Crystalline silicon ingot casting crucible rotation control method for improving solid-liquid interface and impurity distribution
By using intermittent forward and reverse rotation modes and a staged controlled silicon melt crucible rotation method, the problems of unstable interface morphology, uneven impurity distribution, and excessive thermal stress in the production of silicon ingots by casting were solved, thus realizing the production of high-quality crystalline silicon ingots.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-26
- Publication Date
- 2026-03-24
AI Technical Summary
In existing silicon ingot production using the casting method, it is difficult to maintain a stable solid-liquid interface, control the growth of polycrystalline material at the edges, uniformly remove impurities, and reduce thermal stress, leading to a decline in crystal quality and yield.
The silicon melt crucible is controlled by an intermittent forward and reverse rotation mode. The rotation rate, time and pause time are dynamically adjusted in stages to form a strong transient shear flow, optimize the interface morphology and impurity distribution, and reduce thermal stress.
It significantly optimizes the solid-liquid interface morphology, suppresses polycrystalline growth at the edges, reduces impurity enrichment, lowers thermal stress, increases the proportion of single crystals in the central region of silicon ingots and the overall crystal quality, and improves the yield.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of directional solidification preparation of crystalline silicon material, and particularly relates to a crystalline silicon ingot crucible rotation control method for improving solid-liquid interface and impurity distribution. BACKGROUND
[0002] In the production of crystalline silicon material, the cast method crystalline silicon ingot is widely used in the photovoltaic and semiconductor industries. However, the existing ingot production technology still faces many challenges, especially in how to maintain a stable growth interface, control the edge polycrystalline growth, uniformly remove impurities and reduce thermal stress.
[0003] The conventional ingot furnace adopts a heat dissipation mode combining an upper heat insulation cage and a bottom heat exchange table, and controls the temperature field of the melt through side heat dissipation to realize the regulation of the crystallization process. However, this heat dissipation structure inevitably leads to excessive side heat dissipation, so that the solid-liquid interface tends to be concave, and then the edge polycrystalline growth extends to the inside, affecting the crystal quality of the silicon ingot. Although the traditional heat dissipation mode can slow down the side crystallization by increasing the side power and attempt to maintain an approximately convex growth interface, due to the limitation of side heat dissipation, the interface is still difficult to maintain an ideal micro-convex shape, and finally forms an approximately convex W-shaped interface, which is prone to cause the growth of edge polycrystalline, reducing the proportion of single crystal region.
[0004] In addition, the conventional technology also has the problem of excessive thermal stress. Due to uneven heat dissipation, the temperature and composition of each part of the melt are inconsistent, resulting in thermal stress concentration, especially at the end of crystallization, the volume of the melt gradually decreases, and the temperature gradient and thermal field imbalance problem becomes more and more significant. Excessive thermal stress can cause cracks or warping of the silicon ingot, thereby affecting the final yield.
[0005] At the same time, the uneven distribution of impurities is also a long-standing problem in the process of casting silicon ingot. Oxygen, carbon, nitrogen and other impurities tend to accumulate near the solid-liquid interface, forming an impurity band, which leads to the decline of the performance of downstream devices. Due to the existing heat dissipation structure, the melt flow field cannot be effectively controlled, and the phenomenon of impurity enrichment often cannot be effectively curbed.
[0006] At present, the traditional thermal field design and crucible rotation method cannot effectively solve these problems, which significantly affects the crystal quality of the silicon ingot, the distribution of impurities and the final yield.
[0007] Therefore, it is of great significance to provide a crystalline silicon ingot crucible rotation control method for improving the uniformity of the melt flow field, optimizing the interface shape, reducing the unevenness of the impurity distribution, and effectively reducing the thermal stress, thereby improving the quality and yield of the silicon ingot. SUMMARY
[0008] The purpose of this invention is to provide a method for controlling the rotation of a crystalline silicon ingot crucible to improve the solid-liquid interface and impurity distribution, thereby solving the technical problem in existing ingot casting technology that it is difficult to simultaneously control interface morphology, optimize impurity distribution, and reduce thermal stress.
