A method of directional solidification of polysilicon

Abstract

The application provides a polycrystalline silicon directional solidification method, which solves the problems of cell dislocation in polycrystalline silicon and the like, and comprises the following steps: S1: after a single crystal silicon wafer is pickled and impurities are removed, the single crystal silicon wafer is placed into a crucible, and then the crucible is placed into a melting furnace to be heated, melted and kept stationary; S2: the bottom of the crucible is rapidly cooled to make the bottom silicon liquid rapidly condense; S3: the crucible is pulled down to make the silicon liquid uniformly crystallize; S4: a blowing device is started, and the temperature of the silicon ingot rapidly drops; S4: the melting furnace is heated and kept at a constant temperature, and then the temperature slowly drops; and S5: the silicon ingot is taken out and naturally cooled. The application has the advantages of high crystallization quality, elimination of layering defects and the like.

Description

Technical Field

[0001] This invention belongs to the field of polycrystalline silicon production technology, specifically relating to a method for directional solidification of polycrystalline silicon. Background Technology

[0002] Polycrystalline silicon is a form of elemental silicon. When molten elemental silicon solidifies under supercooled conditions, silicon atoms arrange themselves into numerous crystal nuclei in a diamond lattice. If these nuclei grow into grains with different crystal orientations, these grains combine to crystallize into polycrystalline silicon. Currently, most polycrystalline silicon production involves smelting and purifying quartz sand in an electric arc furnace to produce industrial silicon, which is then further processed and purified to obtain polycrystalline silicon. However, directly producing polycrystalline silicon from quartz sand is costly, while recycling single-crystal silicon waste can significantly reduce the difficulty of polycrystalline silicon purification, thereby lowering production costs. However, in actual production, the silicon melt solidifies under supercooled conditions, resulting in significant residual stress and a tendency to fracture. Furthermore, when annealing is used to eliminate residual stress within the silicon ingot, the buffer time within the furnace heating mechanism and the large temperature differences between the inside and outside, as well as between the top and bottom of the ingot, lead to cell misalignment and, consequently, delamination defects.

[0003] To address the shortcomings of existing technologies, people have conducted long-term explorations and proposed various solutions. For example, Chinese patent literature discloses a method for rapid solidification of polycrystalline silicon [201310533033.8], which includes the steps of material preparation, melting, and solidification. The solidification step is carried out as follows: the molten silicon placed in the polycrystalline silicon reverse solidification device is directionally solidified, and solidification is stopped when the volume of the remaining molten silicon is 1% to 25% of the initial volume; a water-cooled copper plate with a temperature of 0 to 500°C is brought into contact with the remaining molten silicon until the remaining molten silicon solidifies.

[0004] The above solution has solved the problem of residual internal stress in silicon ingots to some extent, but it still has many shortcomings, such as slow annealing response rate leading to cell dislocation. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned problems by providing a rationally designed method for the directional solidification of polycrystalline silicon that effectively reduces cell dislocation.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for directional solidification of polycrystalline silicon, comprising the following steps:

[0007] S1: After the single crystal silicon wafer is acid-washed and impurities removed, it is placed in a crucible, then placed in a melting furnace for heating and melting, and kept still;

[0008] S2: Rapid cooling of the bottom of the crucible causes the molten silicon at the bottom to solidify rapidly;

[0009] S3: Pulling the crucible down causes the silicon liquid to crystallize at a uniform rate;

[0010] S4: The blowing device starts, and the temperature of the silicon ingot drops rapidly;

[0011] S4: The melting furnace heats up and maintains a constant temperature, then the temperature slowly decreases;

[0012] S5: Remove the silicon ingot and allow it to cool naturally. After the silicon melts, it solidifies rapidly, and then the silicon crystals grow at a uniform rate. When the temperature is lower than the preset value, the temperature is rapidly increased to eliminate internal stress and ensure that the temperature inside and outside the silicon ingot tends to be consistent, thereby reducing cell dislocation and eliminating stacking defects.

[0013] In the aforementioned method for directional solidification of polycrystalline silicon, the melting circuit temperature is heated to 1550℃ in step S1; the crucible bottom temperature is lowered to 1380℃ in step S2 until 3cm of solidification occurs at the bottom of the crucible; the silicon melt crystallization rate is maintained at 0.8-1cm / m in step S3; and the melting furnace temperature is raised back to 1100℃ in step S4. The initial solidification at the bottom of the crucible helps reduce impurities inside the silicon ingot, and the temperature difference between the inside of the melting furnace and the center of the silicon ingot is linear, avoiding crystallization misalignment caused by excessive temperature differences.

