Crystal pulling control method

Abstract

The embodiment of the invention relates to the technical field of monocrystalline silicon preparation, and provides a crystal pulling control method which at least can improve the axial resistivity uniformity of a monocrystalline silicon rod. The control method comprises the following steps: acquiring a prediction curve, wherein the prediction curve is expressed as a change curve of resistivity corresponding to different equal-diameter lengths of a silicon single crystal rod comprising a first dopant; obtaining a preset isodiametric slope table based on the prediction curve, the preset isodiametric slope table and corresponding preset process parameters, wherein the preset process parameters comprise a power ratio of the set power of the upper heater to the set power of the lower heater; the preparation method comprises the following steps: preparing a target monocrystalline silicon rod, adding a silicon material and a first dopant into a crucible, sequentially carrying out a melting process, a seeding process, a shouldering process and an equal-diameter process to obtain an initial monocrystalline silicon rod, adjusting process parameters of the equal-diameter process according to preset process parameters, and after the equal-diameter length of the initial monocrystalline silicon rod reaches a target length, carrying out continuous casting on the target monocrystalline silicon rod to obtain the target monocrystalline silicon rod. And entering an ending process to obtain the target single crystal silicon rod.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of single crystal silicon preparation, and in particular to a method for controlling crystal pulling. Background Art

[0002] As a semiconductor material, single crystal silicon is mainly used in the photovoltaic and semiconductor fields. There are currently two technologies used in the actual production of single crystal silicon: the zone melting method and the Czochralski method. The zone melting method does not use a crucible to produce single crystal silicon. Instead, the silicon rod is partially melted using a coil, and a magnetic support is set at the melting zone, so that the melting zone can always be in a suspended state. The molten silicon is pulled using a rotating seed crystal to prepare single crystal silicon below the melting zone. The Czochralski method is also known as the Czochralski method, or CZ method for short. The process is relatively simple. Silicon is melted in a quartz crucible and single crystal silicon is gradually pulled using a rotating seed crystal. This method has a relatively low production cost and can be mass-produced. It can produce high-quality, large-size semiconductor-grade or solar-grade single crystal silicon wafers, so it is widely used in the preparation of single crystal silicon.

[0003] In the production of single crystal silicon rods, a certain amount of dopants are often added to meet the requirements for its electrical properties. Common dopants are: boron, phosphorus, arsenic and antimony. Due to the phenomenon of impurity segregation during the crystal solidification process, the later the single crystal silicon rod is, the higher the dopant concentration is, and the lower the resistivity is, resulting in the non-uniformity of the axial resistivity of the single crystal silicon rod, especially for dopants with small segregation coefficients (such as phosphorus or arsenic), the axial resistivity uniformity of the single crystal silicon rod is worse.

[0004] Therefore, there is an urgent need to improve the control method of crystal pulling to enhance the axial resistivity uniformity of single crystal silicon rods. Summary of the invention

[0005] The embodiment of the present application provides a method for controlling crystal pulling, which is at least beneficial to improving the axial resistivity uniformity of a single crystal silicon rod.

[0006] According to some embodiments of the present application, on the one hand, the embodiments of the present application provide a crystal pulling control method, which is suitable for a single crystal furnace with segmented heating, and the heater of the single crystal furnace includes: an upper heater and a lower heater arranged on the outer wall of the crucible, the upper heater is located above the lower heater, and the upper heater and the lower heater jointly distribute a preset total power; the control method includes: obtaining a prediction curve, the prediction curve is represented by a resistivity change curve corresponding to different equal-diameter lengths of a single crystal silicon rod including a first dopant; based on the prediction curve, a preset equal-diameter slope table is obtained, the preset equal-diameter slope table is represented by preset process parameters in the equal-diameter process corresponding to the single crystal silicon rod at different equal-diameter lengths, and the preset process parameters include the power ratio of the set power of the upper heater to the set power of the lower heater, and the sum of the set power of the upper heater and the set power of the lower heater. equal to the preset total power, wherein, under the same equal-diameter length, if the corresponding resistivity in the predicted curve is greater than or equal to the first resistivity, the corresponding power ratio in the preset process parameters is greater than 1; if the corresponding resistivity in the predicted curve is less than or equal to the second resistivity, the corresponding power ratio in the preset process parameters is less than 1; if the corresponding resistivity in the predicted curve is greater than the second resistivity and less than the first resistivity, the corresponding power ratio in the preset process parameters is 1; prepare a target single crystal silicon rod, add silicon material and a first dopant into a crucible, and sequentially perform a melting process, a seeding process, a shouldering process and an equal-diameter process to obtain an initial single crystal silicon rod, the process parameters of the equal-diameter process are adjusted with reference to the preset process parameters, and after the equal-diameter length of the initial single crystal silicon rod reaches the target length, enter the finishing process to obtain the target single crystal silicon rod.