[0009] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for controlling the rotation of a crystalline silicon ingot crucible to improve the solid-liquid interface and impurity distribution, comprising the following steps: The crucible containing molten silicon is controlled by an intermittent forward and reverse rotation mode, wherein each rotation cycle includes a forward rotation stage, a pause stage and a reverse rotation stage in sequence. Based on the real-time growth height h of the silicon ingot during the directional solidification process, the rotation rate and duration of the forward and reverse rotation stages, as well as the pause time of the pause stage, are dynamically adjusted in stages.
[0010] Furthermore, the growth height h is divided into four stages according to normalization: the initial stage h is 0~0.2, the middle stage h is 0.2~0.7, the later stage h is 0.7~0.9, and the final stage h is 0.9~1.0.
[0011] Furthermore, the control parameters for the initial stage are as follows: forward rotation speed is 2.0~3.0 rpm, duration is 45~75 seconds; reverse rotation speed is 1.5~2.5 rpm, duration is 45~75 seconds; and the rotation cycle for the initial stage is 120~210 seconds.
[0012] Furthermore, the control parameters for the intermediate stage are as follows: the forward rotation speed is 1.0~2.0 rpm, and the duration is 75~105 seconds; the reverse rotation speed is 0.8~1.8 rpm, and the duration is 75~105 seconds; the rotation cycle of the intermediate stage is 180~270 seconds.
[0013] Furthermore, the control parameters for the later stage are: forward rotation speed of 0.5~1.2 rpm and duration of 105~135 seconds; reverse rotation speed of 0.4~1.0 rpm and duration of 105~135 seconds; and rotation cycle of 215~300 seconds for the later stage.
[0014] Furthermore, the control parameters for the final stage are as follows: forward rotation speed is 0.1~0.5 rpm, duration is 135~165 seconds; reverse rotation speed is 0.1~0.4 rpm, duration is 135~165 seconds; and the rotation cycle for the final stage is 275~360 seconds.
[0015] Furthermore, the pause times for the initial and intermediate stages are independently 30-60 seconds, and the pause times for the later and final stages are independently 5-30 seconds.
[0016] Furthermore, within the same rotation cycle, the reverse rotation rate is lower than the forward rotation rate.
[0017] Furthermore, during the switching process between forward and reverse rotation, the maximum acceleration of the rotational rate is ≤0.3 rpm / s.
[0018] The beneficial effects of this invention are: 1) The method of the present invention can significantly optimize the solid-liquid interface morphology and effectively suppress the growth of polycrystalline material at the edge. Through intermittent forward and reverse rotation, a periodically changing melt flow field is formed near the side wall of the crucible, which completely breaks the steady boundary layer formed by unidirectional flow. This transient shear flow weakens the radial temperature gradient caused by heat dissipation at the side, making the melt thermal field distribution more uniform, thereby suppressing the evolution of the solid-liquid interface to a concave shape and effectively maintaining the ideal micro-convex interface morphology. The optimization of the interface morphology effectively blocks the extension of polycrystalline material at the edge into the interior, significantly improving the single crystal ratio in the central region of the silicon ingot and the overall crystal quality. 2) The method of the present invention can efficiently control the distribution of impurities and suppress the phenomenon of impurity enrichment. The rotation mode of forward rotation-pause-reverse rotation utilizes fluid inertia and flow direction switching to generate strong transient shear flow at the front of the solid-liquid interface. This intense convection can deeply clean the interface, break through the diffusion boundary layer of impurities such as oxygen, carbon, and nitrogen at the interface, greatly reduce the enrichment and deposition of impurities, thereby significantly reducing the density of impurity points inside the silicon ingot and effectively blocking the formation of impurity bands. 3) The method of this invention can systematically reduce thermal stress and suppress structural defects. The strategy of dynamically adjusting the rotation rate based on the crystallization process, especially the gradual reduction of the rate in the later and final stages of crystallization, is crucial. When the melt volume shrinks and the thermal gradient intensifies at the end of crystallization, reducing flow field disturbance can effectively smooth out thermal fluctuations caused by uneven convection, significantly reducing the accumulation of thermal stress inside the silicon ingot. The reduction in thermal stress significantly suppresses the generation of structural defects such as microcracks and dislocations, completely avoiding the risk of warping and cracking of the silicon ingot. 4) The method of this invention achieves synergistic improvement in silicon ingot quality and production yield. Relying on the triple mechanism of interface morphology optimization, impurity distribution control and thermal stress reduction, this method significantly improves the overall crystal quality of cast crystalline silicon ingots. The simultaneous reduction of defects and impurities directly translates into a leap in yield, fundamentally solving the problem of low yield in existing technologies, and has significant industrial application value. Detailed Implementation
[0019] This invention provides a method for controlling the rotation of a crystalline silicon ingot crucible to improve the solid-liquid interface and impurity distribution, comprising the following steps: The crucible containing molten silicon is controlled by an intermittent forward and reverse rotation mode, wherein each rotation cycle includes a forward rotation stage, a pause stage and a reverse rotation stage in sequence. Based on the real-time growth height h of the silicon ingot during the directional solidification process, the rotation rate and duration of the forward and reverse rotation stages, as well as the pause time of the pause stage, are dynamically adjusted in stages.
