Crystal growth crucible and crystal growth furnace

Abstract

The application provides a crystal growth crucible, which is provided with a mounting position for fixing a seed crystal on a top wall, and a heat transfer layer is further arranged on the mounting position, and the heat transfer layer has a thermal conductivity coefficient in a plane direction greater than a thickness direction. The crystal growth crucible and the crystal growth furnace provided by the application can effectively reduce the radial temperature gradient of a crystal thermal field, thereby solving the problem that a crystal is prone to cracking when growing a large-size crystal.

Description

Technical Field

[0001] This invention belongs to the field of crystal growth technology, specifically relating to a crystal growth crucible and a crystal growth furnace. Background Technology

[0002] Silicon carbide, as a third-generation semiconductor material, has excellent physical and chemical properties and has broad application prospects and market space in high-end optoelectronics, high power and microwave radio frequency fields.

[0003] Currently, physical vapor transport (PVT) is the most mature and widely used method for growing silicon carbide. The working principle of PVT is as follows: silicon carbide raw material is placed at the bottom of a crucible, and a seed crystal is fixed at the top of the crucible. Under high temperature (e.g., above 2200℃) and low pressure, the silicon carbide raw material sublimates. The sublimation gas utilizes the temperature gradient of the crystal's thermal field to finally crystallize on the seed crystal. The temperature gradient includes axial and radial temperature gradients. Temperature gradient is one of the stress sources in silicon carbide crystal growth. Excessive stress makes large-sized silicon carbide crystals more prone to cracking during growth. Therefore, temperature gradient is one of the reasons affecting crystal cracking in the growth of large-sized silicon carbide crystals. Among these, the radial temperature gradient has a relatively greater impact on crystal stress than the axial temperature gradient. An important manifestation of the radial temperature gradient is the crystal's convexity, which refers to the difference between the maximum and minimum thickness of the crystal.

[0004] Therefore, reducing the radial temperature gradient is the key to solving the problem of easy crystal cracking. At present, there is an urgent need for a crystal growth crucible and crystal growth furnace that can reduce the radial temperature gradient. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art, and proposes a crystal growth crucible and crystal growth furnace, which can effectively reduce the radial temperature gradient of the crystal thermal field, thereby solving the problem of easy crystal cracking when growing large-sized crystals.

[0006] To address one of the aforementioned problems, the present invention provides a crystal growth crucible with a mounting position for fixing a seed crystal on its top wall, and a heat transfer layer is also provided on the mounting position, wherein the thermal conductivity of the heat transfer layer in its plane is greater than the thermal conductivity in its thickness direction.

[0007] Preferably, the thermal conductivity of the plane in which it is located differs from the thermal conductivity in the thickness direction by at least two orders of magnitude.

[0008] Preferably, the heat transfer layer is graphite paper.

[0009] Preferably, a planarization layer is also provided at the mounting position, and the graphite paper and the planarization layer are stacked together.

[0010] Preferably, the graphite paper and the planarization layer are alternately stacked.

[0011] Preferably, the planarization layer is a graphite sheet.

[0012] Preferably, the entire back side of the seed crystal is fixed to the mounting position by adhesive bonding.

[0013] Preferably, the total thickness of all the graphite paper is in the range of 1mm-10mm.

[0014] Preferably, the number of graphite sheets is 2 or 3.

[0015] Preferably, the thickness of each graphite sheet is in the range of 2mm-3mm.

[0016] The present invention also provides a crystal growth furnace, including a crystal growth crucible and a heating device, wherein the heating device is used to heat the crystal growth crucible so that the growth environment inside the crucible reaches the process temperature, and the crystal growth crucible is the crystal growth crucible provided by the present invention as described above.

[0017] The present invention has the following beneficial effects:

[0018] The crystal growth crucible provided by this invention has a thermal conductivity in the plane of the heat transfer layer that is greater than that in the thickness direction. That is, the thermal conductivity of the crystal thermal field is good in the radial direction but poor in the axial direction. The good thermal conductivity of the crystal thermal field in the radial direction helps to balance the crystal thermal field in the radial direction. The good thermal conductivity in the radial direction is beneficial to the radial heat transfer and can reduce the radial temperature gradient. The poor thermal conductivity in the axial direction will further reduce the radial temperature gradient, thereby effectively reducing the radial temperature gradient of the crystal thermal field.

