Method for pulling a single crystal silicon rod and a silicon wafer

Abstract

The present disclosure relates to the field of photovoltaic technology, and particularly relates to a method for drawing a single crystal silicon rod and a silicon wafer. The method comprises sequentially performed melting, seeding, shoulder-removing and constant-diameter processes. In the constant-diameter process, the following steps are implemented: setting a target furnace pressure and a preset upper limit value of a dry pump opening; adjusting the dry pump opening to control an actual furnace pressure in the furnace at the target furnace pressure; when the current opening of the dry pump is lower than the preset upper limit value, increasing the flow of protective gas into the single crystal furnace, and returning to perform the step of adjusting the dry pump opening based on the furnace pressure change until the opening of the dry pump is greater than or equal to the preset upper limit value. The present disclosure is at least beneficial to improving the electrical performance and yield of the single crystal silicon rod.

Description

Technical Field

[0001] This disclosure relates to the field of photovoltaic technology, and in particular to a method for pulling monocrystalline silicon rods and silicon wafers. Background Technology

[0002] Crystal rods are essential raw materials for the manufacture of photovoltaic panels and semiconductor devices. In recent years, with the rapid expansion of the photovoltaic market and technological advancements, the production capacity and quality of crystal rods have been significantly improved. The maturity of technologies such as Czochralski (CZ) monocrystalline silicon and floating zone (FZ) melting methods has ensured the purity and crystal quality of crystal rods, thereby improving the conversion efficiency of solar cells and the performance of semiconductor devices.

[0003] Currently, argon is commonly used as a protective atmosphere in Czochralski (CZ) single-crystal silicon growth processes to suppress oxidation of the silicon melt and maintain a stable thermal environment. However, the argon atmosphere is susceptible to contamination by impurities such as oxygen and carbon. These impurities are easily introduced into the silicon melt during crystal growth, subsequently becoming incorporated into the crystal lattice and affecting the electrical properties and yield of the single-crystal silicon. Therefore, improving the purity of the protective atmosphere is crucial for ensuring the quality of single-crystal silicon and enhancing the performance of the final device. Summary of the Invention

[0004] This disclosure provides a method for pulling monocrystalline silicon rods and silicon wafers, which at least helps to improve the electrical properties and yield of monocrystalline silicon rods.

[0005] This disclosure provides a method for pulling a single-crystal silicon rod, including a melting process, a crystal pulling process, a shoulder forming process, and a diameter equalization process performed sequentially. In the diameter equalization process, the following steps are implemented: setting a target furnace pressure and a preset upper limit value for the dry pump opening; adjusting the dry pump opening to control the actual furnace pressure at the target furnace pressure; when the current opening of the dry pump is lower than the preset upper limit value, increasing the flow rate of the protective gas introduced into the single-crystal furnace, and returning to the step of adjusting the dry pump opening based on the furnace pressure change, until the opening of the dry pump is greater than or equal to the preset upper limit value.

[0006] Optionally, setting the preset upper limit value of the dry pump opening includes: setting the preset upper limit value as a first upper limit value in the initial stage of the equal diameter process; setting the preset upper limit value as a second upper limit value in the middle stage of the equal diameter process; and setting the preset upper limit value as a third upper limit value in the later stage of the equal diameter process; wherein the second upper limit value is greater than the first upper limit value, and the second upper limit value is greater than the third upper limit value.

[0007] Optionally, the preset upper limit value is 95% to 98% of the rated opening of the dry pump.

[0008] Optionally, increasing the flow rate of the protective gas introduced into the single crystal furnace when the current opening degree of the dry pump is lower than the preset upper limit value includes: adjusting the increase rate of the protective gas based on the difference between the current opening degree and the preset upper limit value.

[0009] Optionally, adjusting the increase rate of the protective gas based on the difference between the current opening and the preset upper limit value includes: determining whether the difference between the current opening and the preset upper limit value is greater than or equal to a first threshold; if so, increasing the flow rate of the protective gas at a first rate; if not, increasing the flow rate of the protective gas at a second rate; wherein the first rate is greater than the second rate.

[0010] Optionally, adjusting the opening degree of the dry pump includes: adjusting the opening degree of the dry pump based on the difference between the target furnace pressure and the actual furnace pressure.

[0011] Optionally, during the equal diameter process, the interstitial oxygen content in the single crystal silicon rod is monitored in real time; the real-time oxygen content is compared with a second threshold; and based on the comparison result, the preset upper limit value and / or the rate of increase of the protective gas flow rate are adjusted.

[0012] Optionally, adjusting the preset upper limit value based on the comparison result includes: increasing the preset upper limit value when the real-time oxygen content is greater than or equal to the second threshold; and decreasing the preset upper limit value when the real-time oxygen content is less than the second threshold.

[0013] Optionally, adjusting the rate of increase of the protective gas flow rate based on the comparison result includes: increasing the rate of increase of the protective gas flow rate when the real-time oxygen content is greater than or equal to the second threshold; and decreasing the rate of increase of the protective gas flow rate when the real-time oxygen content is less than the second threshold.