[0020] In this invention, the growth height h is divided into four stages according to normalization: the initial stage h is 0~0.2, the middle stage h is 0.2~0.7, the later stage h is 0.7~0.9, and the final stage h is 0.9~1.0.
[0021] In this invention, the control parameters for the initial stage are: a forward rotation speed of 2.0~3.0 rpm and a duration of 45~75 seconds; a reverse rotation speed of 1.5~2.5 rpm and a duration of 45~75 seconds; and a rotation cycle of 120~210 seconds for the initial stage.
[0022] In this invention, the purpose of the initial stage is to form strong convection. In the initial stage, the melt volume is large, and strong stirring is required to homogenize the composition and temperature field and establish a good initial growth interface.
[0023] In this invention, the reverse rotation rate is slightly lower than the forward rotation rate in order to create asymmetric flow disturbances and prevent the formation of flow dead zones.
[0024] In this invention, the control method in the initial stage is to use a higher rotational speed and a shorter cycle.
[0025] In this invention, the control parameters for the intermediate stage are: forward rotation speed of 1.0~2.0 rpm and duration of 75~105 seconds; reverse rotation speed of 0.8~1.8 rpm and duration of 75~105 seconds; and rotation cycle of the intermediate stage of 180~270 seconds.
[0026] In this invention, the purpose of the intermediate stage is to stabilize growth. As the melt volume decreases, it is necessary to maintain a stable micro-convex interface, balance the convection intensity and growth rate, and prevent impurity accumulation.
[0027] In this invention, the control method for the intermediate stage is to use a moderate rotation speed and a moderate cycle.
[0028] In this invention, the control parameters for the later stage are: forward rotation speed of 0.5~1.2 rpm and duration of 105~135 seconds; reverse rotation speed of 0.4~1.0 rpm and duration of 105~135 seconds; and rotation cycle of the later stage of 215~300 seconds.
[0029] In this invention, the purpose of the later stage is to reduce stress and prevent defects. With less melt and a large thermal gradient, thermal stress is easily generated. It is necessary to reduce disturbances to ensure smooth interface transition and avoid stress concentration and crystal breakage caused by drastic changes in the flow field.
[0030] In this invention, the control method in the later stage is to further reduce the rotation speed and extend the cycle.
[0031] In this invention, the control parameters for the final stage are: forward rotation speed of 0.1~0.5 rpm and duration of 135~165 seconds; reverse rotation speed of 0.1~0.4 rpm and duration of 135~165 seconds; and rotation cycle of the final stage of 275~360 seconds.
[0032] In this invention, the purpose of the final stage is to maintain a stable interface. As the melt approaches the completion of crystallization and the interface advances to the top, an extremely low rate must be maintained to ensure the final smooth closure of the interface.
[0033] In this invention, the pause time for the initial stage and the intermediate stage is independently 30 to 60 seconds, and the pause time for the later stage and the final stage is independently 5 to 30 seconds.
