Silicon carbide crystal growth apparatus and seed cover plate assembly therefor

Abstract

The utility model discloses a seed crystal cover plate subassembly, including from top to bottom the cover plate body and graphite ring of arrangement in proper order, the bottom surface middle part recessed arrangement of cover plate body is provided with the positioning slot, the bottom surface of the slot mouth outer edge part of positioning slot cooperates with the top surface interval of graphite ring, to form the positioning interval that the edge part of silicon carbide seed crystal inserts and clamps. This seed crystal cover plate subassembly can reliably fix silicon carbide seed crystal, and can make the heat conduction more uniform in the process of silicon carbide crystal growth, and the crystal forming effect is better. The utility model discloses still a kind of silicon carbide crystal growth device of application above-mentioned seed crystal cover plate subassembly.

Description

Technical Field

[0001] This utility model relates to the technical field of supporting equipment for silicon carbide crystal growth, and in particular to a seed crystal cover plate assembly. This utility model also relates to a silicon carbide crystal growth device using the seed crystal cover plate assembly. Background Technology

[0002] At present, when the industry uses the vapor deposition method to grow silicon carbide (SiC) single crystals, the presence of edge stress has a significant impact on the forming effect of silicon carbide crystals. In particular, when the edge stress is too large, it is very easy to cause quality loss of silicon carbide crystals, which will have an adverse effect on the growth and forming of silicon carbide crystals.

[0003] Correspondingly, the generation of edge stress during the growth and forming of silicon carbide crystals is a complex issue, mainly caused by various physical and chemical factors during the silicon carbide crystal growth process. Specifically, the causes of edge stress in silicon carbide crystals include, but are not limited to: thermal stress on the crystal, uneven growth rate of the crystal in different parts, crystal geometry, seed crystal contact, cooling process during crystal growth and forming, impurities and defects in the silicon carbide material, external mechanical stress on the crystal, crystal growth environment factors, and improper control of process parameters.

[0004] Generally, in existing silicon carbide crystal growth and forming processes, the silicon carbide seed crystal is usually bonded to the base or other structure of the crystal growth device or equipment using adhesive. This ensures the basic positioning and reliable fixation of the silicon carbide seed crystal, serving as the structural basis for subsequent silicon carbide crystal growth and forming.

[0005] However, although the existing silicon carbide seed fixing methods mentioned above can meet the basic requirements for silicon carbide crystal growth and shaping, the adhesive used for bonding and fixing will generate gas during the curing and carbonization process. During the exhaust process, these gases are very likely to generate structural pores. The presence of these structural pores will lead to uneven heat conduction in the early stage of silicon carbide seed growth, resulting in greater stress on the silicon carbide seed, thereby increasing the dislocation density in the early stage of silicon carbide crystal growth and adversely affecting the subsequent growth and shaping of silicon carbide crystals.

[0006] In view of this, how to optimize the fixation method of silicon carbide seed crystals to make the heat conduction more uniform and the crystal forming effect better during the growth of silicon carbide crystals is an important technical problem that needs to be solved by those skilled in the art. Utility Model Content

[0007] The purpose of this invention is to provide a seed crystal cover plate assembly that can reliably fix the silicon carbide seed crystal and make heat conduction more uniform during silicon carbide crystal growth, resulting in better crystal formation. Another purpose of this invention is to provide a silicon carbide crystal growth apparatus using the aforementioned seed crystal cover plate assembly.

[0008] To solve the above-mentioned technical problems, this utility model provides a seed crystal cover plate assembly, which fits snugly on the top of the crucible. It includes a cover plate body and a graphite ring arranged sequentially from top to bottom. A positioning groove is recessed in the middle of the bottom surface of the cover plate body. The bottom surface of the outer edge of the positioning groove is clearance-fitted with the top surface of the graphite ring to form a positioning gap for the edge of the silicon carbide seed crystal to be embedded and engaged.

[0009] Preferably, the bottom of the positioning groove has a growth bearing surface that can contact and adapt to the silicon carbide seed crystal, and the positioning gap is arranged in annularly on the outer periphery of the growth bearing surface.

[0010] Preferably, the growth bearing surface is a high-roughness plane parallel to the main extension surface of the cover plate body.

