Crystal pulling device and crystal pulling method

Abstract

The invention relates to a crystal pulling device and a crystal pulling method. In one aspect, a crystal pulling apparatus is provided, the crystal pulling apparatus comprising: a crucible containing a silicon melt; the driver drives the crucible to move; and the controller is in communication connection with the driver, and the controller is configured to control the driver to drive the crucible to simultaneously execute alternate forward and reverse rotation movement around the central axis of the crucible and vertical reciprocating lifting movement in the vertical direction after it is detected that the silicon melt in the crucible is completely melted and before crystal lifting is started. Therefore, the air hole defect rate of the crystal bar can be reduced, and the quality of the crystal bar is improved.

Description

Technical Field

[0001] This disclosure relates to the field of semiconductor manufacturing technology, and more specifically, to a crystal pulling apparatus and a crystal pulling method. Background Technology

[0002] In silicon wafer manufacturing, the Czochralski (CZ) method is a commonly used single crystal growth technique. During crystal pulling, a seed crystal is typically immersed in molten material and slowly pulled and rotated to grow a single crystal rod. Therefore, a stable reaction environment is crucial for ensuring the processing quality and production yield of the crystal rod.

[0003] However, in the existing crystal pulling process, the pulled crystal rods often have pinhole defects. These defects can lead to a decrease in the product quality of the single crystal rods, affecting the subsequent processing and use of silicon wafers. Summary of the Invention

[0004] This section is based on the general summary of this disclosure, and not on a full disclosure of the entire scope or all features of this disclosure.

[0005] According to one aspect of this disclosure, a crystal pulling apparatus is provided. The apparatus includes a crucible, a driver, and a controller. The crucible contains molten silicon. The driver is used to drive the movement of the crucible. The controller is communicatively connected to the driver and is configured to, upon detecting that the silicon melt in the crucible has melted, before initiating crystal pulling, control the driver to simultaneously perform alternating forward and reverse rotational motions around the crucible's central axis and vertical reciprocating lifting motions in the vertical direction.

[0006] According to another aspect of this disclosure, a crystal pulling method is also provided. The crystal pulling method includes: providing a silicon melt in a crucible; heating the silicon melt to melt it; after the silicon melt has melted, before starting crystal pulling, simultaneously driving the crucible to perform alternating forward and reverse rotation around the crucible's central axis and vertical reciprocating lifting and lowering motion in the vertical direction; and pulling the crystal from the molten silicon melt.

[0007] According to the above technical solution, a controller controls the driver to simultaneously perform alternating forward and reverse rotation and vertical reciprocating lifting and lowering motions of the crucible. The alternating forward and reverse rotation generates inertia to peel off bubbles adhering to the crucible wall, while the vertical reciprocating lifting and lowering motion allows the crucible to periodically pass through the high-temperature zone of the heater at various positions, enhancing melt convection. The synergistic effect of these two motions efficiently promotes the movement of bubbles to the surface of the silicon melt and their volatilization and discharge. This significantly reduces the porosity defect rate of the crystal rod, improves the purity and integrity of the single crystal rod, and thus provides a high-quality substrate for subsequent semiconductor silicon wafer processing. Attached Figure Description

[0008] The features and advantages of embodiments of the present disclosure will become more readily understood from the following description with reference to the accompanying drawings. The drawings are not drawn to scale and some features may be enlarged or reduced to show details of specific components.

[0009] In the attached diagram: Figure 1 This is a schematic diagram showing the distribution of bubbles generated inside the crucible during the crystal pulling process.

[0010] Figure 2 This is a schematic diagram of a crystal pulling apparatus provided according to an embodiment of the present disclosure.

[0011] Figure 3 This is a system architecture diagram of a crystal pulling apparatus provided according to an embodiment of the present disclosure.

[0012] Figure 4 This is a schematic diagram showing the crucible rotation of a crystal pulling apparatus according to an embodiment of the present disclosure.

[0013] Figure 5 This is a schematic diagram showing the change of crucible position in a crystal pulling apparatus according to an embodiment of the present disclosure.

[0014] Figure 6 This is a schematic diagram of a crystal pulling apparatus provided according to another embodiment of the present disclosure.

[0015] Figure 7 This is a schematic diagram of a crystal pulling apparatus provided according to yet another embodiment of the present disclosure.

