Preparation method of monocrystalline silicon

Abstract

The invention relates to the technical field of monocrystalline silicon processing, particularly provides a preparation method of monocrystalline silicon, and aims to solve the problem that the crystal quality is influenced by crystal distortion in the existing monocrystalline silicon preparation process. In order to achieve the purpose, the preparation method of the monocrystalline silicon comprises the steps that in the first stage of equal-diameter growth of the monocrystalline silicon, the crystal pulling speed is controlled to be gradually increased to the preset pulling speed, and the liquid opening distance is controlled to be gradually reduced to the preset distance; and in the second stage of equal-diameter growth of the monocrystalline silicon, controlling the crystal pulling speed to maintain the preset pulling speed, and controlling the liquid opening distance to maintain the preset distance. According to the method, the two technological parameters of the liquid opening distance and the crystal pulling speed in the monocrystalline silicon growth process are adjusted in advance, the temperature consistency of the area nearby the molten silicon liquid level can be improved, a stable thermal field is formed at the junction of the crystal and the silicon solution, and therefore the distortion proportion of the crystal can be reduced, and the crystal forming quality is improved.

Description

Technical Field

[0001] The present application relates to the technical field of single crystal silicon processing, and specifically provides a method for preparing single crystal silicon. Background Art

[0002] The Czochralski method for preparing single crystal silicon is a commonly used method in the current production of single crystal silicon. After putting silicon powder into a quartz crucible, the silicon powder is first heated to melt, and then the seed crystal is immersed in the silicon solution above the crucible. By controlling the melt temperature, the rotation and rising speed of the seed crystal, the silicon atoms form regular crystals at the solid-liquid interface.

[0003] In order to ensure production capacity, it is usually necessary to control the crystal pulling speed within a certain range during the growth of single crystal silicon. Increasing the pulling speed will cause the temperature of the molten silicon liquid surface to drop, and then during the rotation of the crystal, the local crystallization rate near the molten silicon liquid surface is too fast, causing the crystal to distort, thereby affecting the crystal molding quality and even causing crystal growth failure.

[0004] Accordingly, a new solution is needed in the art to solve the above problems. Summary of the invention

[0005] The present application aims to solve the above technical problem, that is, to solve the problem that the quality of the crystal is affected by the crystal distortion in the existing single crystal silicon preparation process.

[0006] In a first aspect, the present application provides a method for preparing single crystal silicon, comprising:

[0007] In the first stage of the uniform diameter growth of single crystal silicon, the crystal pulling speed is controlled to gradually increase to a preset pulling speed, and the liquid nozzle distance is controlled to gradually decrease to a preset distance;

[0008] In the second stage of the isodiameter growth of the single crystal silicon, the crystal pulling speed is controlled to maintain the preset pulling speed, and the liquid port distance is controlled to maintain the preset distance.

[0009] In a technical solution of the above preparation method, the first stage includes an initial stage and a transition stage, the initial stage is a stage when the crystal grows to a first length, the transition stage is a stage when the crystal grows from the first length to a second length, and the second stage is a stage when the crystal grows from the second length to the end of equal diameter growth;

[0010] In the first stage of the uniform growth of the single crystal silicon, controlling the crystal pulling speed to gradually increase to a preset pulling speed and controlling the liquid nozzle distance to gradually decrease to a preset distance comprises:

[0011] In the initial stage of the uniform diameter growth of the single crystal silicon, the crystal pulling speed is controlled to gradually increase, and the liquid mouth distance is controlled to gradually decrease. At the end of the initial stage, the crystal pulling speed is increased to a preset pulling speed;

[0012] During the transition stage of the equal-diameter growth of the single crystal silicon, the liquid-to-mouth distance is controlled to continue to decrease. When the transition stage ends, the liquid-to-mouth distance is reduced to a preset distance.

[0013] In a technical solution of the above preparation method, the first length is 450-550 mm; and / or

[0014] The second length is 650-750 mm.

