CN220335361U

CN220335361U - Thermal field structure and single crystal furnace

Info

Publication number: CN220335361U
Application number: CN202321695421.1U
Authority: CN
Inventors: 张振宇; 刘有益
Original assignee: Inner Mongolia Zhonghuan Crystal Materials Co Ltd
Current assignee: Inner Mongolia Zhonghuan Crystal Materials Co Ltd
Priority date: 2023-06-30
Filing date: 2023-06-30
Publication date: 2024-01-12
Anticipated expiration: 2033-06-30

Abstract

The application provides a thermal field structure, which comprises a guide cylinder and a furnace cover matched with the guide cylinder, wherein the guide cylinder is at least provided with a body, the body comprises a vertical section, a curved section and an inner diameter section which are sequentially connected, and the vertical section is connected with the curved section through a transition section; the curved surface section is configured as an outwardly convex arc surface. According to the thermal field structure optimization method, the gap between the lower bottom surface of the guide cylinder and the solid-liquid interface is reduced, the volatilization speed of the oxygen content taken away by gas is increased, the concentration of oxygen in the peripheral atmosphere is reduced, and the influence of shearing convection on oxygen volatilization is reduced. Meanwhile, the bonding compactness of the auxiliary body and the furnace cover is improved, and the loss of inert gas is reduced, so that the utilization rate of the gas can be improved, the crystal pulling quality can be improved, and the generation of oxygen content is reduced. The application also provides a single crystal furnace with the thermal field structure.

Description

Thermal field structure and single crystal furnace

Technical Field

The application belongs to the technical field of Czochralski crystal production, and particularly relates to a thermal field structure and a single crystal furnace with the thermal field structure.

Background

Along with iteration and development of photovoltaic cells, the industry requirements on single crystal quality are also continuously improved. Because the process is limited by the solar-grade Czochralski silicon production process, oxygen impurities are introduced in the crystal growth process, and in the later solar cell manufacturing process, the high-temperature cell process is easy to induce oxygen precipitation defects in the silicon wafer, so that the service life is reduced, the concentric circle proportion is increased, and the conversion efficiency of the cell is further affected. Oxygen concentration is a core index for single crystal quality control, and oxygen reduction is a continuous improvement direction. Because the structure of the crystal pulling thermal field directly influences the oxygen content in the crystal pulling process, the existing thermal field structure is unreasonable in design, so that the oxygen generation in the crystal pulling process is directly influenced, the oxygen content generation degree and the volatilization speed degree are influenced, and the oxygen content value directly determines the quality of the single crystal.

Disclosure of Invention

The application provides a thermal field structure and be equipped with single crystal furnace of this thermal field structure, solved among the prior art the too high technical problem that directly influences product quality of oxygen content when pulling the crystal.

In order to solve at least one of the technical problems, the technical scheme adopted in the application is as follows:

the thermal field structure comprises a guide cylinder and a furnace cover matched with the guide cylinder, wherein the guide cylinder is at least provided with a body, the body comprises a vertical section, a curved section and an inner diameter section which are sequentially connected, and the vertical section is connected with the curved section through a transition section; the curved surface section is configured as an outwardly convex arc surface.

Further, the inner diameter section is a straight line section which is transversely arranged, and the radius of the transition section is smaller than that of the curved surface section; and the length of the arc surface of the curved surface section is larger than that of the inner diameter section.

Further, the included angle corresponding to the arc length of the curved surface section is larger than 20 degrees and not larger than 60 degrees.

Further, the thickness of the end part of the curved surface section, which is close to the inner diameter section, is larger than the thickness of the end part of the curved surface section, which is far away from the inner diameter section, and the thickness of the curved surface section, which is far away from the inner diameter section, is the same as the thickness of the vertical section.

Further, the end part of the inner diameter section, which is far away from one side of the curved surface section, is a stepped surface, and the minimum thickness of the stepped surface in the inner diameter section is the same as the thickness of the vertical section.

Further, a diameter-variable cylindrical auxiliary body is also arranged outside the upper end face of the body, and the auxiliary body is in an up-inclined and down-straight structure.

Further, the inclined section of the auxiliary body is configured to be inclined outwardly, and has a horizontal angle of not more than 60 ° with the top surface of the body.