[0014] This disclosure also provides a silicon wafer, which is cut from a single-crystal silicon rod prepared by the above-described single-crystal silicon rod pulling method, wherein the oxygen content of the silicon wafer is less than or equal to 10 ppma and the carbon content of the silicon wafer is less than or equal to 0.5 ppma.

[0015] The technical solution provided in this disclosure has at least the following advantages: This disclosure sets a target furnace pressure and a preset upper limit for the dry pump opening during the equal diameter process, and adjusts the dry pump opening to maintain a stable actual furnace pressure. When the current dry pump opening is lower than the preset upper limit, the protective gas flow rate is increased. The dry pump opening is then adjusted back based on the furnace pressure change feedback. This process is repeated until the dry pump opening reaches or exceeds the preset upper limit. Thus, while maintaining a constant furnace pressure, the exhaust margin of the dry pump is fully utilized to continuously increase the protective gas flow rate, enhance the atmosphere replacement effect in the furnace, effectively reduce impurity retention, and significantly improve the purity of the protective gas acting on the crystal growth region, thereby improving the electrical performance and yield of the single crystal silicon rod. Attached Figure Description

[0016] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0017] Figure 1 This is a schematic diagram of the furnace pressure control process in the prior art; Figure 2 This is a schematic diagram of a furnace pressure control process in a single-crystal silicon rod pulling method provided in this embodiment of the disclosure; Figure 3 This is another schematic diagram of the furnace pressure control process in the single-crystal silicon rod pulling method provided in this embodiment of the disclosure. Detailed Implementation

[0018] As is known from the background technology, in the Czochralski single-crystal silicon process, argon is typically used as a protective atmosphere. Closed-loop control is implemented at each stage, including crystal pulling, shoulder formation, and diameter equalization, according to preset parameters such as fixed argon flow rate and furnace pressure, to maintain thermal stability and suppress silicon melt oxidation. (Reference) Figure 1 The existing control system sets the target furnace pressure and receives the actual furnace pressure feedback and argon flow input through the main control PD controller. After calculating the deviation between the two, it adjusts the opening of the dry pump to maintain the current actual furnace pressure at the target furnace pressure, thereby achieving closed-loop stability of the furnace pressure.

[0019] However, in actual production, it was found that as the crystal pulling time increased, the argon atmosphere in the single crystal furnace was gradually contaminated by impurities such as oxygen and carbon, and the degree of contamination continued to increase over time, resulting in a decrease in the electrical properties of the prepared single crystal silicon rod, an increase in defect density, and a significant deterioration in crystal quality.

[0020] Further analysis revealed that the root cause of the problem lies in the fact that the protective gas flow rate and the operating parameters of the exhaust system in the traditional process are fixed values, which cannot dynamically respond to changes in the accumulation of impurities in the furnace. When impurities are continuously released or released from the furnace material, the fixed flow rate of protective gas is difficult to effectively replace and dilute the pollutants, resulting in a continuous deterioration of the purity of the atmosphere in the furnace.

[0021] To address or improve the aforementioned technical problems, this disclosure provides a method for pulling monocrystalline silicon rods. In the equal diameter process, a target furnace pressure and a preset upper limit for the dry pump opening are set. The furnace pressure is kept constant by adjusting the dry pump opening in real time. When the dry pump opening does not reach the upper limit, the protective gas flow rate is actively increased. The flow rate is then adjusted cyclically based on the furnace pressure feedback until the dry pump opening reaches the upper limit. This maximizes the efficiency of protective gas introduction and replacement while ensuring process stability, effectively suppresses atmosphere contamination, and significantly improves the electrical properties and yield of monocrystalline silicon.

[0022] In the description of the embodiments of this disclosure, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary or secondary relationship of the indicated technical features. In the description of the embodiments of this disclosure, "multiple" means two or more, unless otherwise explicitly defined. Similarly, "multiple sets" refers to two or more sets (including two sets), and "multiple pieces" refers to two or more pieces (including two pieces).

[0023] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this disclosure. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0024] In the description of the embodiments of this disclosure, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0025] In the description of the embodiments of this disclosure, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the embodiments of this disclosure and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the embodiments of this disclosure. For example, if the device or element in the illustration is inverted, then the element described as "below," "under," "below," or "bottom" of other elements or features will be oriented "above" or "top" of said other elements or features. Therefore, the term "below" may, depending on the context in which the term is used, encompass both above and below orientations, which will be obvious to those skilled in the art. Materials may be oriented in other ways (e.g., rotated 90 degrees, inverted, flipped), and the spatial relative descriptive terms used herein may be interpreted accordingly.

[0026] In the description of the embodiments of this disclosure, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this disclosure according to the specific circumstances.

[0027] In the accompanying drawings corresponding to the embodiments of this disclosure, the thickness and area of ​​the layers are enlarged for better understanding and ease of description. Furthermore, when describing a component as "generally" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor on a portion of the edge of the entire surface.