[0015] In a technical solution of the above preparation method, the first stage is the stage when the crystal grows to the third length, and the second stage is the stage when the crystal grows from the third length to the end of equal diameter growth;

[0016] In the first stage of the uniform growth of the single crystal silicon, controlling the crystal pulling speed to gradually increase to a preset pulling speed and controlling the liquid nozzle distance to gradually decrease to a preset distance comprises:

[0017] In the first stage of isodiameter growth of single crystal silicon, the crystal pulling speed is controlled to gradually increase, and the liquid nozzle distance is controlled to gradually decrease. At the end of the first stage, the crystal pulling speed increases to a preset pulling speed, and the liquid nozzle distance decreases to a preset distance.

[0018] In a technical solution of the above preparation method, the third length is 650-750 mm.

[0019] In a technical solution of the above preparation method, the preset pulling speed is 1.6-1.7 mm / min.

[0020] In a technical solution of the above preparation method, the preset distance is 15-20 mm.

[0021] In a technical solution of the above preparation method, controlling the liquid outlet distance to gradually decrease to a preset distance comprises:

[0022] With the heat shield stationary, the crucible is controlled to rise gradually.

[0023] In a technical solution of the above preparation method, the preparation method further comprises:

[0024] During the growth of the single crystal silicon, the initial value of the crystal pulling speed is controlled to be 0.9-1.1 mm / min at the beginning of the isodiameter growth stage of the single crystal silicon; and / or

[0025] During the growth of single crystal silicon, the initial value of the liquid mouth distance is controlled to be 28-32 mm when the single crystal silicon begins to grow at the equal diameter growth stage.

[0026] In a technical solution of the above preparation method, the preparation method further comprises:

[0027] During the growth of single crystal silicon, the difference between the crystal diameter and the heat shield opening diameter is controlled within a preset range;

[0028] Wherein, the preset range is 60-90mm.

[0029] As mentioned above, under the condition of adopting the above technical scheme, the present application controls the two main parameters of the liquid mouth distance and the crystal pulling speed during the equal diameter growth stage of the crystal. Specifically, by controlling the speed of the liquid mouth distance reduction and the speed of the crystal pulling speed increase, the time when the liquid mouth distance is reduced to the preset distance is not earlier than the time when the crystal pulling speed increases to the preset pulling speed, thereby improving the consistency of the temperature in the area near the molten silicon liquid surface, forming a relatively stable thermal field at the junction of the crystal and the silicon solution, thereby reducing the distortion ratio of the crystal. Moreover, the above technical scheme of the present application is a pre-adjustment of the process parameters during the crystal growth process, without the need for manual intervention during the crystal growth process, thereby reducing the uncontrollable factors caused by manual intervention, as well as the hysteresis of adjusting after the crystal is distorted, and improving the fault tolerance rate, so it not only simplifies the process complexity, but also improves the crystal molding quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The preferred embodiments of the present application are described below in conjunction with the accompanying drawings, in which:

[0031] Figure 1 is a flow chart of the main steps of a method for preparing single crystal silicon according to an embodiment of the present application;

[0032] Figure 2 It is a line graph of experimental data drawn based on actual experiments;

[0033] Figure 3 is a detailed step flow chart of a method for preparing single crystal silicon according to an embodiment of the present application;

[0034] Figure 4 is a detailed step flow chart of a method for preparing single crystal silicon according to another embodiment of the present application;

[0035] Figure 5 It is a schematic diagram of the longitudinal section of a single crystal furnace.

[0036] In the figures, the reference numerals refer to the following:

[0037] 1. The first curve; 2. The second curve; 3. The third curve; 4. The fourth curve; 5. The fifth curve. DETAILED DESCRIPTION

[0038] The preferred embodiments of the present application are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present application and are not used to limit the scope of protection of the present application. Those skilled in the art can make adjustments to them as needed to adapt to specific application scenarios.

[0039] It should be noted that in the description of this application, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the drawings. This is only for the convenience of description, and does not indicate or imply that the relevant devices or components must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on this application. In addition, the ordinal numbers "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0040] In addition, it should be noted that in the description of this application, unless otherwise clearly specified and limited, the terms "installation" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For those skilled in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0041] In order to facilitate understanding of the technical solution of the present invention, a simple description of the single crystal silicon pulling process is first given.

