A polysilicon deposition method based on AC / DC integrated control

Abstract

The present invention relates to the technical field of polysilicon deposition used as the main raw material in the semiconductor or solar energy industries, and in particular to a polysilicon deposition method based on integrated AC and DC regulation. The method comprises determining the stable tendency type of the silicon core rod based on the average temperature fluctuation value in the process from the beginning of the growth of the silicon core rod to the point of meeting the growth standard and the maximum time difference in the process from the beginning of the growth of the silicon core rod to the point of meeting the growth standard; determining whether to introduce AC power to heat the silicon core rod based on the stable tendency type of the silicon core rod based on the diameter of the silicon core rod or based on the maximum temperature fluctuation value of the silicon core rod; and determining whether to obtain image data of the gas diffusion area in the enclosed space during the deposition process or to start the air inlet preheating device based on the fluctuation degree of the growth uniformity of the silicon core rod within a preset time after the introduction of AC power and / or the minimum distance between the silicon core rod and the air inlet. The present invention improves the polysilicon deposition efficiency by introducing AC and DC electric fields to comprehensively regulate the polysilicon deposition process.

Description

Technical Field

[0001] The present invention relates to the technical field of polysilicon deposition used as a main raw material in semiconductor or solar energy industries, and in particular to a polysilicon deposition method based on AC / DC integrated control. Background Art

[0002] Polycrystalline silicon (also known as polysilicon), used as the main raw material in the semiconductor or solar energy industries, is prepared by a variety of methods, including the Siemens process, the fluidized bed process, the VLD (vapor-liquid deposition) process, and the direct purification of metal-grade silicon. The most widely used method is the Siemens process, which involves thermally decomposing a mixed raw gas of chlorosilane or monosilane and hydrogen, and depositing the resultant gas on a silicon core rod to produce polycrystalline silicon. However, traditional processes often only set the DC current intensity based on experience, lacking systematic consideration of key parameters such as the deposition surface temperature and the gas introduction rate. This results in the inability of the DC current to adapt to the dynamic changes of the deposition process in real time, resulting in unstable deposition rates, uneven crystallization quality of the polysilicon, and difficulty in guaranteeing product performance.

[0003] For example, Chinese patent publication number: CN101919028B discloses a polysilicon deposition device including: an electrode unit, including a first electrode and a second electrode arranged at the bottom of a reactor and separated by a predetermined distance, the reactor is formed with a gas inlet for adding raw gas and a gas outlet for discharging gas to the outside; a silicon core rod unit, inputting current from the first electrode of the electrode unit, so that the current flows to the second electrode of the electrode unit, causing itself to generate heat; a silicon core rod heating unit, including a heating element, the heating element is separated from the silicon core rod by a predetermined interval and surrounds the silicon core rod, and a heating unit is arranged inside; and a gas injection unit, which is formed on the surface of the heating element in such a way that the raw gas added to the inside of the heating element through the gas inlet of the reactor flows toward the silicon core rod.

[0004] However, the existing technology has the problem of insufficiently precise control of the AC and DC heating processes during polysilicon deposition, which makes it difficult to achieve fine-grained control of the AC and DC during the polysilicon deposition process, thereby causing problems such as unstable deposition rate and poor polysilicon crystallization quality. Summary of the Invention

[0005] To this end, the present invention provides a polysilicon deposition method based on integrated AC / DC regulation, which is used to overcome the problem that the existing technology has insufficient control over the AC / DC heating process during the polysilicon deposition process, making it difficult to achieve fine-grained AC / DC regulation of the polysilicon deposition process, thereby causing unstable deposition rate and poor polysilicon crystallization quality.

[0006] To achieve the above objectives, the present invention provides a polysilicon deposition method based on AC / DC integrated control, comprising:

[0007] Preheating the silicon core rod with direct current to make the temperature of the silicon core rod reach the initial reaction temperature, and monitoring in real time the temperature data after the preheating is completed and the silicon core rod begins to grow to meet the growth standard and the growth data of the silicon core rod;

[0008] Calculating a stability tendency value of the silicon core rod based on an average temperature fluctuation value during the process of the silicon core rod starting to grow until it meets the growth standard and a maximum time difference during the process of the silicon core rod growing until it meets the growth standard, and determining a stability tendency type of the silicon core rod based on the stability tendency value of the silicon core rod;