[0019] The crystal growth furnace provided by this invention, by employing the crystal growth crucible provided by this invention, can effectively reduce the radial temperature gradient of the crystal thermal field, thereby solving the problem of easy crystal cracking when growing large-sized crystals. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the crystal growth crucible provided in the embodiment of the present invention during application;

[0021] Figure 2 for Figure 1 Schematic diagram of the working principle of the crystal growth crucible;

[0022] Figures 3a-3c for Figure 1 A schematic diagram showing the various positional relationships between the graphite paper and the planarization layer.

[0023] The reference numerals in the attached figures include: 1, insulation felt; 2, heat transfer layer; 3, planarization layer; 4, seed crystal; 5, crystal; 6, raw material. Detailed Implementation

[0024] To enable those skilled in the art to better understand the technical solution of the present invention, the crystal growth crucible and crystal growth furnace provided by the present invention will be described in detail below with reference to the accompanying drawings.

[0025] Example 1

[0026] Figure 1 Please refer to the schematic diagram of the crystal growth crucible provided in the embodiment of the present invention when it is used. Figure 1 The crystal growth crucible provided in this embodiment of the invention has a mounting position (e.g., for fixing the seed crystal 4) on its top wall. Figure 1 At the location of seed crystal 4, raw material 6 for crystal growth is placed inside the crucible; a heat transfer layer 2 is also provided at the mounting position. The thermal conductivity of the plane containing the heat transfer layer 2 is greater than the thermal conductivity in the thickness direction, which is along the thickness direction. Figure 1 The vertical direction in the middle.

[0027] In this invention, since the thermal conductivity of the heat transfer layer 2 on its plane is greater than that in its thickness direction, that is, the thermal conductivity of the crystal 5 thermal field is good in the radial direction but poor in the axial direction; the good thermal conductivity of the crystal 5 thermal field in the radial direction will help to balance the thermal field of the crystal 5 in the radial direction, and the good thermal conductivity in the radial direction is beneficial to the radial heat transfer, which can reduce the radial temperature gradient; while the poor thermal conductivity in the axial direction will further reduce the radial temperature gradient, thereby effectively reducing the radial temperature gradient of the crystal 5 thermal field.

[0028] The following is combined Figure 2 This section explains the principle that poor axial thermal conductivity can further reduce the radial temperature gradient. Please refer to [link / reference needed]. Figure 2 , Figure 2In the diagram, the radial thermal conductivity of crystal 5 is K1, the axial thermal conductivity is K2, and the temperatures at two radial positions are T1 and T2, respectively; the temperatures at two axial positions are T2 and T3, respectively. The radial temperature gradient is set to T1 - T2. Heat is transferred along the direction of the arrow in the diagram. Since the amount of heat transferred at each position along a transmission path is the same, the heat transfer is Q = (T1 - T3) / (R1 + R2) = (T1 - T2) / (R1) = (T2 - T3) / (R2), where R1 is the thermal resistance corresponding to the radial thermal conductivity K1, and R2 is the thermal resistance corresponding to the axial thermal conductivity K2. Thermal conductivity and thermal resistance are inversely proportional. Therefore, when the axial thermal conductivity K2 is small (R2 is large), (T2-T3) / (R2) is small. If the radial thermal conductivity K1 remains unchanged at this time, then (T2-T3) / (R2) will decrease accordingly, that is, the radial temperature gradient T1-T2 will decrease, thereby reducing the radial temperature gradient.

[0029] Preferably, the thermal conductivity of the plane is at least two orders of magnitude different from that of the thickness direction, which makes the difference between the two very large, thus further reducing the radial temperature gradient.

[0030] Specifically, in this embodiment, the heat transfer layer 2 is graphite paper, which is made by chemically treating high-carbon phosphorus flake graphite and then expanding and rolling it at high temperature. The thermal conductivity of the graphite paper in its plane is much greater than that in its thickness direction, by two orders of magnitude. Of course, the present invention is not limited to this. In practical applications, the heat transfer layer 2 can also be made of other materials, as long as they meet the requirements of the present invention.