[0034] In this invention, in order to fully buffer the flow inertia and generate an effective transient shear flow, a pause time is set at each forward and reverse switching. In the early and middle stages of crystallization, due to the large melt volume and high rotation speed, the required inertial buffering time is longer, so a longer pause time (30-60 seconds) is preferred; in the later and final stages, the melt volume is smaller and the rotation speed is lower, so the pause time can be appropriately shortened (5-30 seconds).
[0035] In this invention, the purpose of the pause phase is to use inertia to eliminate the flow in the previous direction, so that the melt is briefly still, in preparation for generating stronger shear force when it starts up in the reverse direction.
[0036] In this invention, the control method for the final stage is extremely low speed and the longest cycle.
[0037] In this invention, within the same rotation cycle, the reverse rotation rate is lower than the forward rotation rate.
[0038] In this invention, during the switching process between forward and reverse rotation, the maximum acceleration of the rotation rate is ≤0.3 rpm / s.
[0039] In this invention, in order to prevent the molten material from sloshing and impacting the fragile crystal interface during growth, and to achieve high-quality crystal growth, the switching between forward and reverse rotation must be carried out smoothly: at the end of forward (or reverse) rotation, the rotation speed is gradually reduced to 0 rpm and a brief pause is maintained to fully buffer the flow inertia. After the pause, reverse (or forward) rotation begins, and the speed is gradually accelerated from 0 rpm to the set target speed. The acceleration and deceleration during the switching process are precisely adjusted by the control program to ensure that the entire process is smooth and shock-free.
[0040] In this invention, the rotation process is automatically executed by a program control system, and the specific control logic is as follows: Real-time data is collected through temperature sensors, torque sensors, and melt height monitoring equipment; the control system automatically adjusts the rotation speed, cycle, duration, and switching timing of forward and reverse rotation based on the real-time growth height, crystallization stage, and set target parameters of the silicon ingot, to achieve closed-loop or open-loop control of the entire process.
[0041] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.
[0042] Example 1
[0043] A crystalline silicon ingot casting experiment was conducted in a directional solidification ingot casting furnace. The silicon ingot had a mass of 600 kg and a growth height of 350 mm. The following crucible rotation control method was used during the crystallization process: alternating forward and reverse rotation, with each rotation cycle consisting of a forward rotation stage, a pause stage, and a reverse rotation stage. The rotation speeds for each stage of the forward rotation were 3.0 rpm, 1.5 rpm, 1.2 rpm, and 0.5 rpm, respectively. After forward rotation, the speed dropped to 0 rpm, paused for 30 seconds, and then reversed rotation. The rotation speeds for each stage of the reverse rotation were 2.5 rpm, 1.3 rpm, 1.0 rpm, and 0.2 rpm, respectively. The rotation cycles were 150 seconds, 200 seconds, 230 seconds, and 280 seconds, respectively.
[0044] Example 1 employed intermittent forward and reverse rotation and phased reduction of rotation speed. The initial higher rotation speed and shorter cycle provided sufficient convective stirring, which helped to homogenize the melt composition and temperature field, and establish a good initial interface. The rotation speed was reduced in the middle stage to maintain stable interface growth. The rotation speed was further reduced in the final stage to reduce flow field disturbance, effectively reduce thermal stress, and thus reduce the generation of defects. The setting of the pause time made full use of fluid inertia, enhanced the interface cleaning effect, and significantly reduced the impurity ratio.
[0045] Example 2
[0046] A crystalline silicon ingot casting experiment was conducted in a directional solidification ingot casting furnace. The silicon ingot had a mass of 800 kg and a growth height of 350 mm. The following crucible rotation control method was used during the crystallization process: initially, the forward rotation was 2.8 rpm and the reverse rotation was 2.0 rpm, with a cycle of 210 seconds; as the height increased, the speed was automatically adjusted every 30% of the crystallization height, and reduced to 0.2 rpm in the final stage; the pause time was increased to 30 seconds to more fully buffer the flow inertia; the control system adjusted the rotation rhythm in a closed loop based on the melt temperature and interface position.