[0007] In some embodiments, the resistivity required for the target single crystal silicon rod is the target resistivity, and the ratio of the first resistivity to the target resistivity is 1.12-1.17; the ratio of the second resistivity to the target resistivity is 0.83-0.88.

[0008] In some embodiments, after preparing the target single crystal silicon rod, the method includes: performing a resistivity test on the target single crystal silicon rod to obtain an actual resistivity curve corresponding to the target single crystal silicon rod at different equal diameter lengths; obtaining the resistivity deviation between the actual curve and the predicted curve at different equal diameter lengths; and adjusting the corresponding preset process parameters in the preset equal diameter slope table according to the resistivity deviation.

[0009] In some embodiments, the power ratio is 0.8-1.2.

[0010] In some embodiments, the step of obtaining a prediction curve includes: preparing a test single crystal silicon rod, the test single crystal silicon rod is formed through a melting process, a seeding process, a shoulder release process and an equal diameter process, and the raw materials of the test single crystal silicon rod include silicon material and a first dopant; drawing a prediction curve according to the equal diameter length of the test single crystal silicon rod and the resistivity corresponding to the test single crystal silicon rod at each equal diameter length.

[0011] In some embodiments, obtaining a preset constant-diameter slope table based on a prediction curve includes: obtaining a prediction model based on the prediction curve and the corresponding process parameters of the tested single crystal silicon rods at different constant-diameter lengths, the prediction model being represented by the relationship between the predicted resistivity of the single crystal silicon rods grown to different constant-diameter lengths and the corresponding process parameters, and the prediction curve being substituted into the prediction model to obtain the corresponding preset constant-diameter slope table.

[0012] In some embodiments, the step of obtaining a prediction curve includes: in the melting process of preparing a test single crystal silicon rod, adding a second dopant while adding silicon material and a first dopant into a crucible; the control method includes: in the melting process of preparing a target single crystal silicon rod, adding a second dopant while adding silicon material and a first dopant into a crucible.

[0013] In some embodiments, the step of obtaining a prediction curve includes: in the melting process of preparing a test single crystal silicon rod, adding silicon material and a first dopant into a crucible; in the equal-diameter process of preparing the test single crystal silicon rod, after the equal-diameter length of the test single crystal silicon rod reaches a preset length, adding a second dopant into the crucible; the control method includes: in the equal-diameter process of preparing a target single crystal silicon rod, before the equal-diameter length of the initial single crystal silicon rod reaches a target length, after the equal-diameter length of the initial single crystal silicon rod reaches a preset length, adding a second dopant into the crucible.

[0014] In some embodiments, in the equal diameter process of preparing the target single crystal silicon rod, the silicon liquid level is maintained in the area corresponding to the upper heater, and the distance between the silicon liquid level and the lower edge of the upper heater is 40mm to 60mm in the direction from the lower edge to the upper edge of the upper heater.

[0015] In some embodiments, in the vertical direction, the height of the upper heater is greater than the height of the lower heater.

[0016] The technical solution provided by the embodiments of the present application has at least the following advantages:

[0017] In the crystal pulling control method provided in the embodiment of the present application, a single crystal furnace with segmented heating is used to perform a Czochralski method to prepare a single crystal silicon rod. The heater of the single crystal furnace includes an upper heater and a lower heater arranged above and below the outer wall of the crucible. The upper heater and the lower heater jointly distribute a preset total power, so that in the equal diameter process of crystal pulling, the local temperature of the upper and lower parts of the crucible can be precisely controlled. In the control method, a prediction curve is first obtained to predict the change trend of the resistivity corresponding to different equal diameter lengths of the single crystal silicon rod in the equal diameter process of crystal pulling after the first dopant is added. Furthermore, the preset process parameters in the corresponding equal-diameter process in the preset equal-diameter slope table are set according to the change trend in the prediction curve. For example, under the same equal-diameter length, if the corresponding resistivity in the prediction curve is greater than or equal to the first resistivity, the corresponding power ratio in the preset process parameters is greater than 1, so that the power allocated to the upper heater is larger and the power allocated to the lower heater is smaller, so that the heating temperature of the upper part of the crucible is higher than the heating temperature of the lower part, thereby inhibiting the volatilization of the first dopant, and more first dopant can enter the single crystal silicon rod, so that the resistivity of the single crystal silicon rod is reduced to below the first resistivity; if the corresponding resistivity in the prediction curve is less than or equal to the second resistivity, the preset process parameters The corresponding power ratio is less than 1, so the power allocated to the upper heater is smaller and the power allocated to the lower heater is larger, so that the heating temperature of the upper part of the crucible is lower than the heating temperature of the lower part, thereby promoting the volatilization of the first dopant, and less first dopant can enter the single crystal silicon rod, so that the resistivity of the single crystal silicon rod is increased to above the second resistivity; if the corresponding resistivity in the predicted curve is greater than the second resistivity and less than the first resistivity, the corresponding power ratio in the preset process parameters is 1, and when the resistivity of the single crystal silicon rod is within a controllable range, the power of the upper and lower heaters is evenly distributed, so that the heating temperature of the upper part of the crucible is synchronized with the heating temperature of the lower part, thereby keeping the resistivity of the single crystal silicon rod within a controllable range. After obtaining the preset equal-diameter slope table in combination with the prediction curve, in the process of preparing the target single crystal silicon rod, the silicon material and the first dopant are added into the crucible, and then the melting process, the crystal seeding process, the shoulder release process and the equal-diameter process are carried out in sequence, wherein the process parameters of the equal-diameter process are adjusted with reference to the preset process parameters, so as to realize the regulation of the resistivity distribution of the initial single crystal silicon rod prepared by actual crystal pulling, and after the equal-diameter length of the initial single crystal silicon rod reaches the target length, the finishing process is entered to obtain the target single crystal silicon rod, and the target single crystal silicon rod obtained in this way has higher axial resistivity uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplified descriptions do not constitute a limitation on the embodiments. Unless otherwise specified, the pictures in the drawings do not constitute a scale limitation. In order to more clearly illustrate the embodiments of the present application or the technical solutions in the traditional technology, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 A schematic diagram of the structure of a single crystal furnace provided in an embodiment of the present application;

