A single crystal pulling method and a single crystal pulling apparatus

Abstract

The application discloses a single crystal pulling method and a single crystal pulling device. The method comprises the following steps: in the first stage, a camera is used to acquire a pixel image of a seed crystal shaft and a lower edge of a heat shield, an image processing device is used to fit a reference circle according to the pixel image of the lower edge of the heat shield, the reference circle has a reference line extending along a second direction, and the center of the reference circle falls on the reference line; when the seed crystal shaft is lowered, the pixel image of the seed crystal shaft gradually approaches the reference line; and when the bottom edge of the pixel image of the seed crystal shaft intersects with the reference line, the bottom surface of the seed crystal shaft is flush with the lower edge of the heat shield. Compared with the prior art, the lower edge position of the heat shield is used as a calibration, the camera and the image processing device are used to position the seed crystal shaft, the bottom end of the seed crystal shaft is flush with the lower edge of the heat shield, then the seed crystal shaft is lowered by a fixed height, the seed crystal shaft is accurately lowered and fused, and the problem of fusion abnormality caused by large position deviation of the seed crystal shaft is avoided.

Description

Technical Field

[0001] This invention relates to the field of monocrystalline silicon manufacturing technology, and in particular to a monocrystalline silicon pulling method and monocrystalline silicon pulling equipment. Background Technology

[0002] In the existing single-crystal pulling process, once the silicon material added to the quartz crucible in the single-crystal furnace has melted completely and the silicon molten surface becomes calm, it indicates that the melting process is complete. At this point, the crucible and heat shield positions are already in place. Next, after the seed crystal shaft is installed, the preheating and welding process begins. When the temperature of the molten silicon surface in the quartz crucible reaches the welding temperature, the seed crystal shaft is manually lowered for welding. This manual method of controlling the descent of the seed crystal shaft is inefficient and lacks precision. Summary of the Invention

[0003] The purpose of this invention is to provide a single crystal pulling method and equipment to solve the technical problems in the prior art. It can accurately determine the relative position of the seed crystal shaft head and the liquid surface, laying the foundation for the automation of the crystal pulling process.

[0004] This invention provides a single crystal pulling method, comprising the following steps:

[0005] The silicon material is placed in a crucible and melted to form molten silicon liquid;

[0006] The heat shield is lowered to a preset position, at which point a first preset distance is formed between the lower edge of the heat shield and the surface of the molten silicon liquid;

[0007] In the first stage, the seed crystal axis is suspended by a weight and gradually lowered along the first direction. A camera device is used to acquire pixel images of the seed crystal axis and the lower edge of the heat shield. An image processing device is used to fit a reference circle based on the pixel image of the lower edge of the heat shield. The reference circle has a reference line extending along the second direction. The center of the reference circle falls on the reference line. As the seed crystal axis descends, the pixel image of the seed crystal axis gradually approaches the reference line.

[0008] When the bottom edge of the pixel image of the seed crystal axis intersects with the reference line, the bottom surface of the seed crystal axis is flush with the lower edge of the heat shield. At this time, the second stage begins. The image processing device records the position of the seed crystal axis at this time, and then continues to lower the seed crystal axis by a fixed height. The bottom end of the seed crystal axis extends into the molten silicon for welding.

[0009] Perform shoulder pull;

[0010] Perform shoulder relaxation;

[0011] Perform equal diameter measurements;

[0012] To wrap things up.

[0013] In the above-described single-crystal pulling method, preferably, in the first stage, the seed crystal shaft is gradually lowered to a second preset distance from the surface of the molten silicon. When the surface temperature of the molten silicon is heated to gradually approach the welding temperature, the seed crystal shaft can be lowered again to be flush with the lower edge of the heat shield. At this point, the second stage begins. When the surface temperature of the molten silicon reaches the welding temperature condition, the seed crystal shaft is lowered by a fixed height, and the bottom of the seed crystal shaft extends into the molten silicon for welding.

[0014] In the single crystal pulling method described above, preferably, in the first stage, the seed crystal axis descends from its initial position to a third preset distance from the surface of the molten silicon liquid and is maintained for a first time interval; then the seed crystal axis descends to a fourth preset distance from the surface of the molten silicon liquid and is maintained for a second time interval; finally, the seed crystal axis descends to a second preset distance from the surface of the molten silicon liquid and is maintained for a third time interval.

[0015] In the single-crystal pulling method described above, preferably, the fixed height is equal to the sum of a first preset distance and the fine diameter of the seed crystal axis.

[0016] In the single-crystal pulling method described above, preferably, the first direction is perpendicular to the second direction.

[0017] In the single crystal pulling method described above, preferably, the axial direction of the seed crystal axis coincides with the axial direction of the heat shield.