[0009] Direct current is used to heat the silicon core rods, and based on the stable tendency type of the silicon core rods, based on the diameter of the silicon core rods and / or based on the maximum temperature fluctuation value of the silicon core rods, whether to introduce alternating current to heat the silicon core rods is determined;

[0010] Based on the degree of fluctuation in the uniformity of silicon core rod growth within a preset time after the introduction of alternating current and the minimum distance between the silicon core rod and the gas inlet, image data of the gas diffusion area in the confined space during the deposition process is obtained, or the gas inlet preheating device is turned on;

[0011] The average interval of gas pixels in the gas diffusion area is determined based on image data of the gas diffusion area in the confined space during the deposition process, and whether to adjust the parameters affecting the growth of the silicon core rod is determined based on a comparison result of the average interval with a preset average interval.

[0012] Furthermore, the calculation of the stability tendency value of the silicon core rod includes:

[0013] Acquire temperature data when the silicon core rod starts to grow until it meets the growth standard, and calculate the average value of the difference between the temperature at different moments in the process when the silicon core rod starts to grow until it meets the growth standard and the average temperature to obtain an average temperature fluctuation value;

[0014] Record the earliest time stamp and the latest time stamp at different positions of the silicon core rod from the start of growth to the time when the silicon core rod meets the growth standard, and obtain the maximum time difference;

[0015] The stability tendency value is obtained by taking the weighted average of the average temperature fluctuation value and the maximum time difference.

[0016] Furthermore, the types of stability tendencies of the silicon core rods are determined to include:

[0017] If the stability tendency value of the silicon core rod is less than the preset stability tendency value, the stability tendency type of the silicon core rod is determined to be a strong stability tendency type;

[0018] If the stability tendency value of the silicon core rod is greater than or equal to the preset stability tendency value, it is determined that the stability tendency type of the silicon core rod is a weak stability tendency type.

[0019] Further, determining whether to introduce alternating current to heat the silicon core rods based on the diameter of the silicon core rods and / or based on the maximum temperature fluctuation value of the silicon core rods includes:

[0020] If the stability tendency type of the silicon core rod is a strong stability tendency type, determining whether to introduce alternating current to heat the silicon core rod based on the diameter of the silicon core rod;

[0021] If the stability tendency type of the silicon core rod is a weak stability tendency type, whether to introduce alternating current to heat the silicon core rod is determined based on the diameter of the silicon core rod and the maximum temperature fluctuation value of the silicon core rod.

[0022] Furthermore, determining whether to introduce alternating current to heat the silicon core rod includes:

[0023] If the stability tendency type of the silicon core rod is a strong stability tendency type, determining to introduce alternating current to heat the silicon core rod under the condition that the diameter of the silicon core rod is greater than a preset diameter;

[0024] If the stability tendency type of the silicon core rod is a weak stability tendency type, it is determined to introduce AC to heat the silicon core rod under the conditions that the diameter of the silicon core rod is greater than the preset diameter and the maximum temperature fluctuation value of the silicon core rod is less than the preset maximum temperature fluctuation value.

[0025] Furthermore, determining the maximum temperature fluctuation value of the silicon core rod includes:

[0026] Select several sections at equal intervals along the axial direction of the silicon core rod, and select multiple points at equal angles in the circumferential direction on each section as temperature monitoring points;

[0027] Record the temperature value of each temperature monitoring point at different time points, average the temperature values ​​of the temperature monitoring points of each section, and obtain the average temperature value of each section at different time points to form a temperature data set;

[0028] The absolute value of the difference between the average temperature value of each section in each time interval and the average temperature value of the adjacent time interval is calculated to obtain the temperature fluctuation value of each section in each time interval, and the largest temperature fluctuation value is taken as the maximum temperature fluctuation value of the silicon core rod.

[0029] Further, determining to obtain image data of a gas diffusion area in a confined space during a deposition process or to start an air inlet preheating device includes:

[0030] If the fluctuation degree of the growth uniformity of the silicon core rod within the preset time period after the introduction of the alternating current is greater than the preset fluctuation degree and the minimum distance between the silicon core rod and the air inlet is less than the preset distance, it is determined to start the air inlet preheating device;

[0031] If the fluctuation degree of the uniformity of silicon core rod growth within a preset time after the introduction of alternating current is greater than a preset fluctuation degree and the minimum distance between the silicon core rod and the gas inlet is greater than or equal to a preset distance, it is determined that image data of the gas diffusion area in the confined space during the deposition process is obtained.