[0014] In the aforementioned method for directional solidification of polycrystalline silicon, the melting furnace includes a heating mechanism and a lifting mechanism that moves the crucible up and down. A cooling mechanism is installed at the upper end of the lifting mechanism, opposite to the bottom of the crucible. An insulation mechanism is provided on the inner wall of the melting furnace, opposite to the side of the crucible. The internal lifting mechanism within the melting furnace facilitates the removal of the silicon ingot and allows for slow demolding and cooling of the ingot during the lifting process, ensuring crystallization stability.

[0015] In the aforementioned method for directional solidification of polycrystalline silicon, the heating mechanism includes a clamping mechanism positioned at the top of the melting furnace. This clamping mechanism clamps and fixes an electrode rod opposite to the upper end of the crucible, and a stirring mechanism is positioned at the lower end of the crucible. The clamping mechanism includes a clamping cylinder positioned at the top of the melting furnace, with a clamping cavity inside the cylinder opposite to the interior of the melting furnace. Electrode grippers are installed inside the clamping cylinder, and these grippers are connected to the clamping cylinder via a lifting screw. A lifting limit mechanism is provided between the electrode grippers and the clamping cylinder. The lifting limit mechanism includes a limit groove located inside the clamping cylinder, and the electrode grippers have limit strips that slide in connection with the limit groove. The stirring mechanism includes a rotating disk mounted at the bottom of the crucible and in contact with it. The rotating disk is rotatably mounted on a fixed disk, and an inductive circuit is provided between the rotating disk and the fixed disk to drive the rotating disk to rotate when energized. The heating mechanism uses electric arc heating, which has a high heat conversion rate. During the silicon wafer melting process, the bottom stirring mechanism can accelerate heat transfer and improve the silicon ingot melting efficiency.

[0016] In the aforementioned method for directional solidification of polycrystalline silicon, the lifting mechanism includes a lifting base that seals the lower end of the melting furnace. A lifting mechanism is provided between the lower end of the lifting base and the ground, and a sealing mechanism is provided between the lifting base and the melting furnace. The lifting mechanism includes a lifting guide rail installed parallel to the ground, a lifting slider slidably mounted on the lifting guide rail, a lifting rod rotatably mounted between the lifting slider and the lifting base, a lifting screw provided between the lifting slider and the lifting guide rail, and the lifting base and the melting furnace being slidably connected to a limiting column vertically fixed to the ground via limiting sleeves. The sealing mechanism includes a sealing edge surrounding the circumference of the lifting base, an arc-shaped sealing surface provided on the inner side of the sealing edge, a sealing strip provided at the lower end of the melting furnace, the sealing strip having an arc-shaped sealing surface that fits and presses tightly against the sealing edge, and a one-to-one corresponding sealing groove between the sealing edge and the sealing strip, the sealing groove being filled with a corrugated metal gasket. The lifting mechanism and its internal lifting mechanism limit the lifting base and melting furnace, ensuring that their central axes match and ensuring the sealing effect after closure.

[0017] In the aforementioned method for directional solidification of polycrystalline silicon, the cooling mechanism includes a grid-structured cooling frame with a cooling copper plate fixed to its upper end. Coiled cooling copper tubes, attached to the cooling copper plate, are installed inside the cooling frame. An external blowing device connects to the cooling copper tubes. A separation assembly is positioned between the cooling copper plate and the cooling copper tubes. The cooling copper tubes are annular and their centers are aligned. The separation assembly includes a separation ring circumferentially surrounding the outer side of the cooling copper tubes. A centrally symmetrical separation support rod is rotatably connected between the separation ring and the center of the cooling frame. The separation support rod is slidably connected to the cooling copper tubes via a cross-shaped adapter sleeve. A balancing assembly is provided between the cross-shaped adapter sleeve and the cooling frame. The separation ring is connected to an electric telescopic rod via a separation pull rod. This cooling mechanism achieves stepped cooling at the bottom of the crucible, enabling rapid solidification of impurities deposited at the bottom and improving the quality of silicon ingot casting. The adjustable cooling copper tubes maintain a consistent solidification rate at the bottom center and outer side of the silicon ingot, effectively reducing crystal growth misalignment.