[0028] In the description of the embodiments of this disclosure, when a component "includes" another component, other components are not excluded unless otherwise stated, and may be further included. The formation or placement of a second component above or on a first component, or on the surface of a first component, or on one side of a first component, may include embodiments where the first and second components are in direct contact, and may also include embodiments where an additional component may be placed between the first and second components, thereby preventing direct contact between the first and second components. For simplicity and clarity, various components may be drawn at different scales. In the drawings, some layers / components may be omitted for simplicity. Unless otherwise specified, the formation or placement of a second component on the surface of a first component refers to direct contact between the first and second components. The term "component" can refer to a layer, film, region, portion, structure, etc.

[0029] The terminology used in the description of the various embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various embodiments and the appended claims, the term "component" is also intended to include the plural form unless the context clearly indicates otherwise. Components include layers, films, regions, or plates, etc.

[0030] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this disclosure to facilitate a better understanding of the disclosure. However, the technical solutions claimed in this disclosure can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0031] refer to Figure 2 The method for pulling a single-crystal silicon rod provided in this embodiment includes a melting process, a seeding process, a shoulder-forming process, and a constant-diameter process performed sequentially; in the constant-diameter process, the following steps are implemented: S1: Set the target furnace pressure and the preset upper limit of the dry pump opening.

[0032] Specifically, a target furnace pressure suitable for stable crystal growth is set, along with a preset upper limit for the dry pump opening. This upper limit reflects the maximum allowable exhaust capacity under current equipment conditions, while also taking into account thermal stability requirements.

[0033] S2: Adjust the opening of the dry pump to control the actual furnace pressure at the target furnace pressure.

[0034] S3: When the current opening degree of the dry pump is lower than the preset upper limit value, increase the flow rate of the protective gas introduced into the single crystal furnace, and return to the step of adjusting the opening degree of the dry pump based on the furnace pressure change, until the opening degree of the dry pump is greater than or equal to the preset upper limit value.

[0035] Specifically, while maintaining the actual furnace pressure within the furnace at the target furnace pressure, the current opening degree of the dry pump is continuously monitored. If the current opening degree is lower than the preset upper limit, it indicates that the exhaust system still has a margin. At this time, the flow rate of the protective gas introduced into the single crystal furnace is actively increased. Since the increase in the protective gas flow rate will cause the furnace pressure to rise, the system immediately returns to step S2 based on the feedback of the furnace pressure change, readjusts the opening degree of the dry pump to restore the target furnace pressure, and repeats the above judgment and adjustment process until the opening degree of the dry pump reaches or exceeds the preset upper limit.

[0036] This disclosure sets a target furnace pressure and a preset upper limit for the dry pump opening during the equal diameter process, and adjusts the dry pump opening to maintain a stable actual furnace pressure. When the current dry pump opening is lower than the preset upper limit, the protective gas flow rate is increased. The dry pump opening is then adjusted back based on the furnace pressure change feedback. This process is repeated until the dry pump opening reaches or exceeds the preset upper limit. Thus, while maintaining a constant furnace pressure, the exhaust margin of the dry pump is fully utilized to continuously increase the protective gas flow rate, enhance the atmosphere replacement effect in the furnace, effectively reduce impurity retention, and significantly improve the purity of the protective gas acting on the crystal growth region, thereby improving the electrical performance and yield of the single crystal silicon rod.

[0037] The embodiments of this disclosure will now be described in more detail with reference to the accompanying drawings.

[0038] In some embodiments, setting a preset upper limit value for the opening degree of the dry pump includes: setting the preset upper limit value to a first upper limit value in the initial stage of the equal diameter process; setting the preset upper limit value to a second upper limit value in the middle stage of the equal diameter process; and setting the preset upper limit value to a third upper limit value in the later stage of the equal diameter process; wherein the second upper limit value is greater than the first upper limit value and the second upper limit value is greater than the third upper limit value.

[0039] It should be noted that the preset upper limit of the dry pump opening is not fixed, but is set in segments according to different stages of the equal diameter process. Specifically, in the initial stage of the equal diameter process, the preset upper limit is set to the first upper limit. At this stage, the crystals have just begun to grow stably, the melt surface is small, and the release of impurities in the furnace is relatively low. Using a lower first upper limit helps to maintain a stable thermal field and avoid airflow disturbance caused by excessive exhaust.

[0040] During the middle stage of the constant diameter process, the diameter of the single-crystal silicon rod reaches its maximum, and the exposed area of ​​the melt is also at its largest. Simultaneously, the crucible continuously releases impurities such as oxygen and water vapor at high temperatures, causing the risk of furnace contamination to peak. Therefore, the preset upper limit is raised to a second upper limit. This value is higher than the first upper limit and also higher than the upper limits for subsequent stages. A larger dry pump opening allows the system to introduce more protective gas while maintaining the target furnace pressure, thereby enhancing the furnace atmosphere's displacement capacity, effectively reducing impurity concentration, and improving the actual purity of the protective gas.

[0041] In the later stages of the constant diameter process, the molten silicon level drops significantly, thermal symmetry weakens, and the crystal tail becomes more sensitive to airflow disturbances. Maintaining a high venting intensity can easily lead to temperature gradient fluctuations, and even cause dislocations or wire breaks. Therefore, the preset upper limit value is adjusted to the third upper limit value, which is lower than the second upper limit value. By appropriately reducing the maximum allowable opening of the dry pump, the interference of gas flow on the thermal field can be reduced, ensuring the basic purity of the atmosphere while ensuring the stability of the crystal tail quality.