[0016] Figure 8 This is a flowchart of a crystal pulling method provided according to an embodiment of the present disclosure.

[0017] In the accompanying drawings, the same or corresponding technical features, parts or components are represented by the same or corresponding reference numerals. Detailed Implementation

[0018] The present disclosure will now be described in detail with reference to the accompanying drawings and exemplary embodiments. It should be noted that the following detailed description of the present disclosure is for illustrative purposes only and is not intended to limit the scope of the disclosure.

[0019] It should be noted that, for clarity, not all features of a particular embodiment are described or shown in the specification and drawings. Furthermore, to avoid unnecessary details obscuring the technical solutions of interest in this disclosure, only the device structures and parts closely related to the technical solutions of this disclosure are described and shown in the specification and drawings, while other details that are not closely related to the technical content of this disclosure and are known to those skilled in the art are omitted.

[0020] In silicon wafer manufacturing, the Czochralski (CZ) method is commonly used to pull single crystals. First, polycrystalline silicon is loaded into a quartz crucible and melted under an inert atmosphere (such as argon) using a graphite heater. This completes the loading and melting stages of the crystal pulling process. Next, the pulling stage begins, where a seed crystal is immersed in the molten silicon, guiding its growth along the seed crystal. During the pulling process, precise control of steps such as seeding, shoulder formation, shoulder rotation, equal diameter control, and finishing is crucial to ultimately producing the crystal ingot.

[0021] During crystal pulling, gaps exist between silicon particles within the quartz crucible and between the silicon and the crucible itself. These gaps trap a large number of bubbles during the melting of the silicon molten metal. Furthermore, the reaction between the silicon and the quartz crucible produces silicon monoxide, which, if not promptly removed, also generates bubbles. Additionally, rough areas, pits, and scratches on the surface of the quartz crucible, as well as those resulting from contact with polycrystalline silicon, are prone to trapping argon bubbles. Figure 1 As shown, it schematically illustrates the bubble distribution diagram generated in the crucible 120 of the crystal pulling device 100 during the crystal pulling process (the distribution area of ​​the bubbles is shown in hollow circles in the figure).

[0022] However, if these bubbles are not removed in time, they will be drawn into the single crystal ingot during the subsequent crystal pulling process, causing pinhole defects in the pulled ingot. Pinholes refer to the tiny holes formed by unremoved bubbles within the single crystal ingot; these holes are critical defects affecting silicon wafer quality.

[0023] Therefore, combining the diagrams with a complete description of the crystal pulling process, it can be concluded that the generation of bubbles during the crystal pulling process is unavoidable.

[0024] Because traditional crystal pulling equipment and methods are still used, bubbles generated during the crystal pulling process cannot be completely eliminated. However, related technologies have developed methods to reduce porosity formation by setting appropriate process conditions. For example, using quartz crucibles with low microbubble content in the transparent layer, avoiding scratches on the quartz crucible during loading, and filling polycrystalline silicon materials of different sizes in a specific ratio to reduce voids between silicon particles. These are methods to improve porosity by reducing bubble generation.

[0025] Improving porosity by promoting bubble overflow requires addressing process conditions. In related technologies, high power is often used during the material preparation stage, and the time allotted for the stabilization stage (after material preparation and before crystal pulling) is typically short. Therefore, bubbles often cannot be completely expelled naturally. In this situation, these unexpelled bubbles will still form pores during subsequent crystal pulling, leading to a decrease in the quality of the single crystal ingot and affecting the subsequent processing and use of silicon wafers.

[0026] Therefore, in order to solve the problem of porosity defects in crystal rods caused by the inability to effectively expel bubbles during the crystal pulling process, this disclosure provides a crystal pulling apparatus 100. The following will be combined with... Figures 2 to 7 The crystal pulling apparatus 100 is described in detail.

[0027] First, such as Figure 2 As shown, Figure 2 This is a schematic diagram of the overall structure of a crystal pulling apparatus 100 provided for an embodiment of the present disclosure. The crystal pulling apparatus 100 includes a crucible 120, a driver 140, and a controller 160.