[0011] Preferably, the bottom surface of the cover plate body is further recessed with an assembly slot, the assembly slot is arranged in a ring around the outer periphery of the positioning groove, and the bottom of the assembly slot can overlap and fit with the top surface of the crucible.

[0012] Preferably, the inner ring wall of the assembly slot is recessed with an annularly extended lower temperature control groove, and the opening of the lower temperature control groove is connected to the external environment.

[0013] Preferably, the lower temperature control groove is located above the positioning groove, and the side wall of the positioning groove has a through-hole that connects the positioning groove and the lower temperature control groove, and the distance between the axis of the through-hole and the axis of the positioning groove increases from bottom to top.

[0014] Preferably, the top surface of the cover plate body is recessed with an annularly extending upper temperature control groove.

[0015] Preferably, it further includes an outer positioning sleeve fitted onto the outer periphery of the cover plate body and the graphite ring, wherein the cover plate body and the graphite ring are fixedly connected by the outer positioning sleeve.

[0016] This utility model also provides a silicon carbide crystal growth apparatus, including a crucible capable of containing silicon carbide crystals and a seed crystal cover plate assembly that is aligned and fastened to the top of the crucible, wherein the seed crystal cover plate assembly is the seed crystal cover plate assembly as described in any of the above claims.

[0017] Preferably, the seed crystal cover plate assembly further includes an outer positioning sleeve sleeved on the cover plate body and the outer periphery of the graphite ring. The outer positioning sleeve and the crucible are integrally connected, and the cover plate body and the graphite ring are fixedly connected through the outer positioning sleeve.

[0018] Compared to the aforementioned background technology, the seed crystal cover plate assembly provided by this utility model, during installation, aligns and embeds the edge of the silicon carbide seed crystal to be grown into the positioning gap and snaps it into place. This positioning gap reliably installs and fixes the silicon carbide seed crystal onto the bottom surface of the cover plate body. In this way, the edge of the silicon carbide seed crystal can be reliably clamped and fixed by the alignment and fit between the top of the graphite ring and the bottom of the cover plate body. Therefore, no glue or other adhesives or auxiliary connecting materials are needed to reliably install the silicon carbide seed crystal onto the main structure of the seed crystal cover plate assembly. This process effectively avoids the formation of structural pores caused by gas leakage from the adhesive during subsequent silicon carbide seed crystal growth processes, such as adhesive curing and carbonization. This ensures uniform heat conduction in the early stages of silicon carbide crystal growth, optimizes the structural stress distribution of the silicon carbide seed crystal, and prevents excessive structural stress. Consequently, it reduces the dislocation density in the early stages of silicon carbide crystal growth, thereby optimizing the subsequent growth and forming effects of the silicon carbide crystal and ultimately improving the quality of the final silicon carbide crystal product.

[0019] In another preferred embodiment of this invention, the bottom of the positioning groove has a growth bearing surface that can contact and adapt to the silicon carbide seed crystal, and the positioning gap is arranged in a ring around the outer periphery of the growth bearing surface. After the edge of the silicon carbide seed crystal is aligned and embedded in the positioning gap, the main structural part of the silicon carbide seed crystal can be fully fitted and arranged in the positioning groove, so that the growth bearing surface and the inner wall of the positioning groove can provide reliable structural support and sufficient growth space for the silicon carbide seed crystal. This, in conjunction with the internal space of the crucible located below the seed crystal cover plate assembly, further optimizes the growth effect and forming quality of the silicon carbide crystal. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A front view of the seed crystal cover plate assembly provided in a specific embodiment of this utility model;

[0022] Figure 2for Figure 1 Top view.

[0023] in:

[0024] 11-Cover plate body; 111-Positioning groove; 112-Growth bearing surface; 113-Assembly slot; 114-Lower temperature control groove; 115-Air guide hole; 116-Upper temperature control groove;

[0025] 12-Graphite rings;

[0026] 13 - Positioning gap. Detailed Implementation

[0027] The core of this utility model is to provide a seed crystal cover plate assembly, which can reliably fix the silicon carbide seed crystal and make the heat conduction more uniform and the crystal forming effect better during the growth of silicon carbide crystal; in addition, a silicon carbide crystal growth device using the above-mentioned seed crystal cover plate assembly is also provided.