[0032] Furthermore, determining the degree of fluctuation of the growth uniformity of the silicon core rod within a preset time period after the introduction of the alternating current includes:

[0033] Select several sections at equal intervals along the axial direction of the silicon core rod, and select multiple points at equal angles in the circumferential direction on each section as growth uniformity monitoring points;

[0034] Record the diameter data of the monitoring point at each time point to form a three-dimensional data set;

[0035] For the measured data at each time point, the standard deviation of the inner diameter of each cross section was calculated, and then the standard deviations of all cross sections were averaged to obtain the growth uniformity at that time point;

[0036] The absolute values ​​of the differences in growth uniformity at adjacent time points are calculated, and the absolute values ​​of the differences are averaged to obtain the fluctuation degree of the growth uniformity of the silicon core rod within a preset time period.

[0037] Furthermore, determining whether to adjust the parameters affecting the growth of the silicon core rod includes:

[0038] If the average interval of the gas pixels in the gas diffusion area is greater than or equal to the preset average interval, determining to adjust the gas introduction speed;

[0039] If the average interval of the gas pixels in the gas diffusion area is smaller than the preset average interval, it is determined to adjust the alternating current intensity.

[0040] Furthermore, the adjustment amount of the gas introduction speed is positively correlated with the average interval of gas pixels in the gas diffusion region, and the adjustment amount of the alternating current intensity is negatively correlated with the fluctuation degree of the growth uniformity of the silicon core rod.

[0041] Compared with the prior art, the present invention has the beneficial effect of calculating the stability tendency value by comprehensively considering the average temperature fluctuation value and the maximum time difference within the preheating period. From the two dimensions of the amplitude of temperature change and the time difference for reaching the reaction temperature at different positions, the present invention comprehensively and accurately evaluates the stability characteristics of the silicon core rods in the preheating stage, classifies the stability tendency type of the silicon core rods according to the stability tendency value, and then specifically selects whether to introduce AC heating based on the diameter or the maximum temperature fluctuation value. This makes the selection of heating strategy more in line with the actual state of the silicon core rods, avoids the energy waste or adverse effects on the growth of the silicon core rods caused by blindly introducing AC power, effectively improves the rationality and effectiveness of process decisions, and ensures the stable progress of the polysilicon deposition process. In the application scenario of co-deposition of multiple groups of silicon core rods, the stability tendency values ​​of the silicon core rods are different due to equipment differences. This method can quickly verify the stability tendency type of the silicon core rods. Through preset calculation steps and judgment logic, the stability tendency value and stability tendency type of the silicon core rods can be quickly determined in the preheating stage, providing a quick and accurate basis for subsequent process adjustments, thereby improving production efficiency.

[0042] Furthermore, the present invention determines whether to introduce AC heating based on the diameter or the maximum temperature fluctuation value according to the stability tendency type of the silicon core rod, and can more accurately control the heating according to the different states of the silicon core rod. For silicon core rods with strong stability tendency, AC can be introduced in time to optimize the deposition process when its diameter exceeds the normal range based on diameter judgment; for silicon core rods with weak stability tendency, measures can be taken in time when temperature fluctuations may affect the deposition quality based on maximum temperature fluctuation value judgment. The maximum temperature fluctuation value of the silicon core rod is determined through detailed steps, and the temperature changes of the silicon core rod during the heating process can be accurately monitored. Abnormal temperature fluctuations can be discovered in time so that corresponding measures can be taken to ensure the deposition quality of polysilicon. The present invention improves the polysilicon deposition efficiency by introducing AC and DC electric fields to comprehensively regulate the polysilicon deposition process.