[0028] The crucible 120 contains molten silicon. The crucible 120 itself is usually made of quartz, and its interior can form a cavity to contain the molten silicon, with a portion of the molten silicon in contact with the crucible wall 122. The molten silicon here usually refers to the liquid silicon material formed after polycrystalline silicon is heated above its melting point by the heater 110, and it is the raw material for pulling single crystal rods.

[0029] The crucible 120 may be supported, for example, by a crucible shaft 130 via a crucible tray 150 connected to one end of the crucible shaft 130. The crucible 120 may be driven to move by the rotation of the crucible shaft 130 to provide a uniform and stable crystal growth environment within the crucible 120.

[0030] The driver 140 can, for example, be drive-connected to the crucible shaft 130 to drive the crucible 120 to move. And refer to... Figure 3 , Figure 3 A system architecture diagram of a crystal pulling apparatus 100 provided in one embodiment of this disclosure is shown. The driver 140 may include, for example, a rotation drive assembly 142 and a lifting drive assembly 144 to ensure the stability of motion transmission. The rotation drive assembly 142 is driven to the bottom of the crucible 120 to provide rotational power, and the lifting drive assembly 144 is connected to the crucible 120 to drive the entire crucible 120 to move vertically. Figure 2 The hollow arrows in the middle schematically indicate the direction of the rotation and lifting motion of the crucible 120.

[0031] The controller 160 is communicatively connected to the driver 140. The controller 160 is configured to, after detecting that the silicon melt in the crucible 120 has melted completely, and before starting to pull the crystal, control the driver 140 to drive the crucible 120 to simultaneously perform alternating forward and reverse rotation around the central axis of the crucible 120 and vertical reciprocating lifting and lowering motion in the vertical direction.

[0032] For example, the controller 160 may have a built-in temperature detection module to determine whether the silicon melt in the crucible 120 has completely melted based on the feedback signal from the temperature sensor. Furthermore, the controller 160 may be, for example, a programmable logic controller (PLC), an industrial computer, or a dedicated microcontroller unit. The controller 160 is communicatively connected to the driver 140 via signal lines to achieve coordinated control of the various drive components of the driver 140.

[0033] As mentioned earlier, during the melting process of silicon melt, a large number of bubbles are trapped inside the crucible 120. Furthermore, during the stabilization phase after melting, the temperature of the silicon melt tends to stabilize, and it remains in a uniform flow state without forming a solid crystal structure. In this situation, the inertial force and convection generated by the movement of the crucible 120 can directly act on the silicon melt without interfering with crystal growth, thus effectively removing bubbles and promoting their upward movement. However, it is understandable that after crystal pulling begins, i.e., when the single crystal rod has initially formed, the movement of the crucible 120 will cause melt disturbance, disrupting the stability of crystal growth and leading to problems such as lattice defects and uneven diameter. Therefore, controlling the movement of the crucible 120 after the silicon melt has melted and before crystal pulling begins can effectively remove bubbles while ensuring stable crystal growth.

[0034] It is conceivable that the rotational motion of the crucible 120 driven by the actuator 140 can be a periodic rotational motion around the central axis of the crucible 120, alternating between clockwise and counterclockwise directions. For example, it can include a complete motion process of acceleration, maintaining a constant speed, deceleration, and switching rotational directions. Furthermore, the rotational direction switching period of the crucible 120 can be the time interval between the crucible 120 switching from one rotational direction (e.g., clockwise) to the opposite rotational direction (e.g., counterclockwise).

[0035] Accordingly, the lifting and lowering motion of the crucible 120 can be a periodic up-and-down displacement motion along the vertical direction (i.e., the direction parallel to the central axis of the crucible 120), and has a defined stroke range and switching cycle. One stroke cycle of the crucible 120 can be, for example, a complete time interval from rising from the lowest stroke position to the highest stroke position, and then falling from the highest stroke position to the lowest stroke position.

[0036] Based on the above technical solution, the inventors of this disclosure have verified through experiments that the improvement in the crystal rod porosity defect rate brought about by the combination of the crucible 120 up-and-down lifting and forward and reverse rotation methods compared with the crystal pulling method of the control group is shown in Table 1 below.