[0020] Figure 2 This is a flowchart corresponding to the crystal pulling control method provided in an embodiment of the present application. DETAILED DESCRIPTION

[0021] As can be seen from the background technology, there is an urgent need to improve the control method of crystal pulling to increase the axial resistivity uniformity of single crystal silicon rods.

[0022] The present application provides a crystal pulling control method, which is at least beneficial to improving the axial resistivity uniformity of a single crystal silicon rod.

[0023] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0024] In the description of the embodiments of the present application, “plurality” means more than two, unless otherwise clearly and specifically defined.

[0025] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0026] In the description of the embodiments of the present application, technical terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0027] The following will describe the various embodiments of the present application in detail with reference to the accompanying drawings. However, it will be appreciated by those skilled in the art that in the various embodiments of the present application, many technical details are provided in order to enable the reader to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solution claimed in the present application can be implemented.

[0028] Figure 1 A schematic diagram of the structure of a single crystal furnace provided in an embodiment of the present application; Figure 2 This is a flowchart corresponding to the crystal pulling control method provided in an embodiment of the present application.

[0029] refer to Figure 1 The crystal pulling control method provided in the embodiment of the present application is suitable for a single crystal furnace with segmented heating. The heater of the single crystal furnace includes: an upper heater 101 and a lower heater 102 arranged on the outer wall of a crucible (not shown in the figure), the upper heater 101 is located above the lower heater 102, and the upper heater 101 and the lower heater 102 jointly distribute the preset total power.

[0030] Generally, the process of preparing single crystal silicon rods by the Czochralski method includes several stages, namely, melting process, seeding process, shoulder release process, equal diameter process and finishing process.

[0031] In the melting process, silicon material and dopants are added to the crucible of the single crystal furnace, and then the single crystal furnace is evacuated to maintain it within a certain pressure range, and then filled with protective gas with a certain flow rate and pressure. Finally, it is heated to a temperature exceeding the melting point of the silicon material to fully melt it.

[0032] In the seeding process, when the silicon melt stabilizes to a certain temperature, the seed crystal is immersed in the silicon melt and lifted at a certain pulling speed, so that the silicon atoms grow along the seed crystal into a thin neck with a certain diameter until the thin neck reaches a predetermined length. The main function of the seeding process is to eliminate the dislocation defects formed by single crystal silicon due to thermal shock, and to use the supercooling of the crystallization front to drive the silicon atoms to arrange in order on the silicon solid at the solid-liquid interface to form single crystal silicon.

[0033] Then, the shoulder release process begins. When the neck reaches a predetermined length, the speed of pulling the seed crystal upward is slowed down, and the temperature of the silicon melt is slightly reduced. The purpose of cooling is to promote the lateral growth of the single crystal silicon and increase the diameter of the single crystal silicon.

[0034] Then it enters the shoulder turning stage. When the diameter of the single crystal silicon increases to the set diameter, the heating power of the heater is increased, the temperature of the silicon melt is increased, and the speed of pulling the seed crystal upward, the speed of rotation, and the rotation speed of the crucible are adjusted at the same time to inhibit the lateral growth of the single crystal silicon and promote its longitudinal growth, so that the single crystal silicon grows with almost equal diameter.

[0035] Then it enters the equal diameter process. The cylindrical crystal rod formed in this stage is an equal diameter section. By adjusting the crucible temperature, crystal pulling speed, crucible rotation speed and crystal rotation speed, the growth rate is stabilized so that the crystal diameter remains unchanged until the crystal pulling is completed. The equal diameter process is the main stage of single crystal silicon growth, which can last for dozens of hours or even more than a hundred hours.