[0018] In the aforementioned method for directional solidification of polycrystalline silicon, the cross-shaped adapter sleeve includes a horizontal sleeve through which a cooling copper tube passes and is rotatably connected to the cooling copper tube. A vertical sleeve, arranged perpendicularly to the horizontal sleeve, is located in the middle of the horizontal sleeve. The vertical sleeve is slidably connected to a separation support rod. Cooling copper tubes are connected to cooling copper sheets that adhere to cooling copper plates. An elastic reset element is provided between the cooling copper tube and the cooling frame. The balancing assembly includes a balance plate vertically arranged within the cooling frame with an L-shaped cross-section. The balance plate is symmetrical about the center of the cross-shaped adapter sleeve, and its sides respectively adhere to and abut against the horizontal and vertical sleeves of the cross-shaped adapter sleeve. The cross-shaped adapter sleeve enables the transmission connection between the cooling copper tube and the separation support rod, thereby guiding the cooling copper sheets on each cooling copper tube to adhere to the cooling copper plate one by one.

[0019] In the aforementioned method for directional solidification of polycrystalline silicon, the heat insulation mechanism includes an aluminum silicate fiber layer covering the inner side of the melting furnace, a rock wool layer inside the melting furnace, a protective cover outside the melting furnace, a vacuum layer between the protective cover and the melting furnace, and a heat buffer assembly inside the melting furnace. The heat insulation mechanism improves the heat preservation effect of the melting furnace, effectively reducing heat loss, and the equipped heat buffer assembly provides some of the heat required for annealing.

[0020] In the aforementioned method for directional solidification of polycrystalline silicon, the heat buffer assembly includes a heat buffer plate disposed inside the melting furnace. Isolation fins covering the heat buffer plate are disposed inside the melting furnace. The isolation fins are connected to a linkage motor via a linkage bracket. The isolation fins have outwardly extending isolation cover plates that fit against the inner wall of the melting furnace. The opening and closing of the isolation fins temporarily stores heat, shortening the heating time required during the heating and annealing process in conjunction with the heating mechanism, and extending the cooling time during the secondary cooling process to ensure sufficient release of internal stress in the silicon ingot.

[0021] In the aforementioned method for directional solidification of polycrystalline silicon, the crucible is made of quartz and is square or cylindrical. A circumferential demolding edge is provided at the top of the crucible, and reinforcing ribs are provided between the demolding edge and the outer side of the crucible. A demolding flap, which fits against the lower end of the demolding edge, is provided inside the melting furnace. The demolding flap is connected to a demolding motor via a transmission gear set. The crucible separates from the silicon ingot using the weight of the lifting mechanism, eliminating the need for manual demolding.

[0022] Compared with existing technologies, the advantages of this invention are as follows: after the silicon ingot crystallization is completed, annealing is performed to eliminate internal stress, the temperature inside and outside the silicon ingot tends to be uniform and the cooling time is extended, thereby effectively reducing cell dislocation; the melting furnace used for silicon wafer melting adopts electric arc heating, which has a high heat conversion rate and heating response rate, ensuring the production efficiency of polycrystalline silicon; the lifting mechanism realizes the automatic demolding of crucible and silicon ingot while the melting furnace is opened and closed, improving the production efficiency of silicon ingot. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the method principle of the present invention;

[0024] Figure 2 This is a schematic diagram of the structure of the melting furnace of the present invention;

[0025] Figure 3 This is a schematic diagram of the heating mechanism of the present invention;

[0026] Figure 4 This is a partial cross-sectional view of the melting furnace of the present invention;

[0027] Figure 5 This is a structural cross-sectional view of the cooling mechanism of the present invention;

[0028] Figure 6 This is a cross-sectional view of the heat caching component of the present invention;

[0029] In the diagram, the components are: crucible 1, demolding edge 11, reinforcing rib 12, demolding flap 13, transmission gear set 14, demolding motor 15, melting furnace 2, sealing strip 21, blowing device 3, heating mechanism 4, electrode rod 41, clamping cylinder 42, clamping cavity 43, electrode gripper 44, lifting screw 45, limiting groove 46, limiting strip 47, rotating disk 48, fixed disk 49, lifting mechanism 5, lifting base 51, lifting guide rail 52, lifting slider 53, lifting rod 54, lifting screw 55, limiting sleeve 56, limiting column 57, sealing edge 58, and sealing surface. 59. Sealing groove 591. Metal gasket 592. Cooling mechanism 6. Cooling frame 61. Cooling copper plate 62. Cooling copper pipe 63. Separation ring 64. Separation support rod 65. Cross adapter sleeve 66. Horizontal sleeve 661. Vertical sleeve 662. Cooling copper sheet 663. Separation pull rod 67. Electric telescopic rod 68. Balance plate 69. Heat insulation mechanism 7. Aluminum silicate fiber layer 71. Rock wool interlayer 72. Protective cover 73. Vacuum layer 74. Heat buffer assembly 8. Heat buffer plate 81. Isolation fins 82. Linkage bracket 83. Linkage motor 84. Isolation cover plate 85. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0031] like Figure 1 As shown, a method for directional solidification of polycrystalline silicon includes the following steps:

[0032] S1: After the monocrystalline silicon wafers are acid-washed and impurities removed, they are placed in crucible 1, then placed in melting furnace 2 for heating and melting, and kept still; the collected monocrystalline silicon wafers need to be crushed and acid-washed to remove impurities before they can be smelted. During the process of placing them into crucible 1, a small piece of monocrystalline silicon wafer is placed in the center of crucible 1, and a large piece of monocrystalline silicon wafer is placed near the side wall of crucible 1 with the gaps filled with silicon powder. The upper end of crucible 1 is open and faces the electric arc device inside melting furnace 2.

[0033] S2: After the silicon crystal inside crucible 1 is completely melted, heating is stopped and the crucible is kept warm. After standing for a period of time, the suspended metal or non-metal impurities inside are deposited at the bottom. Then the bottom of crucible 1 is rapidly cooled, causing the bottom silicon liquid to solidify quickly. The final silicon ingot product needs to have its bottom layer cut off.

[0034] S3: The downward pull of crucible 1 causes the silicon liquid to crystallize at a uniform speed. At the same time, crucible 1 and silicon ingot are separated. After the silicon ingot and crucible 1 are taken out in sequence, the silicon ingot is put back into the melting furnace 2 for the next annealing process.

[0035] S4: After the melting furnace 2 is resealed, the blowing device 3 is started, and the inert gas introduced causes the surface temperature of the silicon ingot to drop rapidly.

[0036] S4: The melting furnace 2 heats the surface of the silicon ingot and keeps the temperature constant, thereby fully releasing the internal residual stress. Then the temperature is slowly reduced to room temperature to avoid internal crystal misalignment.

[0037] S5: Remove the silicon ingot and allow it to cool naturally before encapsulation.

[0038] Specifically, the melting point of elemental silicon is 1410℃. Since the main component of the recycled single-crystal silicon wafer is elemental silicon, the melting temperature in step S1 only needs to be raised to 1550℃ until it is completely melted. In step S2, the temperature at the bottom of crucible 1 is lowered to 1380℃ to solidify until a 3cm thick bottom layer solidifies at the bottom of crucible 1. In step S3, the silicon melt is kept at a crystallization rate of 0.8-1cm / m by controlling the internal temperature of melting furnace 2. During annealing, in step S4, the temperature of melting furnace 2 is raised back to 1100℃, and the active free silicon inside the silicon ingot completely releases the internal stress.

[0039] like Figure 3 As shown, the melting furnace 2 has a built-in heating mechanism 4, which uses electric arc heating to shorten the preheating time inside the melting furnace 2 and has a high heat conversion rate. The melting furnace 2 is also equipped with a lifting mechanism 5 that drives the crucible 1 to move up and down, realizing the opening and closing of the melting furnace 2 and the internal material replacement. The upper end of the lifting mechanism 5 is equipped with a cooling mechanism 6 opposite to the bottom of the crucible 1 to achieve supercooling of the bottom of the crucible 1 to generate polycrystalline silicon, with only silicon crystals growing from the bottom upwards. The inner wall of the melting furnace 2 is provided with a heat insulation mechanism 7 opposite to the side of the crucible 1 to play a role in heat preservation, reducing heat loss and improving heat utilization.

[0040] Furthermore, unlike conventional fixed electric arc heating devices, this heating mechanism 4 includes a clamping mechanism located at the top of the melting furnace 2. The clamping mechanism clamps and fixes an electrode rod 41 opposite to the upper end of the crucible 1. The electrode rod 41 can be detached, its specifications adjusted, or replaced, or its relative distance to the crucible 1 can be adjusted. A stirring mechanism is provided at the lower end of the crucible 1 to adjust the orientation of the crucible 1 relative to the melting furnace 2, causing the molten silicon inside the crucible 1 to sway slightly, thus fully expelling air bubbles from the molten silicon.