[0042] The process of pulling single crystal silicon mainly includes raw material preparation, melting, seeding, shouldering, equal diameter, finishing, cooling and crystal extraction. Specifically, raw material preparation refers to processing large-volume solid raw materials such as silica into high-purity silicon powder through crushing, grinding, sorting and other steps. The melting stage refers to adding silicon powder into the quartz crucible of the single crystal furnace, and filling argon gas after vacuuming the single crystal furnace, and then turning on the heating power to melt the silicon powder to form a silicon solution. In the seeding stage, after the temperature of the silicon solution is stable, the seed crystal is slowly immersed in the silicon solution from the top of the single crystal furnace, and the seed crystal is rotated upward to reduce the diameter of the grown crystal rod to a certain size and form a thin neck. The shouldering stage refers to the reduction of temperature and pulling speed after the thin neck is grown in the seeding stage, so that the diameter of the crystal gradually increases to the required size. The equal diameter stage refers to the continuous adjustment of the pulling speed and temperature after the thin neck and shoulder are grown to maintain the diameter of the crystal rod within a certain range. The part of the crystal rod grown in this stage is called the equal diameter part. The finishing stage refers to the stage after the equal-diameter portion is grown. In order to avoid a sudden increase in thermal stress due to the rapid separation of the crystal rod from the molten silicon liquid surface, which may cause defects such as dislocations in the crystal rod, the diameter of the bottom end of the crystal rod must be slowly reduced until it separates from the molten silicon liquid surface.

[0043] Among them, the crystal growth rate in the equal-diameter growth stage determines the production efficiency of single crystal silicon. Therefore, in the equal-diameter growth stage, the crystal pulling speed needs to be controlled within a certain range. Under the premise of ensuring the quality of the crystal, the faster the crystal pulling speed, the higher the production capacity. However, in the equal-diameter growth process, if the crystal pulling speed is too large, the temperature near the molten silicon liquid surface will drop too quickly, resulting in a decrease in the temperature of the molten silicon liquid surface. At this time, the crystal and the crucible are both in a rotating state, which will cause the temperature of the silicon melt around the molten silicon liquid surface to be asymmetric. In this case, the local crystallization rate of the silicon melt is too fast, resulting in crystal distortion.

[0044] In order to improve the above-mentioned crystal distortion phenomenon, in some related technologies, during the equal diameter growth process of the crystal, when the crystal is distorted, the consistency of the molten silicon liquid surface temperature is balanced by adjusting the crystal rotation speed, crucible rotation speed, liquid mouth distance (the distance between the molten silicon liquid surface and the lower port of the heat shield), crystal pulling speed or heater power, so as to prevent the distortion phenomenon from further deteriorating. However, this method is not a preventive measure, and it has a lag. Even if the staff makes real-time adjustments to the above-mentioned parameters during the crystal growth process based on actual experience, it will still cause irreversible quality defects in the crystal. Moreover, the above-mentioned manual adjustment method has high requirements on the experience of the staff. Once the scale is not well grasped, the crystal may be dislocated and disconnected, resulting in the failure of crystal growth. Therefore, the above-mentioned method has great disadvantages.

[0045] Reference Figure 1 , is a flow chart of the main steps of a method for preparing single crystal silicon according to an embodiment of the present application, which includes the following steps:

[0046] S101: In the first stage of the uniform diameter growth of single crystal silicon, the crystal pulling speed is controlled to gradually increase to a preset pulling speed, and the liquid inlet distance is controlled to gradually decrease to a preset distance.

[0047] S102: In the second stage of the equal-diameter growth of the single crystal silicon, the crystal pulling speed is controlled to maintain a preset pulling speed, and the liquid nozzle distance is controlled to maintain a preset distance.

[0048] It should be noted that the method for preparing single crystal silicon of the present application is mainly aimed at the isodiameter growth process of single crystal silicon, so before step S101, the processes of melting, seeding, shoulder release, etc. of single crystal silicon have been completed.