[0036] Finally, the finishing process begins. During the finishing process, the lifting rate is accelerated and the temperature of the silicon melt is increased, so that the diameter of the crystal rod gradually decreases and forms a cone. When the cone tip is small enough, it will eventually leave the melt surface. The finished crystal rod is lifted to the upper furnace chamber and cooled for a period of time before being taken out, completing a growth cycle.

[0037] refer to Figure 1 The heater of the single crystal furnace also includes a bottom heater 103. Usually, when a single crystal is grown by vertical pulling, the upper heater 101, the lower heater 102 and the bottom heater 103 work simultaneously in the early melting process, the seeding process and the shoulder release process. In the equal diameter process, the upper heater 101 and the lower heater 102 work, and the bottom heater 103 does not participate in the work. Because the bottom heater 103 is turned on, normal crystal growth cannot be completed.

[0038] refer to Figure 2 The control method of the single crystal silicon rod provided in the embodiment of the present application includes:

[0039] Step 11: obtaining a prediction curve, where the prediction curve is represented by a resistivity variation curve corresponding to different equal diameter lengths of a single crystal silicon rod including a first dopant;

[0040] Step 12: obtaining a preset equal-diameter slope table based on the prediction curve, wherein the preset equal-diameter slope table is represented by preset process parameters in the equal-diameter process corresponding to the single crystal silicon rod at different equal-diameter lengths, wherein the preset process parameters include a power ratio of a set power of an upper heater to a set power of a lower heater, and the sum of the set power of the upper heater and the set power of the lower heater is equal to a preset total power, wherein, under the same equal-diameter length, if the corresponding resistivity in the prediction curve is greater than or equal to the first resistivity, the corresponding power ratio in the preset process parameters is greater than 1; if the corresponding resistivity in the prediction curve is less than or equal to the second resistivity, the corresponding power ratio in the preset process parameters is less than 1; if the corresponding resistivity in the prediction curve is greater than the second resistivity and less than the first resistivity, the corresponding power ratio in the preset process parameters is 1;

[0041] Step 13: Prepare the target single crystal silicon rod, add silicon material and the first dopant into the crucible, and sequentially perform the melting process, the seeding process, the shoulder release process and the equal diameter process to obtain the initial single crystal silicon rod. The process parameters of the equal diameter process are adjusted with reference to the preset process parameters. After the equal diameter length of the initial single crystal silicon rod reaches the target length, enter the finishing process to obtain the target single crystal silicon rod.

[0042] In the crystal pulling control method provided in the embodiment of the present application, a single crystal furnace with segmented heating is used to perform a Czochralski method to prepare a single crystal silicon rod. The heater of the single crystal furnace includes an upper heater and a lower heater arranged above and below the outer wall of the crucible. The upper heater and the lower heater jointly distribute a preset total power, so that in the equal diameter process of crystal pulling, the local temperature of the upper and lower parts of the crucible can be precisely controlled. In the control method, a prediction curve is first obtained to predict the change trend of the resistivity corresponding to different equal diameter lengths of the single crystal silicon rod in the equal diameter process of crystal pulling after the first dopant is added. Furthermore, the preset process parameters in the corresponding equal-diameter process in the preset equal-diameter slope table are set according to the change trend in the prediction curve. For example, under the same equal-diameter length, if the corresponding resistivity in the prediction curve is greater than or equal to the first resistivity, the corresponding power ratio in the preset process parameters is greater than 1, so that the power allocated to the upper heater is larger and the power allocated to the lower heater is smaller, so that the heating temperature of the upper part of the crucible is higher than the heating temperature of the lower part, thereby inhibiting the volatilization of the first dopant, and more first dopant can enter the single crystal silicon rod, so that the resistivity of the single crystal silicon rod is reduced to below the first resistivity; if the corresponding resistivity in the prediction curve is less than or equal to the second resistivity, the preset process parameters The corresponding power ratio is less than 1, so the power allocated to the upper heater is smaller and the power allocated to the lower heater is larger, so that the heating temperature of the upper part of the crucible is lower than the heating temperature of the lower part, thereby promoting the volatilization of the first dopant, and less first dopant can enter the single crystal silicon rod, so that the resistivity of the single crystal silicon rod is increased to above the second resistivity; if the corresponding resistivity in the predicted curve is greater than the second resistivity and less than the first resistivity, the corresponding power ratio in the preset process parameters is 1, and when the resistivity of the single crystal silicon rod is within a controllable range, the power of the upper and lower heaters is evenly distributed, so that the heating temperature of the upper part of the crucible is synchronized with the heating temperature of the lower part, thereby keeping the resistivity of the single crystal silicon rod within a controllable range. After obtaining the preset equal-diameter slope table in combination with the prediction curve, in the process of preparing the target single crystal silicon rod, the silicon material and the first dopant are added into the crucible, and then the melting process, the crystal seeding process, the shoulder release process and the equal-diameter process are carried out in sequence, wherein the process parameters of the equal-diameter process are adjusted with reference to the preset process parameters, so as to realize the regulation of the resistivity distribution of the initial single crystal silicon rod prepared by actual crystal pulling, and after the equal-diameter length of the initial single crystal silicon rod reaches the target length, the finishing process is entered to obtain the target single crystal silicon rod, and the target single crystal silicon rod obtained in this way has higher axial resistivity uniformity.