[0041] The clamping mechanism includes a clamping cylinder 42 disposed on top of the melting furnace 2 for receiving electrode rods 41. The clamping cylinder 42 has a clamping cavity 43 located inside the melting furnace 2, allowing the electrode rods 41 to be completely received within the clamping cavity 43. Electrode grippers 44 are installed inside the clamping cylinder 42. The electrode grippers 44 open and close to clamp and fix the electrode rods 41, maintaining a distance between adjacent electrode rods 41 to allow for discharge space. The electrode gripper 44 is connected to the clamping cylinder 42 via a lifting screw 45. A lifting limit mechanism is provided between the electrode gripper 44 and the clamping cylinder 42 to ensure that the electrode gripper 44 always moves vertically. The lifting limit mechanism includes a limit groove 46 located inside the clamping cylinder 42. The electrode gripper 44 has a limit strip 47 that slides with the limit groove 46. The electrode rod 41 is within the range of motion of the limit groove 46 and the limit strip 47, preventing the electrode rod 41 from being directly inserted into the silicon material. The stirring mechanism includes a rotating disk 48 installed at the bottom of the crucible 1 and attached to it. The rotating disk 48 is rotatably mounted on a fixed disk 49. An inductive circuit is provided between the rotating disk 48 and the fixed disk 49 to drive the rotating disk 48 to rotate when energized. When the inductive circuit is energized, the rotating disk 48 causes the crucible 1 and its internal silicon liquid to deflect periodically, allowing the silicon wafer to fully settle and melt.

[0042] Furthermore, the lifting mechanism 5 includes a lifting base 51 that seals the lower end of the melting furnace 2, completely enclosing the interior of the melting furnace 2. A lifting mechanism is provided between the lower end of the lifting base 51 and the ground to enable the vertical lifting of the lifting base 51, thereby opening and closing the melting furnace 2 or completely separating it from the lifting base 51. After separation, a large inlet and outlet are left to facilitate the entry and exit of silicon ingots. A sealing mechanism is provided between the lifting base 51 and the melting furnace 2, which works in conjunction with the lifting mechanism to ensure a tight seal at the joint between the lifting base 51 and the melting furnace 2. After the interior of the melting furnace 2 is completely sealed, a vacuum is drawn and inert gas is introduced. Then, the heating mechanism 4 is activated to melt the silicon material. The inert gas is circulated into the melting furnace 2 through an external cooling system to promote silicon liquid crystallization.

[0043] like Figure 2 As shown, the lifting mechanism includes lifting guide rails 52 installed parallel to the ground. Multiple lifting guide rails 52 are installed side-by-side, and lifting sliders 53 are slidably mounted on each of the lifting guide rails 52. Lifting rods 54 are rotatably mounted between the lifting sliders 53 and the lifting base 51. A lifting screw 55 is provided between the lifting sliders 53 and the lifting guide rails 52. The lifting rod 54 rotates crosswise with the lifting screw 55, driving the lifting base 51 to rise and fall vertically, while simultaneously providing good support for the lifting base 51, keeping it in a horizontal position. The lifting base 51 and the melting furnace 2 are slidably connected to a limiting column 57 vertically fixed on the ground via a limiting sleeve 56. The limiting column 57 keeps the melting furnace 2 and the lifting base 51 on the same vertical axis. Figure 4As shown, the sealing mechanism includes a sealing edge 58 that surrounds the circumference of the lifting base 51. An arc-shaped sealing surface 59 is provided on the inner side of the sealing edge 58. A sealing strip 21 is provided at the lower end of the melting furnace 2. The sealing strip 21 has an arc-shaped sealing surface 59 that fits tightly against the sealing edge 58. Corresponding sealing grooves 591 are formed between the sealing edge 58 and the sealing strip 21, and the sealing grooves 591 are filled with corrugated metal gaskets 592. During the lifting process of the lifting base 51, the sealing surface 59 guides the sealing edge 58 and the sealing strip 21 to fit and press against each other. The metal gasket 592 replaces the conventional rubber sealing method and is less prone to deformation and failure when heated.

