Seed crystal for drawing columnar polycrystalline silicon rod and processing method of seed crystal head of seed crystal

Abstract

The invention provides a seed crystal for drawing a columnar polycrystalline silicon rod and a processing method of a seed crystal head of the seed crystal, and belongs to the technical field of polycrystalline silicon rod production, the seed crystal head comprises the seed crystal head, the seed crystal head is made of a polycrystalline silicon material with uniform crystal flowers, and the seed crystal head sequentially comprises a bottom, a middle part and a clamping part from bottom to top, the bottom part is designed to be a convex arc surface, the middle part is designed to be a conical inclined surface, the diameter of the bottom surface of the conical inclined surface is consistent with that of a polycrystalline silicon rod to be drawn, and the clamping part is used for connecting a seed crystal with a lifting mechanism through the connecting part. A polycrystalline silicon rod drawn by the seed crystal is a columnar polycrystalline silicon rod which is free of inclusions and uniform in crystal pattern distribution in the horizontal direction, the drawing efficiency is higher than that of a conical fine seed crystal, the shouldering process is omitted, and the percent of pass is increased.

Description

Technical Field

[0001] The invention relates to the technical field of polycrystalline silicon rod production, and in particular to a method for processing a seed crystal for drawing a columnar polycrystalline silicon rod and a seed crystal head thereof. Background Art

[0002] In recent years, most of the silicon components used in etching machines around the world are made of polycrystalline silicon. Although polycrystalline silicon has more impurities and poorer mechanical properties than single crystal silicon produced by the CZ method, the manufacturing cost of polycrystalline silicon ingots is low, the manufacturing efficiency is high, and it meets the use of chip etching environment. However, with the rapid development of the chip field, the quality requirements for semiconductor silicon wafers and their supporting silicon vulnerable parts are getting higher and higher. It is particularly important to study the behavior of various impurities in polycrystalline silicon materials, control the type and number of defects, improve crystal integrity and crystal uniformity, and product mechanical properties.

[0003] There are two main process methods for producing high-purity polysilicon ingots. One is to use an ingot furnace to melt the silicon material by directional solidification and then cast it into a silicon ingot. It has high manufacturing efficiency and low cost, but there are more nitride and carbide impurities in the silicon ingot, and the material purity is slightly low. The other is to use polycrystalline seed crystals with the same shape characteristics as single crystal seed crystals and use the method of pulling single crystals by direct pulling to manufacture polycrystalline silicon rods. It has low manufacturing efficiency and high processing cost, but high material purity. The horizontal crystal flower distribution of the polycrystalline silicon rods pulled by fine seed crystals is uneven, resulting in unstable mechanical properties in the horizontal direction and poor processing performance. Summary of the invention

[0004] In view of this, the present invention provides a method for processing a seed crystal for pulling a columnar polycrystalline silicon rod and a seed crystal head thereof, so as to solve the technical problem of uneven horizontal crystal flower distribution of a polycrystalline silicon rod pulled from a fine seed crystal.

[0005] The technical solution adopted by the present invention to solve its technical problem is: A seed crystal for drawing a columnar polycrystalline silicon rod comprises a seed crystal head, wherein the seed crystal head is made of polycrystalline silicon material with uniform crystal flowers, and the seed crystal head comprises a bottom, a middle part and a clamping part from bottom to top, wherein the bottom is designed as a convex arc surface, the middle part is designed as a conical inclined surface, and the bottom surface diameter of the conical inclined surface is consistent with the diameter of the polycrystalline silicon rod to be drawn, and the clamping part is used to connect the seed crystal to a pulling mechanism through a connecting part.

[0006] Preferably, the clamping portion comprises an upper clamping portion and a lower clamping portion, an annular groove is provided between the upper clamping portion and the lower clamping portion, and positioning slots are provided on opposite sides of the lower clamping portion.