[0018] In the single crystal pulling method described above, preferably, the first preset distance is 30mm-50mm.

[0019] In the single crystal pulling method described above, preferably, the second preset distance is 350-450mm.

[0020] This application also provides a single crystal pulling apparatus, which uses the aforementioned single crystal pulling method to pull crystals, including:

[0021] The furnace body contains a crucible and heating elements. The crucible is used to hold molten silicon, and the heating elements are used to heat the crucible.

[0022] A heat shield is installed inside the furnace and positioned above the crucible.

[0023] A weight is suspended inside the heat shield. A seed crystal shaft is connected to the lower end of the weight. The seed crystal shaft can move along the first direction to get closer to or away from the surface of the molten silicon.

[0024] The camera device is located above the heat shield and is used to acquire pixel images of the seed crystal axis and the lower edge of the heat shield.

[0025] An image processing device is connected to a camera device. The image processing device can fit a reference circle based on the pixel image of the lower edge of the heat shield. The reference circle has a reference line extending along a second direction. The center of the reference circle falls on the reference line. When the bottom edge of the pixel image of the seed crystal axis intersects the reference line, the bottom surface of the seed crystal axis is flush with the lower edge of the heat shield.

[0026] In the single crystal pulling equipment described above, preferably, the imaging device is a CCD camera.

[0027] Compared with the prior art, the present invention uses the lower edge of the heat shield as a calibration point and uses a camera device and an image processing device to locate the seed crystal axis, so that the bottom end of the seed crystal axis is flush with the lower edge of the heat shield. Then, the seed crystal axis is lowered by a fixed height, which realizes accurate descent and welding of the seed crystal axis and avoids welding abnormality caused by large deviation of the seed crystal axis position. Attached Figure Description

[0028] Figure 1 This is a flowchart of the crystal pulling method provided in this application;

[0029] Figure 2 A flowchart illustrating the seed crystal axis welding method of Embodiment 1 provided in this application;

[0030] Figure 3 A schematic pixel image of the seed crystal axis and the lower edge of the heat shield in Embodiment 1 provided in this application. Figure 1 ;

[0031] Figure 4 A schematic pixel image of the seed crystal axis and the lower edge of the heat shield in Embodiment 1 provided in this application. Figure 2 ;

[0032] Figure 5 A schematic diagram of the image captured by the camera device of Embodiment 2 provided in this application;

[0033] Figure 6 A schematic diagram of the image captured by the camera device of Embodiment 3 provided in this application;

[0034] Figure 7 A flowchart illustrating the shoulder-releasing control scheme of Embodiment 3 provided in this application;

[0035] Figure 8 This is a schematic diagram of the single crystal pulling equipment provided in this application;

[0036] Explanation of reference numerals in the attached drawings: 1-furnace body, 2-crucible, 3-heating component, 4-molten silicon liquid, 5-heat shield, 6-weight, 7-seed crystal axis, 8-camera device, 9-reference circle, 10-reference line, 11-first measuring frame, 12-second measuring frame. Detailed Implementation

[0037] The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0038] With the development of the semiconductor and photovoltaic industries, there is a greater market demand for monocrystalline silicon. Currently, the Czochralski method is the most widely used technology for producing monocrystalline silicon. In this method, a solid silicon block is loaded into a crucible 2 and heated to melt by a heater with a certain power. Then, the heater power is reduced and a certain degree of supercooling is controlled. An oriented seed crystal axis 7 is brought into contact with the molten silicon liquid 4 for fusion. By adjusting the temperature of the solution and the speed of the seed crystal axis 7, the seed crystal axis 7 is grown to the specified length. Then, operations such as shoulder formation, shoulder expansion, and equal diameter are performed to achieve the growth of monocrystalline silicon with equal diameter. When there is less molten silicon liquid 4 in the crucible 2, a finishing operation is performed after the equal diameter is completed to improve the yield.

[0039] In the welding process, existing welding technology is carried out by manual control and has not achieved automation. There are also technical solutions that determine the position of the seed crystal axis and lower the seed crystal axis for welding. This solution requires continuous adjustment of process parameters and has a large error, which puts higher demands on production management and is prone to welding accidents due to parameter setting errors.

[0040] To solve the aforementioned technical problems encountered in the welding process, refer to Figures 1 to 4 as well as Figure 8 As shown, this application provides a single crystal pulling method, including the following steps:

[0041] The silicon material is placed into crucible 2 for melting until the surface of the molten silicon liquid 4 becomes calm, thus completing the melting process.

[0042] A heat shield 5 is provided above the molten silicon liquid 4 along the direction of gravity. The heat shield 5 can move back and forth along the direction of gravity. After the melting is completed, the heat shield 5 is lowered to a preset position. At this time, a first preset distance is formed between the lower edge of the heat shield 5 and the liquid surface of the molten silicon liquid 4.