[0031] Furthermore, preferably, a planarization layer 3 is also provided at the mounting position. The graphite paper and the planarization layer 3 are stacked. This is because the graphite paper has a certain elasticity, and excessively thick graphite paper may cause unevenness on the surface fixed to the seed crystal 4. Therefore, the planarization layer 3 can solve this problem. Figure 1 As shown, three graphite papers are first stacked and fixed at the mounting position, and then a planarization layer 3 is fixed on the graphite papers, with the seed crystal 4 fixed on the planarization layer 3.

[0032] Specifically, in this embodiment, the planarization layer 3 is a graphite sheet. The graphite sheet has high strength, and when it is laminated and fixed with graphite paper, it can reduce the unevenness of the surface fixed with the seed crystal 4.

[0033] More preferably, the graphite paper and the planarization layer 3 are alternately stacked, such as... Figures 3a-3c As shown, in Figure 3a In the middle, a planarization layer 3 is located between two graphite papers (i.e., heat transfer layers 2), in Figure 3b In this structure, a graphite paper (i.e., heat transfer layer 2) is located between two planarization layers 3; Figure 3cIn the middle, two graphite paper layers (i.e., heat transfer layer 2) and two planarization layers 3 are alternately arranged; Figures 3a-3c In the middle, the seed crystals 4 are all fixed downwards. Graphite paper and planarization layer 3 are alternately stacked to form a relatively... Figure 1 The method shown can effectively reduce the unevenness of the surface fixed with the seed crystal 4.

[0034] Preferably, the entire back side of the seed crystal 4 is fixed to the mounting position by adhesive bonding to improve the reliability of the seed crystal 4 fixation.

[0035] Preferably, the total thickness of all graphite paper is in the range of 1mm-10mm, which can further effectively reduce the radial temperature gradient.

[0036] Preferably, the number of graphite sheets is 2 or 3, which can effectively reduce the unevenness of the fixed surface with the seed crystal 4.

[0037] Preferably, the thickness of each graphite sheet is in the range of 2mm-3mm, which can well ensure strength.

[0038] When applying, such as Figure 1 As shown, the crucible is placed on the insulating felt 1 to keep the crucible warm, thereby improving the radial temperature gradient of the crystal thermal field from another aspect.

[0039] It should be noted that the crucible provided in the embodiments of the present invention can be used not only to grow silicon carbide crystals, but also to grow aluminum nitride crystals. Of course, it can also grow other crystals, which will not be described in detail here.

[0040] Example 2

[0041] This invention provides a crystal growth furnace, including a crystal growth crucible and a heating device. The heating device is used to heat the crystal growth crucible so that the growth environment inside the crucible reaches the process temperature. The crystal growth crucible is the crystal growth crucible provided in Embodiment 1 of this invention.

[0042] The crystal growth furnace provided in this embodiment of the invention uses the crystal growth crucible provided in Embodiment 1 above, which can effectively reduce the radial temperature gradient of the crystal thermal field, thereby solving the problem of easy crystal cracking when growing large-sized crystals.

[0043] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A crystal growth crucible, wherein a mounting position for fixing a seed crystal is provided on its top wall, characterized in that, A heat transfer layer is also provided at the mounting position. The thermal conductivity of the heat transfer layer in its plane is greater than that in its thickness direction, so as to reduce the radial temperature gradient of the crystal thermal field during crystal growth. The heat transfer layer is graphite paper; the total thickness of all the graphite paper is in the range of 1mm-10mm; A planarization layer, which is a graphite sheet, is also provided at the mounting position, and the graphite paper and the graphite sheet are stacked together.

2. The crystal growth crucible according to claim 1, characterized in that, The thermal conductivity of the plane in which it is located differs from the thermal conductivity in the thickness direction by at least two orders of magnitude.

3. The crystal growth crucible according to claim 1, characterized in that, The graphite paper and the planarization layer are alternately stacked.

4. The crystal growth crucible according to claim 1, characterized in that, The entire back side of the seed crystal is fixed to the mounting position by adhesive bonding.

5. The crystal growth crucible according to claim 1, characterized in that, The number of graphite sheets is 2 or 3.

6. The crystal growth crucible according to claim 5, characterized in that, The thickness of each graphite sheet ranges from 2mm to 3mm.

7. A crystal growth furnace, comprising a crystal growth crucible and a heating device, wherein the heating device is used to heat the crystal growth crucible to bring the growth environment inside the crucible to the process temperature, characterized in that, The crystal growth crucible is the crystal growth crucible according to any one of claims 1-6.

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