[0007] Preferably, it also includes a connecting part, which includes two seed crystal clamping rings, a seed crystal connecting rod, and a seed crystal fixing sleeve. The lower parts of the two seed crystal clamping rings are assembled and connected to the seed crystal head, and the upper parts of the two seed crystal clamping rings are assembled and connected to the lower parts of the seed crystal connecting rods. The upper part of the seed crystal connecting rod is connected to the polycrystal weight, so as to connect the seed crystal to the pulling mechanism through the polycrystal weight and the seed crystal rope hook.

[0008] Preferably, the seed crystal retaining ring includes an upper part and a lower part, the upper part is provided with a first assembly groove, the first assembly groove is used to assemble with the seed crystal connecting rod; the lower part is provided with a second assembly groove, the second assembly groove is used to assemble with the clamping part, and a retaining ring boss is provided at the bottom of the lower part.

[0009] Preferably, the upper circle diameter of the seed crystal fixing sleeve is smaller than the lower circle diameter, and the inner wall is conical.

[0010] A method for processing a seed crystal head for drawing a columnar polycrystalline silicon rod comprises the following steps: S1. Select a polysilicon rod of a preset diameter for cutting to obtain a cylindrical silicon ingot of a preset height, and grind the cylindrical silicon ingot so that the parallelism and flatness of the upper and lower planes of the cylindrical silicon ingot are within 0.08 mm; S2, processing the clamping part and the middle part of the seed crystal head on the cylindrical silicon ingot; S3, using a turntable to process a convex arc surface at the bottom of the cylindrical silicon ingot.

[0011] Preferably, in step S2, the following steps are used to process the clamping portion and the middle portion of the seed crystal head on the cylindrical silicon ingot: S21, roughening the cylindrical silicon ingot multiple times using a turntable; S22, performing external feature finishing on the cylindrical silicon ingot using a turntable; S23, machining an annular groove on the cylindrical silicon ingot using a turntable; S24, machining a positioning groove on the cylindrical silicon ingot.

[0012] Preferably, in step S23, using a turntable to process an annular groove on the cylindrical silicon ingot includes: using a metal-based diamond T-shaped tool with a diameter of 80-100 mm, a grinding thickness of 8-10 mm, and a mesh of 100-200 to process the annular groove, the turntable speed is 200-250 rpm, the tool adopts a horizontal feed mode, radial feed 1-2 mm / min, axial feed 200-300 mm / min, and the rotation speed is 2500-3500 rpm.

[0013] Preferably, in step S24, the following steps are used to process the positioning groove on the cylindrical silicon ingot: a. Adhere the cylindrical silicon ingot to a quartz plate using yellow wax, and clamp the quartz plate on a working platform; b. Use a tool with a diameter of 10-15mm, a grinding thickness of 8-10mm, and a mesh of 200-300 to perform positioning slot processing. The tool adopts a horizontal feed method, with a radial feed of 1000-1500mm / min, an axial feed of 200-500mm / min, a down-cut step of 0.03-0.05mm, and a rotation speed of 6500-7500 rpm.

[0014] Preferably, in step S3, machining a convex arc surface on the bottom of the cylindrical silicon ingot using a turntable comprises the following steps: S31, using yellow wax to bond the cylindrical silicon ingot to the adapter plate, and clamping the adapter plate on the working platform through negative pressure suction of the turntable; S32, roughening the bottom of the cylindrical silicon ingot multiple times step by step; S33, after roughing, fine machining is performed to obtain a convex arc surface.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The diameter of the seed crystal of the present invention is consistent with the diameter of the polycrystalline silicon rod to be drawn, so the seeding and shoulder release processes are omitted. In the welding process, the seed crystal will only grow downward, and its crystal flower in the horizontal direction is fixed, that is, the crystal flower of the seed crystal is maintained, and the crystal rod grows downward along the crystal flower, so that the crystal flower of the polycrystalline silicon rod is always uniform and consistent with the crystal flower of the seed crystal. Therefore, the polycrystalline silicon rod drawn by the seed crystal of the present invention is a columnar polycrystalline and inclusion-free polycrystalline silicon rod with uniform crystal flower distribution in the horizontal direction, and the drawing efficiency is higher than that of the tapered fine seed crystal, the shoulder release process is omitted, and the qualified rate is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a three-dimensional diagram of the seed crystal head of the present invention.