[0028] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] In specific implementation methods, in conjunction with references Figure 1 and Figure 2 As shown, the seed crystal cover plate assembly provided by this utility model fits snugly to the top of the crucible and includes a cover plate body 11 and a graphite ring 12 arranged sequentially from top to bottom. A positioning groove 111 is recessed in the middle of the bottom surface of the cover plate body 11. The bottom surface of the outer edge of the positioning groove 111 is gap-fitted with the top surface of the graphite ring 12 to form a positioning gap 13 for the edge of the silicon carbide seed crystal to be embedded and engaged.

[0030] During the component installation and arrangement before implementing the silicon carbide crystal growth process, the edge of the silicon carbide seed crystal to be grown is aligned and embedded into the positioning gap 13 and snapped into place. The positioning gap 13 reliably installs and fixes the silicon carbide seed crystal to the bottom surface of the cover plate body 11. In this way, the top of the graphite ring 12 aligns and matches with the bottom of the cover plate body 11 to reliably clamp and fix the edge of the silicon carbide seed crystal. Therefore, no glue or other adhesives or auxiliary connecting materials are needed to reliably install the silicon carbide seed crystal and the main structure of the seed crystal cover plate component. This process effectively avoids the formation of structural pores caused by gas leakage from the adhesive during subsequent silicon carbide seed crystal growth processes, such as adhesive curing and carbonization. This ensures uniform heat conduction in the early stages of silicon carbide crystal growth, optimizes the structural stress distribution of the silicon carbide seed crystal, and prevents excessive structural stress. Consequently, it reduces the dislocation density in the early stages of silicon carbide crystal growth, thereby optimizing the subsequent growth and forming effects of the silicon carbide crystal and ultimately improving the quality of the final silicon carbide crystal product.

[0031] Specifically, the bottom of the positioning groove 111 has a growth bearing surface 112 that can contact and adapt to the silicon carbide seed crystal, and the positioning gap 13 is arranged in a ring around the outer periphery of the growth bearing surface 112. After the edge of the silicon carbide seed crystal is aligned and embedded in the positioning gap 13, the main structural part of the silicon carbide seed crystal can be fully fitted and arranged in the positioning groove 111, so that the growth bearing surface 112 and the inner wall of the positioning groove 111 can provide reliable structural support and sufficient growth space for the silicon carbide seed crystal. This, in conjunction with the internal space of the crucible located below the seed crystal cover plate assembly, further optimizes the growth effect and forming quality of the silicon carbide crystal.

[0032] Correspondingly, the bottom and sidewalls of the positioning groove 111, as well as the extended structure of the outer edge of the groove opening of the positioning groove 111, cooperate to form a stepped surface structure. This allows for further structural limitation between the main structure of the positioning groove 111 and the positioning gap 13 and the installed silicon carbide seed crystal, thereby making the installation of the silicon carbide seed crystal at the bottom of the cover plate body 11 more secure and reliable, and further optimizing the positioning and installation accuracy.

[0033] It is easy to understand that in practical applications, the cover plate body 11 and graphite ring 12 used in this solution are preferably in a disc-shaped structure. Therefore, the corresponding component adaptation descriptions use structural descriptions such as "circumferential", "outer periphery" and "ring" that can be adapted to the disc-shaped structure. In principle, the shape and structure of the cover plate body 11 and graphite ring 12 can also be flexibly adjusted and selected according to specific working conditions and assembly requirements. The corresponding adaptation structure descriptions can also be understood accordingly, and will not be elaborated further.

[0034] Correspondingly, the positioning gap 13 also extends in an annular shape so as to fully align and adapt with the outer peripheral edge of the silicon carbide seed crystal, ensuring reliable embedding and fixing of each part of the outer peripheral edge of the silicon carbide seed crystal, thereby further improving the positioning accuracy and connection strength of the silicon carbide seed crystal on the seed crystal cover plate assembly, making the installation arrangement of the silicon carbide seed crystal more stable and reliable.

[0035] Furthermore, the growth bearing surface 112 is a plane parallel to the main extension surface of the cover plate body 11. This planar extension structure allows the growth bearing surface 112 to better fit with the main structure of the silicon carbide seed crystal, thereby ensuring the support strength and corresponding positioning adaptation effect of the growth bearing surface 112 for the silicon carbide seed crystal, thus optimizing the forming effect of the silicon carbide crystal formed after the silicon carbide seed crystal is grown.

