Thermal field for controlling temperature gradient by changing air gap of coil and heating crystal growth equipment

Abstract

The invention discloses a thermal field and heating crystal growth equipment for controlling a temperature gradient by changing coil air gaps, which is characterized in that a graphite heating cylinder can be heated up and down at the same time in a manner that a plurality of upper annular coils are arranged above the graphite heating cylinder and a plurality of lower annular coils are arranged below the graphite heating cylinder; the air gaps of the plurality of upper annular coils and the plurality of lower annular coils are adjusted, so that eddy current loss generated by cutting the heating cylinder by an alternating magnetic field generated by alternating current on the coils can be homogenized, the uniformity of radial heating of the graphite heating cylinder is ensured, and a material area is uniformly heated in the vertical direction.

Description

Technical Field

[0001] The invention relates to the technical field of crystal growth or epitaxial heating, and in particular to a thermal field and heating crystal growth equipment. Background Art

[0002] Compared with resistance heating, induction heating has the advantages of no need for direct contact with the heating material, higher heating efficiency, and faster speed. At present, most SiC crystal growth equipment uses double cylindrical coils that are externally placed and distributed up and down outside the quartz tube to ensure the growth temperature of the crystal and the axial temperature gradient control. However, there are currently two problems:

[0003] 1) Due to the fact that the coil is placed outside and far away from the heating body and the thermal magnetic field coupling efficiency decreases significantly as the coil diameter increases, it takes 1 hour or more for the process area to rise from room temperature to process temperature; after the crystal growth process is completed in the process area, the product cooling process is very slow due to the lack of cooling measures. The above seriously affects the process cycle and production efficiency;

[0004] 2) The traditional cylindrical double coils distributed up and down will cause serious electromagnetic coupling when working at the same time, which poses great challenges to process adjustment, has a great impact on thermal field temperature control and power consumption, and may even damage the heating equipment.

[0005] Compared with cylindrical coils, disc coils have better heating efficiency and heating speed, and have been used in the field of CVD wafer epitaxy. However, due to the influence of various factors such as the large outer diameter of the coil, the eddy current loss inside the graphite heating tube is not uniform, resulting in a poor temperature gradient on the disc surface; therefore, a new technical solution is needed to solve this problem. Summary of the invention

[0006] Purpose of the invention: The present invention provides a thermal field that controls the temperature gradient by changing the coil air gap, so as to solve the problem of uneven eddy current loss inside the graphite heating tube resulting in poor temperature gradient on the disk surface.

[0007] The invention also provides a heating crystal growth device comprising the thermal field.

[0008] Technical solution: To solve the above problems, the present invention provides a thermal field control method for the temperature gradient by changing the coil air gap, and the following technical solution can be adopted.

[0009] A thermal field for controlling a temperature gradient by changing the air gap of a coil, comprising a graphite heating tube, an upper coil group located above the graphite heating tube, and a lower coil group located below the graphite heating tube; the upper coil group comprises a plurality of upper annular coils arranged from the inside to the outside, and the centers of all the upper annular coils are located on the central axis of the graphite heating tube; the lower coil group comprises a plurality of lower annular coils arranged from the inside to the outside, and the centers of all the lower annular coils are located on the central axis of the graphite heating tube; the number of upper annular coils in the upper coil group and the size of the upper annular coils are the same as the number of lower annular coils in the lower coil group and the size of the lower annular coils;

[0010] In the upper coil group, the air gap of the upper annular coil located in the middle of all the upper annular coils is the largest, and the air gaps of the upper annular coils outside the upper annular coils at the middle position decrease in sequence, and the air gaps of the upper annular coils inside the upper annular coils at the middle position also decrease in sequence;

[0011] In the lower coil group, the air gap of the lower annular coil located in the middle of all the lower annular coils is the largest, and the air gaps of the lower annular coils outside the lower annular coils at the middle position decrease in sequence, and the air gaps of the lower annular coils inside the lower annular coils at the middle position also decrease in sequence;

[0012] The air gap is the distance from the bottom of each upper annular coil to the upper surface of the graphite heating tube or the distance from the fixed part of each lower annular coil to the lower surface of the graphite heating tube.