[0043] Taking the resistivity required by the target single crystal silicon rod as the target resistivity, the ratio of the first resistivity to the target resistivity is 1.12-1.17, for example, it can be 1.12, 1.15, 1.16 or 1.17; the ratio of the second resistivity to the target resistivity is 0.83-0.88, for example, it can be 0.83, 0.85, 0.86 or 0.88.

[0044] In a specific example, taking the required resistivity of the target single crystal silicon rod as 1Ω·cm as an example, the first resistivity can be set to 1.15Ω·cm, and the second resistivity can be set to 0.85Ω·cm. In the prediction curve, at different equal-diameter lengths, the predicted resistivity change trend of the single crystal silicon rod fluctuates around 1Ω·cm. When the corresponding resistivity in the prediction curve is between 0.85Ω·cm and 1.15Ω·cm, it means that the resistivity change of the single crystal silicon rod meets the requirements, and the power ratio of the set power of the upper heater to the set power of the lower heater in the preset process parameters can be kept set to 1; when the corresponding resistivity in the prediction curve is greater than 1.15Ω·cm, it means that the resistivity of the single crystal silicon rod is higher at the corresponding equal-diameter length, and the volatilization of the first dopant needs to be promoted at this time, and the power ratio in the corresponding preset process parameters can be set to less than 1; when the corresponding resistivity in the prediction curve is less than 0.85Ω·cm, it means that the resistivity of the single crystal silicon rod is lower at the corresponding equal-diameter length, and the volatilization of the first dopant needs to be suppressed at this time, and the power ratio in the corresponding preset process parameters can be set to greater than 1.

[0045] That is to say, when the resistivity change of the single crystal silicon rod in the prediction curve changes within the preset range, the impact on the overall axial resistivity uniformity of the single crystal silicon rod is small, and the power ratio of the upper heater can be kept synchronized; when the resistivity change of the single crystal silicon rod is higher or lower than the range of the preset interval, it is necessary to adjust the heating temperature of the upper part and the heating temperature of the lower part of the crucible in combination with the set power of the upper heater and the set power of the lower heater, so as to achieve the effect of inhibiting the volatilization of the dopant or promoting the volatilization of the dopant, and then realize the resistivity control of the single crystal silicon rod, so that the actual resistivity corresponding to the target single crystal silicon rod prepared after crystal pulling according to the corresponding preset process parameters can have a higher axial resistivity uniformity.

[0046] In some embodiments, after preparing the target single crystal silicon rod, the method includes: performing a resistivity test on the target single crystal silicon rod to obtain an actual resistivity curve corresponding to the target single crystal silicon rod at different equal diameter lengths; obtaining the resistivity deviation between the actual curve and the predicted curve at different equal diameter lengths; and adjusting the corresponding preset process parameters in the preset equal diameter slope table according to the resistivity deviation. That is, according to the resistivity of the target single crystal silicon rod actually prepared, the actual resistivity curve corresponding to the target single crystal silicon rod at different equal diameter lengths is obtained, and it can be verified whether the corresponding preset process parameters in the preset equal diameter slope table achieve the expected effect. If it does not meet the expected effect, the preset process parameters can be adjusted in combination with the deviation between the preset curve and the actual curve, so that the single crystal silicon rod prepared subsequently can have a higher axial resistivity uniformity.

[0047] In the regulation of the power ratio, the power ratio of the set power of the upper heater to the set power of the lower heater is adjusted between 0.8 and 1.2, for example, it can be 0.8, 0.9, 0.95, 1.0, 1.05, 1.11 or 1.12, etc. In the equal diameter process, the power ratio of the set power of the upper heater to the set power of the lower heater needs to be adjusted within an appropriate range. A power ratio lower than 0.8 or higher than 1.2 is likely to cause a large temperature difference between the upper and lower parts of the crucible, which in turn leads to temperature runaway in the equal diameter process, making the resistivity distribution of the target single crystal silicon rod finally formed uncontrollable.

[0048] In some embodiments, the step of obtaining a prediction curve includes: preparing a test single crystal silicon rod, the test single crystal silicon rod is formed by a melting process, a seeding process, a shouldering process and an equal diameter process, and the raw materials of the test single crystal silicon rod include silicon material and a first dopant; according to the equal diameter length of the test single crystal silicon rod and the resistivity corresponding to the test single crystal silicon rod at each equal diameter length, a prediction curve is drawn. Among them, the drawing of the prediction curve can be obtained by linear regression. That is to say, before preparing the target single crystal silicon rod, a test single crystal silicon rod is first prepared, and a prediction curve is drawn according to the actual resistivity change of the test single crystal silicon rod, so that the influence of the first dopant on the resistivity of the single crystal silicon rod during the crystal pulling process can be obtained. Among them, the number of test single crystal silicon rods can be multiple, and a more accurate prediction curve can be obtained according to the resistivity change curves of multiple test single crystal silicon rods.