[0017] Figure 2 It is the front view of the seed crystal head of the present invention.

[0018] Figure 3 It is a side view of the seed head of the present invention.

[0019] Figure 4 It is a top view of the seed crystal head of the present invention.

[0020] Figure 5 It is a schematic diagram of the assembly of the seed crystal and the polycrystalline weight of the present invention.

[0021] Figure 6 It is a stereoscopic view of the seed crystal retaining ring of the present invention.

[0022] Figure 7 It is a schematic structural diagram of the seed crystal clamp ring of the present invention.

[0023] Figure 8 It is a schematic diagram of the partial assembly of the seed crystal clamp ring and the seed crystal head of the present invention.

[0024] Fig. 9 It is a schematic diagram of the complete assembly of the seed crystal clamp ring and the seed crystal head of the present invention.

[0025] Fig.10 It is a schematic structural diagram of the seed crystal connecting rod of the present invention.

[0026] Fig.11 It is a schematic diagram of assembling the seed crystal connecting rod and the seed crystal clamping ring of the present invention.

[0027] Fig.12 It is a schematic diagram of assembling the seed crystal connecting rod and the seed crystal head of the present invention.

[0028] Fig.13 It is a schematic structural diagram of the seed crystal fixing sleeve of the present invention.

[0029] Fig.14 It is a schematic diagram of assembling the seed crystal fixing sleeve of the present invention.

[0030] Fig.15 It is a schematic diagram of the structure after the initial processing of the present invention.

[0031] Fig.16 It is a schematic diagram of the structure of the annular groove after processing of the present invention.

[0032] Fig.17 It is a schematic diagram of the structure of the positioning slot after processing of the present invention.

[0033] Fig.18 It is a schematic diagram of the structure of the bottom arc surface after the first roughening of the present invention.

[0034] Fig.19 It is a schematic diagram of the structure of the bottom arc surface after the second roughening of the present invention.

[0035] Fig. 20 It is a schematic diagram of the structure of the bottom arc surface after the third roughening of the present invention.

[0036] Fig.21 It is a schematic diagram of the structure after the bottom arc surface of the present invention is finely processed.

[0037] In the figure: seed crystal head 10, bottom 11, middle part 12, clamping part 13, upper clamping part 131, lower clamping part 132, annular groove 133, positioning groove 134, seed crystal clamping ring 20, first assembly groove 21, second assembly groove 22, positioning port 23, clamping ring boss 24, seed crystal connecting rod 30, assembly part 31, positioning block 32, air hole 33, seed crystal fixing sleeve 40, polycrystalline weight 50, seed crystal rope hook 60. DETAILED DESCRIPTION

[0038] The technical solutions and technical effects of the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings of the present invention.

[0039] Please also see Figures 1 to 4 A seed crystal for drawing a columnar polycrystalline silicon rod includes a seed crystal head 10. The seed crystal head 10 is made of polycrystalline silicon material with uniform crystal flowers. The seed crystal head 10 includes a bottom 11, a middle part 12 and a clamping part 13 from bottom to top. The bottom 11 is designed as a convex arc surface, and the middle part 12 is designed as a conical inclined surface. The bottom diameter of the conical inclined surface is consistent with the diameter of the polycrystalline silicon rod to be drawn. The clamping part 13 is used to connect the seed crystal to the pulling mechanism through a connecting part.