[0013] Furthermore, each upper annular coil and each lower annular coil are in a projection corresponding relationship above and below the graphite heating tube, and the air gap value of an upper annular coil is equal to the air gap value of a lower annular coil corresponding to the projection.

[0014] Furthermore, when the number of upper annular coils in the upper coil group is an odd number, the air gap of the upper annular coil located in the middle position is the largest; when the number of upper annular coils in the upper coil group is an even number, the air gaps of the two upper annular coils located in the middle position are the largest.

[0015] Furthermore, the cross section of the coil is rectangular, and a hollow coolant channel is provided inside the coil.

[0016] Furthermore, the periphery of the graphite heating tube is provided with an inwardly recessed annular groove, in which an annular side surrounding screen is installed.

[0017] Furthermore, an upper graphite baffle is installed above the graphite heating tube, and a lower graphite baffle is installed below the graphite heating tube; the upper graphite baffle and the upper surface of the graphite heating tube together form an upper receiving cavity, and the upper coil group is located in the upper receiving cavity; the lower graphite baffle and the lower surface of the graphite heating tube together form a lower receiving cavity, and the lower coil group is located in the lower receiving cavity.

[0018] Furthermore, a top insulation layer located above the upper graphite partition and a bottom insulation layer located below the lower graphite partition are provided. The top insulation layer and the bottom insulation layer are surrounded by side walls to form an insulation space. The graphite heating tube, the upper receiving cavity, the lower receiving cavity and the side surrounding screen are all located in the insulation space.

[0019] Furthermore, the upper surface and the lower surface of the graphite heating tube are both circular surfaces, the top insulation layer is connected to the upper surface of the graphite heating tube through an upper support shaft, the bottom insulation layer is connected to the lower surface of the graphite heating tube through a lower support shaft, the upper support shaft and the lower support shaft are coaxially arranged, and the upper support shaft is connected to the center of the upper surface, and the lower support shaft is connected to the center of the lower surface; each upper annular coil is arranged around the upper support shaft, and each lower annular coil is arranged around the lower support shaft.

[0020] Furthermore, the inner diameter of the graphite heating tube is 300mm, and there are 5 upper annular coils, and the air gap values ​​of each upper annular coil from the inside to the outside are 11mm, 14mm, 19mm, 18mm, and 16mm respectively; there are 5 lower annular coils, and the air gap values ​​of each lower annular coil from the inside to the outside are 11mm, 14mm, 19mm, 18mm, and 16mm respectively.

[0021] Beneficial effect: Compared with the prior art, the present invention can heat the graphite heating tube simultaneously from top to bottom by arranging a plurality of upper annular coils above the graphite heating tube and a plurality of lower annular coils below the graphite heating tube. The coil induction thermal magnetic field coupling efficiency in this manner is high, and rapid heating of the material area of ​​the graphite heating tube can be achieved; and the air gaps of the plurality of upper annular coils and the plurality of lower annular coils are adjusted, and the arrangement manner in which the air gaps of all the upper annular coils and the lower annular coils are equal is not adopted, so that the alternating magnetic field generated by the alternating current on the coil can be uniformly cut to cut the eddy current loss generated by the heating tube, thereby ensuring the uniformity of radial heating of the graphite heating tube, and thus uniformly heating the material area in the vertical direction.

[0022] The heating crystal growth equipment provided by the present invention comprises the above-mentioned thermal field. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the longitudinal cross-sectional structure of the thermal field in the present invention.

[0024] Figure 2 It is a schematic diagram of the arrangement relationship between the upper coil group and the lower coil group in the thermal field of the present invention, and shows the simulation data of the loss distribution of the graphite disk.

[0025] Figure 3 It is a schematic diagram of the arrangement relationship between the upper coil group and the lower coil group in the thermal field in the prior art, and shows the simulation data of the loss distribution of the graphite disk.

[0026] Figure 4 The figure shows the comparison of graphite disk loss distribution under different air gaps and the statistical range of loss uniformity of the two.