[0043] The aforementioned preset position is a calibrated position. At this preset position, the lower edge of the heat shield 5 and the liquid surface of the molten silicon 4 are maintained at a calibrated first preset distance. This first preset distance serves as a reference value. When the seed crystal axis 7 reaches the same horizontal plane as the lower edge of the heat shield 5, it means that the distance between the bottom end of the seed crystal axis 7 and the liquid surface of the molten silicon 4 is the first preset distance. The initial position of the seed crystal axis 7 is thus accurately positioned, providing a positioning basis for the subsequent automatic descent of the seed crystal axis 7 for welding. This can avoid welding abnormalities caused by the seed crystal axis 7 descending too much or too little.

[0044] In the first stage, the seed crystal shaft 7 is suspended by the weight 6 and gradually lowered along the first direction. In the embodiments of this application, the first direction is set as the direction of gravity. The other end of the weight 6 is connected to an automatic lifting device, which is used to drive the lifting action of the seed crystal shaft 7.

[0045] A camera device 8 is positioned above the heat shield 5 in the direction of gravity. The camera device 8 is communicatively connected to an image processing device. The camera device 8 acquires pixel images of the seed crystal axis 7 and the lower edge of the heat shield 5. The camera direction of the camera device 8 forms a preset angle with the first direction, resulting in the pixel image of the lower edge of the heat shield 5 not being a standard circle, but rather an ellipse-like structure. Furthermore, due to different fixed points of the camera device 8, its camera direction varies, leading to different elliptical structures in the acquired pixel images. To eliminate this difference in pixel images caused by different fixed points of the camera device 8, the image processing device fits a reference circle 9 based on the pixel image of the lower edge of the heat shield 5. This reference circle 9 is a standard circle and has a reference line 10 extending along a second direction. In this embodiment, the first direction is perpendicular to the second direction, and the second direction is set to be perpendicular to the seed crystal axis 7. The center of the reference circle 9 falls on the reference line 10. As the seed crystal axis 7 descends, the pixel image of the seed crystal axis 7 gradually approaches the reference line 10.

[0046] When the bottom edge of the pixel image of the seed crystal axis 7 intersects with the reference line 10, it indicates that the bottom surface of the seed crystal axis 7 is flush with the lower edge of the heat shield 5. At this time, the second stage begins. The image processing device records the position of the seed crystal axis 7 at this time and then sends a command signal to the automatic lifting device. The automatic lifting device continues to lower the seed crystal axis 7 by a fixed height. This fixed height is a user-defined height. Since the initial position of the seed crystal axis 7 has been determined, it is only necessary to determine the parameters of the fixed height in advance. There is no need to continuously adjust the process parameters. After the bottom end of the seed crystal axis 7 is lowered to a fixed height, it extends into the molten silicon 4 for welding. Then, the shoulder raising, shoulder placement, equal diameter, and finishing operations are performed in sequence.

[0047] The above embodiment uses the lower edge of the heat shield 5 as a calibration point, and uses the camera device 8 and the image processing device to position the seed crystal axis 7 so that the bottom end of the seed crystal axis 7 is flush with the lower edge of the heat shield 5. Then, the seed crystal axis 7 is lowered by a fixed height, which realizes the accurate lowering and welding of the seed crystal axis 7 and avoids the welding abnormality problem caused by the large position deviation of the seed crystal axis 7.

[0048] In the embodiments provided in this application, in the first stage, the seed crystal shaft 7 is gradually lowered to a second preset distance from the surface of the molten silicon 4. The gradual lowering of the seed crystal shaft 7 is to allow it to be gradually and fully preheated, preventing it from reaching high temperatures too quickly and causing crystal defects. When the surface temperature of the molten silicon 4 is heated to near the welding temperature, the heat shield 5 is at a preset position, and the seed crystal shaft 7 is lowered again until it is flush with the lower edge of the heat shield 5. At this point, the bottom of the seed crystal shaft 7 is at a first preset distance from the surface of the molten silicon 4, thus defining a definite initial position for the seed crystal shaft 7 to facilitate subsequent lowering operations and avoid excessive or insufficient lowering, which could cause instability in the welding process. Then, in the second stage, when the surface temperature of the molten silicon 4 reaches the welding temperature, the seed crystal shaft 7 is lowered by a fixed height, and the bottom of the seed crystal shaft 7 extends into the molten silicon 4 for welding.