[0040] Since the existing fine seed crystals are pulled by seeding and shouldering to make the pulled crystal rod reach a predetermined diameter, in this process, the crystal flower of the seed crystal starts to grow from the middle to both sides, and the diameter of the crystal rod in the shouldering process does not increase uniformly, so the crystal flower is also uneven in the horizontal direction; while the seed crystal of the present invention has a diameter consistent with the diameter of the polycrystalline silicon rod to be pulled, so the seeding and shouldering processes are omitted, and the seed crystal will only grow downward in the welding process, and its crystal flower in the horizontal direction is fixed, that is, the crystal flower of the seed crystal is maintained, and the crystal rod grows downward along the crystal flower, so that the crystal flower of the polycrystalline silicon rod is always uniform and consistent with the crystal flower of the seed crystal. Therefore, the polycrystalline silicon rod pulled by the seed crystal of the present invention is a columnar polycrystalline without inclusions, a polycrystalline silicon rod with uniform crystal flower distribution in the horizontal direction, and has a higher pulling efficiency than the conical fine seed crystal, omitting the shouldering process, and improving the qualified rate.

[0041] Furthermore, the bottom of the seed crystal of the present invention is designed as a convex arc surface. Due to the radial temperature gradient, the temperature in the center is the lowest and the temperature around is high. If the bottom of the seed crystal is a plane, the middle of the seed crystal is cool, and the temperature around it suddenly rises, causing the seed crystal to be easily broken due to thermal expansion and contraction. Therefore, it is designed as a convex arc surface, so that during the welding process, the arc surface of the seed crystal can be gradually melted, gradually from the center to both sides, so that the seed crystal is heated evenly, and the large surface is prevented from being directly contacted and broken. The middle part is designed as a conical slope, and the downward gravity of the crystal rod is dispersed by the design of the slope, so as to prevent the seed crystal from falling off due to shaking during the crystal pulling process; and the height of the conical slope is also designed to a certain extent. If it is too low, the thickness of the middle connecting part will be reduced, affecting the tensile strength of the seed crystal. If it is too high, the weight of the seed crystal will be increased, thereby affecting the control of the seed crystal lifting and rotation by the pulling mechanism. Therefore, the conical slope needs to select a suitable height to increase the height between the clamping part and the silicon liquid level, so that the clamping part and the connecting part maintain a certain distance from the silicon liquid to prevent the clamping part and the connecting part from being burned during the welding process. In some embodiments, the seed crystal head is made of polycrystalline silicon material with uniform crystal flowers and low impurities.

[0042] For further information, see Figure 3 The clamping part includes an upper clamping part 131 and a lower clamping part 132. An annular groove 133 is provided between the upper clamping part 131 and the lower clamping part 132. Positioning slots 134 are provided on both sides of the lower clamping part 132. The annular groove is to ensure that the seed crystal will not fall during the crystal pulling process. The positioning slot is to cooperate with the clamping ring boss on the seed crystal clamping ring to ensure that the seed crystal can rotate in the same direction and speed as the central axis during the crystal pulling process.

[0043] For further information, see Figure 5 The seed crystal for drawing a columnar polycrystalline silicon rod of the present invention also includes a connecting portion, which includes two seed crystal clamping rings 20, a seed crystal connecting rod 30, and a seed crystal fixing sleeve 40. The lower parts of the two seed crystal clamping rings 20 are assembled and connected with the seed crystal head 10, and the upper parts of the two seed crystal clamping rings 20 are assembled and connected with the lower parts of the seed crystal connecting rod 30. The upper part of the seed crystal connecting rod 30 is connected with the polycrystalline weight 50, so as to connect the seed crystal to the pulling mechanism through the polycrystalline weight 50 and the seed crystal rope hook 60. The seed crystal fixing sleeve 40 is sleeved on the seed crystal clamping ring 20 to fix the seed crystal clamping ring to the seed crystal connecting rod. Among them, the seed crystal clamping ring, the seed crystal connecting rod and the seed crystal fixing sleeve can be made of a material that is resistant to high temperature and does not produce metal pollution, such as graphite.