[0047] Example 2 further optimized the control strategy for heavier silicon ingots. Asymmetric forward and reverse rotation speeds (2.8 rpm forward, 2.0 rpm reverse) created asymmetric flow disturbances, preventing the formation of flow dead zones. Closed-loop adjustment based on melt temperature and interface position allowed for more precise matching of rotation parameters to the actual needs of the crystallization process. A longer dwell time (30 seconds) enhanced the cleaning effect of the transient shear flow, significantly suppressing impurity enrichment and sidewall polycrystalline growth, thereby greatly improving the yield of the finished product.
[0048] Example 3
[0049] Using the same 600kg ingot furnace, a smoother rotation rate decay curve was adopted while ensuring a 10% reduction in the total crystallization time. The initial rate was 2.0 rpm, decreasing linearly in increments of 5% height; the initial rotation cycle was shortened to 150 seconds to accelerate the overall process; the duration of reverse rotation was relatively shortened to avoid excessive disturbance to the interface.
[0050] Example 3 achieves fine control of the flow field by shortening the crystallization time and by using a smoother linear deceleration rate curve and a shorter rotation period. The smooth rate change avoids drastic fluctuations in the flow field and helps maintain stable interface advancement. The shortened reverse rotation time and period accelerate the crystallization process while ensuring a certain disturbance intensity. This improves production efficiency while maintaining high crystal quality and yield.
[0051] Comparative Example 1
[0052] Compared with Example 1, the difference is that Comparative Example 1 uses a conventional non-rotation process for ingot casting: the crucible is fixed and crystal growth is controlled only by adjusting the thermal field; other parameters are kept consistent with the Example (furnace type, crucible, temperature control program).
[0053] When using the traditional non-rotation process in Comparative Example 1, the lack of forced convection makes it easy for impurities in the melt to accumulate at the solid-liquid interface, resulting in a significant increase in the proportion of impurity points. At the same time, the lack of flow field disturbance makes it impossible to effectively suppress the interface depression caused by lateral heat dissipation, which greatly increases the risk of polycrystalline growth at the edge. In the final stage of crystallization, the lack of flow field adjustment can easily lead to thermal stress concentration, which in turn increases the defect ratio and ultimately results in a low yield of finished products.
[0054] Comparative Example 2
[0055] Compared with Example 1, the difference is that Comparative Example 2 adopts a constant intermittent forward and reverse rotation strategy throughout the crystallization process: forward rotation 2.0 rpm, reverse rotation 2.0 rpm, pause for 30 seconds, cycle 180 seconds, and the parameters remain unchanged throughout the entire crystallization process.
[0056] Although Comparative Example 2 employed intermittent forward and reverse rotation technology, it failed to effectively adapt to the dynamic changes in melt volume and thermal field gradient at different crystallization stages due to maintaining a constant rotation speed and cycle throughout the crystallization process. In the early stages of crystallization, the constant rotation speed resulted in insufficient disturbance, leading to incomplete impurity cleaning and a significantly higher impurity ratio compared to the Example. Conversely, in the later stages of crystallization, the constant rotation speed caused excessive disturbance, resulting in greater thermal stress and a significantly higher defect ratio compared to the Example. This fully demonstrates the necessity of dynamically adjusting the rotation parameters in stages.
[0057] The performance of Examples 1-3 and Comparative Examples 1-2 was tested, and the test results are shown in Table 1.