[0049] In the embodiments provided in this application, in the first stage, the seed crystal shaft 7 descends from its initial position to a third preset distance from the surface of the molten silicon 4 and maintains this position for a first time interval. Then, the seed crystal shaft 7 descends to a fourth preset distance and maintains this position for a second time interval. Finally, the seed crystal shaft 7 descends to a second preset distance from the surface of the molten silicon 4 and maintains this position for a third time interval. The seed crystal shaft 7 descends to the second preset distance above the liquid surface in three steps, thereby preventing the seed crystal shaft 7 from heating up too quickly and causing crystal defects. In a feasible embodiment, during this process, the seed crystal shaft 7 first descends from its initial position to a distance of 1300mm-1700mm from the surface of the molten silicon 4 and maintains this position for 5min-10min, then descends again to a distance of 500mm-900mm and maintains this position for 5min-10min, and then descends again to a distance of 350mm-450mm and maintains this position for 10min-15min. Those skilled in the art will understand that the process position and time can be adjusted in the control system. To achieve gradual preheating of the seed crystal shaft 7 and meet the time requirements for pre-temperature adjustment, preferably, the seed crystal shaft 7 first descends from its initial position to a distance of 1500 mm from the surface of the molten silicon liquid 4 and maintains this position for 10 minutes, then descends again to 700 mm and maintains this position for 5 minutes, and then descends again to 400 mm and maintains this position for 10 minutes, thereby allowing the seed crystal shaft 7 to be gradually and fully preheated, preventing the seed crystal shaft 7 from reaching the high temperature too quickly and causing the formation of crystal defects.

[0050] In the embodiments provided in this application, the fixed height is equal to the sum of the first preset distance and the fine diameter length of the seed crystal shaft 7. This fine diameter length is the length by which the seed crystal shaft 7 extends into the molten silicon 4. This fine diameter length is preferably 130-140mm, specifically, the fine diameter length can be 130mm, 132mm, 134mm, 136mm, 138mm, 140mm, etc. The fine diameter length of the seed crystal shaft 7 can be uniformly required in production management and set in the parameters. Since the position of the heat shield 5 is already determined, the first preset distance value is a fixed value, and the fine diameter length of the seed crystal shaft 7 is also a fixed value. Thus, the fixed length is also a fixed parameter, avoiding the need to frequently adjust the process parameters in the control system, and reducing the occurrence of welding accidents due to parameter setting errors.

[0051] In the embodiments provided in this application, the axial direction of the seed crystal axis 7 coincides with the axial direction of the heat shield 5. The seed crystal axis 7 and the heat shield 5 are aligned. In the pixel image of the lower edge of the seed crystal axis 7 and the heat shield 5, the pixel image of the seed crystal axis 7 is a strip structure extending along the direction of gravity. The extension direction of the seed crystal axis 7 passes through the center of the reference circle 9. Thus, the central area of ​​the reference line 10 can be defined as the test area. When the gray value of the reference line 10 changes within the test area, it means that the seed crystal axis 7 has descended to contact the reference line 10. Therefore, it can be determined that the seed crystal axis 7 has descended to a position horizontal with the heat shield 5.

[0052] In the embodiments provided in this application, the first preset distance is 30mm-50mm, including the endpoint value. Specifically, the first preset distance can be 30mm, 35mm, 40mm, 45mm, 50mm, etc. As a feasible implementation, when the heat shield 5 reaches its lowest point, it also reaches the preset position. This eliminates the need for positioning the heat shield 5, avoiding the technical problem of welding defects caused by the parameter settings of the heat shield 5. Preferably, the first preset distance is 30mm. Those skilled in the art will know that the value of this first preset distance can be adjusted in the control system and set in the parameters.

[0053] In the embodiments provided in this application, the second preset distance is 350-450mm, including the endpoint value. Specifically, the second preset distance can be 350mm, 375mm, 400mm, 425mm, 450mm, etc. The second preset distance should not be too large, as this will result in insufficient preheating, nor should it be too small, as this will result in overheating. Both of these conditions can lead to the generation of crystal defects. Preferably, the second preset distance is 400mm. As those skilled in the art will know, this second preset distance can be adjusted in the control system and set in the parameters.

[0054] The following is a specific embodiment of this solution:

[0055] Step S10: The solid polycrystalline silicon material is loaded into crucible 2. The solid polycrystalline silicon material is heated at high temperature in crucible 2 and gradually melts. When the solid polycrystalline silicon material has completely melted into liquid molten silicon liquid 4 and the surface of molten silicon liquid 4 becomes calm, it is considered that the melting is complete.

[0056] S20 Step: After the melting is completed, the seed crystal shaft 7 is installed on the seed crystal chuck. Through the seed crystal rotation / sub-chamber purification process, the seed crystal shaft 7 is rotated in the sub-chamber of the single crystal furnace and connected to the main chamber of the single crystal path. After the sub-chamber is evacuated and purified by argon gas, the main and sub-chamber isolation valves are opened when the sub-chamber pressure is consistent with the main chamber pressure.