[0042] In some embodiments, the preset upper limit is 95% to 98% of the rated opening of the dry pump, for example, it can be 95%, 96%, 97% or 98%.

[0043] Understandably, the rated opening of the dry pump represents the maximum design opening of the dry pump under safe and reliable operating conditions. If the preset upper limit is set greater than 98%, the dry pump opening is too high, and long-term operation may put the dry pump on the verge of overload, increasing the risk of failure and affecting the continuity of crystal pulling. On the other hand, if the upper limit is lower than 95%, the dry pump opening is too low, which cannot fully utilize the dry pump's exhaust capacity, limits the potential for increasing the protective gas flow rate, and makes it difficult to effectively replace impurities in the furnace.

[0044] Setting the preset upper limit between 95% and 98% retains a 2% to 5% safety margin to ensure stable operation of the dry pump while maximizing its exhaust potential. Within this range, the system can maintain the target furnace pressure while introducing as much high-purity protective gas as possible, significantly enhancing the flushing effect on impurities such as oxygen and carbon, thereby improving the purity of the furnace atmosphere. This setting balances equipment reliability and process performance, which is beneficial for obtaining high-quality, low-defect single-crystal silicon rods.

[0045] In some embodiments, when the current opening degree of the dry pump is lower than a preset upper limit value, increasing the flow rate of the protective gas introduced into the single crystal furnace includes: adjusting the increase rate of the protective gas based on the difference between the current opening degree and the preset upper limit value.

[0046] Specifically, the larger the difference between the current opening of the dry pump and the preset upper limit, the larger the exhaust margin of the dry pump. At this time, it is permissible to increase the protective gas flow rate at a faster rate. Conversely, when the difference is small, it indicates that the opening of the dry pump is close to the upper limit. Continuing to increase the gas flow rate significantly may lead to furnace pressure overshoot or unstable control. Furnace pressure overshoot refers to the actual pressure inside the furnace briefly exceeding the target furnace pressure during the adjustment process. Therefore, a slower rate of increase is adopted.

[0047] This method, based on differential flow rate adjustment, effectively utilizes available exhaust capacity to rapidly improve atmosphere replacement efficiency during periods of severe contamination. Furthermore, it avoids drastic furnace pressure fluctuations caused by sudden increases in gas flow, thus maintaining the stability of the thermal field and crystal growth interface. This strategy efficiently improves the actual purity of the protective gas while ensuring process safety.

[0048] In some embodiments, adjusting the increase rate of the protective gas based on the difference between the current opening degree and a preset upper limit value includes: determining whether the difference between the current opening degree and the preset upper limit value is greater than or equal to a first threshold; if so, increasing the flow rate of the protective gas at a first rate; if not, increasing the flow rate of the protective gas at a second rate; wherein the first rate is greater than the second rate.

[0049] Specifically, if the difference is greater than or equal to the first threshold, it indicates that the dry pump still has sufficient exhaust capacity. At this time, increasing the flow rate of the protective gas at a larger first rate can quickly improve the gas replacement intensity in the furnace, effectively cope with the situation of high impurity concentration, and improve the purity of the protective atmosphere in a timely manner.

[0050] If the difference is less than the first threshold, it indicates that the current dry pump opening is close to the preset upper limit, and the remaining exhaust capacity is limited. If the gas flow rate is increased at a high rate at this point, it can easily lead to furnace pressure overshoot or unstable control. Therefore, a smaller second rate is used to slowly increase the protective gas flow rate to ensure stable furnace pressure regulation and avoid disturbance to the crystal growth interface.

[0051] By employing the aforementioned rate control strategy, the exhaust capacity at different stages can be flexibly matched while ensuring precise and stable furnace pressure. This allows for rapid improvement of atmosphere purity when conditions permit, as well as a smooth transition when approaching the limit, thus balancing efficiency and process stability.

[0052] In some embodiments, adjusting the opening degree of the dry pump includes: adjusting the opening degree of the dry pump based on the difference between the target furnace pressure and the actual furnace pressure.

[0053] Specifically, when the actual furnace pressure is higher than the target furnace pressure, it indicates that there is too much gas in the furnace or insufficient exhaust. At this time, the opening of the dry pump should be increased to enhance the pumping capacity and reduce the furnace pressure to the target value. When the actual furnace pressure is lower than the target furnace pressure, it indicates that the exhaust is too strong or the intake is insufficient. At this time, the opening of the dry pump should be reduced to decrease the pumping rate and allow the furnace pressure to rise back to the target value.

[0054] This adjustment process typically employs closed-loop control logic to ensure that changes in the dry pump opening match the pressure deviation; the larger the difference, the greater the opening adjustment range; the smaller the difference, the smaller the opening adjustment range.

[0055] Through this dynamic adjustment method based on pressure difference, the system can quickly respond to changes in furnace pressure and maintain the furnace pressure within the target range, providing a reliable thermal field and atmosphere environment for the stable growth of monocrystalline silicon.