[0044] like Figure 5 As shown, the cooling mechanism 6 includes a cooling frame 61 with a grid structure and sufficient internal space for component installation. A cooling copper plate 62 is fixedly attached to the upper end of the cooling frame 61 to adhere to the bottom of the crucible 1, enabling rapid cooling of the bottom of the crucible 1 and rapid condensation of the molten silicon. Cooling copper pipes 63 are coiled inside the cooling frame 61 and adhere to the cooling copper plate 62. The cooling copper pipes 63 are connected to an external air blower 3 for circulating air intake, and can also be connected to an external water cooling device to further improve the cooling effect. A separation component is provided between the cooling copper plate 62 and the cooling copper pipes 63 to control the number and position of contact between the cooling copper pipes 63 and the cooling copper plate 62. The cooling copper pipes 63 are annular and their centers are aligned. The separation assembly includes a separation ring 64 that surrounds the outer side of the cooling copper pipes 63 circumferentially. A separation support rod 65, arranged symmetrically at the center, is rotatably connected between the separation ring 64 and the center of the cooling frame 61. The separation support rod 65 and the cooling copper pipes 63 are slidably connected via a cross-shaped adapter sleeve 66. A balancing assembly is provided between the cross-shaped adapter sleeve 66 and the cooling frame 61. The separation ring 64 is connected to an electric telescopic rod 68 via a separation pull rod 67. When the electric telescopic rod 68 drives the separation pull rod 67 to slide, the separation ring 64 rises and falls accordingly. The angle between the separation support rod 65, which is movably connected via the cross-shaped adapter sleeve 66, and the horizontal plane changes accordingly. The connected cooling copper pipes 63 rise and fall accordingly, contacting the cooling copper plates 62 one by one from the inside out or from the outside in.

[0045] Meanwhile, the cross-shaped adapter sleeve 66 is positioned between the separation support rod 65 and the cooling copper pipe 63 to serve as a transition point, without affecting the normal flow of fluid inside the cooling copper pipe 63. The cross-shaped adapter sleeve 66 includes a horizontal sleeve 661 through which the cooling copper pipe 63 passes and is rotatably connected to the cooling copper pipe 63. A vertical sleeve 662 is provided in the middle of the horizontal sleeve 661, which is perpendicular to the horizontal sleeve 661. The vertical sleeve 662 is slidably connected to the separation support rod 65. The cooling copper pipe 63 is connected to a cooling copper sheet 663 that is in contact with the cooling copper plate 62. The cooling copper sheet 663 has a certain degree of elasticity, and its deformation under pressure increases the heat exchange area between the cooling copper pipe 63 and the cooling copper plate 62. An elastic reset component is provided between the cooling copper pipe 63 and the cooling frame 61 to assist in the automatic reset of the cooling copper pipe 63. The balancing assembly includes a balance plate 69 with an L-shaped cross-section, which is vertically installed inside the cooling frame 61. The balance plate 69 is symmetrical about the center of the cross adapter sleeve 66, and its sides are respectively attached to and abut against the horizontal sleeve 661 and the vertical sleeve 662 of the cross adapter sleeve 66. The balance plate 69 clamps and fixes the cooling copper pipe 63 to ensure that the cooling copper pipe 63 can move vertically.

[0046] from Figure 2 As can be seen, the heat insulation mechanism 7 adopts a composite structure, including an aluminum silicate fiber layer 71 covering the inner side of the melting furnace 2, and a rock wool interlayer 72 inside the melting furnace 2. The rock wool interlayer 72 has gradually decreasing thermal conductivity to prevent heat loss and also has good heat resistance. A protective cover 73 is installed on the outside of the melting furnace 2, and a vacuum layer 74 is installed between the protective cover 73 and the melting furnace 2. The vacuum layer improves the protective performance of the protective cover 73 after pressure treatment. A heat buffer assembly 8 is installed inside the melting furnace 2 to improve heat utilization and meet the annealing temperature rise requirements of the protective cover 73.

[0047] like Figure 6 As shown, the heat buffer assembly 8 includes a heat buffer plate 81 disposed inside the melting furnace 2. The heat buffer plate 81 is typically made of a material with high specific heat capacity. The melting furnace 2 is equipped with insulating fins 82 that cover the heat buffer plate 81. When the insulating fins 82 are open, they continuously release heat; when they are closed, the heat is temporarily stored. The insulating fins 82 are connected to a linkage motor 84 via a linkage bracket 83. The linkage motor 84 controls the rapid opening and closing of the insulating fins 82, and the opening and closing time is flexibly adjusted in conjunction with a temperature sensor. An insulating cover plate 85 extending outwards and fitting against the inner wall of the melting furnace 2 around the insulating fins 82 improves the sealing effect of the insulating fins 82, preventing heat loss from the heat buffer plate 81 when the melting furnace 2 is opened.

[0048] Preferably, the crucible 1 is made of quartz and is square or cylindrical. A circumferential demolding edge 11 is provided at the upper end of the crucible 1, and reinforcing ribs 12 are provided between the demolding edge 11 and the outer side of the crucible 1 to provide overall structural strength. A demolding flap 13, which fits against the lower end of the demolding edge 11, is provided inside the melting furnace 2. When the demolding flap 13 swings to a horizontal position, it faces the lower end of the demolding edge 11, achieving demolding while the crucible 1 remains fixed and the silicon ingot falls. The demolding flap 13 is connected to the demolding motor 15 via a transmission gear set 14. During the flipping process, the demolding flap 13 will not collide with the demolding edge 11 and will have sufficient contact area with the lower end of the demolding edge 11.