[0037] Table 1

[0038] Referring to Table 1, by way of example, according to one embodiment of this disclosure, the crucible rotor 120 can employ variable frequency forward and reverse rotation (e.g., the peak speeds for forward and reverse rotation are +1 rpm and -1 rpm, respectively), and the crucible position can be adjusted vertically (e.g., the peak amplitudes for vertical movement are +60 mm and -60 mm, respectively). Here, the zero position for the vertical adjustment of the crucible 120 is the position where the crucible 120 is flush with the heater 110, as detailed in Table 1. Figure 2 The horizontal height is indicated by the dashed line. In this way, air bubbles on the crucible wall 122 can be effectively separated, and the overflow of air bubbles can be promoted.

[0039] Therefore, according to Table 1, it can be concluded that by using the crystal pulling apparatus 100 of this disclosure for crystal growth, the porosity of the crystal rod is reduced from 0.99% to 0.28%, which significantly reduces the generation of porosity.

[0040] By configuring the controller 160, after detecting the completion of silicon molten metal melting in the crucible 120 and before starting crystal pulling, the controller driver 140 drives the crucible 120 to simultaneously perform alternating forward and reverse rotation around the central axis of the crucible 120 and vertical reciprocating lifting and lowering motion. That is, by raising and lowering the crucible 120 to change the relative position of the crucible 120 and the heater 110, the convection intensity of the silicon molten metal is enhanced. Combined with the inertia of the forward and reverse rotation, this helps to peel off bubbles adhering to the crucible wall 122. The two motion modes work together to allow bubbles to quickly move to the surface of the silicon molten metal and overflow, achieving timely cleaning of bubbles generated within the crucible 120. This reduces the possibility of porosity defects in the crystal rod during the crystal pulling process, thereby reducing porosity defects caused by residual bubbles and improving the product quality of the single crystal rod.

[0041] It is conceivable that when the controller 160 controls the crucible 120 to perform alternating forward and reverse rotation, the controller 160 can be configured to control the crucible 120 to accelerate in a first rotational direction to a first rotational speed and maintain it for a first duration, then decelerate and switch to a second rotational direction opposite to the first rotational direction, accelerate to a second rotational speed and maintain it for a second duration.

[0042] For example, the first rotation direction can be clockwise. The controller 160 controls the driver 140 to drive the crucible 120 to gradually accelerate to a first rotational speed during clockwise rotation. The first rotational speed can be, for example, 1 rpm. At this time, the crucible 120 is controlled to maintain the first rotational speed for a first duration to stabilize the crucible 120 in stripping bubbles. Subsequently, the crucible 120 is driven to gradually decelerate to a stop, switching to a second rotational direction opposite to the first rotational direction, which can be counterclockwise. Then, the crucible 120 gradually accelerates to a second rotational speed during counterclockwise rotation. The second rotational speed can be, for example, the same as the first rotational speed of 1 rpm. At this time, the crucible 120 is controlled to maintain the second rotational speed for a second duration. In this way, the crucible 120 can be controlled to perform cyclical alternating clockwise and counterclockwise rotation.

[0043] By controlling the crucible 120 to perform a gradual, variable-speed rotation, the molten silicon can be prevented from experiencing severe disturbances due to sudden changes in the crucible 120's rotation speed. Simultaneously, setting a stable, uniform rotation phase ensures that bubbles have sufficient time to detach from the crucible wall 122, preventing incomplete bubble removal due to improper rotation control, thereby further improving the stability and efficiency of bubble removal.

[0044] It is conceivable that the absolute value of the first speed and the second speed can be less than or equal to 1 rpm.

[0045] Reference Figure 4 , Figure 4 A schematic diagram illustrating the crucible rotation variation of a crystal pulling apparatus according to an embodiment of this disclosure is shown. A lower rotational speed R is suitable for silicon melts with low viscosity after melting, preventing molten metal splashing caused by excessively high speed R. A rotational speed R close to its upper peak value is suitable for silicon melts with higher viscosity after melting, enhancing the bubble removal effect by increasing inertial force. Here, the viscosity of the silicon melt refers to the physical properties of the liquid silicon material formed after polycrystalline silicon is heated and melted by a graphite heater, resisting its own flow and deformation; it is a core parameter characterizing the fluidity of the silicon melt. The lower the viscosity, the stronger the fluidity of the silicon melt.