Further, the height of the inclined section in the auxiliary body is larger than the height of the straight line section of the auxiliary body, and the height of the inclined section in the auxiliary body is not smaller than 1/2 of the height of the auxiliary body; the thickness of the auxiliary body is the same as that of the body.

Furthermore, the inner wall surface of the furnace cover is provided with an inner wall surface matched with the auxiliary body, and the inner wall surface is also of an upper-inclined lower-straight structure.

A single crystal furnace is provided with the thermal field structure.

By adopting the thermal field structure designed by the application, the thermal field structure is optimized, so that the gap between the lower bottom surface of the guide cylinder and the solid-liquid interface is reduced, namely, the gas flow area is reduced, the circulation speed of unit volume of gas can be increased, the volatilization speed of the oxygen content taken away by the gas is increased, the concentration of oxygen in the peripheral atmosphere is reduced, and the influence of shearing convection on oxygen volatilization is reduced. Meanwhile, the bonding compactness of the auxiliary body and the furnace cover is improved, and the loss of inert gas is reduced, so that the utilization rate of the gas can be improved, the crystal pulling quality can be improved, and the generation of oxygen content is reduced. The application also provides a single crystal furnace with the thermal field structure.

Drawings

FIG. 1 is a schematic illustration of a thermal field structure according to an embodiment of the present application;

FIG. 2 is a block diagram of a pod according to one embodiment of the present application;

FIG. 3 is a block diagram of a body of an embodiment of the present application;

FIG. 4 is a block diagram of an accessory according to an embodiment of the present application;

FIG. 5 is a comparison of the oxygen content of a silicon round rod after being prepared using the crystal pulling process of the present application and a prior art crystal pulling process.

In the figure:

1. guide shell 10, body 11, vertical section

12. Curved surface section 13, inner diameter section 14 and transition section

20. Auxiliary body 21, inclined section 22, straight line section

3. Furnace cover 3 and single crystal furnace

Detailed Description

The present application will now be described in detail with reference to the accompanying drawings and specific examples.

The embodiment provides a thermal field structure, as shown in fig. 1, including a guide shell 1 and a furnace cover 2 matched with the guide shell 1, wherein the guide shell 1 and the furnace cover 2 are both arranged in a single crystal furnace 3, the outer wall surface of the furnace cover 2 is connected to the inner wall of the single crystal furnace 3, and the top of the guide shell 1 is fixedly arranged on the inner avoidance surface of the furnace cover 2. Specifically, the guide cylinder 1 is provided with a body 10 and an auxiliary body 20 having a diameter-variable cylindrical structure provided outside the upper end surface of the body 10. The body 10 comprises a vertical section 11, a curved surface section 12 and an inner diameter section 13 which are sequentially connected, wherein the vertical section 11 is connected with the curved surface section 12 through a transition section 14; the curved surface section 12 is configured as an outwardly convex circular arc surface; and the auxiliary body 20 is constructed in an up-inclined and down-straight structure. The outwards-protruding curved surface section 12 can reduce the gap between the lower bottom surface of the guide cylinder 1 and the solid-liquid interface, namely, reduce the gas flow area, thereby improving the flow speed of the gas in unit volume, expanding the volatilization speed of the gas to take away the oxygen content, reducing the concentration of oxygen in the peripheral atmosphere and reducing the influence of shearing convection on oxygen volatilization. Meanwhile, the auxiliary body 20 with the structure of the upper inclined lower straight type is matched with the inner wall surface of the furnace cover 2 with the structure of the upper inclined lower straight type, so that the compactness of the joint connection of the auxiliary body 20 and the furnace cover 2 can be improved, the loss of inert gas is reduced, the utilization rate of gas can be improved, the crystal pulling quality can be improved, and the generation of oxygen content is reduced.