[0044] Further, please also see Figures 6 to 9The seed crystal clamping ring 20 includes an upper part and a lower part. The upper part is provided with a first assembly groove 21, which is used to assemble with the seed crystal connecting rod 30; the lower part is provided with a second assembly groove 22, which is used to assemble with the clamping part, and a clamping ring boss 24 is provided at the bottom of the lower part. Specifically, the shape of the second assembly groove 22 matches the shape of the upper clamping part 131 and the annular groove 133 of the clamping part, so as to be assembled with the clamping part 13 through the second assembly groove 22. The clamping ring boss 24 cooperates with the positioning groove 134 of the seed crystal head clamping part to play the role of connecting the seed crystal connecting rod and the seed crystal head up and down. In addition, there is a certain thickness between the first assembly groove 21 and the second assembly groove 22. This is because the crystal rod is pulled out to weigh several hundred kilograms, and a certain thickness is used to enhance the tensile strength of the seed crystal clamping ring to prevent the seed crystal clamping ring from cracking in the middle.

[0045] Further, please also see Figure 5 , Figures 10 to 12 The upper part of the seed crystal connecting rod 30 is hollow inside and is processed with screw threads to fit with the threads of the polycrystalline weight 50 for assembly. The polycrystalline weight 50 is a standard part in the single crystal furnace. When pulling crystals, the rotation of the weight can drive the seed crystal clamp ring and the seed crystal head to rotate in turn. The bottom of the seed crystal connecting rod is provided with an assembly portion 31 and a positioning block 32. The assembly portion 31 is used to assemble with the first assembly groove 21 of the seed crystal clamp ring 20, and the positioning block 32 is used to assemble with the positioning port 23 of the seed crystal clamp ring 20 to locate the assembly position of the seed crystal connecting rod 30. The length of the seed crystal connecting rod can be designed according to the initial height of the seed crystal required when pulling crystals in the single crystal furnace.

[0046] In some embodiments, see Fig.10 The upper part of the seed crystal connecting rod 30 is also provided with an air hole 33. Since the upper part of the seed crystal connecting rod 30 cooperates with the polycrystalline weight 50, the two are made of different materials, have different heating rates, and different expansion coefficients, water vapor will be generated during the crystal pulling process as the temperature rises, causing thermal expansion, resulting in internal explosion. Therefore, the air hole 33 is designed to release the gas inside the seed crystal connecting rod, thereby releasing the internal stress and preventing the seed crystal connecting rod from bursting.

[0047] Further, please also see Figure 13 to Figure 14 , the upper diameter of the seed crystal fixing sleeve 40 is smaller than the lower diameter, and the inner wall is tapered. After the seed crystal connecting rod 30 and the seed crystal head 10 are assembled through the seed crystal clamping ring 20, the seed crystal clamping ring 20 is movable, so the seed crystal fixing sleeve 40 needs to be inserted from top to bottom to tighten the seed crystal clamping ring 20. In addition, the upper diameter of the seed crystal fixing sleeve 40 is smaller than the lower diameter, and the inner wall is tapered, which can ensure that the seed crystal fixing sleeve 40 will not loosen and fall due to vibration during the crystal pulling process.

[0048] A method for processing a seed crystal head for drawing a columnar polycrystalline silicon rod comprises the following steps: S1. Select a polycrystalline silicon rod with a preset diameter for cutting to obtain a cylindrical silicon ingot with a preset height, and grind the cylindrical silicon ingot flat so that the parallelism and flatness of the upper and lower planes of the cylindrical silicon ingot are within 0.08 mm; S2, processing the clamping part and the middle part of the seed crystal head on the cylindrical silicon ingot; S3. A turntable is used to process a convex arc surface at the bottom of a cylindrical silicon ingot.

[0049] Specifically, a polysilicon rod with a preset diameter is selected, and the silicon rod is cut by a diamond wire cutter to obtain a cylindrical silicon ingot with a preset height. Among them, the polysilicon rod should be a polysilicon rod with uniform crystals and less impurities. The preset diameter refers to the diameter consistent with the diameter of the polysilicon rod to be pulled, thereby saving the shoulder placement and shoulder rotation processes, shortening the crystal pulling process cycle, and improving the crystal pulling efficiency. The preset height is 55-75mm.