[0043] Furthermore, the present invention decides whether to obtain image data of the gas diffusion area, turn on the air inlet preheating device, or maintain the original state based on the degree of fluctuation in the growth uniformity of the silicon core rod within a preset time after the introduction of alternating current and the minimum distance between the silicon core rod and the air inlet. This decision-making method can accurately handle different production conditions. For example, when the growth uniformity fluctuates greatly and the silicon core rod is close to the air inlet, it means that the air inlet is close to the silicon core rod, causing the gas to react before reaching the reaction temperature, resulting in uneven generation. At this time, turning on the air inlet preheating device can improve the air intake conditions, optimize the gas distribution, and thereby improve the uniformity of silicon core rod growth; when the growth uniformity fluctuates greatly but the silicon core rod is far from the air inlet, obtaining image data of the gas diffusion area is helpful for in-depth analysis of the gas diffusion situation. The present invention improves the polysilicon deposition efficiency by introducing AC and DC electric fields to comprehensively regulate the polysilicon deposition process.

[0044] Furthermore, the present invention can precisely control the gas diffusion state and the growth of the silicon core rod by specifically adjusting the gas introduction speed or the alternating current intensity according to the comparison result of the average spacing of the gas pixels in the gas diffusion area with the preset average spacing. By reasonably adjusting these two parameters, the distribution of the gas in the confined space can be optimized, so that the gas can be diffused more evenly to the surface of the silicon core rod, thereby improving the uniformity of the growth of the silicon core rod and the quality of the polysilicon deposition. For example, when the average spacing of the gas pixels is greater than the preset average spacing, adjusting the gas introduction speed can accelerate mass transfer and make the gas more quickly distributed to the surface of the silicon core rod. Around the silicon core rod, ensure that all parts of the silicon core rod can obtain sufficient reaction gas to avoid uneven growth caused by uneven gas distribution. Through CFD simulation software combined with electric field simulation module, the gas flow field, electric field distribution and silicon core rod growth under different extension lengths and multiples are simulated, which can determine the optimal gas diffusion area range and find the gas diffusion area with the most uniform gas concentration distribution on the silicon core rod surface and the best growth quality, which helps to optimize the polysilicon deposition process and improve product quality. The present invention improves the polysilicon deposition efficiency by introducing AC and DC electric fields to comprehensively regulate the polysilicon deposition process. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a workflow diagram of a polysilicon deposition method based on integrated AC and DC control according to an embodiment of the present invention;

[0046] Figure 2 This is a flowchart of a process for determining the maximum temperature fluctuation value of a silicon core rod in a polysilicon deposition method based on AC / DC integrated control according to an embodiment of the present invention;

[0047] Figure 3 This is a flowchart of a method for determining the degree of fluctuation in the growth uniformity of silicon core rods within a preset time period after the introduction of alternating current in a polysilicon deposition method based on integrated AC and DC control according to an embodiment of the present invention;

[0048] Figure 4 This is a workflow diagram for determining the stability tendency type of a silicon core rod in a polysilicon deposition method based on integrated AC and DC control according to an embodiment of the present invention. DETAILED DESCRIPTION

[0049] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are merely used to explain the present invention and are not intended to limit the present invention.

[0050] The preferred embodiments of the present invention 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 invention and are not intended to limit the scope of protection of the present invention.

[0051] See also Figure 1-Figure 4 As shown, Figure 1 This is a workflow diagram of a polysilicon deposition method based on integrated AC and DC control according to an embodiment of the present invention; Figure 2 This is a flowchart of a process for determining the maximum temperature fluctuation value of a silicon core rod in a polysilicon deposition method based on AC / DC integrated control according to an embodiment of the present invention; Figure 3 This is a flowchart of a method for determining the degree of fluctuation in the growth uniformity of silicon core rods within a preset time period after the introduction of alternating current in a polysilicon deposition method based on integrated AC and DC control according to an embodiment of the present invention; Figure 4 This is a workflow diagram for determining the stability tendency type of a silicon core rod in a polysilicon deposition method based on integrated AC and DC control according to an embodiment of the present invention.