[0049] In some embodiments, obtaining a preset equal-diameter slope table based on a predicted curve includes: obtaining a preset equal-diameter slope table based on the predicted curve and the process parameters corresponding to the test single crystal silicon rod. The corresponding process parameters in the preparation process of the test single crystal silicon rod have a certain influence on the resistivity of the test single crystal silicon rod. Based on the process parameters in the actual test single crystal silicon rod preparation process and the predicted curve drawn by the resistivity of the test single crystal silicon rod, after adjusting the process parameters, the obtained predicted equal-diameter slope table can realize the resistivity control of the subsequently prepared single crystal silicon rod. When the number of test single crystal silicon rods is multiple, the preset process parameters in the preset equal-diameter slope table can be comprehensively adjusted in combination with multiple groups of test single crystal silicon rods and their corresponding process parameters.

[0050] In other embodiments, obtaining a preset constant-diameter slope table based on a prediction curve includes: obtaining a prediction model based on the prediction curve and the corresponding process parameters of the tested single crystal silicon rods at different constant-diameter lengths, the prediction model being expressed as the relationship between the predicted resistivity of the single crystal silicon rods grown to different constant-diameter lengths and the corresponding process parameters, and bringing the prediction curve into the prediction model to obtain the corresponding preset constant-diameter slope table. Based on the prediction model, the relationship between the predicted resistivity of the single crystal silicon rods grown to different constant-diameter lengths and the corresponding process parameters can be used to predict the adjusted process parameters to predict whether the adjusted process parameters can meet the preset expectations, thereby obtaining a more accurate preset constant-diameter slope table and the corresponding preset process parameters. When the number of tested single crystal silicon rods is multiple, the accuracy of the prediction model is higher, which is conducive to improving the accuracy of the preset constant-diameter slope table and the corresponding preset process parameters.

[0051] The prediction model can be obtained by using a neural network model, such as a BP network (Backpropagation network), a Hopfield network (Hopfield network), an ART network (Adaptive resonance theory network), an RBF network (Radial basis function network) or a self-organizing feature mapping network (Self-Organizing Feature Mapping).

[0052] In some embodiments, the target single crystal silicon rod to be prepared may have two dopants, wherein the two dopants are added in two ways: one is to add the two dopants at the same time in the step of adding silicon material and dopants to the crucible before the melting process; the other is to add silicon material and one dopant to the crucible before the melting process, and in the equal diameter process, when the single crystal silicon rod grows to a certain length, add another dopant. When the target single crystal silicon rod has two dopants, the corresponding single crystal silicon rod preparation method has the following two ways:

[0053] In one example, the step of obtaining a prediction curve by preparing a test single crystal silicon rod further includes: in the melting process of preparing the test single crystal silicon rod, adding the silicon material and the first dopant to the crucible and adding the second dopant; correspondingly, in the melting process of preparing the target single crystal silicon rod, adding the silicon material and the first dopant to the crucible and adding the second dopant. The target single crystal silicon rod prepared by the crystal pulling control method may include the first dopant and the second dopant.

[0054] In another example, the step of obtaining a prediction curve by preparing a test single crystal silicon rod also includes: in the melting process of preparing the test single crystal silicon rod, adding silicon material and a first dopant into a crucible; in the equal-diameter process of preparing the test single crystal silicon rod, after the equal-diameter length of the test single crystal silicon rod reaches a preset length, adding a second dopant into the crucible; correspondingly, in the equal-diameter process of preparing the target single crystal silicon rod, before the equal-diameter length of the initial single crystal silicon rod reaches a target length, after the equal-diameter length of the initial single crystal silicon rod reaches a preset length, adding a second dopant into the crucible.

[0055] That is to say, the preparation method of the test single crystal silicon rod is kept the same as the preparation method of the target single crystal silicon rod. In this way, the preparation steps of the test single crystal silicon rod are the same as the steps of actually preparing the target single crystal silicon rod, and the influence of other different factors can be eliminated. The change trend of the resistivity corresponding to the test single crystal silicon rod is more in line with the actual situation, and the prediction curve obtained in combination with the test single crystal silicon rod is more accurate. Then, the corresponding preset process parameters in the preset equal-diameter slope table obtained in combination with the prediction curve can be more accurately adjusted, so that the axial resistivity of the actually prepared target single crystal silicon rod is more uniform.

[0056] Referring to the above method for preparing the target single crystal silicon rod with two dopants, the target single crystal silicon rod may also have multiple dopants, such as 3, 4 or 5. Accordingly, the steps for preparing the test single crystal silicon rod are the same as the steps for preparing the target single crystal silicon rod.