[0050] After the cutting is completed, the cylindrical silicon ingot is flat-ground so that the parallelism and flatness of the upper and lower planes of the cylindrical silicon ingot are maintained within 0.08 mm, which is convenient for subsequent processing. The clamping part and the middle features of the seed crystal head are processed on the cylindrical silicon ingot, and the convex arc surface is processed at the bottom of the cylindrical silicon ingot, thereby completing the processing of the seed crystal head. The polycrystalline silicon rod drawn by the seed crystal head of the present invention is a columnar polycrystalline and inclusion-free polycrystalline silicon rod with uniform crystal flower distribution in the horizontal direction, and the drawing efficiency is higher than that of the conical fine seed crystal, eliminating the shoulder release process and improving the qualified rate.

[0051] In the specific implementation process, the following steps are used to process the clamping part and the middle part of the seed crystal head on the cylindrical silicon ingot: S21, using a turntable to perform multiple roughing of the cylindrical silicon ingot; S22, performing external feature finishing on a cylindrical silicon ingot using a rotary table; S23, machining an annular groove on the cylindrical silicon ingot using a turntable; S24. Processing positioning slots on the cylindrical silicon ingot.

[0052] Since the bottom of the polycrystalline seed crystal head is a convex arc surface, the seed crystal head assembly part, that is, the clamping part and the middle part of the seed crystal head, is processed first. First, the approximate shape of the clamping part and the middle part needs to be processed (such as Fig.15 The structure shown in the figure) is then finely processed into the annular groove and the positioning groove to complete the processing of the clamping part and the middle part.

[0053] In some embodiments, when machining the approximate shape of the clamping portion and the middle portion, due to the large amount of grinding, multiple roughing operations are required to achieve the finishing conditions. The cylindrical silicon ingot is roughed multiple times using a turntable, including preliminary roughing and secondary roughing. Specifically, preliminary roughing is performed first. In order to ensure machining efficiency, a turntable is used in conjunction with a machining center for machining. The cylindrical silicon ingot is first bonded to the adapter plate with yellow wax, and the adapter plate is clamped on the work platform through negative pressure suction on the turntable. The adapter plate can be a silicon circular wafer that is easily obtained on site and is made of the same material as the seed crystal, or a quartz plate, which is not limited here. Secondly, use a metal-based diamond tool with a diameter of 60-80mm, a grinding thickness of 8-10mm, and a mesh of 100-150 to roughen the shape. The turntable speed is 200-250 rpm, the tool is fed vertically downward, the radial feed is 100-200mm / min, the axial feed is 1-1.5mm / min, and the speed is 3500-4500 rpm.

[0054] Then carry out secondary roughing, use the metal matrix diamond tool with diameter of 60-80mm, grinding thickness of 8-10mm, 100-150 mesh to roughen the shape, the turntable speed is 200-250 rpm, the vertical downward feed method is adopted, the radial feed is 100-200mm / min, the axial feed is 1-1.5mm / min, and the speed is 3500-4500 rpm.

[0055] In some embodiments, finishing the external features of a cylindrical silicon ingot using a turntable includes: using a metal-based diamond tool with a diameter of 30-40 mm, a grinding thickness of 8-10 mm, and a mesh size of 200-300 to roughen the shape, the turntable speed is 200-250 rpm, the tool adopts a vertical downward feed method, the radial feed is 500-100 mm / min, the axial feed is 2-3 mm / min, and the rotation speed is 5500-6500 rpm.

[0056] In the specific implementation process, the use of a turntable to machine an annular groove on a cylindrical silicon ingot includes: using a metal-based diamond T-shaped tool with a diameter of 80-100mm, a grinding thickness of 8-10mm, and a mesh of 100-200 to machine the annular groove, the turntable speed is 200-250 rpm, the tool adopts a horizontal feed mode, radial feed 1-2mm / min, axial feed 200-300mm / min, and the speed is 2500-3500 rpm. After the processing is completed, the following is obtained Fig.16 The structure shown.