[0036] Furthermore, the growth bearing surface 112 is a high-roughness plane formed by any one of the following processes: coating treatment, acid pickling treatment, alkaline pickling treatment, or chemical vapor infiltration treatment. Generally, the high-roughness plane structure formed by the corresponding process can significantly improve the roughness of the growth bearing surface 112 compared to the existing conventional cover plate surface, thereby further optimizing the contact adaptation effect between the growth bearing surface 112 and the silicon carbide seed crystal. This results in more uniform heat conduction during the initial stage of silicon carbide crystal growth, a corresponding reduction in the stress of the silicon carbide seed crystal structure, and a further reduction in the dislocation density during the initial stage of silicon carbide crystal growth. Consequently, the growth effect and forming quality of the silicon carbide crystal are further optimized.

[0037] On the other hand, the bottom surface of the cover plate body 11 is also recessed with an assembly slot 113. The assembly slot 113 is arranged in a ring around the outer periphery of the positioning groove 111, and the bottom of the assembly slot 113 can overlap and fit with the top surface of the crucible. The assembly slot 113 can be aligned and fitted with the top edge of the crucible to further optimize the alignment and assembly effect and structural fit of the seed crystal cover plate assembly and the crucible. This makes the assembled silicon carbide crystal growth device more regular and compact, and avoids impurities in the external environment from contaminating or otherwise adversely affecting the silicon carbide crystal in the internal space of the silicon carbide crystal growth device, thus ensuring the growth and forming quality of the silicon carbide crystal.

[0038] Specifically, an annularly extended lower temperature control groove 114 is recessed on the inner ring wall of the assembly slot 113, and the groove opening of the lower temperature control groove 114 is connected to the external environment. In the conventional cover plate assembly structure used in the prior art, due to the self-heating of the graphite cover plate, the silicon carbide crystal arranged in contact with the bottom of the cover plate exhibits an M-shaped growth trajectory during its growth process. That is, the growth rate from the edge of the silicon carbide crystal to its center position is slow-fast-slow. The uneven crystal growth rate leads to an increase in the edge stress of the silicon carbide crystal, resulting in a corresponding increase in the dislocation density in the early stage of silicon carbide crystal growth.

[0039] Correspondingly, the structure of the lower temperature control groove 114 allows the thickness of the cover plate body 11 at the corresponding position of the lower temperature control groove 114 to be slightly smaller or basically the same as the thickness of the cover plate body 11 at other parts, and the position corresponding to the lower temperature control groove 114 is exactly the part of the main structure of the cover plate body 11 between its center and edge. This effectively reduces the self-heating of the cover plate body 11 at the corresponding position of the lower temperature control groove 114, ensuring that the growth rate of the silicon carbide crystal at each part of the cover plate body 11 remains uniform. This correspondingly reduces the edge stress of the silicon carbide crystal, lowering the dislocation density in the early stage of crystal growth, thereby further optimizing the overall growth effect and forming quality of the silicon carbide crystal.

[0040] More specifically, the lower temperature control groove 114 is located above the positioning groove 111. A vent 115, connecting the positioning groove 111 and the lower temperature control groove 114, runs through the side wall of the positioning groove 111. The distance between the axis of the vent 115 and the axis of the positioning groove 111 increases from bottom to top. In the prior art, the cover plate body 11 also has corresponding straight-outlet vent structures with axes parallel to the axis of the cover plate body 11 to discharge silicon carbide vapor. However, due to the limitations of the existing straight-outlet vent structure, the silicon carbide vapor discharge rate is relatively fast, causing the silicon carbide at the corresponding position of the straight-outlet vent to easily form rapid crystals. This leads to an accelerated growth rate of silicon carbide crystals at the affected position, thereby increasing the dislocation density in the early stages of silicon carbide crystal growth and affecting the overall growth effect and forming quality of the silicon carbide crystal.