[0046] By limiting the rotational speed range of the crucible 120, the crystal pulling device 100 can provide sufficient inertial force to remove bubbles and avoid damaging the stability of the silicon melt due to excessive rotational speed of the crucible 120. This allows the rotational speed of the crucible 120 to be adapted to the optimal range for bubble removal and crystal growth, thereby further improving the bubble removal effect.

[0047] It is conceivable that the controller 160, while controlling the crucible 120 to perform vertical reciprocating lifting and lowering motion, can also control the crucible 120 to perform periodic displacement relative to the upper end of the heater 110.

[0048] like Figure 2As shown, the zero point of the crucible 120 can be flush with the horizontal plane at the upper end of the heater 110. Furthermore, referring to the reference... Figure 5 , Figure 5 A schematic diagram illustrating the crucible position change of a crystal pulling apparatus according to an embodiment of this disclosure is shown. The vertical axis H represents the vertical height of the crucible 120 relative to the upper end of the heater 110. It can be clearly seen from the diagram that the controller 160 controls the driver 140 to drive the crucible 120 from its lowest travel position, first moving it vertically upwards by 120 mm to its highest travel position. Then, it moves vertically downwards by 120 mm back to its lowest travel position, repeating this cycle to achieve periodic displacement of the crucible 120 relative to the upper end of the heater 110.

[0049] By controlling the periodic displacement of the crucible 120, all areas of the crucible 120 can receive high-temperature radiation from the heater 110 uniformly, avoiding unstable melt convection due to uneven heating in certain areas. This results in a more uniform temperature distribution in the silicon melt and enhanced convection, making it easier for bubbles to rise under the influence of the temperature gradient. Compared to setting the positions of the crucible 120 and the heater 110 relatively fixed, this method is more effective in carrying bubbles out of the melt, thereby improving bubble removal efficiency.

[0050] It can be assumed that the amplitude of the vertical reciprocating lifting motion of the crucible 120 can be less than or equal to 120 mm.

[0051] The amplitude here refers to the unidirectional displacement distance of the crucible 120 during its vertical reciprocating lifting and lowering motion, moving upwards or downwards in the vertical direction. Setting the amplitude to a lower value is suitable for small-capacity crucibles to avoid excessive displacement that could cause physical interference between the crucible 120 and other components, leading to increased melt fluctuations and overflow. Setting the amplitude to a higher value is suitable for large-capacity crucibles to increase the melt convection range, enhance the convection effect, and thus improve the bubble removal effect.

[0052] By setting different amplitude ranges for crucible 120 to accommodate crucibles of different capacities, the lower amplitude is used to ensure the safety of using small-capacity crucibles, while the higher amplitude is used to enhance the convection intensity of the melt in large-capacity crucibles, which allows for maximizing bubble removal efficiency while ensuring safety.

[0053] It is conceivable that the controller 160 can also be configured to control the rotation direction switching cycle of the crucible 120's alternating forward and reverse rotation to be shorter than the lifting switching cycle of the vertical reciprocating lifting motion.

[0054] As previously mentioned, the forward and reverse rotation of crucible 120 utilizes inertia to detach bubbles from the crucible wall 122. Therefore, it is understandable that the inertial force is more pronounced when crucible 120 changes its rotation direction. When crucible 120 moves in the same rotation direction for an extended period, bubbles are more likely to re-attach to the crucible wall 122 after detachment. In this case, the controller 160 controls the rotation direction switching cycle of crucible 120 to be shorter than the lifting / lowering switching cycle. This ensures that bubbles are detached more frequently through rotational motion during the lifting / lowering process, preventing re-attachment. For example, the lifting / lowering switching cycle can be set to 60 seconds, and the rotation switching cycle to 30 seconds. In this way, crucible 120 can complete two bubble detachments during one vertical lifting / lowering motion, significantly improving the bubble detachment efficiency.

[0055] Understandably, the ratio of the two motion cycles can be adjusted according to the bubble content. When the bubble content is high, the ratio of the rotation switching cycle to the lifting switching cycle can be set to 1:3 to further increase the rotation switching frequency. When the bubble content is low, the ratio can be set to 1:2 to balance the efficiency and energy consumption of the crystal pulling process.