[0049] In the shoulder release stage before step S101, in order to ensure the formation of a thin neck, the pulling speed of the crystal is at a relatively low value. After entering the equal diameter growth stage, in order to ensure the crystal growth rate, the pulling speed needs to be gradually increased, that is, in step S101, the crystal pulling speed is controlled to gradually increase to a preset pulling speed. At the same time, in order to ensure that the crystal is cooled in time by the heat shield during the pulling process to promote crystal formation, the liquid mouth distance needs to be controlled to be gradually reduced. Optionally, in step S101, "controlling the liquid mouth distance to be gradually reduced" adopts a method of controlling the crucible to gradually rise while the heat shield remains stationary. During the rise of the crucible, the molten silicon liquid level also rises, while the position of the heat shield remains unchanged, thereby achieving the purpose of reducing the liquid mouth distance.

[0050] Step S102 shows that after the crystal pulling speed rises to the preset pulling speed, the preset pulling speed is maintained in the second stage of equal diameter growth, and after the liquid mouth distance is reduced to the preset distance, the preset distance is also maintained. It should be noted that "controlling the liquid mouth distance to maintain the preset distance" requires controlling the crucible to rise slowly in the second stage, and the rising speed is significantly lower than that in the first stage. This is because during the crystal growth process, the molten silicon liquid level continues to drop, while the heat shield position does not move. Therefore, if the liquid mouth distance is to be maintained at a fixed distance, the crucible needs to be controlled to rise so that the rising speed is equal to the falling speed of the molten silicon liquid level.

[0051] Reference Figure 2 Based on actual experiments, the inventors conducted statistics on the crystal distortion ratios shown in Table 1 below, with the crystal pulling speed unchanged and the liquid nozzle distance adjusted to different working conditions during the preparation of single crystal silicon. Specifically, Figure 2 In the figure, the horizontal axis is the crystal length (mm), the left vertical axis is the crystal pulling speed (mm / min), and the right vertical axis is the liquid-to-mouth distance (mm), wherein the first curve 1 represents the first operating condition in which the liquid-to-mouth distance changes with the crystal length, the second curve 2 represents the second operating condition in which the liquid-to-mouth distance changes with the crystal length, the third curve 3 represents the third operating condition in which the liquid-to-mouth distance changes with the crystal length, the fourth curve 4 represents the fourth operating condition in which the liquid-to-mouth distance changes with the crystal length, and the fifth curve 5 represents the changing trend of the crystal pulling speed with the crystal length under the above four operating conditions. Working conditions Crystal distortion ratio First working condition 40％ Second working condition 8％ The third working condition 90％ The fourth working condition 5％ Table 1

[0052] Combination Figure 2 From Table 1, we can see that the distortion probability of the crystal is the smallest under the fourth working condition, and the distortion probability of the crystal is also small under the second working condition, which is not much different from the distortion probability under the fourth working condition. In the third working condition, the distortion probability of the crystal is the largest. Figure 2As can be seen from Table 1, the significant difference between the third working condition and the other three working conditions in the figure is that the inflection point of the third curve 3 corresponding to the third working condition is the earliest, which is reflected in the earliest time when the liquid mouth distance drops to the preset distance during the equal-diameter growth of single crystal silicon, and this time is earlier than the time when the crystal pulling speed is increased to the preset pulling speed. Similarly, under the first and second working conditions, the time when the liquid mouth distance drops to the preset distance during the equal-diameter growth of single crystal silicon is basically the same as the time when the crystal pulling speed is increased to the preset pulling speed, while the fourth working condition reflects that when the time when the liquid mouth distance drops to the preset distance during the equal-diameter growth of single crystal silicon is later than the time when the crystal pulling speed is increased to the preset pulling speed, the probability of crystal distortion is the lowest.

[0053] Therefore, it can be concluded from the above that the time when the liquid mouth distance drops to the preset distance during the uniform growth of single crystal silicon cannot be earlier than the time when the crystal pulling speed is increased to the preset pulling speed, otherwise the probability of crystal distortion will increase.