[0041] Correspondingly, the inclined and extended air guide hole 115 structure provided in this solution can effectively reduce the exhaust rate of silicon carbide vapor, allowing the silicon carbide vapor at the positioning groove 111 to be discharged more slowly and steadily. This effectively controls the silicon carbide crystallization rate at the corresponding position of the air guide hole 115, slows down the silicon carbide growth rate at that position, thereby reducing the dislocation density in the early stage of silicon carbide crystal growth. This makes the silicon carbide crystal growth rate at the positioning groove 111 more balanced, and the overall growth effect and the corresponding silicon carbide crystal forming quality are optimized accordingly.

[0042] In addition, an annularly extending upper temperature control groove 116 is recessed on the top surface of the cover plate body 11. Similar to the lower temperature control groove 114 mentioned above, the upper temperature control groove 116 also ensures that the structural thickness of the cover plate body 11 at its corresponding position is slightly smaller or basically the same as the structural thickness of other parts of the cover plate body 11. Furthermore, the position corresponding to the upper temperature control groove 116 is precisely the part of the main structure of the cover plate body 11 located between its center and edge. This effectively reduces the self-heating of the cover plate body 11 at the position corresponding to the lower temperature control groove 114, ensuring that the growth rate of the silicon carbide crystals arranged at the bottom of the cover plate body 11 remains uniform. This correspondingly reduces the edge structural stress of the silicon carbide crystals, lowering the dislocation density in the early stages of crystal growth, thereby further optimizing the overall growth effect and molding quality of the silicon carbide crystals. If the upper temperature control groove 116 and the lower temperature control groove 114 are integrated on the cover plate body 11, the dislocation density in the early stage of silicon carbide crystal growth can be further rationally controlled by the coordinated cooperation of the upper temperature control groove 116 and the lower temperature control groove 114, thereby further optimizing the overall growth effect of silicon carbide crystal and further improving the crystal forming quality.

[0043] Furthermore, the seed crystal cover plate assembly also includes an outer positioning sleeve fitted around the outer periphery of the cover plate body 11 and the graphite ring 12, with the cover plate body 11 and the graphite ring 12 fixedly connected by the outer positioning sleeve. This outer positioning sleeve provides ample assembly space and reliable structural support for the cover plate body 11 and the graphite ring 12. Correspondingly, the outer positioning sleeve can be assembled with the cover plate body 11 and the graphite ring 12 using threaded connection adapter structures, thereby effectively ensuring the assembly strength between the cover plate body 11 and the graphite ring 12 and the outer positioning sleeve, thus improving the overall structural reliability of the seed crystal cover plate assembly.

[0044] In a specific embodiment, the silicon carbide crystal growth apparatus provided by this utility model includes a crucible capable of accommodating a silicon carbide crystal and a seed crystal cover plate assembly aligned and fastened to the top of the crucible. The seed crystal cover plate assembly is as described above. This seed crystal cover plate assembly of the silicon carbide crystal growth apparatus can reliably fix the silicon carbide seed crystal and enables more uniform heat conduction during the silicon carbide crystal growth process, resulting in better crystal forming.

[0045] Based on this, the seed crystal cover plate assembly also includes an outer positioning sleeve fitted around the outer periphery of the cover plate body 11 and the graphite ring 12. The outer positioning sleeve and the crucible are integrally connected, and the cover plate body 11 and the graphite ring 12 are fixedly connected through the outer positioning sleeve. This integral connection structure can further optimize the stress distribution and structural fit between the outer positioning sleeve and the crucible. Combined with the reliable assembly between the outer positioning sleeve and the cover plate body 11 and the graphite ring 12, the component integration and assembly structural strength of the silicon carbide crystal growth device can be further improved.

[0046] Generally, the aforementioned integrated connection structure can reliably connect the outer positioning sleeve to the crucible body structure through welding or bonding, or it can be directly integrally formed by processing the outer positioning sleeve and the crucible during component manufacturing. In short, in practical applications, the matching structure between the outer positioning sleeve and the crucible can be flexibly selected according to specific working conditions and processing requirements. In principle, any structure that can meet the actual application needs of the silicon carbide crystal growth device is acceptable.