[0027] Figure 5 This is a cloud diagram of the induced current distribution in the graphite cylinder in the thermal field of the present invention. DETAILED DESCRIPTION

[0028] like Figure 1 As shown, it includes a graphite heating tube 1, an upper coil group located above the graphite heating tube 1, and a lower coil group located below the graphite heating tube 1. The upper coil group includes a plurality of upper annular coils 2 arranged from the inside to the outside, and the centers of all the upper annular coils 2 are located on the central axis of the graphite heating tube 1. The lower coil group includes a plurality of lower annular coils 3 arranged from the inside to the outside, and the centers of all the lower annular coils 3 are also located on the central axis of the graphite heating tube. The alternating current of the upper coil group and the lower coil group generates an alternating magnetic field to cut the graphite heating tube 1 to generate an induced current, and the induced current flows through the graphite heating tube 1 to form eddy current loss as the heat source of the equipment; the induction coil in this form has a high thermal magnetic field coupling efficiency, and the high power density per unit volume on the graphite heating tube 1 can achieve rapid heating in the material area. The axial temperature gradient in the material area is adjusted by adjusting the current and power of the upper coil group and the lower coil group.

[0029] The periphery of the graphite heating tube 1 is provided with an inwardly recessed annular groove, in which an annular side surrounding screen 4 is installed. An upper graphite baffle 5 is installed above the graphite heating tube 1, and a lower graphite baffle 6 is installed below the graphite heating tube 1; the upper graphite baffle 5 and the upper surface of the graphite heating tube 1 together form an upper receiving chamber, and the upper coil group is located in the upper receiving chamber. The lower graphite baffle 6 and the lower surface of the graphite heating tube 1 together form a lower receiving chamber, and the lower coil group is located in the lower receiving chamber. A top insulation layer 7 is also provided above the upper graphite baffle 5, and a bottom insulation layer 8 is also provided below the lower graphite baffle 6. The top insulation layer 7 and the bottom insulation layer 8 together form an insulation space through the side wall. The graphite heating tube 1, the upper receiving chamber, the lower receiving chamber, and the side surrounding screen 4 are all located in the insulation space.

[0030] The number of upper annular coils in the upper coil group and the size of the upper annular coils are the same as the number of lower annular coils in the lower coil group and the size of the lower annular coils; the cross-section of each upper annular coil or lower annular coil is rectangular, and a hollow coolant channel is provided inside the coil. The upper and lower surfaces of the graphite heating tube 1 are both circular surfaces. The top insulation layer 7 is connected to the upper surface of the graphite heating tube 1 through the upper support shaft 9; the bottom insulation layer 8 is connected to the lower surface of the graphite heating tube 1 through the lower support shaft 10. The upper support shaft 9 and the lower support shaft 10 are coaxially arranged, and the upper support shaft 9 is connected to the center of the upper surface, and the lower support shaft 10 is connected to the center of the lower surface. Each upper annular coil 2 is arranged around the upper support shaft 9, and each lower annular coil 3 is arranged around the lower support shaft 10.

[0031] Please combine Figure 2 As shown, in the upper coil group, the air gap of the upper annular coil 2 located in the middle of all the upper annular coils is the largest, and the air gap of the upper annular coil outside the upper annular coil from the middle position decreases successively, and the air gap of the upper annular coil inside the upper annular coil from the middle position also decreases successively. In the lower coil group, the air gap of the lower annular coil located in the middle of all the lower annular coils is the largest, and the air gap of the lower annular coil outside the lower annular coil from the middle position decreases successively, and the air gap of the lower annular coil inside the lower annular coil from the middle position also decreases successively; the air gap is the distance from the bottom of each upper annular coil to the upper surface of the graphite heating tube or the distance from the fixed part of each lower annular coil to the lower surface of the graphite heating tube. Each upper annular coil and each lower annular coil are in a projection correspondence relationship above and below the graphite heating tube 1, and the air gap value of an upper annular coil 2 is equal to the air gap value of a lower annular coil 3 corresponding to the projection.