As shown in fig. 2, the guide cylinder 1 has a cylindrical structure, the inner diameter section 13 is a straight line section structure horizontally and transversely arranged, the vertical section 11 is a straight line section structure vertically arranged, the curved surface section 12 is an arc curved surface structure obliquely downwards and outwards protruding from one end close to the vertical section 11, compared with the existing straight line type obliquely arranged structure, the curved surface section 12 is convexly curved towards one side close to a solid-liquid interface in a quartz crucible (omitted in the drawing), the gap between the curved surface section 12 and the solid-liquid interface is further reduced, the gas flow area overflowed from the inner side of the guide cylinder 1 along the lower bottom surface of the curved surface section 12 is further reduced, and under the condition of unchanged unit volume, the circulation speed of unit volume of gas can be improved, so that the volatilization speed of oxygen content of gas is increased, the concentration of oxygen in peripheral atmosphere is reduced, and the influence of shear convection on oxygen volatilization is reduced.

In this embodiment, the transition section 14 has a circular arc structure, which is used to connect the vertical section 11 and the curved section 12, and the radius of the transition section 14 is smaller than the radius of the curved section 12; and the length of the arc surface of the curved surface section 12 is larger than the length of the inner diameter section 12.

Preferably, the included angle θ1 corresponding to the arc length of the curved surface section 12 is greater than 20 ° and not greater than 60 °, the curved surface section 12 of the curved surface arc structure is more beneficial to the circulation of gas along the outer wall surface thereof, and the gap distance between the curved surface section 12 and the solid-liquid interface is reduced, so that the circulation speed of the gas per unit volume can be improved. If the included angle θ1 corresponding to the arc length of the curved surface section 12 is smaller than or equal to 20 °, the shorter the curved surface section 12 is, the water cooling jacket at the inner side of the guide cylinder 1 cannot be supported; the included angle θ1 corresponding to the arc length of the curved surface section 12 is larger than 60 °, so that the convex curved surface bending degree is increased, the curved surface section 12 directly crosses the surface of the solid-liquid interface, the circulation of gas is interfered, and the crystal pulling quality is directly affected. Preferably, when the included angle θ1 corresponding to the arc length of the curved surface section 12 is 30-40 ° and the radius of the curved surface section 12 is 280-380mm, the curved protrusion effect is best, and the length of the perimeter can perfectly connect the vertical section 11 and the inner diameter section 13, and on the basis of having the convex arc surface, the curved surface section has a structure of being inclined and bent downwards, so that the gas is more beneficial to flowing upwards along the outer wall of the curved surface section 12.

As shown in fig. 3, the thickness of the end of the curved surface section 12 near the inner diameter section 13 is thicker than the thickness of the end of the curved surface section away from the inner diameter section 13, so as to improve the strength of the lower bottom surface of the guide cylinder 1 to support the water cooling jacket. For the end of the curved surface section 12 near the inner diameter section 13, the thickness of the curved surface section 12 far away from the inner diameter section 13 is the same as the thickness of the vertical section 11, and the thickness of the transition section 14 is the same as the thickness of the vertical section 11, so that the convenience and consistency of the processing of the guide cylinder 1 can be improved.

Further, the end of the inner diameter section 13 far away from the curved section 12 is a step surface, and the minimum thickness D of the step surface in the inner diameter section 13 is the same as the thickness of the vertical section 11; and the difference between the maximum thickness D1 of the stepped surface in the inner diameter section 13 and the thickness D is 1-5mm.

As shown in fig. 4, the inclined section 21 of the auxiliary body 20 is constructed in an outward inclined configuration, and has a horizontal angle θ2 with respect to the top surface of the body 10 of not more than 60 °, that is, the inclined section 21 has an angle θ2 with respect to the horizontal and the lateral direction of not more than 60 °, that is, the inclined section 21 has an angle θ3 of not less than 120 ° inclined outward on both sides. The more the inclined section 21 inclines outwards, the longer the inclined section 21 is, so that the inclined surface area of the inclined section is larger than that of the inclined section matched with the furnace cover 3, the joint area of the auxiliary body 20 and the furnace cover 2 can be further increased, the tightness of the matched connection of the guide cylinder 1 and the furnace cover 2 is enhanced, the loss of inert gas through the matched gap between the guide cylinder 1 and the furnace cover 2 can be reduced, the gas utilization rate can be improved, the crystal pulling quality can be improved, and the oxygen content can be reduced.