[0047] In summary, the seed crystal cover plate assembly provided by this utility model, during installation, involves aligning and embedding the edge of the silicon carbide seed crystal to be grown into the positioning gap and securing it in place. This positioning gap allows the silicon carbide seed crystal to be reliably installed and fixed to the bottom surface of the cover plate body. Furthermore, the top of the graphite ring aligns and matches with the bottom of the cover plate body to reliably clamp and fix the edge of the silicon carbide seed crystal. Therefore, reliable installation between the silicon carbide seed crystal and the main structure of the seed crystal cover plate assembly can be completed without the need for adhesives or other bonding or auxiliary connecting materials. This effectively avoids the formation of structural pores caused by gas leakage from the adhesive during subsequent silicon carbide seed crystal growth processes, such as adhesive curing and carbonization. This ensures uniform heat conduction in the early stages of silicon carbide crystal growth, optimizes the structural stress distribution of the silicon carbide seed crystal, and prevents excessive structural stress in the silicon carbide seed crystal. Consequently, it reduces the dislocation density in the early stages of silicon carbide crystal growth, thereby optimizing the subsequent growth and forming effects of the silicon carbide crystal and ultimately improving the forming quality of the silicon carbide crystal product.

[0048] This invention also provides a silicon carbide crystal growth device, whose seed crystal cover plate assembly can reliably fix the silicon carbide seed crystal and make the heat conduction more uniform during the silicon carbide crystal growth process, resulting in better crystal forming effect.

[0049] The seed crystal cover plate assembly and the silicon carbide crystal growth apparatus using the seed crystal cover plate assembly provided by this utility model have been described in detail above. Specific examples have been used to illustrate the principle and implementation of this utility model. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core idea of ​​this utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made to this utility model without departing from the principle of this utility model, and these improvements and modifications also fall within the protection scope of the claims of this utility model.

Claims

1. A seed crystal cover plate assembly, which fits snugly onto the top of a crucible, characterized in that, The device includes a cover plate body and a graphite ring arranged sequentially from top to bottom. A positioning groove is recessed in the center of the bottom surface of the cover plate body. The bottom surface of the outer edge of the positioning groove is fitted with the top surface of the graphite ring to form a positioning gap for the edge of the silicon carbide seed crystal to be embedded and engaged.

2. The seed crystal cover plate assembly as described in claim 1, characterized in that, The bottom of the positioning groove has a growth bearing surface that can contact and adapt to the silicon carbide seed crystal, and the positioning gap is arranged in annularly on the outer periphery of the growth bearing surface.

3. The seed crystal cover plate assembly as described in claim 2, characterized in that, The growth bearing surface is a high-roughness plane parallel to the main extension surface of the cover plate body.

4. The seed crystal cover plate assembly as described in claim 2, characterized in that, The bottom surface of the cover plate body is also recessed with an assembly slot, which is arranged in a ring around the outer periphery of the positioning groove, and the bottom of the assembly slot can overlap and fit with the top surface of the crucible.

5. The seed crystal cover plate assembly as described in claim 4, characterized in that, The inner ring wall of the assembly slot is recessed with an annular extending lower temperature control groove, and the opening of the lower temperature control groove is connected to the external environment.

6. The seed crystal cover plate assembly as described in claim 5, characterized in that, The lower temperature control groove is located above the positioning groove. A vent hole is provided through the side wall of the positioning groove to connect the positioning groove and the lower temperature control groove. The distance between the axis of the vent hole and the axis of the positioning groove increases from bottom to top.

7. The seed crystal cover plate assembly as described in claim 1, characterized in that, The top surface of the cover plate body is recessed and has an annular, extending upper temperature control groove.

8. The seed crystal cover plate assembly as described in claim 1, characterized in that, It also includes an outer positioning sleeve fitted around the cover plate body and the graphite ring, with the cover plate body and the graphite ring being fixedly connected by the outer positioning sleeve.

9. A silicon carbide crystal growth apparatus, comprising a crucible capable of containing a silicon carbide crystal and a seed crystal cover plate assembly aligned and fastened to the top of the crucible, characterized in that, The seed crystal cover plate assembly is the seed crystal cover plate assembly as described in any one of claims 1 to 8.

10. The silicon carbide crystal growth apparatus as described in claim 9, characterized in that, The seed crystal cover plate assembly also includes an outer positioning sleeve fitted around the cover plate body and the outer periphery of the graphite ring. The outer positioning sleeve and the crucible are integrally connected, and the cover plate body and the graphite ring are fixedly connected through the outer positioning sleeve.

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