[0032] The upper coil group and the lower coil group adopt a variable air gap structure (i.e., the air gap size of each coil is not completely equal), the purpose of which is to even out the loss caused by the alternating magnetic field generated by the alternating current in the upper coil group and the lower coil group when cutting the graphite heating tube 1, thereby uniformly heating the material area in the vertical direction and realizing precise control of the radial temperature gradient in the material area; Figure 2 It is a schematic diagram of the arrangement relationship between the upper coil group and the lower coil group in the thermal field of the present invention. Figure 3 It is a schematic diagram of the arrangement relationship between the upper coil group and the lower coil group in the thermal field in the prior art. Figure 3 As a prior art comparative example, it can be seen that:

[0033] Under the action of the skin effect of induction heating, the loss is concentrated on the upper and lower outer surfaces of the graphite heating tube 1;

[0034] See also Figure 3 and Figure 4 As shown in the figure, due to the characteristics of the alternating magnetic field of the disc coil generating induced current in the graphite cylinder (the induced current in the upper and lower centers of the graphite plate is close to 0), the coil is pressed Figure 3 In the prior art, when the air gap is designed, the distribution of the outer surface of the graphite tube increases first and then decreases radially from the center, wherein the loss is highest in the middle and lowest at the outermost part, and the loss is lowest at the center of the graphite heating tube.

[0035] See also Figure 2 and Figure 4 After the variable air gap structure design was carried out on the upper and lower heating coils of the equipment, the loss distribution uniformity of the outer surface of the graphite cylinder was improved. The following table compares the data of the two coils under air gap in the present invention and the comparative example by selecting the upper and lower 5-turn coils as an embodiment, where:

[0036] The outer diameter of the coils in the two air gap forms is the same, and the inner diameter is variable;

[0037] The number of coil turns in both air gap forms is 5;

[0038] The air gap under the equal air gap structure is 14mm;

[0039] The other simulation boundary conditions given in the two air gap forms remain the same.

[0040]

[0041] From the results, it can be seen that when the coil adopts a variable air gap structure, the loss deviation of the graphite heating tube disk changes from 40.86% to 4.43%, and the loss distribution standard deviation changes from 4.53E+5 to 8.12E+4, and the uniformity is improved.

[0042] The alternating current of the upper and lower annular coils generates low losses at the center of the graphite heating tube, so the top and bottom insulation screens are set to reduce the heat dissipation of the graphite tube along the axial direction and improve the heating uniformity of the graphite tube.

[0043] As shown in the figure, the magnetic flux lines generated by the disc coil decay sharply along the axial direction. Under the influence of the distance between the upper and lower annular coils, the mutual inductance coupling effect of the two coils is weak, which reduces the power loss and equipment failure rate caused by mutual inductance when the upper and lower annular coils are working; the following are the self-inductance and mutual inductance coefficients of the upper and lower double coils calculated in the simulation calculation;

[0044]

[0045] The mutual inductance coefficient between the two is -328.4pH, and the mutual inductance coupling efficiency between the upper and lower coils is extremely low, so the electromagnetic coupling effect between the upper and lower coils can be ignored.

[0046] Although the above embodiment in which the number of upper and lower annular coils is 5 turns is selected for comparison, in other embodiments, the number of upper and lower annular coils can be selected as odd or even numbers. When the number of upper annular coils in the upper coil group is an odd number, the air gap of the upper annular coil located in the middle position is the largest; when the number of upper annular coils in the upper coil group is an even number, the air gap of the two upper annular coils located in the middle position is the largest. For example, the parameters that can be selected are: when the material area diameter is 300-500mm, the number of coil turns ranges from 5-7 turns, and the air gap ranges from 8-20mm; when the material area diameter is 500-1000mm, the number of coil turns ranges from 7-10 turns, and the air gap ranges from 8-20mm.