[0057] In the specific implementation process, the following steps are used to process the positioning slot on the cylindrical silicon ingot: a. Use yellow wax to bond the cylindrical silicon ingot to the quartz plate, and clamp the quartz plate on the working platform; since the positioning slots on both sides cannot be processed on the turntable, it is necessary to use yellow wax to bond it to the quartz plate and use a fixed processing method.

[0058] b. Use a tool with a diameter of 10-15mm, a grinding thickness of 8-10mm, and a mesh of 200-300 to process the positioning slot. The tool adopts a horizontal feed mode, a radial feed of 1000-1500mm / min, an axial feed of 200-500mm / min, a down-cut step of 0.03-0.05mm, and a rotation speed of 6500-7500 rpm. After the processing is completed, the following is obtained Fig.17 The structure shown.

[0059] In a specific implementation process, the arc surface is processed at the bottom of the cylindrical silicon ingot by using a turntable, including the following steps: S31, using yellow wax to bond the cylindrical silicon ingot to the adapter plate, and clamping the adapter plate on the working platform through negative pressure suction of the turntable; S32, roughening the bottom of the cylindrical silicon ingot step by step for multiple times; S33, after roughing, fine machining is performed to obtain a convex arc surface.

[0060] Specifically, the protruding arc surface is processed at the bottom of the cylindrical silicon ingot. Due to the large amount of grinding, three steps of roughening are required to achieve the finishing conditions. First, the cylindrical silicon ingot is bonded to the adapter plate with yellow wax, and the adapter plate is clamped on the work platform by the negative pressure suction of the turntable, wherein the adapter plate can be a silicon circular sheet. The multiple steps of roughening the bottom of the cylindrical silicon ingot include: using a metal-based diamond tool with a diameter of 60-80mm, a grinding thickness of 8-10mm, and 100-150 mesh to roughen the shape, and the turntable speed is 200-250 rpm. The tool adopts a vertical downward feed method, with a radial feed of 100-200mm / min, an axial feed of 0.8-1.2mm / min, and a rotation speed of 3500-4500 rpm. The tools and parameters used for the three steps of roughening are the same. After the first roughening, the following is obtained. Fig.18 The structure shown in the figure is obtained after the second roughing. Fig.19 The structure shown in the figure is obtained after the third roughing. Fig. 20 The structure shown.

[0061] After roughing, fine machining is performed to obtain a convex arc surface, including: using a metal-based diamond tool with a diameter of 30-40mm, a grinding thickness of 8-10mm, and a mesh of 200-300 to roughen the shape, the rotary table speed is 200-250 rpm, the tool adopts a vertical downward feed method, radial feed 500-100mm / min, axial feed 2-3mm / min, and speed 5500-6500 rpm. After fine machining, the following is obtained Fig.21 The convex arc surface shown is formed, thereby completing the processing of the bottom of the seed crystal head and obtaining a complete seed crystal head.

[0062] In some embodiments, after the convex arc surface of the bottom is processed, the seed crystal head can be cleaned and etched to remove dirt and mechanical damage on the surface after processing.

[0063] What is disclosed above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A seed crystal for drawing a columnar polycrystalline silicon rod, characterized in that: It includes a seed crystal head, which is made of polycrystalline silicon material with uniform crystal flowers. The seed crystal head includes a bottom, a middle part and a clamping part from bottom to top. The bottom is designed to be a convex arc surface, the middle part is designed to be a conical slope, and the bottom diameter of the conical slope is consistent with the diameter of the polycrystalline silicon rod to be drawn. The clamping part is used to connect the seed crystal to the pulling mechanism through the connecting part.

2. The seed crystal for pulling a columnar polycrystalline silicon rod according to claim 1, characterized in that: The clamping part comprises an upper clamping part and a lower clamping part, an annular groove is provided between the upper clamping part and the lower clamping part, and positioning slots are provided on two opposite sides of the lower clamping part.