Preferably, the overall height H of the auxiliary body 20 is 80-100mm, wherein the height H1 of the inclined section 21 is greater than the height of the straight section 22 thereof, and the height H1 of the inclined section 21 in the auxiliary body 20 is not less than 1/2 of the height H of the auxiliary body 20, preferably the height of the inclined section 21 is 42-65. Wherein the thickness of the auxiliary body 20 is the same as the thickness D of the vertical section 11 in the body 10. The greater the height of the inclined section 21, the longer the length of the inclined surface thereof, and the area of the auxiliary body 20 attached to the furnace cover 2 can be increased, so that the tightness of the fit connection between the guide cylinder 1 and the furnace cover 2 can be enhanced.

Further, in order to enhance the strength of the cooperation between the furnace cover 2 and the guide cylinder 1, the inner wall of the furnace cover 2 is configured with an inner wall surface adapted to the auxiliary body 20, that is, the inner wall surface of the furnace cover 2 is also in an upper inclined lower straight structure and is closely matched with the outer wall surface of the auxiliary body 20.

A single crystal furnace is provided with the thermal field structure.

The crystal pulling process adopts the single crystal furnace 3 to pull crystal, and comprises the following steps:

the initial value of the pot rotation speed of the quartz crucible is 4-6rpm when in fusion welding; and then carrying out seeding, shoulder expanding and shoulder rotating by taking the pot rotating speed of the quartz crucible during welding as a reference.

Prior to pulling, it is necessary to weld the molten silicon single crystal with a seed crystal in preparation for seeding, and to grow the desired silicon single crystal on the seed crystal. During welding, the speed of the pot rotation directly influences the crystal pulling quality and the oxygen content of the silicon round rod. In the application, a lower pot rotation starting speed is set, so that the pot rotation speed during welding is lower than that in the prior art, seed crystals can be welded slowly, then the seeding, the shoulder expanding and the shoulder rotating are continued based on the pot rotation speed during welding, namely, during seeding, shoulder expanding and shoulder rotating, pulling is still carried out at the initial pot rotation speed during welding of 4-6rpm, and the seeding, the shoulder expanding and the shoulder rotating are continued to be carried out under the condition of low-speed pot rotation.

Further, the pot rotation speed of the Dan Danying crucible is increased by 1-2rpm when the diameter is equal to that of the shoulder rotation, and the pot rotation speed is kept unchanged until the drawing is finished.

After the shoulder turning is completed, the constant diameter drawing is started, at this time, the rotation speed of the pot is required to be increased, the rotation speed of the pot during shoulder turning is taken as the basis, namely, the rotation speed of the pot is rapidly increased by 1-2rpm on the basis of 4-6rpm, so that the rotation speed of the pot is directly increased to the stable rotation speed of the pot during constant diameter, namely, the rotation speed of the pot is 5-8rpm, and then the crystal pulling constant diameter production is continuously carried out by the rotation speed of the cover pot, and other sizes are unchanged. And after the constant diameter is finished, ending the process by using the rotation speed of the pot at the constant diameter until the drawing is finished.

Furthermore, in the whole crystal pulling process, whether welding, seeding, shoulder expanding or shoulder rotating, or equal diameter and ending, the furnace pressure in the single crystal furnace 3 is kept unchanged all the time and is always in a low pressure state, namely the range of the furnace pressure is 5-9torr.

The process for pulling the silicon round rod by adopting the single crystal furnace provided by the application has the advantages that the rotating speed of the welding crucible is 4-6rpm, which is different from the conventional process of 6-8rpm, the rotating speed of the pot in the equal diameter is always kept in the low range of 5-8rpm, which is different from the rotating speed of the pot in the conventional equal diameter, the generation of strong convection in the melt can be slowed down, and the oxygen generated by the decomposition of the quartz crucible can be further delayed, so that the concentration of the oxygen in a solution can be controlled.

The silicon round rod with the single crystal is pulled by adopting the process, meanwhile, the silicon round rod with the same specification is pulled by adopting the conventional high-pressure cooker rotary crystal pulling process, and the length and the oxygen content of the obtained silicon round rod are compared, as shown in figure 5, a is the silicon round rod pulled by adopting the prior art crystal pulling process, b is the silicon round rod pulled by adopting the crystal pulling process, after the obtained silicon round rod is respectively cut, the average oxygen content of each cut segment is obtained, and as can be seen from the figure, the oxygen content in each segment can be reduced by 1.1-1.3ppma by adopting the crystal pulling process.