Claims

1. A thermal field for controlling a temperature gradient by changing the coil air gap, characterized in that: It includes a graphite heating tube, an upper coil group located above the graphite heating tube, and a lower coil group located below the graphite heating tube; the upper coil group includes a plurality of upper annular coils arranged from the inside to the outside, and the centers of all the upper annular coils are located on the central axis of the graphite heating tube; the lower coil group includes a plurality of lower annular coils arranged from the inside to the outside, and the centers of all the lower annular coils are located on the central axis of the graphite heating tube; the number of upper annular coils in the upper coil group and the size of the upper annular coils are the same as the number of lower annular coils in the lower coil group and the size of the lower annular coils; In the upper coil group, the air gap of the upper annular coil located in the middle of all the upper annular coils is the largest, and the air gaps of the upper annular coils outside the upper annular coils at the middle position decrease in sequence, and the air gaps of the upper annular coils inside the upper annular coils at the middle position also decrease in sequence; In the lower coil group, the air gap of the lower annular coil located in the middle of all the lower annular coils is the largest, and the air gaps of the lower annular coils outside the lower annular coils at the middle position decrease in sequence, and the air gaps of the lower annular coils inside the lower annular coils at the middle position also decrease in sequence; The air gap is the distance from the bottom of each upper annular coil to the upper surface of the graphite heating tube or the distance from the fixed part of each lower annular coil to the lower surface of the graphite heating tube.

2. The thermal field according to claim 1, characterized in that Each upper annular coil and each lower annular coil are in a projection corresponding relationship above and below the graphite heating tube, and the air gap value of an upper annular coil is equal to the air gap value of a lower annular coil corresponding to the projection.

3. The thermal field according to claim 2, characterized in that When the number of upper annular coils in the upper coil group is an odd number, the air gap of the upper annular coil located in the middle position is the largest; When the number of upper annular coils in the upper coil group is an even number, the air gaps of the two upper annular coils located in the middle are the largest.

4. The thermal field according to claim 3, characterized in that The cross section of the coil is rectangular, and a hollow coolant channel is provided inside the coil.

5. The thermal field according to any one of claims 1 to 4, characterized in that The periphery of the graphite heating tube is provided with an inwardly recessed annular groove, in which an annular side surrounding screen is installed.

6. The thermal field according to claim 5, characterized in that An upper graphite partition is installed above the graphite heating tube, and a lower graphite partition is installed below the graphite heating tube; the upper graphite partition and the upper surface of the graphite heating tube together form an upper receiving cavity, and the upper coil group is located in the upper receiving cavity; The lower graphite partition plate and the lower surface of the graphite heating tube together form a lower receiving cavity, and the lower coil group is located in the lower receiving cavity.

7. The thermal field according to claim 6, characterized in that A top insulation layer located above the upper graphite partition and a bottom insulation layer located below the lower graphite partition are also provided. The top insulation layer and the bottom insulation layer are surrounded by side walls to form an insulation space. The graphite heating tube, the upper receiving cavity, the lower receiving cavity and the side surrounding screen are all located in the insulation space.

8. The thermal field according to claim 7, characterized in that The upper surface and the lower surface of the graphite heating tube are both circular surfaces, the top insulation layer is connected to the upper surface of the graphite heating tube through an upper support shaft, the bottom insulation layer is connected to the lower surface of the graphite heating tube through a lower support shaft, the upper support shaft and the lower support shaft are coaxially arranged, and the upper support shaft is connected to the center of the upper surface, and the lower support shaft is connected to the center of the lower surface; each upper annular coil is arranged around the upper support shaft, and each lower annular coil is arranged around the lower support shaft.

9. The thermal field according to any one of claims 1 to 4, characterized in that: The inner diameter of the graphite heating tube is 300mm. There are 5 upper annular coils, and the air gap values ​​of each upper annular coil from the inside to the outside are 11mm, 14mm, 19mm, 18mm, and 16mm respectively; there are 5 lower annular coils, and the air gap values ​​of each lower annular coil from the inside to the outside are 11mm, 14mm, 19mm, 18mm, and 16mm respectively.

10. A heating crystal growth device, characterized in that: Comprising the thermal field as claimed in any one of claims 1 to 9.

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