[0054] Based on the above test rules, refer to Figure 3 , is a detailed step flow chart of a method for preparing single crystal silicon according to an embodiment of the present application, wherein the first stage of the uniform growth of single crystal silicon is divided into an initial stage and a transition stage, wherein the initial stage is the stage when the crystal grows to a first length, and the transition stage is the stage when the crystal grows from the first length to a second length, and correspondingly, the second stage of the uniform growth of single crystal silicon is the stage when the crystal grows from the second length to the end of the uniform growth. Specifically, the method for preparing single crystal silicon may include the following steps:

[0055] S1011: In the initial stage of the equal-diameter growth of single crystal silicon, the crystal pulling speed is controlled to gradually increase, and the liquid mouth distance is controlled to gradually decrease. At the end of the initial stage, the crystal pulling speed is increased to the preset pulling speed.

[0056] S1012: During the transition stage of the equal-diameter growth of the single crystal silicon, the liquid-inlet distance is controlled to continue to decrease. At the end of the transition stage, the liquid-inlet distance is reduced to a preset distance.

[0057] S102: In the second stage of the equal-diameter growth of the single crystal silicon, the crystal pulling speed is controlled to maintain a preset pulling speed, and the liquid nozzle distance is controlled to maintain a preset distance.

[0058] This embodiment corresponds to Figure 2In the fourth working condition shown by the fourth curve 4, optionally, the first length corresponding to the initial stage is 450-550mm, and the second length is 650-750mm. Step S1011 indicates that in the process of the crystal growing to the first length, that is, the initial stage, the crystal pulling speed is gradually increasing, and the liquid mouth distance is also gradually decreasing. When the crystal length is equal to the first length, the crystal pulling speed reaches the preset pulling speed and no longer increases, but the liquid mouth distance is still gradually decreasing. Step S1012 indicates that in the process of the crystal growing from the first length to the second length, that is, the transition stage, the crystal pulling speed has remained unchanged, but the liquid mouth distance is still gradually decreasing. When the crystal length is equal to the second length, that is, at the end of the transition stage, the liquid mouth distance is equal to the preset distance and no longer decreases.

[0059] After testing, it was verified that when the preset pulling speed was 1.6-1.7 mm / min, the probability of crystal distortion was the lowest. Therefore, in the above-mentioned actual test of this application, the test was conducted under the condition of the preset pulling speed of 1.65 mm / min. Similarly, when the preset distance was 15-20 mm, the probability of crystal distortion was the lowest. Therefore, in the above-mentioned actual test of this application, the preset distance was selected to be 15 mm, 19 mm, 21 mm, etc.

[0060] And in one embodiment of the present application, when the monocrystalline silicon starts the isodiameter growth stage, the initial value of the crystal pulling speed is 0.9-1.1 mm / min. When the initial value of the crystal pulling speed is too large, it may cause the crystal to be difficult to form at the beginning of the isodiameter growth, or the lower end of the crystal may be locally distorted or cracked due to the excessive pulling speed. When the initial value of the crystal pulling speed is too small, it will affect the growth rate of the monocrystalline silicon during the entire preparation process, thereby affecting the production capacity. Therefore, controlling the initial value of the crystal pulling speed within the above range is conducive to improving the crystal quality while ensuring the production capacity.

[0061] Reference Figure 4 , is a detailed step flow chart of a method for preparing single crystal silicon according to another embodiment of the present application, wherein the first stage is the stage when the crystal grows to the third length, and the second stage is the stage when the crystal grows from the third length to the end of equal diameter growth. Specifically, the method for preparing single crystal silicon includes the following steps:

[0062] S1013: In the first stage of the equal-diameter growth of single crystal silicon, the crystal pulling speed is controlled to gradually increase, and the liquid nozzle distance is controlled to gradually decrease. At the end of the first stage, the crystal pulling speed increases to a preset pulling speed, and the liquid nozzle distance decreases to a preset distance.

[0063] S102: In the second stage of the equal-diameter growth of the single crystal silicon, the crystal pulling speed is controlled to maintain a preset pulling speed, and the liquid nozzle distance is controlled to maintain a preset distance.

[0064] This embodiment corresponds to Figure 2In the first working condition or the second working condition, optionally, the third length is 650-750 mm. Step S1013 indicates that during the process of the crystal growing to the third length, the crystal pulling speed is gradually increasing, and the liquid mouth distance is gradually decreasing, and when the crystal length is equal to the third length, the crystal pulling speed is equal to the preset pulling speed and no longer increases, and the liquid mouth distance is equal to the preset distance and no longer decreases.