[0049] In summary, the principle of this embodiment is as follows: after the silicon material inside the crucible 1 is completely melted, it is kept still. Then, the bottom is rapidly cooled to form a polycrystalline silicon layer. After that, the silicon liquid inside the crucible 1 gradually cools and crystallizes from bottom to top and from outside to inside. Then, the melting furnace 2 is heated and annealed to release the internal stress, and finally the finished silicon ingot is obtained.

[0050] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

[0051] Although this paper extensively uses crucible 1, demolding edge 11, reinforcing rib 12, demolding flap 13, transmission gear set 14, demolding motor 15, melting furnace 2, sealing strip 21, blowing device 3, heating mechanism 4, electrode rod 41, clamping cylinder 42, clamping cavity 43, electrode gripper 44, lifting screw 45, limiting groove 46, limiting strip 47, rotating disk 48, fixed disk 49, lifting mechanism 5, lifting base 51, lifting guide rail 52, lifting slider 53, lifting rod 54, lifting screw 55, limiting sleeve 56, limiting column 57, sealing edge 58, sealing surface 59, sealing groove The terms 591, 592, 6, 6, 7, 8, 9, 1, 1, 1, 1, 2, 3, 1, 1, 1, 1, 2, 1 ...

Claims

1. A method for directional solidification of polycrystalline silicon, characterized in that, Includes the following steps: S1: After the single crystal silicon wafer is acid-washed and impurities removed, it is placed in a crucible (1), and then placed in a melting furnace (2) for heating and melting while keeping it still; S2: Rapid cooling of the bottom of the crucible (1) causes the molten silicon at the bottom to solidify rapidly; S3: The crucible (1) is pulled down to make the silicon liquid crystallize at a uniform speed; S4: The blowing device (3) is started, and the temperature of the silicon ingot drops rapidly; S4: The melting furnace (2) is heated and kept at a constant temperature, and then the temperature slowly decreases; S5: Remove the silicon ingot and allow it to cool naturally; The melting furnace (2) includes a heating mechanism (4) and a lifting mechanism (5) that drives the crucible (1) to move up and down. The upper end of the lifting mechanism (5) is equipped with a cooling mechanism (6) that is opposite to the bottom of the crucible (1). The inner wall of the melting furnace (2) is provided with a heat insulation mechanism (7) that is opposite to the side of the crucible (1). The cooling mechanism (6) includes a cooling rack (61) with a grid structure. The upper end of the cooling rack (61) is attached and fixed with a cooling copper plate (62). The cooling rack (61) is equipped with a coiled arrangement that is connected to the cooling plate. A cooling copper pipe (63) is attached to a copper plate (62), and a blower (3) is connected to the cooling copper pipe (63). A separation assembly is provided between the cooling copper plate (62) and the cooling copper pipe (63). The cooling copper pipe (63) is annular and its center is aligned. The separation assembly includes a separation ring (64) that surrounds the outside of the cooling copper pipe (63) circumferentially. A separation support rod (65) is rotatably connected between the separation ring (64) and the center of the cooling frame (61) and is arranged in a centrally symmetrical manner. The separation support rod (65) and the cooling plate (62) are connected in a centrally symmetrical manner. The cooling copper pipe (63) is slidably connected via a cross-shaped adapter sleeve (66). A balancing assembly is provided between the cross-shaped adapter sleeve (66) and the cooling frame (61). The separation ring (64) is connected to the electric telescopic rod (68) via a separation pull rod (67). The cross-shaped adapter sleeve (66) includes a horizontal sleeve (661) through which the cooling copper pipe (63) passes and is rotatably connected to the cooling copper pipe (63). A vertical sleeve (662) is provided in the middle of the horizontal sleeve (661) and is arranged perpendicularly to the horizontal sleeve (661). 62) Sliding connection with the separation support rod (65), the cooling copper pipe (63) is connected to a cooling copper sheet (663) that fits against the cooling copper plate (62), and an elastic reset component is provided between the cooling copper pipe (63) and the cooling frame (61); the balancing assembly includes a balancing plate (69) that is vertically arranged in the cooling frame (61) and has an L-shaped cross section, the balancing plate (69) is symmetrical about the center of the cross adapter sleeve (66) and its sides fit against the horizontal sleeve (661) and the vertical sleeve (662) of the cross adapter sleeve (66) respectively.