[0057] S30 step: Place the crucible. Place the crucible 2 in the position required by the process. After completion, start the preheating and welding process. The seed crystal shaft 7 is lowered to 1500mm from the liquid surface and held for 5 minutes. It is then lowered to 700mm and held for 5 minutes. Finally, it is lowered to 400mm and held for 10 minutes.

[0058] Step S40: When the surface temperature of the molten silicon liquid 4 gradually approaches the welding temperature under the power adjustment of the preheating welding process, the seed crystal axis 7 is lowered again. At this time, the camera device 8 is used to acquire pixel images of the seed crystal axis 7 and the lower edge of the heat shield 5. The image processing device is used to fit a reference circle 9 based on the pixel image of the lower edge of the heat shield 5. The reference circle 9 has a reference line 10 extending along the second direction. When the seed crystal axis 7 is lowered to the point where the bottom edge of the pixel image of the seed crystal axis 7 intersects with the reference line 10, that is, when the bottom surface of the seed crystal axis 7 is flush with the lower edge of the heat shield 5, the seed crystal axis 7 stops descending. At this time, the distance between the seed crystal axis 7 and the surface of the molten silicon liquid 4 is 30mm.

[0059] S50 step: The control system automatically adjusts the heating power to regulate the surface temperature of the molten silicon liquid 4. When the surface temperature of the molten silicon liquid 4 reaches the welding temperature, the control system triggers the descent of the seed crystal shaft 7 to perform welding. After welding is completed, the temperature adjustment process begins.

[0060] S60 step: When the surface temperature of the molten silicon liquid 4 reaches the target temperature required by the process and is maintained for 15 minutes, it is determined that the crystal pulling process can be started. After the crystal pulling begins, the silicon single crystal begins to grow from liquid to solid along the crystal atomic sequence of the seed crystal axis 7. The crystal pulling requires the crystal diameter to reach 6 mm and the length required by the process in order to eliminate dislocations inside the crystal.

[0061] S70 step: When the crystal length of the lead crystal reaches the requirement, the system enters the shoulder-forming process. During the shoulder-forming process, the crystal diameter gradually increases until it reaches the diameter required by the process.

[0062] Step S80, finishing touches.

[0063] In some embodiments of this application, during the melting process, a full melt detection is required to determine whether the silicon material has completely melted into liquid silicon liquid 4, referring to... Figure 5 as well as Figure 8 As shown, a camera device 8 and an image processing device are used to perform a full melt detection on the silicon material in the crucible 2.

[0064] During the monocrystalline silicon pulling process, polycrystalline silicon material is added into the monocrystalline furnace. After the furnace is closed, the heater is turned on to generate high temperature. At the same time, Ar gas is introduced into the furnace body 1 as a protective gas to isolate oxygen. The entire furnace body 1 is evacuated to a certain degree of vacuum using a dry pump to ensure that volatiles generated by the high temperature are continuously removed from the furnace body 1. At this time, the solid polycrystalline silicon material begins to melt due to the high temperature inside the furnace body 1. When the silicon material has melted to a certain extent, it can be added again using a feeding cylinder until the silicon material required for production is added to the crucible 2. Feeding stops at this time, and the heater power is continuously applied until the silicon material is completely melted, and all the solid polycrystalline silicon material is melted into liquid silicon liquid 4.

[0065] During this process, the camera device 8 and image processing device are used to observe the changes in the silicon liquid surface within the hot zone and control the system parameters to determine whether the melting process is complete. The camera device 8 acquires a pixel image of the lower edge of the heat shield 5. In the elliptical pixel image formed by the lower edge of the heat shield 5, there are several different regions. The first region is the part that has melted into molten silicon liquid 4, and the second region is the part of the polycrystalline silicon block that has not yet melted. There is a significant difference in grayscale values ​​between the first region and the second region. The image processing device defines a first measurement frame 11 with a fixed position in the pixel image. The first measurement frame 11 is used to determine the range of data sampling. Generally, the height * width range is defined as 900 ± 100mm*250±50mm (This value is set according to the pixel coordinates of the CCD resolution. For CCDs with higher resolution, the number of pixels increases, but the measurement range remains the same, so the measurement coordinates need to be adjusted according to the actual situation). Specifically, the range values ​​can be 800mm*200mm, 820mm*210mm, 840mm*220mm, 860mm*230mm, 880mm*240mm, 900mm*250mm, 920mm*260mm, 940mm*270mm, 960mm*280mm, 980mm*290mm, 1000mm*300mm, etc. The central coordinates are set at a position where the molten silicon 4 is not affected by the reflection of the heat shield 5, to determine the range of data. When the solid silicon block is close to complete melting, the last silicon block floats on the surface of the molten silicon. Because the crucible 2 operates at a low speed at this time, and the protective gas Ar flows from the upper part of the furnace body 1 downwards into the lower part of the furnace body 1, the solid silicon block floats and moves back and forth on the surface of the molten silicon 4, causing continuous and disordered changes in grayscale values ​​within the first measurement frame 11. When the silicon surface becomes calm, the average grayscale of the image within the first measurement frame 11 no longer changes within a certain period of time. When changes occur, the average grayscale value is generally within 50±5 pixels. The set time parameter can be 15 minutes, or it can be 10 minutes, 12 minutes, 17 minutes or 20 minutes. When the grayscale value is within 50±5 pixels within this time range, it can be considered that the melting is complete. This determination can be made by calculating the change in grayscale value within the first measurement frame 11 based on the vision software in the image processing device, combined with the boundary condition parameters set in the control system, such as the minimum difference in grayscale value change, the determination time, and the time to enter the preheating and welding process after the determination conditions are met.

