Silicon carbide crystal growth thermal field and control method

Abstract

The application discloses a silicon carbide crystal growth thermal field, which comprises a crucible, a heat preservation screen assembly and a graphite heater; the heat preservation screen assembly comprises two layers of side heat preservation screens, and the inner side heat preservation screen can be lifted through a lifting mechanism; the graphite heater is connected with direct current or alternating current; when the graphite heater is connected with alternating current, the crucible is inductively heated; when the graphite heater is connected with direct current, the graphite heater is a resistance heater; the inner side heat preservation screen is lifted by the lifting mechanism by a distance, so that an unobstructed radiation channel is formed between the graphite heater and the crucible. The application combines the advantages of resistance heating and induction heating, and discards the shortcomings of both, so that the effects of efficient induction heating and convenient temperature gradient construction of resistance heating are achieved.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide single crystal furnace technology. Background Technology

[0002] There are two methods for silicon carbide crystal growth: induction and resistance methods, each with its own advantages and disadvantages. In induction methods, the heat source is the graphite crucible itself, which generates eddy currents. For example, in patent application CN103332693A, a ring-shaped electromagnetic coil surrounds the graphite crucible, heating both the crucible and the silicon block through electromagnetic induction.

[0003] The resistance method uses the heat radiation from a graphite heater to heat the crucible. For example, the heating element 3 surrounding the crucible in patent CN211734528U is a graphite heater for heating a graphite crucible.

[0004] The two heating methods mentioned above each have their own problems: Although induction heating equipment has high heating efficiency and rapid temperature rise, the non-uniformity of magnetic field lines makes it difficult to construct an ideal temperature field, which affects the stability and yield of crystal growth. Although resistance heating equipment is relatively easy to construct a temperature gradient, its heating components include heaters, crucibles, raw materials, etc., resulting in lower efficiency.

[0005] Therefore, a new technical solution is needed to solve the above-mentioned technical problems. Summary of the Invention

[0006] Purpose of the invention: The purpose of this invention is to achieve both resistance heating and medium-frequency induction heating through a silicon carbide crystal growth thermal field.

[0007] Technical solution: To solve the above problems, the present invention can adopt the following technical solution:

[0008] A silicon carbide crystal growth thermal field includes a crucible, a heat insulation screen assembly, and a graphite heater. The heat insulation screen assembly includes a bottom heat insulation screen at the bottom of the crucible, a top heat insulation screen at the top of the crucible, an inner heat insulation screen surrounding the crucible, an outer heat insulation screen surrounding the inner heat insulation screen, and a lifting mechanism above the inner heat insulation screen. The graphite heater is located between the inner and outer heat insulation screens. The lifting mechanism is connected to the inner heat insulation screen. The graphite heater is supplied with direct current or alternating current. When the graphite heater is supplied with alternating current, the crucible is induction heated. The bottom of the inner heat insulation screen rests on the bottom heat insulation screen, and the top of the inner heat insulation screen contacts the top heat insulation screen. The crucible is completely located within the space enclosed by the inner, bottom, and top heat insulation screens. When the graphite heater is supplied with direct current, it is a resistance heater. The lifting mechanism lifts the inner heat insulation screen a certain distance, creating an unobstructed radiation channel between the graphite heater and the crucible.

[0009] Furthermore, the crucible, the heat preservation screen assembly, and the graphite heater are all located within a stainless steel cavity; the lifting mechanism includes a lifting rod connected to the top of the inner heat preservation screen and a bellows housing the lifting rod, the top of the lifting rod being fixedly connected to the upper flange of the bellows, and the lower flange of the bellows sealing the stainless steel cavity; the lifting mechanism also includes a lifting module connected to the upper flange, which is used to drive the lifting rod and the inner heat preservation screen to move up and down; the top of the stainless steel cavity and the lower flange are provided with openings for the lifting rod to pass through, and the bellows maintains a seal with the openings and between the inside of the bellows and the outside by expansion and contraction.