[0056] By shortening the rotation switching cycle of crucible 120, bubbles can be continuously stripped during crystal pulling. Furthermore, setting the rotation switching cycle and the lifting switching cycle to a specific ratio allows for continuous bubble stripping, while simultaneously enhancing convection due to the lifting motion, enabling bubbles to rapidly migrate to the melt surface. This avoids discontinuous bubble stripping caused by a mismatch between the two motion cycles. Consequently, the bubble removal time can be further shortened.

[0057] It is conceivable that the crystal pulling device 100 may also include a magnetic field control device 180, which is communicatively connected to the controller 160.

[0058] like Figure 6 As shown, the magnetic field control device 180 is arranged around the middle furnace cylinder area outside the crucible 120 and is communicatively connected to the controller 160. The controller 160 is configured to dynamically adjust the magnetic field parameters according to the viscosity and bubble content of the silicon melt.

[0059] For example, after the melting process is completed, the magnetic field strength generated by the magnetic field control device 180 can be set in the range of 1000~1200GS. Furthermore, setting the magnetic field position at a distance of -161mm to -151mm between the upper edge of the magnetic field and the upper edge of the furnace cylinder, and setting the center of the magnetic field approximately 80mm below the solution, allows the center of the magnetic field to coincide with the convection core region of the melt, thereby optimizing the magnetic field's control effect on melt convection. Thus, the magnetic field control device 180 can more precisely control melt convection, regulate the melt flow trajectory, and, in conjunction with the inertial force generated by the rotation of the crucible 120, allows for more efficient removal of bubbles adhering to the crucible wall 122, while accelerating the convergence of bubbles inside the melt to the liquid surface and shortening the bubble removal time.

[0060] By setting an appropriate magnetic field strength, turbulent convection in the silicon melt can be effectively suppressed, stabilizing its flow state and preventing bubbles from being entrained within the melt, while maintaining their upward movement. Furthermore, precise positioning of the magnetic field can further optimize the melt flow state, and in conjunction with the rotation and lifting motion of the crucible 120, reduce the occurrence of obstructed bubble discharge, thereby further improving the stability of bubble discharge.

[0061] It is conceivable that the crystal pulling apparatus 100 may also include a gas supply and control system 190, which is configured to control the gas flow rate into the crucible 120 within the range of 120 L / min to 140 L / min.

[0062] Understandably, a stable reaction environment is necessary during crystal pulling. Poor stability of the heating and insulation systems can lead to temperature differences within the silicon solution, causing unstable convection and making it difficult for bubbles to escape, increasing the probability of porosity formation. Therefore, for example, the gas introduced into the crucible 120 may include an inert gas, such as argon, to remove impurities and heat from the crucible 120.

[0063] like Figure 7 As shown, the gas supply and control system 190 may include an argon storage tank 192, a flow controller 194, a pressure regulating valve 196, and a nozzle 198. Exemplarily, the nozzle 198 may be tilted towards the opening of the crucible 120 to form an annular gas flow, ensuring uniform argon coverage of the liquid surface, thereby improving the efficiency of removing impurities and bubbles and avoiding excessively strong or weak local gas flow.

[0064] However, the argon flow rate affects porosity. If the argon flow rate is too high, it may cause the oxide film on the surface of the silicon solution to be blown away, making it easier for bubbles to enter the silicon solution. If the argon flow rate is too low, it cannot remove bubbles and silicon monoxide impurities from the surface in time, causing bubbles to accumulate in the silicon solution and form pores.

[0065] By setting an appropriate argon gas flow rate, bubbles and impurities on the liquid surface can be carried away in a timely manner, preventing damage to the oxide film on the surface of the silicon melt due to excessive gas flow. Furthermore, in conjunction with the movement of the crucible 120, the probability of porosity formation can be further reduced.

[0066] It is also conceivable that the gas supply and control system 190 can adjust the furnace pressure inside the crucible 120 via the pressure regulating valve 196, for example, by setting the furnace pressure in the range of 8 torr to 10 torr. By setting an appropriate furnace pressure range, sufficient power can be provided for the argon gas flow, while maintaining the dynamic balance of the argon atmosphere inside the crucible, avoiding turbulence or local negative pressure on the melt surface caused by pressure fluctuations, thereby stabilizing the convection state of the silicon melt.

[0067] According to another aspect of this disclosure, referring to Figure 8 Furthermore, a crystal pulling method is also provided.