[0066] In some embodiments of this application, during the preheating and welding process, refer to Figure 6 as well as Figure 8 As shown, a method for measuring the liquid outlet distance of the heat shield 5 is used by employing a camera device 8 and an image processing device.

[0067] When the silicon material is melted, the liquid surface of the molten silicon 4 tends to stabilize. At this time, the heat shield 5 is lowered to the lowest point, which is the preset position, while the crucible position is raised so that the lower edge of the heat shield 5 is a certain distance from the silicon liquid surface. This distance is called the liquid outlet distance.

[0068] The imaging device 8 acquires a pixel image of the lower edge of the heat shield 5. In the elliptical pixel image formed by the lower edge of the heat shield 5, the lower edge boundary of the heat shield 5 has a reflection on the silicon liquid surface. A crescent-shaped image is formed between this reflection and the elliptical boundary. The image processing device defines a second measurement frame 12 in the pixel image to determine the range of data. This range can be set in the software. Generally, the height * width range of this second measurement frame 12 is set to 140±10mm * 90±10mm (this value is determined according to the pixel coordinates of the CCD resolution). The grayscale difference threshold is set in the range of 5-25 pixels, specifically 10 pixels, 15 pixels, or 20 pixels. According to the set range and boundary conditions, the vision software can capture two adjacent arcs of the crescent boundary. The tangent of the fitted circle of the arc can be calculated through the arc. The vertical distance between these two tangents is the liquid outlet distance measurement value.

[0069] In practice, this measurement value can be calibrated using manual or automatic calibration methods. During the calibration process, the system will determine the linear relationship between the actual distance and the measured distance based on the lifting distance of the crucible motor, thereby obtaining the measured value of the liquid outlet distance to calibrate the actual value of the liquid outlet distance.

[0070] The automatic calibration method involves lowering and then raising the crucible to a certain value, typically 8-15mm (the lowering distance is the mechanical distance of the crucible position, which can be converted from the motor speed). The change in this distance is then determined, specifically 10mm, 12mm, or 14mm, to derive a fitting formula. After calibration, the distance between the liquid outlet and the crucible is thus determined.

[0071] In some embodiments of this application, during the shoulder-laying process, it is necessary to automatically control the shoulder shape, referring to... Figure 7 as well as Figure 8 As shown, this embodiment mainly concerns the process flow algorithm logic of the shoulder formation process. During the crystal pulling process, the crystal goes from crystal pulling to shoulder formation and then to equal diameter. The shoulder formation process is the process of gradually increasing the crystal diameter during single crystal pulling. In the embodiment provided in this application, this process is achieved by the single crystal furnace equipment controlling the shoulder forming speed and shoulder forming power through the control system, thereby controlling the shape of the shoulder body. The control system sets a set of basic parameters and provides the control parameters for the PID algorithm.

[0072] Specifically, the steps of the automatic shoulder placement control include:

[0073] Step 1: Begin by relaxing your shoulders;

[0074] Step 2: Specify the initial pulling speed and power reduction value according to the parameter table;

[0075] Step 3: The control system measures the shoulder diameter and calculates the shoulder length;

[0076] Step 4: The control system calculates the angle tangent based on the difference in shoulder length and shoulder diameter per unit time;

[0077] Step 5: Set the angle tangent value according to the shoulder length in the parameter table, and use the PID algorithm and the average shoulder pulling speed to control the actual pulling speed.

[0078] For example, in the crystal pulling stage, the average pulling speed of a single crystal is 300 mm / h. When the crystal length reaches a certain length, the crystal jumps to the shoulder formation stage. In this stage, an initial pulling speed is given, which is set to 60 mm / h. At this pulling speed, the crystal gradually increases in shoulder length, while the power is gradually decreased in the parameter table of the control system. At this time, as the crystal length increases (which can be defined as the Y direction), the crystal diameter begins to increase (which can be defined as the X direction). In the X direction of diameter growth, the crystal pulling system can calculate the rate of change of diameter and the average growth rate (X direction) over a certain period of time. The crystal's upward speed in the Y direction at this time is the crystal pulling speed. This parameter system can calculate the average pulling speed over a certain period of time.

