the inner diameter of the upper part is 21 mm.

[0070] In one specific embodiment of the present application, the silicon carbide seed crystal is a semi-insulating silicon carbide seed crystal with a size of 4 inches, the material of the seed rod, the crucible, the seed holder and the locking nut is high-purity graphite, the heating cylinder is a graphite soft felt heating cylinder, the purity of the graphite felt is not less than 99.9%, the diameter of the seed rod is 15 mm, the diameter of the seed holder is 99 mm, the inner diameter of the graphite crucible is 150 mm, the wall thickness is 15 mm, the density is 1.8 g / cm 3 , and the purity is not less than 99.95%.

[0071] Example 1

[0072] The device of the present application is used for growing silicon carbide crystals by liquid phase method, and the method comprises the following steps:

[0073] (1) Placing a growth raw material containing Si and Cr metal elements in the crucible, heating the crucible by the induction heating device, melting the growth raw material containing Si and Cr metal elements, and simultaneously controlling the seed rod to rotate at a low speed of 10 rpm in one direction;

[0074] (2) Lowering the seed holder while controlling the seed rod to rotate at a low speed of 10 rpm in one direction; making the silicon carbide seed crystal fixed on the seed holder contact the Si alloy melt;

[0075] (3) After the seed crystal contacts the melt, controlling the seed rod to rotate at a high speed in the reverse direction, rotating at a speed of 180 rpm for 30 min, then slowly reducing the speed to 0 rpm, accelerating in the opposite direction to 180 rpm, and the total time of acceleration and deceleration is 10 min, and the cycle is repeated until the growth is completed.

[0076] (4) After the growth is completed, the seed rod is controlled to rotate at a low speed of 10 rpm in one direction, and the seed holder is lifted until the seed is separated from the melt, and the silicon carbide single crystal is obtained after furnace cooling.

[0077] The silicon carbide crystal obtained in this example has an appearance as shown in Figure 4 , and the half width of the rocking curve test is 14.4 arc seconds, as shown in Figure 5 .

[0078] Example 2

[0079] The method for growing the silicon carbide crystal by the liquid phase method used in this example 2 is basically the same as that in example 1, except that after the seed is in contact with the melt surface, the seed rod is started to rotate in both directions at a speed of 100 rpm for 30 min, then is slowed down to 0 rpm, and is accelerated to 100 rpm in the opposite direction, the total time for acceleration and deceleration is 5 min, and the cycle is repeated until the growth is completed.

[0080] The silicon carbide crystal obtained by the device and method described in this example has an appearance as shown in Figure 6 . The half width of the rocking curve test of the crystal is 28.8 arc seconds, as shown in Figure 7 .

[0081] Comparative Example 1

[0082] The device for growing the silicon carbide crystal by the liquid phase method used in this comparative example 1 does not include the self-locking structure as shown in Figure 2 , and the lower end of the seed rod is right-handed external thread, and the seed holder is provided with a right-handed threaded hole, and the two are connected by threads. In addition, the method for growing the silicon carbide crystal by the liquid phase method used in this comparative example 1 is basically the same as that in the above example 1, except that after the seed is in contact with the melt surface, the seed rod is rotated in one direction at a speed of 60 rpm until the growth is completed.

[0083] The silicon carbide crystal obtained by the device and method described in this comparative example has an appearance as shown in Figure 8 , and the half width of the rocking curve test of the crystal is 100.8 arc seconds, as shown in Figure 9 .

[0084] It can be seen that, compared with the conventional device, the silicon carbide crystal obtained by the device and method of the present application has a smooth surface, and the macroscopic defects such as grooves and cracks are greatly reduced compared with the conventional growth process, and the half width of the rocking curve is also narrower, indicating that the crystal quality is better.