[0010] Beneficial Effects: Compared to existing technologies, this invention achieves both resistance heating and medium-frequency induction heating functions using a single resistance heater. Furthermore, the two-layer side insulation screen structure (inner and outer insulation screens) addresses the internal environment requirements of both heating functions. During the initial heating phase, due to the small amount of material being heated (the graphite heater itself does not heat but only receives AC current), heating efficiency is high. At this stage, the inner insulation screen, along with the top and bottom insulation screens, provides insulation. After a certain heating period, the resistance heater is directly heated by DC current. In this case, the inner insulation screen no longer provides insulation but acts as a temperature gradient regulating layer during crystal growth, adjusting the temperature gradient within the thermal field. At this point, the outer insulation screen, along with the top and bottom insulation screens, provides insulation. This invention enables both resistance heating and medium-frequency induction heating to be achieved through the action of a single heater, i.e., the inner insulation screen. It also allows for the use of either resistance heating or medium-frequency induction heating individually, adapting to different crystal growth processes. The same equipment can verify different process routes, saving equipment costs and improving experimental efficiency. This invention combines the advantages of resistance heating and induction heating, achieving the high efficiency of induction heating and the convenient temperature gradient construction of resistance heating.

[0011] This invention also provides a technical solution for the above-mentioned method for controlling the thermal field:

[0012] During initial heating, a medium-frequency alternating current is applied to the graphite heater, and the graphite crucible is directly heated by induction. As heating progresses, the inner insulation screen surrounds the graphite crucible to provide insulation for the thermal field. When the crucible is heated to the predetermined temperature, the medium-frequency alternating current is stopped, and a direct current is applied to the graphite heater. The lifting mechanism drives the inner insulation screen to rise. The lifting stops when the bottom of the inner insulation screen reaches the crystal growth position, and the direct current is gradually increased to the process current range.

[0013] Furthermore, the current value of the graphite heater when energized with medium-frequency AC current is 500-800A; the current value when energized with DC current is 1000-3000A. As the inner insulation screen is raised, the temperature gradient of the thermal field changes accordingly, and the temperature gradient will decrease. Different temperature gradients can be obtained by controlling the height and position of the inner insulation screen, and the optimal crystal growth position is obtained through multiple experiments. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the thermal field structure for silicon carbide crystal growth according to the present invention, showing the state where the inner insulation screen has not moved upward.

[0015] Figure 2 This is a schematic diagram of the thermal field structure for silicon carbide crystal growth according to the present invention, and shows the state after the inner heat insulation screen is moved upward. Detailed Implementation

[0016] Please combine Figure 1 and Figure 2 As shown, this invention discloses a silicon carbide crystal growth thermal field, including a crucible 7, a heat insulation screen assembly, a graphite heater 3, and a stainless steel cavity 9. The crucible 7 contains silicon carbide raw material 6; a seed crystal 2 is grown above the crucible 7. The crucible 7, the heat insulation screen assembly, and the graphite heater 3 are all located within the stainless steel cavity 9.

[0017] The heat preservation screen assembly includes a bottom heat preservation screen 8 located at the bottom of the crucible 7, a top heat preservation screen 1 located at the top of the crucible 7, an inner heat preservation screen 5 surrounding the crucible 7, an outer heat preservation screen 4 surrounding the inner heat preservation screen 5, and a lifting mechanism located above the inner heat preservation screen 5. The graphite heater 3 is located between the inner heat preservation screen 5 and the outer heat preservation screen 4.

[0018] The graphite heater 3 is supplied with either direct current or alternating current to achieve either resistance heating or medium-frequency induction heating, respectively.

[0019] like Figure 1 As shown, when the graphite heater 3 is supplied with alternating current, the crucible 7 is induction heated. The bottom of the inner insulation screen 5 is supported by the bottom insulation screen 8, and the top of the inner insulation screen 5 is in contact with the top insulation screen 1. The crucible 7 is completely located within the space enclosed by the inner insulation screen 5, the bottom insulation screen 8, and the top insulation screen 1.

[0020] like Figure 2 As shown, when a direct current is applied to the graphite heater 3, the graphite heater 3 directly heats the water as a resistance heater. The lifting mechanism raises the inner insulation screen 5 a certain distance, creating an unobstructed radiation channel between the graphite heater 3 and the crucible 7.

[0021] The lifting mechanism includes a lifting rod 11 connected to the top of the inner insulation screen 5 and a bellows 10 housing the lifting rod 11. The top end of the lifting rod 11 is fixedly connected to the upper flange at the top of the bellows 10; the lower flange of the bellows 10 is sealed to the stainless steel cavity 9. The lifting mechanism also includes a lifting module 12 connected to the upper flange, which is used to drive the lifting rod 11 and the inner insulation screen 5 to move up and down. The top and lower flange of the stainless steel cavity 9 are provided with openings through which the lifting rod 11 passes, and the bellows 10 maintains a seal with the openings and between the inside and outside of the bellows 10 through expansion and contraction.