[0079] To facilitate stable control, this embodiment uses the average diameter growth rate over 10 minutes and the average pulling speed over 10 minutes for calculation and control. The tangent function of the shoulder angle can be expressed as TanA = V. 平均直径速率 (mm / min) / V 平均拉速 (mm / min), during the shoulder-laying process, a certain angle value is set at different shoulder-laying lengths. The corresponding value of this angle can be represented by the tangent function, which is TanA. To control the shoulder shape, theoretically, the optimal shoulder shape can be divided into three stages: initial, middle, and late stages, based on the shoulder-laying height. In the initial stage, TanA can be set to the range of 0.48-0.1; in the middle stage, TanA = 0.9-1.9; and in the late stage, TanA = 1.8-2.3. A parameter table of TanA can be given based on the shoulder-laying length. For stable control and ease of control by the PLC system, the actual controlled value of this parameter TanA' is set to V. 10分钟平均直径速率 / V 10分钟平均拉速 The value of TanA'-TanA is calculated after the shoulder-laying starts, and the system can be set to start control after 1-5 minutes. Therefore, a difference is obtained from the TanA'-TanA table, and the PLC control can use this difference to control the system using a PID control model (e.g., Formula 1 is the PID calculation formula), where At is the set pulling speed and A0 is the actual average pulling speed. P, I, and D can be controlled according to the given shoulder-laying length.

[0080]

[0081] In addition, since the volume of single crystal pulled out per unit time during crystal growth is proportional to the power reduction value, a certain power reduction can be set when setting system parameters to meet the requirements of the shoulder-forming process.

[0082] The shoulder-forming process involves controlling crystal growth by setting the pulling speed. In the formula, δB = TanA' - TanA, as shown in Table 1. For the standard shoulder-forming parameters, after 20 minutes, TanA is set to 0.6704. However, the actual calculated TanA' is 0.7 (assumed), therefore δB = 0.0296. Simultaneously, the δB / δt value is collected, which can be set to the actual δB value over 10 seconds, assumed to be 0.01. The program is then set to calculate ∫0 t δB, this value can be set to T=30min, and a value is taken and accumulated every 10s. Assume this calculated value is 0.05. Because the integral effect can be reduced during the shoulder release process in actual control testing, the influence of this integral part on the pulling speed control can be reduced. Therefore, the set value of I can be reduced based on the calculation results.

[0083] Assuming A0 = 90 mm / h, the pulling speed At is set to 90 + 0.0296 * P + 0.05 * I + 0.01 * D. In actual testing, the values ​​of P, I, and D are set according to the actual control of the shoulder release process to achieve control of the shoulder release process.

[0084] Table 1

[0085]

[0086]

[0087] Based on the above embodiments, this application also provides a single crystal pulling device, which uses the aforementioned single crystal pulling method for crystal pulling, with reference to... Figure 3 , Figure 4 as well as Figure 8 As shown, it includes:

[0088] The furnace body 1 contains a crucible 2 and a heating element 3. The crucible 2 holds molten silicon 4, and the heating element 3 heats the crucible 2. In one feasible embodiment, the crucible 2 includes a quartz crucible and a CC crucible. The quartz crucible holds silicon material, such as polycrystalline silicon. The silicon material is heated into molten silicon within it. The CC crucible surrounds the quartz crucible and provides support during heating. The heater is located outside the graphite crucible. A support rod is provided at the bottom of the crucible 2 to support the crucible 2 and the silicon material, and to provide power for the crucible 2 to rotate or move up and down.

[0089] The heat shield 5 is located inside the furnace body 1 and above the crucible 2. The heat shield 5 has an inverted conical screen that extends downward and surrounds the silicon single crystal growth area. It can block the direct thermal radiation from the heater and the high-temperature molten silicon liquid 4 to the grown single crystal silicon rod, thereby reducing the temperature of the single crystal silicon rod. In addition, the heat shield can also concentrate the downward-blown protective gas and spray it directly to the vicinity of the growth interface, further enhancing the heat dissipation of the single crystal silicon rod.

[0090] The weight 6 is suspended inside the heat shield 5 by a pull rope. The lower end of the weight 6 is connected to the seed crystal shaft 7. The seed crystal shaft 7 can move along the first direction to get closer to or away from the liquid surface of the molten silicon 4. In the single crystal growth process, the seed crystal shaft 7 is grown into a single crystal silicon rod through processes such as fusion, crystal introduction, shoulder setting, shoulder turning, and equal diameter.