[0056] In some embodiments, during the constant diameter process, the interstitial oxygen content in the single crystal silicon rod is monitored in real time; the real-time oxygen content is compared with a second threshold; and based on the comparison result, a preset upper limit value and / or the rate of increase of the protective gas flow rate are adjusted.

[0057] In some embodiments, the interstitial oxygen content of the single crystal silicon rod is monitored in real time during the constant diameter process, which can be achieved by an online detection device such as an infrared spectroscopy or an in-situ sensor; the monitored value is used to reflect the purity level of the protective atmosphere in the furnace and the doping of impurities into the crystal.

[0058] For example, the second threshold represents the upper limit of acceptable oxygen concentration, exceeding which may affect the electrical performance and yield of monocrystalline silicon.

[0059] Interstitial oxygen content refers to the concentration of oxygen atoms existing in interstitial states in a single-crystal silicon crystal. A small amount of interstitial oxygen helps to form oxygen deposits, which can be used for internal gettering and improve device yield; however, when the interstitial oxygen content is too high, it will form a large number of oxygen donors or microdefects during subsequent heat treatment, leading to problems such as reduced minority carrier lifetime, resistivity drift, reduced crystal mechanical strength, and reduced solar cell conversion efficiency.

[0060] Therefore, controlling the interstitial oxygen content is one of the key indicators for evaluating the quality of monocrystalline silicon, and also an important basis for optimizing the purity of the protective atmosphere and the crystal pulling process. By using the interstitial oxygen content as a feedback signal and dynamically adjusting the preset upper limit and / or the rate of increase of the protective gas flow rate accordingly, this embodiment achieves closed-loop process control guided by crystal quality. This method can not only respond promptly to changes in furnace contamination, but also ensure low-oxygen crystal quality while taking into account thermal stability and process efficiency.

[0061] In some embodiments, adjusting the preset upper limit value based on the comparison result includes: increasing the preset upper limit value when the real-time oxygen content is greater than or equal to the second threshold; and decreasing the preset upper limit value when the real-time oxygen content is less than the second threshold.

[0062] Specifically, if the real-time oxygen content is greater than or equal to the second threshold, it indicates that the current replacement capacity of the protective gas is insufficient and the concentration of impurities in the furnace is too high. At this time, the system will actively increase the preset upper limit of the dry pump opening to allow for greater exhaust capacity; and / or increase the rate of increase of the protective gas flow rate, thereby increasing the intake volume more quickly, enhancing the atmosphere flushing effect, and inhibiting further oxygen incorporation.

[0063] If the real-time oxygen content is less than the second threshold, it indicates that the current atmosphere purity is good, and there is no need to excessively increase the flow rate or exhaust intensity. At this time, the existing parameters can be maintained, or the adjustment intensity can be appropriately reduced to avoid unnecessary airflow disturbances or increased energy consumption.

[0064] By using this control strategy, which uses interstitial oxygen content as a feedback signal and bidirectionally adjusts the preset upper limit, the system can proactively adapt to changes in the contamination state inside the furnace. It can enhance purification capabilities when there is a high risk of contamination and prioritize growth stability when there is a low risk of contamination, thereby achieving precise control of the oxygen content of monocrystalline silicon and improving the overall quality of the ingot.

[0065] In some embodiments, adjusting the rate of increase of the protective gas flow rate based on the comparison result includes: increasing the rate of increase of the protective gas flow rate when the real-time oxygen content is greater than or equal to a second threshold; and decreasing the rate of increase of the protective gas flow rate when the real-time oxygen content is less than the second threshold.

[0066] Specifically, when the real-time oxygen content is greater than or equal to the second threshold, it indicates that the impurity concentration in the furnace is too high, the purity of the protective atmosphere is insufficient, and oxygen is continuously diffusing into the melt and incorporating into the crystals. At this time, the system increases the rate of increase of the protective gas flow rate. In subsequent adjustments, once the dry pump opening has a margin, the gas intake can be increased more quickly, rapidly enhancing the gas replacement capacity in the furnace and effectively suppressing further increases in oxygen content.

[0067] When the real-time oxygen content is below the second threshold, it indicates that the current atmosphere purity is good and the risk of oxygen contamination is low. At this time, the system reduces the rate of increase of the protective gas flow rate. This can avoid furnace pressure fluctuations or thermal field disturbances caused by excessively rapid gas flow rate increases, while reducing unnecessary gas consumption and maintaining the stability of the crystal growth interface.

[0068] By employing this strategy of adjusting the flow rate in both directions based on oxygen content feedback, the system can intelligently match the intensity of gas regulation under different pollution levels. This not only addresses the risk of high oxygen levels in a timely manner but also avoids process instability caused by over-regulation, thereby more accurately ensuring the low-oxygen quality and growth consistency of monocrystalline silicon.

[0069] Figure 3 This is a schematic flowchart of the single-crystal silicon rod pulling method in the embodiments of this disclosure. The following is a summary of the process. Figure 3 Explain the process of coordinated control of furnace pressure and gas flow involved in this drawing method.

[0070] For example, in this solution, the opening degree of the dry pump is adjusted by the main control PD controller, the flow rate of the protective gas is adjusted by the PID controller, and argon is used as the protective gas.