[0022] One method for controlling crystal growth using this silicon carbide crystal growth thermal field is as follows:

[0023] During initial heating, a medium-frequency alternating current (500-800A) is passed through the graphite heater 3, and the graphite crucible 7 is directly heated by induction. As heating proceeds, the inner insulation screen 5 surrounds the graphite crucible 7 to provide insulation for the thermal field.

[0024] Once crucible 7 is heated to the predetermined temperature, the intermediate frequency AC current is stopped, and a DC current (1000-3000A) is instead applied to the graphite heater 3. The lifting mechanism then raises the inner insulation screen 5. The raising stops when the bottom of the inner insulation screen 5 reaches the crystal growth position, and the DC current is gradually increased to the process current range. As the inner insulation screen 5 is raised, the temperature gradient of the thermal field changes accordingly, decreasing from large to small. Different temperature gradients are obtained by controlling the height of the inner insulation screen 5, and the optimal crystal growth position is determined through multiple experiments.

[0025] There are many methods and approaches to implement this technical solution, and the above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. All components not explicitly stated in this embodiment can be implemented using existing technology.

Claims

1. A method for controlling the thermal field of silicon carbide crystal growth, wherein the silicon carbide crystal growth thermal field includes a crucible, a heat insulation screen assembly, and a graphite heater; characterized in that, The heat preservation screen assembly includes a bottom heat preservation screen located at the bottom of the crucible, a top heat preservation screen located at the top of the crucible, an inner heat preservation screen surrounding the crucible, an outer heat preservation screen surrounding the inner heat preservation screen, and a lifting mechanism located above the inner heat preservation screen; the graphite heater is located between the inner heat preservation screen and the outer heat preservation screen; the lifting mechanism is connected to the inner heat preservation screen. The graphite heater is supplied with direct current or alternating current. When the graphite heater is supplied with alternating current, the crucible is heated by induction. The bottom of the inner insulation screen is supported by the bottom insulation screen, and the top of the inner insulation screen is in contact with the top insulation screen. The crucible is completely located within the space enclosed by the inner insulation screen, the bottom insulation screen, and the top insulation screen. When a direct current is applied to the graphite heater, it becomes a resistance heater; the lifting mechanism raises the inner insulation screen a certain distance, creating an unobstructed radiation channel between the graphite heater and the crucible. During initial heating, a medium-frequency alternating current is passed through the graphite heater, and the graphite crucible is directly heated by induction. As heating progresses, the inner insulation screen surrounds the graphite crucible to provide insulation for the thermal field. When the crucible is heated to the predetermined temperature, the intermediate frequency AC current is stopped and a DC current is switched to the graphite heater. The lifting mechanism drives the inner insulation screen to rise. The lifting stops when the bottom of the inner insulation screen is raised to the crystal growth position, and the DC current is gradually increased to the process current range.

2. The method for controlling the thermal field of silicon carbide crystal growth according to claim 1, characterized in that, The crucible, heat preservation screen assembly, and graphite heater are all located in a stainless steel cavity. The lifting mechanism includes a lifting rod connected to the top of the inner insulation screen and a corrugated pipe that houses the lifting rod. The top of the lifting rod is fixedly connected to the upper flange of the top of the corrugated pipe, and the lower flange of the corrugated pipe is sealed to the stainless steel cavity. The lifting mechanism also includes a lifting module connected to the upper flange, which is used to drive the lifting rod and the inner insulation screen to move up and down. The stainless steel cavity has openings at the top and bottom flange for the lifting rod to pass through, and the bellows maintains a seal with the openings and between the inside of the bellows and the outside by expansion and contraction.

3. The method for controlling the thermal field of silicon carbide crystal growth according to claim 1, characterized in that, The current value of the graphite heater when it is energized with medium-frequency AC current is 500-800A; the current value when it is energized with DC current is 1000-3000A.

4. The method for controlling the thermal field of silicon carbide crystal growth according to claim 3, characterized in that, As the inner insulation screen is raised, the temperature gradient of the thermal field changes accordingly, and the temperature gradient will decrease. Different temperature gradients can be obtained by controlling the height and position of the inner insulation screen, and the optimal crystal growth position is obtained through multiple experiments.

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