[0068] The crystal pulling method includes: Step S110: Provide molten silicon into the crucible; Step S120: Heat the silicon melt to melt it; Step S130: After the silicon melt has melted, before starting to pull the crystal, synchronously drive the crucible to perform alternating forward and reverse rotation around the central axis of the crucible and vertical reciprocating lifting and lowering motion in the vertical direction; and Step S140: Pull the crystal from the molten silicon melt.

[0069] In this way, by pre-setting the movement mode and process parameters of the crucible, and by setting the controller program and driver structure, it is possible to make the stabilization stage compatible with other process stages (such as material preparation, pulling, and finishing), thereby improving the efficiency of bubble removal and simplifying the process flow, which is conducive to the industrial promotion of crystal pulling technology.

[0070] It is conceivable that the steps for driving the crucible's movement could also include, while the crucible completes one lifting motion from the lowest to the highest position of its stroke, the crucible completes at least one rotational motion from forward to reverse.

[0071] By switching the rotational motion multiple times during the crucible's raising and lowering process, it is ensured that bubbles are continuously stripped away during the enhanced melt convection stage, preventing them from re-attaching to the crucible wall during the raising and lowering process. This improves bubble removal efficiency and further reduces the incidence of porosity defects.

[0072] Below, in conjunction with Figures 2 to 7 The crystal pulling apparatus 100 shown illustrates the crystal pulling method.

[0073] The process of growing single crystals using the Czochralski method typically involves five stages: the charging stage, the chemical preparation stage, the stabilization stage, the pulling stage, and the finishing stage.

[0074] First, during the loading stage, polysilicon is placed in crucible 120, and the filling density of polysilicon is controlled to be approximately 1.2 g / cm³ to reduce the gaps between silicon materials, thereby reducing the initial inclusion of gas.

[0075] Next, in the melting stage, under the protection of an argon atmosphere, the crucible 120 is heated in stages via heater 110. For example, the base heating power is gradually increased to approximately 20-25 kW, and the main heating power is gradually increased to approximately 135-145 kW, in order to completely melt the polycrystalline silicon material into a silicon melt and maintain the viscosity of the silicon melt within the optimal range. New bubbles are usually generated during this stage due to the high temperature and reaction.

[0076] After the material is melted, it enters the stabilization stage (i.e., the movement stage of crucible 120). During this stage, the melt temperature is kept stable, and crucible 120 is controlled to synchronously perform frequency conversion forward and reverse rotation and vertical reciprocating lifting and lowering movements. With the help of magnetic field and argon gas parameters, bubbles on the wall are peeled off, melt convection is enhanced, and the bubbles rise to the liquid surface and are carried away by argon gas.

[0077] After the bubbles are expelled, the pulling stage begins. In this stage, seed crystal docking is initiated. By controlling the pulling speed and the crucible rotating in the opposite direction, the crystal is shaped to shoulder (enlarge the crystal diameter to the target size), equal diameter (maintain stable diameter growth), and tail (avoid crystal breakage), forming a single crystal rod.

[0078] In the final stage, after the single crystal rod has grown, the connection between the melt and the crystal is severed, and the single crystal rod is removed after cooling and then proceeds to subsequent processing steps such as slicing and polishing.

[0079] The stabilization stage is a crucial link between the material preparation stage and the pulling stage. By controlling the movement of the crucible 120 during the stabilization stage to actively intervene in the expulsion of bubbles, the problem of bubbles not being able to overflow naturally during the crystal pulling process can be solved, thereby reducing the possibility of porosity defects in the crystal rod.

[0080] In some implementations, the controller may be configured to, when controlling the crucible to perform alternating forward and reverse rotational motion, control the crucible to accelerate in a first rotational direction to a first rotational speed and maintain it for a first duration, then decelerate and switch to a second rotational direction opposite to the first rotational direction, accelerate to a second rotational speed and maintain it for a second duration.

[0081] In some implementations, the absolute value of the first speed and the second speed may be less than or equal to 1 rpm.

[0082] In some implementations, the controller may be configured to, while controlling the crucible to perform vertical reciprocating lifting and lowering motion, also control the crucible to periodically displace relative to the upper end of the heater.

[0083] In some implementations, the amplitude of the crucible's vertical reciprocating lifting motion can be less than or equal to 120 mm.