[0065] Depend on Figure 2 From Table 1, it can be seen that the distortion ratio of the crystal in the first working condition is higher than that in the second working condition. Figure 2 It can be seen that the slopes of the first curve 1 and the second curve 2 are basically the same, that is, the decreasing rates of the liquid-to-mouth distance are basically the same. The difference between the first curve 1 and the second curve 2 lies in their initial points. Under the first working condition corresponding to the first curve 1, the initial value of the liquid-to-mouth distance is approximately 34-35 mm, while the initial value of the liquid-to-mouth distance under the second working condition corresponding to the second curve 2 is approximately 30 mm, and the initial value of the liquid-to-mouth distance under the fourth working condition corresponding to the fourth curve 4 is approximately 29 mm. The distortion ratio of the crystal is relatively low under the second working condition and the fourth working condition. Therefore, further, in some embodiments of the present application, during the growth of single crystal silicon, the initial value of the liquid-to-mouth distance is controlled to be 28-32 mm when the single crystal silicon starts at the equal-diameter growth stage.

[0066] From the above, it can be seen that the present application controls the two main parameters of liquid nozzle distance and crystal pulling speed during the equal-diameter growth stage of the crystal. Specifically, by controlling the speed at which the liquid nozzle distance decreases and the speed at which the crystal pulling speed increases, the time when the liquid nozzle distance decreases to the preset distance is no earlier than the time when the crystal pulling speed increases to the preset pulling speed, thereby reducing the crystal distortion ratio.

[0067] The liquid nozzle distance is an important parameter in the crystal growth process. The liquid nozzle distance will not only affect the carbon and oxygen content in the crystal, thereby affecting the purity and quality of the crystal, but also the liquid nozzle distance will affect the flow of airflow near the molten silicon liquid surface and the distribution of the thermal field. After the equal-diameter growth stage begins, as the liquid nozzle distance decreases, the airflow from the direction of the heat screen and the guide tube has an enhanced ability to blow the molten silicon liquid surface. Therefore, if the liquid nozzle distance is reduced too quickly, it may have a significant impact on the thermal field near the molten silicon liquid surface. At this time, the crystal pulling speed is in a state of continuous increase, which will cause an unstable thermal field at the junction of the crystal and the silicon solution. With the rotation of the crystal and the crucible, the local position of the crystal and the silicon solution may produce an overcooled area, resulting in a temperature asymmetry along the circumference of the crystal, so that the crystallization rate of the colder area on the circumference of the crystal is greater than the crystallization rate of other areas, showing an asymmetric growth, and ultimately causing the crystal to twist.

[0068] Therefore, the present application can improve the consistency of the temperature in the area near the molten silicon liquid surface by controlling the two process parameters of the liquid mouth distance and the crystal pulling speed during the crystal equal diameter growth process, and form a relatively stable thermal field at the junction of the crystal and the silicon solution, thereby reducing the distortion ratio of the crystal. Moreover, the above technical solution of the present application is a pre-adjustment of the process parameters during the crystal growth process, without the need for manual intervention during the crystal growth process, thereby reducing the uncontrollable factors caused by manual intervention, and the hysteresis of adjusting after the crystal is distorted, and improving the fault tolerance rate, so it not only simplifies the process complexity, but also improves the crystal molding quality.

[0069] Reference Figure 5 , is a schematic diagram of a longitudinal cross-section of a single crystal silicon, in which D is the diameter of the heat shield opening (the diameter of the lower end surface of the heat shield), and d is the crystal diameter. In some embodiments of the present application, the above-mentioned preparation method further includes: during the growth process of the single crystal silicon, controlling the difference between the crystal diameter and the heat shield opening diameter to be within a preset range. This is to control the gap size between the crystal and the inner wall of the heat shield opening.