[0071] Specifically, the target furnace pressure is first set and input into the main control PD controller. The actual furnace pressure is detected by a sensor and fed back to the main control PD controller in real time. The main control PD controller calculates the difference between the target furnace pressure and the actual furnace pressure, and adjusts the current dry pump opening accordingly, outputting the current dry pump opening to the limiter. The limiter has a preset upper limit value of X%. The limiter determines whether the current dry pump opening has reached the preset upper limit value of X%. If not, it means that the system still has exhaust capacity. The limiter outputs an argon flow rate adjustment command to the PID controller. The PID controller accepts the command and increases the argon flow rate into the single crystal furnace, thereby enhancing the furnace atmosphere replacement capacity. As the argon flow rate increases, the furnace pressure rises. The main control PD controller automatically adjusts the dry pump opening to maintain the target furnace pressure, forming a closed-loop control. If the current exhaust capacity is fully utilized, the system stops further increasing the gas flow rate, and the control process ends.

[0072] It should be noted that, in order to fully disclose the technical details of the single-crystal silicon rod pulling method involved in the embodiments of this disclosure, the overall process flow of the Czochralski method and its key control parameters are now systematically supplemented and explained.

[0073] The Czochralski (CZ) single-crystal silicon pulling process is a core technology that involves precisely controlling the growth of large-size, high-purity single-crystal silicon rods from molten silicon under inert gas protection. The entire crystal pulling process typically includes multiple stages such as charge melting, crystal pulling and necking, shoulder formation, constant-diameter growth, tail cooling, and optional re-pulping. Each stage requires coordinated control of key parameters such as furnace atmosphere, pressure, gas flow rate, crucible and crystal rotation speed, based on crystal growth kinetics, thermal stability, and impurity control requirements.

[0074] Specifically, in the charging and melting stage, high-purity polycrystalline silicon raw materials and the required dopants are loaded into a quartz crucible. Argon is used as a protective gas, and the mixture is heated to above 1420°C under the protective atmosphere of argon to completely melt the silicon material and form a uniform melt. During this stage, the crucible rotation speed is usually controlled at 0 rpm to 2 rpm, the argon flow rate is in the range of 30 slpm to 200 slpm, and the furnace pressure is 5 Torr to 15 Torr to ensure the stability of the melt and avoid oxidation.

[0075] Entering the crystallization and necking stage, the seed crystal with a specific crystal orientation is slowly lowered to contact the melt surface, and then rapidly pulled to form a narrow neck structure, so as to effectively eliminate dislocations and establish a defect-free crystal growth starting point. This stage is extremely sensitive to thermal field disturbances, so it needs to be precisely controlled: the crucible rotation speed is increased to 4 rpm~10 rpm, the crystal rotation speed is set to 4 rpm~12 rpm, while maintaining the argon flow rate at 30 slpm~200 slpm and the furnace pressure at 5 Torr~15 Torr, so as to balance interface stability and impurity removal.

[0076] The subsequent stage involves shoulder formation and constant-diameter growth: the pulling speed is gradually reduced to expand the crystal diameter from a narrow neck to the target size (e.g., 8 inches or 12 inches). After shoulder formation, the main constant-diameter growth process begins. This stage is crucial for determining crystal quality and oxygen / carbon content. An automatic control system is needed to dynamically adjust the pulling speed, heating power, and atmosphere conditions to maintain a constant diameter and suppress impurity introduction. The process parameters for this stage include: crucible rotation speed of 4-10 rpm, crystal rotation speed of 4-12 rpm, argon flow rate of 30 slpm-200 slpm, and furnace pressure of 5 Torr-15 Torr.

[0077] Especially in the constant diameter stage, due to the intensified high-temperature decomposition of the crucible, the oxygen release rate increases significantly, and the risk of contamination inside the furnace is the greatest. Therefore, it is necessary to enhance the atmosphere replacement capability. Based on this, the embodiments of this disclosure achieve precise furnace pressure control and impurity suppression by dynamically adjusting the opening limit of the dry pump and the flow rate of the protective gas.

[0078] After growth, the crystal enters the finishing and cooling stage. The crystal tail is tapered by increasing the pulling speed to reduce thermal stress concentration. Then, the crystal is separated from the melt and subjected to programmed annealing and cooling in the furnace for tens of hours to fully release residual thermal stress and prevent dislocation multiplication or cracking. During this stage, the crucible rotation speed is maintained at 4 rpm to 10 rpm, the crystal rotation speed at 4 rpm to 12 rpm, the argon flow rate at 30 slpm to 200 slpm, and the furnace pressure at 5 Torr to 15 Torr.

[0079] In addition, a re-feeding process can be implemented in continuous production mode: after completing one crystal pulling, a portion of the melt is retained according to quality control requirements, usually corresponding to 20% to 40% of the full crucible material, and polycrystalline silicon raw materials are added again through a cylindrical feeder. After melting to the full crucible state, the complete process of crystal pulling, shoulder forming, and equal diameter is performed again. The melting process parameters in the re-feeding stage are similar to those in the initial loading, with the crucible speed controlled at 0 rpm to 2 rpm, argon flow rate at 30 slpm to 200 slpm, and furnace pressure at 5 Torr to 15 Torr.