[0052] The polysilicon deposition method based on AC and DC integrated control according to the embodiment of the present invention includes:

[0053] Step S1, preheating the silicon core rod using direct current to make the temperature of the silicon core rod reach the initial reaction temperature, and monitoring in real time the temperature data of the silicon core rod starting to grow to meet the growth standard after the preheating is completed and the growth data of the silicon core rod;

[0054] Step S2, calculating a stability tendency value of the silicon core rod based on an average temperature fluctuation value during the process of the silicon core rod starting to grow until it meets the growth standard and a maximum time difference during the process of the silicon core rod growing until it meets the growth standard, and determining a stability tendency type of the silicon core rod based on the stability tendency value of the silicon core rod;

[0055] Step S3, using direct current to heat the silicon core rods, and determining whether to introduce alternating current to heat the silicon core rods based on the stable tendency type of the silicon core rods, based on the diameter of the silicon core rods and / or based on the maximum temperature fluctuation value of the silicon core rods;

[0056] Step S4, determining whether to acquire image data of the gas diffusion area in the enclosed space during the deposition process or to activate the gas inlet preheating device based on the degree of fluctuation in the uniformity of silicon core rod growth within a preset time period after the introduction of the alternating current and the minimum distance between the silicon core rod and the gas inlet;

[0057] Step S5, determining the average spacing of gas pixels in the gas diffusion area based on the image data of the gas diffusion area in the confined space during the deposition process, and determining whether to adjust the parameters affecting the growth of the silicon core rod based on a comparison result of the average spacing and a preset average spacing.

[0058] The temperature data of the silicon core rod in the embodiment of the present invention includes but is not limited to "temperature change data and temperature gradient data", and the growth data of the silicon core rod includes but is not limited to "diameter data, roughness data and mass growth data"; a thermocouple or infrared thermometer and other equipment can be used to obtain the temperature of the deposition surface, and a gas flow meter can be used to measure the gas introduction rate. For example, a laser diameter gauge is used to regularly measure the diameter of the silicon core rod. The silicon core rod begins to grow to meet the growth standard, including the silicon core rod growing to half of the preset diameter, but the above values ​​are not limited to this, and those skilled in the art can also adjust the values ​​according to actual needs.

[0059] Specifically, in step S2, the step of calculating the stable tendency value of the silicon core rod includes:

[0060] Step S2201, obtaining temperature data when the silicon core rod starts to grow until it meets the growth standard, and calculating the average value of the difference between the temperature at different moments in the process of the silicon core rod starting to grow until it meets the growth standard and the average temperature to obtain an average temperature fluctuation value;

[0061] Step S2202, recording the earliest time stamp and the latest time stamp at different positions of the silicon core rod from the start of growth to the time when the silicon core rod meets the growth standard, and obtaining the maximum time difference;

[0062] Step S2203: Perform weighted average summation on the average temperature fluctuation value and the maximum time difference to obtain a stable tendency value.

[0063] In the embodiment of the present invention, it is judged that the silicon core rod starts to grow to meet the growth standard when the silicon core rod grows to half of the preset diameter, but the above value is not limited to this, and those skilled in the art can also adjust the value according to actual needs; a high-precision infrared thermometer is selected to monitor the temperature of the deposition surface of the silicon core rod in real time, and the temperature data is recorded every 1 minute from the beginning of the growth of the silicon core rod until the silicon core rod grows to half of the preset diameter (in this example, the preset diameter is 100mm, that is, growth to 50mm is considered to meet the growth standard); a laser diameter gauge is used to measure the diameter of the silicon core rod every 10 minutes, and professional roughness measurement equipment is used to record the roughness data. In addition, the timestamps of different positions of the silicon core rod (the silicon core rod is divided into 5 equal sections along the axial direction and marked as positions 1-5) from the beginning of growth to the diameter of 50mm are recorded; a gas flow meter is used to monitor and record the flow rate of the reaction gas introduced during the production process in real time; A total of 200 temperature data points were recorded from the beginning of the rod's growth to the time it reached a diameter of 50 mm. These temperature data points are T1, T2, ⋯, and T200. First, the average temperature is calculated, then the difference between the temperature at each moment and the average temperature is calculated, and then the average of these differences is calculated to obtain the average temperature fluctuation value. The time stamps of the silicon core rod reaching a diameter of 50 mm at five different positions are recorded. The time stamp for position 1 reaching the standard is the 120th minute, position 2 is the 135th minute, position 3 is the 118th minute, position 4 is the 140th minute, and position 5 is the 125th minute. The earliest timestamp is the 118th minute, and the latest timestamp is the 140th minute. The maximum time difference is 22 minutes. Assume that, based on experimental verification, the weight of the average temperature fluctuation value is set to ω1=0.6, the weight of the maximum time difference is set to ω2=0.4, and ω1+ω2=1. The average temperature fluctuation value and the maximum time difference are weighted averaged to obtain the stability tendency value.