[0070] Among them, the above preset range is 60-90mm. It should be noted that the gap between the heat shield mouth and the crystal has an important influence on the thermal field in the single crystal furnace. When the gap between the heat shield mouth and the crystal is too large, the more heat in the single crystal furnace is dissipated outward through the heat shield mouth, which is easy to cause the molten silicon liquid surface temperature to be too low; when the gap between the heat shield mouth and the crystal is too small, it will cause the temperature above the heat shield mouth to be too low. In this case, the temperature difference between the part of the crystal located above the heat shield mouth and the part of the crystal located below the heat shield mouth is too large, which may also cause the crystal to be distorted or broken.

[0071] Therefore, the present application controls the diameter of the crystal during the crystal growth process so that the crystal diameter and the diameter of the heat shield opening are within the above-mentioned preset range, which is beneficial to reducing the proportion of crystal distortion or breakage and improving the crystal molding quality.

[0072] So far, the technical solutions of the present application have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present application is obviously not limited to these specific embodiments. Without departing from the principles of the present application, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present application.

Claims

1. A method for preparing single crystal silicon, characterized in that: include: In the first stage of the uniform diameter growth of single crystal silicon, the crystal pulling speed is controlled to gradually increase to a preset pulling speed, and the liquid nozzle distance is controlled to gradually decrease to a preset distance; In the second stage of the isodiameter growth of the single crystal silicon, the crystal pulling speed is controlled to maintain the preset pulling speed, and the liquid port distance is controlled to maintain the preset distance.

2. The preparation method according to claim 1, characterized in that: The first stage includes an initial stage and a transition stage, wherein the initial stage is a stage when the crystal grows to a first length, the transition stage is a stage when the crystal grows from the first length to a second length, and the second stage is a stage when the crystal grows from the second length to the end of equal diameter growth; In the first stage of the uniform growth of the single crystal silicon, controlling the crystal pulling speed to gradually increase to a preset pulling speed and controlling the liquid nozzle distance to gradually decrease to a preset distance comprises: In the initial stage of the uniform diameter growth of the single crystal silicon, the crystal pulling speed is controlled to gradually increase, and the liquid mouth distance is controlled to gradually decrease. At the end of the initial stage, the crystal pulling speed is increased to a preset pulling speed; During the transition stage of the equal-diameter growth of the single crystal silicon, the liquid-to-mouth distance is controlled to continue to decrease. When the transition stage ends, the liquid-to-mouth distance is reduced to a preset distance.

3. The preparation method according to claim 2, characterized in that: The first length is 450-550 mm; and / or The second length is 650-750 mm.

4. The preparation method according to claim 1, characterized in that: The first stage is the stage when the crystal grows to the third length, and the second stage is the stage when the crystal grows from the third length to the end of equal diameter growth; In the first stage of the uniform growth of the single crystal silicon, controlling the crystal pulling speed to gradually increase to a preset pulling speed and controlling the liquid nozzle distance to gradually decrease to a preset distance comprises: In the first stage of isodiameter growth of single crystal silicon, the crystal pulling speed is controlled to gradually increase, and the liquid nozzle distance is controlled to gradually decrease. At the end of the first stage, the crystal pulling speed increases to a preset pulling speed, and the liquid nozzle distance decreases to a preset distance.

5. The preparation method according to claim 4, characterized in that: The third length is 650-750 mm.

6. The preparation method according to claim 1, characterized in that: The preset pulling speed is 1.6-1.7 mm / min.

7. The preparation method according to claim 1, characterized in that: The preset distance is 15-20 mm.

8. The preparation method according to claim 1, characterized in that: The controlling the liquid port distance to gradually decrease to a preset distance comprises: With the heat shield stationary, the crucible is controlled to rise gradually.

9. The preparation method according to claim 1, characterized in that: The preparation method further comprises: During the growth of the single crystal silicon, the initial value of the crystal pulling speed is controlled to be 0.9-1.1 mm / min at the beginning of the isodiameter growth stage of the single crystal silicon; and / or During the growth of single crystal silicon, the initial value of the liquid mouth distance is controlled to be 28-32 mm when the single crystal silicon begins to grow at the equal diameter growth stage.

10. The preparation method according to any one of claims 1 to 9, characterized in that: The preparation method further comprises: During the growth of single crystal silicon, the difference between the crystal diameter and the heat shield opening diameter is controlled within a preset range; Wherein, the preset range is 60-90 mm.

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