[0085] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the same; although the present application has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that the technical solutions recorded in the foregoing examples can still be modified, or some of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An apparatus for growing silicon carbide crystals by liquid phase method, comprising: Seed crystal rod, seed crystal holder, and lock nut; The seed crystal rod includes a cylindrical first section, a second section, and a third section along its axial direction, wherein the diameter of the second section is larger than the diameter of the first section and larger than the diameter of the third section to form a boss located on the seed crystal rod; the third section is provided with external threads; The seed crystal holder includes a substrate and a first cylindrical section extending circumferentially along one side of the substrate; the first cylindrical section is provided with internal threads and external threads; The locking nut includes a second cylindrical section and a third cylindrical section in its circumferential direction, wherein the inner diameter of the second cylindrical section is smaller than the inner diameter of the third cylindrical section; the third cylindrical section is provided with internal threads. The diameter of the second section is greater than the inner diameter of the second cylindrical section and less than or equal to the inner diameter of the third cylindrical section; The external thread on the third section has the same direction of rotation as the internal thread on the first cylindrical section, allowing the third section of the seed crystal rod to be threadedly connected to the first cylindrical section of the seed crystal holder; the external thread on the first cylindrical section has the same direction of rotation as the internal thread on the third cylindrical section, allowing the third cylindrical section of the locking nut to be threadedly connected to the first cylindrical section of the seed crystal holder, and after connection, the second cylindrical section presses against the boss; and the external thread on the third section has the opposite direction of rotation to the internal thread on the third cylindrical section. The axial length of the third section of the seed crystal rod is 1 to 4 mm longer than the axial length of the first cylindrical section of the seed crystal holder, so that after the third section of the seed crystal rod is threadedly connected to the first cylindrical section of the seed crystal holder, there is a gap distance of 1 to 4 mm between the boss and the first cylindrical section of the seed crystal holder. The axial length of the third cylindrical section of the locking nut is less than the sum of the axial lengths of the second and third sections of the seed crystal rod, so that after the third cylindrical section of the locking nut is threadedly connected to the first cylindrical section of the seed crystal holder, there is a gap distance of 1 to 4 mm between the third cylindrical section of the locking nut and the substrate of the seed crystal holder, thereby ensuring that the locking nut fits tightly with the boss after being tightened. The first cylindrical section of the seed crystal holder has a relief groove on the side near the substrate to ensure that after the seed crystal rod is screwed to the seed crystal holder, the third section of the seed crystal rod can fit tightly with the bottom of the threaded hole of the seed crystal holder.

2. The apparatus for liquid-phase growth of silicon carbide crystals according to claim 1, wherein, The length of the external thread on the third section of the seed crystal rod is 1 to 4 mm longer than the length of the internal thread on the first cylindrical section of the seed crystal holder.

3. The apparatus for liquid-phase growth of silicon carbide crystals according to claim 1, wherein, The diameter of the second section is 4 to 10 mm larger than the inner diameter of the second cylindrical section.

4. The apparatus for liquid-phase growth of silicon carbide crystals according to claim 1, wherein, The seed crystal rod, seed crystal holder, and locking nut are made of high-purity graphite or molybdenum.

5. A method for preparing silicon carbide crystals, using the apparatus for liquid-phase growth of silicon carbide crystals as described in any one of claims 1-4, comprising the following steps: (1) Place the growth material in a crucible and heat the crucible by an induction heating device to melt the growth material into a melt, while controlling the seed crystal rod to rotate unidirectionally at the first speed; (2) While controlling the seed crystal rod to rotate unidirectionally at the first speed, the seed crystal holder is lowered so that the silicon carbide seed crystal fixed on the seed crystal holder comes into contact with the melt; (3) After the seed crystal comes into contact with the surface of the melt, control the seed crystal rod to rotate periodically at the second speed: after rotating at the second speed for a certain period of time, slowly decelerate to zero, then accelerate to the second speed in the opposite direction, maintain for a certain period of time, slowly decelerate to zero, then accelerate to the second speed in the opposite direction, repeat the cycle until the growth ends. (4) After growth is completed, the seed crystal rod is controlled to rotate unidirectionally at the first speed, while the seed crystal holder is raised until the seed crystal separates from the melt. After cooling in the furnace, silicon carbide single crystal is obtained. The first speed is 0 or 1 to 30 rpm; the second speed is 100 to 300 rpm.

6. The method according to claim 5, wherein, The control of the seed crystal rod to periodically rotate at the second speed in step (3) is performed in a method including the following steps: After rotating at the second speed for 30–60 minutes, slowly decelerate to zero, then accelerate back to the second speed in the opposite direction, maintain this speed for 30–60 minutes, then slowly decelerate to zero, then accelerate back to the second speed in the opposite direction, repeating this cycle until growth ends; the total acceleration and deceleration time is 1–15 minutes.

7. The method according to claim 5, wherein, The crucible is a graphite crucible.

8. The method according to claim 7, wherein, The graphite crucible has a purity of not less than 99.95%, an inner diameter 10–150 mm larger than the diameter of the seed crystal ingot, a wall thickness of not less than 10 mm, and a density of 1.7–2.0 g / cm³. 3 .

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