[0058] Table 1 Performance test results of Examples 1-3 and Comparative Examples 1-2
[0059] As can be seen from the above embodiments, the present invention provides a method for controlling the rotation of a crystalline silicon ingot crucible to improve the solid-liquid interface and impurity distribution. The present invention employs staged dynamic adjustment, intermittent forward and reverse rotation, asymmetric rotation speed, pause settings, and smooth switching techniques to break the steady-state boundary layer formed by unidirectional flow. It utilizes the fluid's inertia and direction switching to generate strong transient shear flow, thereby optimizing impurity distribution, dynamically controlling melt convection intensity, maintaining a stable and slightly convex solid-liquid interface morphology, and effectively suppressing polycrystalline phenomena at the ingot edges. Based on the changes in melt volume, viscosity, and thermal field gradient at different crystallization stages of the silicon ingot, the present invention dynamically adjusts the rotation rate and period to ensure sufficient disturbance in the initial stage to homogenize composition and thermal field, while gradually reducing disturbance in the middle and later stages to maintain stable interface growth and avoid excessive thermal stress at the end, reducing internal crystal defects and ultimately comprehensively improving the yield of polycrystalline silicon ingots. Simultaneously, the present invention possesses excellent process adaptability, flexibly adapting to different ingot weights and production cycle requirements through parameter optimization, offering comprehensive and significant technical advantages compared to traditional non-rotating or constant rotation processes.
[0060] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for controlling the rotation of a crystalline silicon ingot crucible to improve the solid-liquid interface and impurity distribution, characterized in that, Includes the following steps: The crucible containing molten silicon is controlled by an intermittent forward and reverse rotation mode, wherein each rotation cycle includes a forward rotation stage, a pause stage and a reverse rotation stage in sequence; Based on the real-time growth height h of the silicon ingot during the directional solidification process, the rotation rate and duration of the forward and reverse rotation stages, as well as the pause time of the pause stage, are dynamically adjusted in stages.
2. The method for controlling the rotation of a crystalline silicon ingot crucible to improve the solid-liquid interface and impurity distribution according to claim 1, characterized in that, The growth height h is divided into four stages according to normalization: the initial stage h is 0~0.2, the middle stage h is 0.2~0.7, the later stage h is 0.7~0.9, and the final stage h is 0.9~1.
0.
3. The method for controlling the rotation of a crystalline silicon ingot crucible to improve the solid-liquid interface and impurity distribution according to claim 2, characterized in that, The control parameters for the initial stage are as follows: forward rotation speed is 2.0~3.0 rpm, duration is 45~75 seconds; reverse rotation speed is 1.5~2.5 rpm, duration is 45~75 seconds; and the rotation cycle for the initial stage is 120~210 seconds.
4. The method for controlling the rotation of a crystalline silicon ingot crucible to improve the solid-liquid interface and impurity distribution according to claim 3, characterized in that, The control parameters for the intermediate stage are as follows: forward rotation speed is 1.0~2.0 rpm, duration is 75~105 seconds; reverse rotation speed is 0.8~1.8 rpm, duration is 75~105 seconds; and the rotation cycle for the intermediate stage is 180~270 seconds.
5. The method for controlling the rotation of a crystalline silicon ingot crucible to improve the solid-liquid interface and impurity distribution according to claim 3 or 4, characterized in that, The control parameters for the later stage are as follows: forward rotation speed is 0.5~1.2 rpm, duration is 105~135 seconds; reverse rotation speed is 0.4~1.0 rpm, duration is 105~135 seconds; and the rotation cycle for the later stage is 215~300 seconds.
6. The method for controlling the rotation of a crystalline silicon ingot crucible to improve the solid-liquid interface and impurity distribution according to claim 5, characterized in that, The control parameters for the final stage are as follows: forward rotation speed is 0.1~0.5 rpm, duration is 135~165 seconds; reverse rotation speed is 0.1~0.4 rpm, duration is 135~165 seconds; and the rotation cycle for the final stage is 275~360 seconds.
7. The method for controlling the rotation of a crystalline silicon ingot crucible to improve the solid-liquid interface and impurity distribution according to claim 6, characterized in that, The pause times for the initial and middle stages are 30-60 seconds each, while the pause times for the later and final stages are 5-30 seconds each.
8. The method for controlling the rotation of a crystalline silicon ingot crucible to improve the solid-liquid interface and impurity distribution according to claim 7, characterized in that, Within the same rotation cycle, the reverse rotation rate is lower than the forward rotation rate.
9. The method for controlling the rotation of a crystalline silicon ingot crucible to improve the solid-liquid interface and impurity distribution according to claim 8, characterized in that, During the switching between forward and reverse rotation, the maximum acceleration of the rotational rate is ≤0.3 rpm / s.