3. The seed crystal for pulling a columnar polycrystalline silicon rod according to claim 1, characterized in that: It also includes a connecting part, which includes two seed crystal clamping rings, a seed crystal connecting rod, and a seed crystal fixing sleeve. The lower parts of the two seed crystal clamping rings are assembled and connected to the seed crystal head, and the upper parts of the two seed crystal clamping rings are assembled and connected to the lower parts of the seed crystal connecting rods. The upper part of the seed crystal connecting rod is connected to a polycrystalline weight, so that the seed crystal is connected to the pulling mechanism through the polycrystalline weight and the seed crystal rope hook.

4. The seed crystal for pulling a columnar polycrystalline silicon rod according to claim 3, characterized in that: The seed crystal retaining ring includes an upper part and a lower part, the upper part is provided with a first assembly groove, the first assembly groove is used to assemble with the seed crystal connecting rod; the lower part is provided with a second assembly groove, the second assembly groove is used to assemble with the clamping part, and a retaining ring boss is provided at the bottom of the lower part.

5. The seed crystal for pulling a columnar polycrystalline silicon rod according to claim 4, characterized in that: The upper circle diameter of the seed crystal fixing sleeve is smaller than the lower circle diameter, and the inner wall is conical.

6. A method for processing a seed crystal head for drawing a columnar polycrystalline silicon rod, characterized in that: The following steps are involved: S1. Select a polysilicon rod of a preset diameter for cutting to obtain a cylindrical silicon ingot of a preset height, and grind the cylindrical silicon ingot so that the parallelism and flatness of the upper and lower planes of the cylindrical silicon ingot are within 0.08 mm; S2, processing the clamping part and the middle part of the seed crystal head on the cylindrical silicon ingot; S3, using a turntable to process a convex arc surface at the bottom of the cylindrical silicon ingot.

7. The method for processing a seed crystal head for drawing a columnar polycrystalline silicon rod according to claim 6, characterized in that: In step S2, the following steps are used to process the clamping portion and the middle portion of the seed crystal head on the cylindrical silicon ingot: S21, roughening the cylindrical silicon ingot multiple times using a turntable; S22, performing external feature finishing on the cylindrical silicon ingot using a turntable; S23, machining an annular groove on the cylindrical silicon ingot using a turntable; S24, machining a positioning groove on the cylindrical silicon ingot.

8. The method for processing a seed crystal head for drawing a columnar polycrystalline silicon rod according to claim 7, characterized in that: In step S23, the annular groove is processed on the cylindrical silicon ingot using a turntable, including: using a metal-based diamond T-shaped tool with a diameter of 80-100 mm, a grinding thickness of 8-10 mm, and a mesh of 100-200 to process the annular groove, the turntable speed is 200-250 rpm, the tool adopts a horizontal feed mode, radial feed 1-2 mm / min, axial feed 200-300 mm / min, and the rotation speed is 2500-3500 rpm.

9. The method for processing a seed crystal head for drawing a columnar polycrystalline silicon rod according to claim 7, characterized in that: In step S24, the positioning slots are machined on the cylindrical silicon ingot by the following steps: a. Adhere the cylindrical silicon ingot to a quartz plate using yellow wax, and clamp the quartz plate on a working platform; b. Use a tool with a diameter of 10-15mm, a grinding thickness of 8-10mm, and a mesh of 200-300 to perform positioning slot processing. The tool adopts a horizontal feed method, with a radial feed of 1000-1500mm / min, an axial feed of 200-500mm / min, a down-cut step of 0.03-0.05mm, and a rotation speed of 6500-7500 rpm.

10. The method for processing a seed crystal head for drawing a columnar polycrystalline silicon rod according to claim 6, characterized in that: In step S3, machining a convex arc surface on the bottom of the cylindrical silicon ingot using a turntable includes the following steps: S31, using yellow wax to bond the cylindrical silicon ingot to the adapter plate, and clamping the adapter plate on the working platform through negative pressure suction of the turntable; S32, roughening the bottom of the cylindrical silicon ingot multiple times step by step; S33, after roughing, fine machining is performed to obtain a convex arc surface.

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