[0057] In some embodiments, in the equal-diameter process of preparing the target single crystal silicon rod, the silicon liquid level is maintained in the area corresponding to the upper heater, and the distance between the silicon liquid level and the lower edge of the upper heater in the direction from the lower edge to the upper edge of the upper heater is 40mm to 60mm, for example, it can be 40mm, 45mm, 50mm, 55mm or 60mm. Since the height of the silicon liquid level in the crucible decreases as the length of the single crystal silicon rod increases during the equal-diameter process, the silicon liquid level is always maintained in the area corresponding to the upper heater during the equal-diameter process, and the distance between the silicon liquid level and the lower edge of the upper heater is within the range of 40mm to 60mm, which is conducive to keeping the upper heater always partially above the silicon liquid level, while another part of the upper heater is below the silicon liquid level, and the lower heater is always maintained below the silicon liquid level, so that most of the heat generated by the upper heater acts above the silicon liquid level, and the heat generated by the lower heater is completely absorbed by the silicon liquid, thereby making the actual temperature distribution above and below the silicon liquid level more in line with the desired effect under the set power ratio. In addition, since there is a gap between the upper heater and the lower heater to avoid ignition problems between the upper heater and the lower heater, the gap is kept below the silicon liquid surface to avoid the problem of uncontrollable temperature at the silicon liquid surface caused by excessive temperature difference in the gap.

[0058] In some embodiments, in the vertical direction, the height of the upper heater is greater than that of the lower heater. The height of the upper heater may be 150 mm to 220 mm, for example, 150 mm, 170 mm, 200 mm, or 220 mm, etc.; the height of the lower heater is 100 mm to 150 mm, for example, 100 mm, 110 mm, 120 mm, 130 mm, 140 mm, or 150 mm.

[0059] In the crystal pulling control method provided in the embodiment of the present application, a single crystal furnace with segmented heating is used to perform a Czochralski method to prepare a single crystal silicon rod. The heater of the single crystal furnace includes an upper heater and a lower heater arranged above and below the outer wall of the crucible. The upper heater and the lower heater jointly distribute a preset total power, so that in the equal diameter process of crystal pulling, the local temperature of the upper and lower parts of the crucible can be precisely controlled. In the control method, a prediction curve is first obtained to predict the change trend of the resistivity corresponding to different equal diameter lengths of the single crystal silicon rod in the equal diameter process of crystal pulling after the first dopant is added. Furthermore, the preset process parameters in the corresponding equal-diameter process in the preset equal-diameter slope table are set according to the change trend in the prediction curve. For example, under the same equal-diameter length, if the corresponding resistivity in the prediction curve is greater than or equal to the first resistivity, the corresponding power ratio in the preset process parameters is greater than 1, so that the power allocated to the upper heater is larger and the power allocated to the lower heater is smaller, so that the heating temperature of the upper part of the crucible is higher than the heating temperature of the lower part, thereby inhibiting the volatilization of the first dopant, and more first dopant can enter the single crystal silicon rod, so that the resistivity of the single crystal silicon rod is reduced to below the first resistivity; if the corresponding resistivity in the prediction curve is less than or equal to the second resistivity, the preset process parameters The corresponding power ratio is less than 1, so the power allocated to the upper heater is smaller and the power allocated to the lower heater is larger, so that the heating temperature of the upper part of the crucible is lower than the heating temperature of the lower part, thereby promoting the volatilization of the first dopant, and less first dopant can enter the single crystal silicon rod, so that the resistivity of the single crystal silicon rod is increased to above the second resistivity; if the corresponding resistivity in the predicted curve is greater than the second resistivity and less than the first resistivity, the corresponding power ratio in the preset process parameters is 1, and when the resistivity of the single crystal silicon rod is within a controllable range, the power of the upper and lower heaters is evenly distributed, so that the heating temperature of the upper part of the crucible is synchronized with the heating temperature of the lower part, thereby keeping the resistivity of the single crystal silicon rod within a controllable range. After obtaining the preset equal-diameter slope table in combination with the prediction curve, in the process of preparing the target single crystal silicon rod, the silicon material and the first dopant are added into the crucible, and then the melting process, the crystal seeding process, the shoulder release process and the equal-diameter process are carried out in sequence, wherein the process parameters of the equal-diameter process are adjusted with reference to the preset process parameters, so as to realize the regulation of the resistivity distribution of the initial single crystal silicon rod prepared by actual crystal pulling, and after the equal-diameter length of the initial single crystal silicon rod reaches the target length, the finishing process is entered to obtain the target single crystal silicon rod, and the target single crystal silicon rod obtained in this way has higher axial resistivity uniformity.

[0060] Those skilled in the art will appreciate that the above-mentioned embodiments are specific examples for implementing the present application, and in practical applications, various changes may be made to the embodiments in form and detail without departing from the spirit and scope of the present application. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present application, and therefore the scope of protection of the present application shall be subject to the scope defined in the claims.