[0080] Furthermore, in some embodiments, corresponding process parameters are set according to the characteristics of each stage of crystal pulling, including the initial protective gas flow rate, target furnace pressure, and preset upper limit values ​​for the dry pump opening. For example, the process parameters are shown in Table 1: Table 1

[0081] Specifically, during the crystal pulling and shoulder formation stages, the crystal diameter is small and the interface curvature is large, making it extremely sensitive to airflow disturbances. Setting the dry pump limiter to 100% and keeping the initial protective gas flow rate constant prevents airflow disturbances in the furnace caused by the automatic increase in gas flow rate, effectively reducing the risk of wire breakage and improving the stability of heating power.

[0082] During the constant diameter and finishing stages, the crystal diameter is at its maximum, the high-temperature decomposition of the crucible leads to the highest oxygen release rate, and the furnace contamination is most severe. At this time, the dry pump limiter setting is set to 95%, allowing the system to dynamically increase the argon flow rate while maintaining the target furnace pressure, thereby enhancing the atmosphere replacement capability. By configuring parameters in stages, the breakage rate is effectively reduced and the purity of the protective gas in the constant diameter stage is improved while ensuring the thermal field stability during the crystal growth stage, thus balancing crystal growth quality and process reliability.

[0083] The technical solutions provided in this disclosure have at least the following advantages: This disclosure sets a target furnace pressure and a preset upper limit for the dry pump opening during the equal-diameter process, and adjusts the dry pump opening to maintain stable actual furnace pressure. When the current dry pump opening is lower than the preset upper limit, the protective gas flow rate is increased. The dry pump opening is then adjusted based on furnace pressure changes, and this process is repeated until the dry pump opening reaches or exceeds the preset upper limit. This maintains constant furnace pressure while fully utilizing the dry pump's exhaust capacity to continuously increase the protective gas flow rate, enhancing the furnace atmosphere replacement effect, effectively reducing impurity retention, and significantly improving the purity of the protective gas acting on the crystal growth region, thereby improving the electrical properties and yield of the monocrystalline silicon rod. Furthermore, by adjusting the preset upper limit for the dry pump opening based on different stages of the equal-diameter process and factors such as the interstitial oxygen content in the monocrystalline silicon rod, the impurity concentration is effectively reduced and the purity of the protective gas is improved while maintaining a stable thermal field and avoiding airflow disturbance caused by excessive exhaust. Additionally, by flexibly adjusting the rate of increase in the protective gas flow rate, the exhaust capacity at different stages is flexibly matched while ensuring precise furnace pressure stability, balancing efficiency and process stability.

[0084] According to some embodiments of this disclosure, another aspect of this disclosure also provides a single-crystal silicon rod, formed using the above-described single-crystal silicon rod pulling method. The single-crystal silicon rod provided in this disclosure will be described below. It should be noted that parts that are the same as or corresponding to those in the foregoing embodiments will not be repeated here.

[0085] The oxygen content of the monocrystalline silicon rod is less than or equal to 10 ppma, and the carbon content of the monocrystalline silicon rod is less than or equal to 0.5 ppma.

[0086] For example, in this embodiment of the disclosure, Fourier transform infrared spectroscopy is used to quantitatively detect the oxygen and carbon concentrations in a single-crystal silicon rod.

[0087] This method is based on the characteristic infrared absorption caused by impurity atoms in the crystal lattice, with interstitial oxygen atoms at approximately 1107 cm⁻¹. -¹A characteristic absorption peak is generated at a wavenumber. By measuring the absorption intensity of this peak and combining it with a standard calibration coefficient, the atomic concentration of oxygen can be calculated; the concentration of substituted carbon atoms is at approximately 605 cm⁻¹. - A characteristic absorption peak is observed at position ¹. By measuring the absorption intensity of this peak and combining it with the standard calibration constant, the atomic concentration of carbon can be accurately calculated.

[0088] Specifically, the detection method includes the following steps: S1: The single-crystal silicon sample is precisely polished on both sides to a mirror finish to minimize the interference of surface scattering on the infrared transmission signal.

[0089] S2: The transmission spectrum of the sample is acquired using a Fourier transform infrared spectrometer at room temperature or low temperature.

[0090] S3: Baseline fitting and subtraction are performed on the original spectrum to accurately extract the net absorption intensity of the characteristic absorption peaks.

[0091] S4: Based on the calculation formula and calibration coefficient specified in the current national standard, convert the absorption coefficient into the corresponding oxygen and carbon concentration values.

[0092] In detecting oxygen and carbon content, the "single-crystal silicon sample" used is generally a silicon wafer made from a pulled single-crystal silicon rod through processes such as wire cutting, grinding, and polishing, with a thickness typically around several hundred micrometers. To meet the requirements of infrared spectroscopy detection, the silicon wafer needs to be polished to a mirror finish on both sides to reduce light scattering and ensure that infrared light can effectively penetrate and obtain a clear absorption signal.