2. The method for directional solidification of polycrystalline silicon according to claim 1, characterized in that, In step S1, the temperature of the melting furnace (2) is heated to 1550℃; in step S2, the temperature of the bottom of the crucible (1) is reduced to 1380℃ until 3cm of the bottom of the crucible (1) solidifies; in step S3, the silicon liquid crystallization rate is maintained at 0.8-1cm / m; in step S4, the temperature of the melting furnace (2) is raised back to 1100℃.

3. The method for directional solidification of polycrystalline silicon according to claim 1, characterized in that, The heating mechanism (4) includes a clamping mechanism located at the top of the melting furnace (2), which clamps and fixes an electrode rod (41) opposite to the upper end of the crucible (1). A stirring mechanism is provided at the lower end of the crucible (1). The clamping mechanism includes a clamping cylinder (42) located at the top of the melting furnace (2). The clamping cylinder (42) has a clamping cavity (43) inside that is opposite to the inside of the melting furnace (2). An electrode gripper (44) is installed inside the clamping cylinder (42). The electrode gripper (44) is connected to the clamping cylinder (42) via a lifting screw (45). Next, a lifting limit mechanism is provided between the electrode gripper (44) and the clamping cylinder (42); the lifting limit mechanism includes a limit groove (46) provided inside the clamping cylinder (42), and the electrode gripper (44) has a limit strip (47) that is slidably connected to the limit groove (46); the stirring mechanism includes a rotating disk (48) installed at the bottom of the crucible (1) and attached to it, the rotating disk (48) is rotatably installed on the fixed disk (49), and an inductive circuit is provided between the rotating disk (48) and the fixed disk (49) to drive the rotating disk (48) to rotate after being energized.

4. The method for directional solidification of polycrystalline silicon according to claim 1, characterized in that, The lifting mechanism (5) includes a lifting base (51) that closes the lower end of the melting furnace (2). A lifting mechanism is provided between the lower end of the lifting base (51) and the ground. A sealing mechanism is provided between the lifting base (51) and the melting furnace (2). The lifting mechanism includes a lifting guide rail (52) installed parallel to the ground. A lifting slider (53) is slidably installed on the lifting guide rail (52). A lifting rod (54) is rotatably installed between the lifting slider (53) and the lifting base (51). A lifting screw (55) is provided between the lifting slider (53) and the lifting guide rail (52). The lifting base (51) and the lifting guide rail (52) are also connected. The melting furnace (2) is slidably connected to the limiting column (57) which is vertically fixed on the ground through the limiting sliding sleeve (56); the sealing mechanism includes a sealing edge (58) that surrounds the lifting base (51) in the circumference, and the inner side of the sealing edge (58) is provided with an arc-shaped sealing surface (59). The lower end of the melting furnace (2) is provided with a sealing strip (21), and the sealing strip (21) has an arc-shaped sealing surface (59) that fits and presses against the sealing edge (58). There is a one-to-one corresponding sealing groove (591) between the sealing edge (58) and the sealing strip (21), and the sealing groove (591) is filled with a corrugated metal gasket (592).

5. The method for directional solidification of polycrystalline silicon according to claim 1, characterized in that, The heat insulation mechanism (7) includes an aluminum silicate fiber layer (71) covering the inside of the melting furnace (2), a rock wool interlayer (72) is provided inside the melting furnace (2), a protective cover (73) is provided outside the melting furnace (2), a vacuum layer (74) is provided between the protective cover (73) and the melting furnace (2), and a heat buffer assembly (8) is provided inside the melting furnace (2).

6. The method for directional solidification of polycrystalline silicon according to claim 5, characterized in that, The heat buffer assembly (8) includes a heat buffer plate (81) disposed inside the melting furnace (2). The melting furnace (2) is provided with an isolation fin (82) covering the heat buffer plate (81). The isolation fin (82) is connected to the linkage motor (84) via a linkage bracket (83). The isolation fin (82) has an isolation cover plate (85) extending outward and fitting against the inner wall of the melting furnace (2) around its periphery.

7. The method for directional solidification of polycrystalline silicon according to claim 1, characterized in that, The crucible (1) is made of quartz and is square or cylindrical. The upper end of the crucible (1) is provided with a demolding edge (11) that surrounds the circumference. A reinforcing rib (12) is provided between the demolding edge (11) and the outer side of the crucible (1). The inner side of the melting furnace (2) is provided with a demolding flap (13) that fits against the lower end of the demolding edge (11). The demolding flap (13) is connected to the demolding motor (15) through a transmission gear set (14).

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