Claims

1. A method for controlling crystal pulling, characterized in that: A single crystal furnace suitable for segmented heating, wherein the heater of the single crystal furnace comprises: an upper heater and a lower heater arranged on the outer wall of the crucible, wherein the upper heater is located above the lower heater, and the upper heater and the lower heater jointly distribute a preset total power; The control method comprises: Obtaining a prediction curve, wherein the prediction curve is represented by a resistivity variation curve corresponding to different equal diameter lengths of a single crystal silicon rod including a first dopant; A preset equal-diameter slope table is obtained based on the prediction curve, and the preset equal-diameter slope table is represented by preset process parameters in the equal-diameter process corresponding to the single crystal silicon rod at different equal-diameter lengths, and the preset process parameters include a power ratio of a set power of the upper heater and a set power of the lower heater, and the sum of the set power of the upper heater and the set power of the lower heater is equal to the preset total power, wherein, under the same equal-diameter length, if the corresponding resistivity in the prediction curve is greater than or equal to the first resistivity, the corresponding power ratio in the preset process parameters is greater than 1; if the corresponding resistivity in the prediction curve is less than or equal to the second resistivity, the corresponding power ratio in the preset process parameters is less than 1; if the corresponding resistivity in the prediction curve is greater than the second resistivity and less than the first resistivity, the corresponding power ratio in the preset process parameters is 1; To prepare a target single crystal silicon rod, silicon material and the first dopant are added into a crucible, and a melting process, a seeding process, a shoulder release process and a diameter equalization process are sequentially performed to obtain an initial single crystal silicon rod. The process parameters of the diameter equalization process are adjusted with reference to the preset process parameters. After the diameter equalization length of the initial single crystal silicon rod reaches the target length, a finishing process is performed to obtain the target single crystal silicon rod.

2. The crystal pulling control method according to claim 1, characterized in that: The resistivity required for the target single crystal silicon rod is a target resistivity, and a ratio of the first resistivity to the target resistivity is 1.12 to 1.17; and a ratio of the second resistivity to the target resistivity is 0.83 to 0.

88.

3. The crystal pulling control method according to claim 1, characterized in that: After preparing the target single crystal silicon rod, the method comprises: Performing a resistivity test on the target single crystal silicon rod to obtain an actual resistivity curve corresponding to the target single crystal silicon rod at different equal diameter lengths; Obtaining resistivity deviations corresponding to the actual curve and the predicted curve at different equal diameter lengths; The corresponding preset process parameters in the preset constant diameter slope table are adjusted according to the resistivity deviation.

4. The crystal pulling control method according to claim 1, characterized in that: The power ratio is 0.8 to 1.

2.

5. The crystal pulling control method according to claim 1, characterized in that: The step of obtaining the prediction curve includes: preparing a test single crystal silicon rod, the test single crystal silicon rod is formed through a melting process, a seeding process, a shoulder release process and a diameter equalization process, and the raw materials of the test single crystal silicon rod include silicon material and the first dopant; The prediction curve is drawn according to the equal diameter length of the tested single crystal silicon rod and the resistivity corresponding to the tested single crystal silicon rod at each equal diameter length.

6. The crystal pulling control method according to claim 5, characterized in that: Acquiring a preset constant-diameter slope table based on the prediction curve includes: According to the prediction curve and the corresponding process parameters of the test single crystal silicon rod at different equal-diameter lengths, a prediction model is obtained. The prediction model represents the relationship between the predicted resistivity of the single crystal silicon rod grown to different equal-diameter lengths and the corresponding process parameters. The prediction curve is substituted into the prediction model to obtain the corresponding preset equal-diameter slope table.

7. The crystal pulling control method according to claim 5, characterized in that: The step of obtaining the prediction curve includes: in a melting process of preparing the test single crystal silicon rod, adding the silicon material and the first dopant into a crucible and adding a second dopant at the same time; The control method comprises: In the melting process of preparing the target single crystal silicon rod, the second dopant is added to the crucible while the silicon material and the first dopant are added to the crucible.

8. The crystal pulling control method according to claim 5, characterized in that: The step of obtaining the prediction curve comprises: in a melting process of preparing the test single crystal silicon rod, adding the silicon material and the first dopant into a crucible; in a diameter equalization process of preparing the test single crystal silicon rod, after the diameter equalization length of the test single crystal silicon rod reaches a preset length, adding a second dopant into the crucible; The control method comprises: In the process of preparing the target single crystal silicon rod with equal diameter, the second dopant is added into the crucible before the equal diameter length of the initial single crystal silicon rod reaches the target length and after the equal diameter length of the initial single crystal silicon rod reaches the preset length.

9. The crystal pulling control method according to claim 1, characterized in that: In the equal diameter process of preparing the target single crystal silicon rod, the silicon liquid level is maintained in the area corresponding to the upper heater, and the distance between the silicon liquid level and the lower edge of the upper heater is 40mm to 60mm in the direction from the lower edge to the upper edge of the upper heater.

10. The crystal pulling control method according to claim 9, characterized in that: In the vertical direction, the height of the upper heater is greater than the height of the lower heater.

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