[0093] It should be noted that the typical oxygen content in conventional Czochralski processes is less than or equal to 12 ppma, and the carbon content is less than or equal to 1 ppma. Compared to conventional Czochralski processes, this disclosure significantly reduces the concentration of interstitial oxygen and carbon impurities in single-crystal silicon rods. This indicates that by introducing a dynamic compensation mechanism for argon flow rate based on dry pump opening limits during the constant diameter stage, the cleanliness of the furnace atmosphere can be effectively improved, thereby enhancing the electrical uniformity and minority carrier lifetime of the single-crystal silicon rod, laying a material foundation for the subsequent fabrication of high-performance semiconductor devices.

[0094] According to some embodiments of this disclosure, another aspect of this disclosure also provides a silicon wafer, which is cut from the aforementioned single-crystal silicon rod, or cut from a single-crystal silicon rod prepared by the aforementioned single-crystal silicon rod pulling method. The silicon wafer provided in the embodiments of this disclosure will be described below. It should be noted that parts that are the same as or corresponding to those in the foregoing embodiments will not be repeated here.

[0095] The silicon wafer has an oxygen content of less than or equal to 10 ppma and a carbon content of less than or equal to 0.5 ppma.

[0096] Silicon wafers can be used to manufacture solar cells. Solar cells can be TOPCON cells (Tunnel Oxide Passivated Contact), BC cells (Back Contact), HJT cells (Heterojunction Technology), etc.

[0097] Those skilled in the art will understand that the above embodiments are specific examples of implementing this disclosure, and in practical applications, various changes in form and detail may be made without departing from the spirit and scope of this disclosure. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of this disclosure; therefore, the scope of protection of this disclosure should be determined by the scope defined in the claims.

Claims

1. A method for pulling a single-crystal silicon rod, characterized in that, This includes the sequential melting process, crystal pulling process, shoulder forming process, and equal diameter process; In the equal diameter process, the following steps are performed: Set the target furnace pressure and the preset upper limit value of the dry pump opening; Adjust the opening of the dry pump to control the actual furnace pressure inside the furnace at the target furnace pressure; When the current opening degree of the dry pump is lower than the preset upper limit value, the flow rate of the protective gas introduced into the single crystal furnace is increased, and the step of adjusting the opening degree of the dry pump is returned to the original based on the furnace pressure change, until the opening degree of the dry pump is greater than or equal to the preset upper limit value.

2. The method for pulling a single-crystal silicon rod according to claim 1, characterized in that, The setting of the preset upper limit value of the dry pump opening includes: In the initial stage of the equal diameter process, the preset upper limit value is set to a first upper limit value; in the middle stage of the equal diameter process, the preset upper limit value is set to a second upper limit value; and in the later stage of the equal diameter process, the preset upper limit value is set to a third upper limit value. Wherein, the second upper limit value is greater than the first upper limit value, and the second upper limit value is greater than the third upper limit value.

3. The method for pulling a single-crystal silicon rod according to claim 2, characterized in that, The preset upper limit value is 95% to 98% of the rated opening of the dry pump.

4. The method for pulling a single-crystal silicon rod according to claim 2, characterized in that, When the current opening degree of the dry pump is lower than the preset upper limit value, increasing the flow rate of the protective gas introduced into the single crystal furnace includes: The rate at which the protective gas increases is adjusted based on the difference between the current opening and the preset upper limit.

5. The method for pulling a single-crystal silicon rod according to claim 4, characterized in that, Adjusting the increase rate of the protective gas based on the difference between the current opening degree and the preset upper limit value includes: Determine whether the difference between the current opening degree and the preset upper limit value is greater than or equal to the first threshold; If yes, increase the flow rate of the protective gas at a first rate; if no, increase the flow rate of the protective gas at a second rate. Wherein, the first rate is greater than the second rate.

6. The method for pulling a single-crystal silicon rod according to claim 1, characterized in that, The adjustment of the dry pump opening includes: The opening degree of the dry pump is adjusted based on the difference between the target furnace pressure and the actual furnace pressure.

7. The method for pulling a single-crystal silicon rod according to claim 1, characterized in that, During the equal diameter process, the interstitial oxygen content in the single crystal silicon rod is monitored in real time. Compare the real-time oxygen content with a second threshold; Based on the comparison results, adjust the preset upper limit value and / or the rate of increase of the protective gas flow rate.

8. The method for pulling a single-crystal silicon rod according to claim 7, characterized in that, Adjusting the preset upper limit value based on the comparison result includes: When the real-time oxygen content is greater than or equal to the second threshold, the preset upper limit value is increased; when the real-time oxygen content is less than the second threshold, the preset upper limit value is decreased.

9. The method for pulling a single-crystal silicon rod according to claim 7, characterized in that, The step of adjusting the rate of increase of the protective gas flow rate based on the comparison results includes: When the real-time oxygen content is greater than or equal to the second threshold, the rate of increase of the protective gas flow rate is increased; when the real-time oxygen content is less than the second threshold, the rate of increase of the protective gas flow rate is decreased.

10. A silicon wafer, characterized in that, The silicon wafer is cut from a single-crystal silicon rod prepared by the pulling method of any one of claims 1-9, wherein the oxygen content of the silicon wafer is less than or equal to 10 ppma, and the carbon content of the silicon wafer is less than or equal to 0.5 ppma.

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