And simultaneously, as the crystal pulling length is increased, the pot rotation speed is reduced, and the pot rotation speed is 5-8rpm at the same diameter, so that the diffusion capability of Si0 in inert gas is improved, the effect of inhibiting the evaporation of Si0 from a solid-liquid interface is weakened, and the reduction of the oxygen content in a melt is facilitated. When the furnace pressure is maintained at a low level, particularly within 5-9torr, it is advantageous to reduce the oxygen concentration in the melt, and according to the current situation of the single crystal furnace 3, the dry pumping rate is increased while the furnace rotation and the furnace pressure are reduced, the flow of inert gas in the single crystal furnace 3 is increased, and the oxygen concentration in the peripheral atmosphere can be reduced.

By adopting the thermal field structure designed by the application, the thermal field structure is optimized, so that the gap between the lower bottom surface of the guide cylinder and the solid-liquid interface is reduced, namely, the gas flow area is reduced, the circulation speed of unit volume of gas can be increased, the volatilization speed of the oxygen content taken away by the gas is increased, the concentration of oxygen in the peripheral atmosphere is reduced, and the influence of shearing convection on oxygen volatilization is reduced. Meanwhile, the bonding compactness of the auxiliary body and the furnace cover is improved, and the loss of inert gas is reduced, so that the utilization rate of the gas can be improved, the crystal pulling quality can be improved, and the generation of oxygen content is reduced. The application also provides a single crystal furnace with the thermal field structure and a crystal pulling process for preparing a single crystal silicon rod by adopting the single crystal furnace.

The foregoing detailed description of the embodiments of the present application is provided merely as a preferred embodiment of the present application and is not intended to limit the scope of the present application. All equivalent changes and modifications can be made within the scope of the present application.

Claims

1. The thermal field structure is characterized by comprising a guide cylinder and a furnace cover matched with the guide cylinder, wherein the guide cylinder is at least provided with a body, the body comprises a vertical section, a curved section and an inner diameter section which are sequentially connected, and the vertical section is connected with the curved section through a transition section; the curved surface section is configured as an outwardly convex arc surface.

2. The thermal field structure of claim 1, wherein the inner diameter section is a transversely disposed straight section, and the radius of the transition section is smaller than the radius of the curved section; and the length of the arc surface of the curved surface section is larger than that of the inner diameter section.

3. A thermal field structure according to claim 1 or 2, wherein the arc length of the curved surface section corresponds to an included angle of more than 20 ° and not more than 60 °.

4. A thermal field structure according to claim 3, wherein the thickness of the end of the curved surface section on the side close to the inner diameter section is greater than the thickness of the curved surface section on the side away from the inner diameter section, and the thickness of the curved surface section on the side away from the inner diameter section is the same as the thickness of the vertical section.

5. The thermal field structure according to claim 4, wherein an end of the inner diameter section away from the curved section is a stepped surface, and a minimum thickness of the stepped surface in the inner diameter section is the same as a thickness of the vertical section.

6. A thermal field structure according to any one of claims 1-2 and 4-5, wherein a reducing cylindrical auxiliary body is further arranged outside the upper end face of the body, and the auxiliary body is configured in an upwardly inclined and downwardly straight structure.

7. A thermal field structure according to claim 6, wherein the inclined section of the auxiliary body is configured to be inclined outwardly and at an angle of no more than 60 ° to the horizontal of the top surface of the body.

8. A thermal field structure according to claim 7, wherein the height of the inclined section in the auxiliary body is greater than the height of the straight section thereof, and the height of the inclined section in the auxiliary body is not less than 1/2 of the height of the auxiliary body; the thickness of the auxiliary body is the same as that of the body.

9. A thermal field structure according to claim 7 or 8, wherein the inner side wall of the furnace cover is configured with an inner wall surface adapted to the auxiliary body, and the inner wall surface is also of an upwardly inclined and downwardly straight structure.

10. A single crystal furnace provided with a thermal field structure according to any one of claims 1-9.