[0064] In the embodiment of the present invention, the weight of the average temperature fluctuation value and the weight of the maximum time difference are determined by experiment, including preparing multiple sets of silicon core rod deposition experimental devices of the same specifications to ensure that the hardware conditions of the reaction chamber, electrode system, heating power supply, etc. of each device are consistent; variable setting: setting a series of different weight combinations (ω1, ω2), and satisfying ω1+ω2=1, for example, selecting (0.1, 0.9), (0.2, 0.8), (0.3, 0.7), (0.4, 0.6), (0.5, 0.5), (0.6, 0.4), (0.7, 0.3), (0.8, 0.2), (0.9, 0.1 ) and other 9 weight combinations were used for experiments; the experimental parameters were unified: in each experiment, the initial state of the silicon core rod (such as initial diameter, material purity, etc.), DC parameters of the preheating process (voltage, current), type and flow of reaction gas, deposition temperature and other process parameters were kept exactly the same; preheating and data collection were performed: for each weight combination, the silicon core rod was preheated, and after the preheating was completed, the silicon core rod began to grow until it met the growth standard. The temperature data was collected in the same way, and the earliest and latest timestamps from the beginning of the growth of the silicon core rod to the meeting of the growth standard at different positions of the silicon core rod were recorded; the stability tendency value was calculated: According to the collected data, the average temperature fluctuation value and the maximum time difference of each group of experiments are calculated respectively, and the stability tendency value is calculated according to the corresponding weight combination. For example, for the weight combination (0.2, 0.8), the average temperature fluctuation value of a certain experiment is 4.2℃, the maximum time difference is 120 seconds, and the stability tendency value is 96.84; Complete polysilicon deposition and evaluate the quality: After the preheating is completed, the polysilicon deposition process is carried out according to the unified process parameters. After the deposition is completed, a variety of detection methods are used to evaluate the quality of polysilicon, including: Crystal structure analysis: Use X-ray diffraction (XRD) technology to detect the grain size of polysilicon The following tests are performed to evaluate the quality of the crystal structure: the size, grain orientation, and grain boundary distribution of the polysilicon; electrical performance testing: By measuring electrical parameters such as the resistivity and carrier concentration of the polysilicon, the electrical performance of the polysilicon is judged; surface quality testing: Using a scanning electron microscope (SEM) to observe the flatness, number, and type of defects on the polysilicon surface, the surface quality is evaluated; growth uniformity evaluation: By measuring the thickness and diameter changes at different locations of the polysilicon, the growth uniformity index (such as the standard deviation of thickness or diameter) is calculated; and a quality evaluation index system is established: In order to comprehensively evaluate the quality of the polysilicon, the above-mentioned test indicators are assigned corresponding weights to construct a quality evaluation function. For example, assuming that the crystal structure accounts for 40%, the electrical performance accounts for 30%, the surface quality accounts for 20%, and the growth uniformity accounts for 10%.Assuming the crystal structure score is crystal, the electrical performance score is electrical, the surface quality score is surface, and the growth uniformity score is growth, then the comprehensive quality score is crystal electrical surface growth. Analyze the relationship between weight and quality: Compare and analyze the weight combination (ω1, ω2) of each experimental group with the corresponding comprehensive quality score Q, draw a scatter plot or trend chart, and observe the impact of weight changes on polysilicon quality. Determine the optimal weight: Through analysis, it was found that when the weight combination is (0.6, 0.4), the comprehensive quality score Q of polysilicon reaches the highest value. Therefore, the optimal weight combination is determined to be ω1 = 0.6 for the average temperature fluctuation value and ω2 = 0.4 for the maximum time difference value. In the subsequent polysilicon deposition process, this weight combination is used to calculate the stable tendency value of the silicon core rod to better guide AC and DC heating strategies and process parameter adjustments, thereby improving the deposition quality of polysilicon.

[0065] Specifically, in step S2, when determining the stable tendency type of the silicon core rod, the stable tendency type of the silicon core rod is determined according to a comparison result of the stable tendency value of the silicon core rod and a preset stable tendency value;

[0066] When the stability tendency value of the silicon core rod is less than a preset stability tendency value, determining that the stability tendency type of the silicon core rod is a strong stability tendency type;

[0067] When the stability tendency value of the silicon core rod is greater than or equal to the preset stability tendency value, the stability tendency type of the silicon core rod is determined to be a weak stability tendency type.