[0084] In some implementations, the controller may also be configured to control the rotation direction switching cycle of the crucible's alternating forward and reverse rotation to be shorter than the lifting switching cycle of the vertical reciprocating lifting motion.

[0085] In some embodiments, the crystal pulling apparatus may further include a magnetic field control device, which is communicatively connected to the controller, and the magnetic field strength generated by the magnetic field control device is in the range of 1000GS to 1200GS.

[0086] In some embodiments, the crystal pulling apparatus may also include a gas supply and control system configured to control the gas flow rate into the crucible within the range of 120 L / min to 140 L / min.

[0087] In summary, based on these technical solutions, by increasing the convection of the melt through the up-and-down movement of the crucible and the forward and reverse rotation of the frequency converter, bubbles adhering to the walls of the quartz crucible can be detached, and bubbles in the silicon solution can be moved to the surface through convection and then evaporate. Furthermore, by setting process parameters such as a lower magnetic field strength, a negative magnetic field position, a lower furnace pressure, and a moderate argon flow rate that match the crucible movement, a complete bubble removal system can be formed, thereby effectively reducing the porosity defect rate of the crystal rod and thus improving the quality of the crystal rod.

[0088] While this disclosure has been described with reference to exemplary embodiments, it should be understood that this disclosure is not limited to the specific embodiments described and shown herein. Various changes to the exemplary embodiments can be made by those skilled in the art without departing from the scope defined by the claims of this disclosure.

[0089] The features mentioned and / or shown in the foregoing description of exemplary embodiments of this disclosure may be combined in the same or similar manner with one or more other embodiments, combined with features in other embodiments, or substituted for corresponding features in other embodiments. Such combinations or substitutions should also be considered as including within the scope of protection of this disclosure.

Claims

1. A crystal pulling apparatus, characterized in that, include: A crucible containing molten silicon; A driver that drives the crucible to move; as well as A controller, communicatively connected to the driver, is configured to, upon detecting that the silicon melt in the crucible has melted completely, before starting crystal pulling, control the driver to drive the crucible to simultaneously perform alternating forward and reverse rotation around the central axis of the crucible and vertical reciprocating lifting and lowering motion in the vertical direction.

2. The crystal pulling apparatus according to claim 1, characterized in that, When the controller controls the crucible to perform the alternating forward and reverse rotation motion, it is configured to control the crucible to accelerate in a first rotation direction to a first rotation speed and maintain it for a first duration, then decelerate and switch to a second rotation direction opposite to the first rotation direction, accelerate to a second rotation speed and maintain it for a second duration.

3. The crystal pulling apparatus according to claim 2, characterized in that, The absolute value of the first speed and the second speed is less than or equal to 1 rpm.

4. The crystal pulling apparatus according to claim 1, characterized in that, When controlling the crucible to perform the vertical reciprocating lifting motion, the controller is configured to also control the crucible to periodically displace relative to the upper end of the heater.

5. The crystal pulling apparatus according to claim 4, characterized in that, The amplitude of the vertical reciprocating lifting motion of the crucible is less than or equal to 120 mm.

6. The crystal pulling apparatus according to claim 1, characterized in that, The controller is also configured to control the rotation direction switching cycle of the alternating forward and reverse rotation of the crucible to be shorter than the lifting switching cycle of the vertical reciprocating lifting motion.

7. The crystal pulling apparatus according to claim 1, characterized in that, It also includes a magnetic field control device, which is communicatively connected to the controller, and the magnetic field strength generated by the magnetic field control device is in the range of 1000GS~1200GS.

8. The crystal pulling apparatus according to claim 1, characterized in that, It also includes a gas supply and control system configured to control the gas flow rate into the crucible within the range of 120 L / min to 140 L / min.

9. A crystal pulling method, characterized in that, include: Silicon melt is provided in the crucible; The silicon melt is heated to melt it. After the silicon melt is melted, before the crystal pulling begins, the crucible is synchronously driven to perform alternating forward and reverse rotation around the central axis of the crucible and vertical reciprocating lifting and lowering motion in the vertical direction. as well as The crystal is pulled from the molten silicon.

10. The crystal pulling method according to claim 9, characterized in that, When the crucible completes one lifting motion from the lowest to the highest position of its stroke, the crucible completes at least one rotational motion from forward to reverse.

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