[0091] The camera device 8 is located above the heat shield 5. The camera device 8 is used to acquire pixel images of the seed crystal axis 7 and the lower edge of the heat shield 5. In one feasible embodiment, the camera device 8 is a CCD camera.

[0092] The image processing device is connected to the camera device 8. The image processing device can fit a reference circle 9 based on the pixel image of the lower edge of the heat shield 5. The reference circle 9 has a reference line 10 extending along a second direction. The center of the reference circle 9 falls on the reference line 10. When the bottom edge of the pixel image of the seed crystal axis 7 intersects with the reference line 10, the bottom surface of the seed crystal axis 7 is flush with the lower edge of the heat shield 5.

[0093] The above description, based on the embodiments shown in the figures, details the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention, but the present invention is not limited to the scope of implementation shown in the figures. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, that do not exceed the spirit covered by the specification and figures, should be within the protection scope of the present invention.

Claims

1. A method for single-crystal pulling, characterized in that: Includes the following steps: The silicon material is placed in a crucible and melted to form molten silicon liquid; The heat shield is lowered to a preset position, at which point a first preset distance is formed between the lower edge of the heat shield and the surface of the molten silicon liquid; In the first stage, a seed crystal axis is suspended by a weight and gradually lowered along a first direction. A camera device acquires pixel images of the seed crystal axis and the lower edge of the heat shield. An image processing device fits a reference circle based on the pixel image of the lower edge of the heat shield. The reference circle has a reference line extending along a second direction, which is perpendicular to the first direction. The center of the reference circle falls on the reference line. As the seed crystal axis descends, the pixel image of the seed crystal axis gradually approaches the reference line. When the gray value of the reference line changes, the seed crystal axis comes into contact with the reference line. When the bottom edge of the pixel image of the seed crystal axis intersects with the reference line, the bottom surface of the seed crystal axis is flush with the lower edge of the heat shield. At this time, the second stage begins. The image processing device records the position of the seed crystal axis at this time, and then continues to lower the seed crystal axis by a fixed height. The bottom end of the seed crystal axis extends into the molten silicon for welding. Perform shoulder pull; Perform shoulder relaxation; Perform equal diameter measurements; To wrap things up.

2. The single crystal pulling method according to claim 1, characterized in that: In the first stage, the seed crystal shaft is gradually lowered to a second preset distance from the surface of the molten silicon liquid. When the surface temperature of the molten silicon liquid is heated to gradually approach the welding temperature, the seed crystal shaft can be lowered again to be flush with the lower edge of the heat shield. At this time, the second stage begins. When the surface temperature of the molten silicon liquid reaches the welding temperature condition, the seed crystal shaft is lowered by a fixed height, and the bottom of the seed crystal shaft extends into the molten silicon liquid for welding.

3. The single crystal pulling method according to claim 1, characterized in that: In the first stage, the seed crystal shaft descends from its initial position to a third preset distance from the surface of the molten silicon liquid and maintains this position for a first time interval. Then, the seed crystal shaft descends to a fourth preset distance from the surface of the molten silicon liquid and maintains this position for a second time interval. Finally, the seed crystal shaft descends to a second preset distance from the surface of the molten silicon liquid and maintains this position for a third time interval.

4. The single crystal pulling method according to claim 1, characterized in that: The fixed height is equal to the sum of the first preset distance and the diameter of the seed crystal axis.

5. The single crystal pulling method according to claim 1, characterized in that: The axial direction of the seed crystal axis coincides with the axial direction of the heat shield.

6. The single crystal pulling method according to claim 1, characterized in that: The first preset distance is 30mm-50mm.

7. The single crystal pulling method according to claim 2, characterized in that: The second preset distance is 350-450mm.

8. A single-crystal crystal pulling apparatus, used for crystal pulling by the single-crystal crystal pulling method according to any one of claims 1-7, characterized in that, include: The furnace body includes a crucible and a heating element. The crucible is used to hold molten silicon, and the heating element is used to heat the crucible. A heat shield is disposed inside the furnace body and is located above the crucible; A weight is suspended inside the heat shield. The lower end of the weight is connected to a seed crystal shaft, which can move along a first direction to approach or move away from the surface of the molten silicon. A camera device is disposed above the heat shield, and the camera device is used to acquire pixel images of the seed crystal axis and the lower edge of the heat shield; An image processing device is signal-connected to the camera device. The image processing device can fit a reference circle based on the pixel image of the lower edge of the heat shield. The reference circle has a reference line extending along a second direction. The center of the reference circle falls on the reference line. When the bottom edge of the pixel image of the seed crystal axis intersects the reference line, the bottom surface of the seed crystal axis is flush with the lower edge of the heat shield.

9. The single crystal pulling equipment according to claim 8, characterized in that: The camera device is a CCD camera.

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