[0068] The preset stable tendency value in the embodiment of the present invention is the average value of the stable tendency values ​​of several groups of silicon core rods of the same specifications starting to grow to meet the growth standards, but the above value is not limited to this. Those skilled in the art can also adjust the value according to actual needs.

[0069] The present invention calculates the stability tendency value by comprehensively considering the average temperature fluctuation value and the maximum time difference from the beginning of silicon core rod growth to meeting the growth standard. From the two dimensions of the amplitude of temperature change and the time difference of reaching the reaction temperature at different positions, the heating stability characteristics of the silicon core rod are comprehensively and accurately evaluated. The stability tendency type of the silicon core rod is divided according to the stability tendency value, and then the diameter or maximum temperature fluctuation value is targeted to determine whether to introduce AC heating. This makes the selection of heating strategy more in line with the actual state of the silicon core rod, avoids the energy waste or adverse effects on the growth of the silicon core rod caused by blindly introducing AC power, effectively improves the rationality and effectiveness of process decision-making, and ensures the stable progress of the polysilicon deposition process. In the application scenario of co-deposition of multiple groups of silicon core rods, the stability tendency values ​​of the silicon core rods are different due to equipment differences. This method can quickly verify the stability tendency type of the silicon core rods. Through preset calculation steps and judgment logic, the stability tendency value and stability tendency type of the silicon core rods can be quickly determined in the preheating stage, providing a fast and accurate basis for subsequent process adjustments, thereby improving production efficiency.

[0070] Specifically, in step S3, when determining whether to introduce AC heating to the silicon core rods based on the diameter of the silicon core rods or based on the maximum temperature fluctuation value of the silicon core rods, determining whether to introduce AC heating to the silicon core rods based on the diameter of the silicon core rods and / or based on the maximum temperature fluctuation value of the silicon core rods is performed according to the stability tendency type of the silicon core rods;

[0071] When the stable tendency type of the silicon core rod is a strong stable tendency type, determining whether to introduce alternating current to heat the silicon core rod based on the diameter of the silicon core rod;

[0072] When the stable tendency type of the silicon core rods is a weak stable tendency type, whether to introduce alternating current to heat the silicon core rods is determined based on the maximum temperature fluctuation value of the silicon core rods.

[0073] Specifically, in step S3, when determining whether to introduce alternating current to heat the silicon core rods, the determination is made based on a comparison result between the diameter of the silicon core rods and a preset diameter and / or a comparison result between a maximum temperature fluctuation value of the silicon core rods and a preset maximum temperature fluctuation value.

[0074] When the stable tendency type of the silicon core rod is a strong stable tendency type, determining to introduce alternating current to heat the silicon core rod under the condition that the diameter of the silicon core rod is greater than a preset diameter;

[0075] When the stable tendency type of the silicon core rod is a strong stable tendency type, it is determined that it is not necessary to introduce alternating current to heat the silicon core rod under the condition that the diameter of the silicon core rod is less than or equal to a preset diameter;

[0076] When the stability tendency type of the silicon core rod is a weak stability tendency type, determining to introduce alternating current to heat the silicon core rod under the condition that the diameter of the silicon core rod is greater than a preset diameter and the maximum temperature fluctuation value of the silicon core rod is less than a preset maximum temperature fluctuation value;

[0077] When the stability tendency type of the silicon core rod is a weak stability tendency type, it is determined that there is no need to introduce AC to heat the silicon core rod under the conditions that the diameter of the silicon core rod is less than or equal to the preset diameter and the maximum temperature fluctuation value of the silicon core rod is greater than or equal to the preset maximum temperature fluctuation value.

[0078] Specifically, in step S3, the step of determining the maximum temperature fluctuation value of the silicon core rod includes:

[0079] Step S3301: selecting a number of cross sections at equal intervals along the axial direction of the silicon core rod, and selecting a number of points at equal angles in the circumferential direction on each cross section as temperature monitoring points;

[0080] Step S3302: Record the temperature value of each temperature monitoring point at different time points, average the temperature values ​​of the temperature monitoring points of each cross section, and obtain the average temperature value of each cross section at different time points to form a temperature data set;

[0081] Step S3303, calculating the absolute value of the difference between the average temperature value of each cross section in each time interval and the average temperature value of the adjacent time interval, obtaining the temperature fluctuation value of each cross section in each time interval, and taking the largest temperature fluctuation value as the maximum temperature fluctuation value of the silicon core rod.

[0082] In the embodiment of the present invention, five cross-sections are selected at equal intervals along the axial direction of the silicon core rod. For ease of description, they are labeled as cross-section 1, cross-section 2, cross-section 3, cross-section 4, and cross-section 5 in sequence. Eight points are selected at equal angles in the circumferential direction on each cross-section as temperature monitoring points. After preheating is completed, the silicon core rod is continuously heated using direct current. The temperature values ​​of all temperature monitoring points are recorded every 10 seconds. Assuming that the entire monitoring process lasts for 10 minutes (i.e., 60 time points), a three-dimensional temperature data array is obtained. The temperature data of the subsequent 59 time points are recorded in the same manner to form a complete temperature data set. The average temperature values ​​of the 60 time points are calculated in sequence to obtain an average temperature sequence. The absolute value of the difference between the average temperature values ​​of adjacent time points is calculated to obtain the temperature fluctuation value for each time interval. The temperature fluctuation values ​​of the remaining 58 time intervals are calculated in the same manner to obtain a temperature fluctuation value sequence. In this temperature fluctuation value sequence, the maximum value is found. This maximum value is the maximum temperature fluctuation value of the silicon core rod.

[0083] The preset diameter described in the embodiments of the present invention can be determined by the following method: collecting diameter data of silicon mandrels at different stages (e.g., after preheating, during deposition, and after deposition) from previous polysilicon deposition experiments and production processes, analyzing the relationship between this data and deposition process parameters (e.g., current intensity, gas flow rate, and deposition time), and identifying the variation pattern and fluctuation range of the silicon mandrel diameter under normal process conditions. Taking into account factors such as process fluctuations and equipment errors, a certain safety margin is set based on the ideal diameter range to determine the preset diameter. Generally speaking, the preset diameter can be set at the upper limit of the ideal diameter range, or slightly larger than the upper limit depending on actual conditions, to ensure that the silicon mandrel diameter meets product quality requirements while triggering the AC heating mechanism to optimize the deposition process. For example, suppose a company produces polysilicon for high-efficiency photovoltaic cells. Based on the cell design requirements, the ideal diameter range of the silicon mandrel after deposition is 8-10 mm. Statistical analysis of the past 100 production data shows that, under normal process conditions, during the continuous DC heating stage after preheating, the average silicon mandrel diameter is 7.5 mm, with a standard deviation of 0.3 mm, and 95% of the data is distributed between 6.9 and 8.1 mm. Considering that process fluctuations may cause the diameter to exceed the ideal range, in order to timely introduce alternating current to optimize the deposition process when the silicon core rod diameter shows a significant growth trend, the preset diameter is set to 8.5 mm.

[0084] The preset maximum temperature fluctuation value in the embodiment of the present invention can be determined by the following method: through a series of comparative experiments, when other process parameters are the same, temperature fluctuations of different degrees are artificially set to observe the changes in the deposition quality of polysilicon. For example, temperature control equipment is used to create temperature fluctuations of different amplitudes during the heating process of the silicon core rod. Then, the crystal structure, surface quality, electrical properties and other indicators of the polysilicon are analyzed by means of XRD, SEM and other detection methods to determine the quantitative relationship between temperature fluctuations and deposition quality, and set an acceptable temperature fluctuation threshold: according to the quality standards of polysilicon products, determine the maximum temperature fluctuation range that the silicon core rod can withstand while ensuring product quality. This range can be determined by fitting experimental data; consider equipment and process fluctuations: combine the accuracy of temperature monitoring equipment, the stability of heating equipment and the fluctuation of process parameters in actual production, and correct the above temperature fluctuation thresholds to finally determine the preset maximum temperature fluctuation value. For example, in the experiment, other process parameters are fixed unchanged, and different temperature fluctuations are artificially created by adjusting the output power of the DC power supply. When the temperature fluctuation value is 2℃-5℃, the crystal structure of polysilicon is good, the grain size is uniform, and there are fewer surface defects; when the temperature fluctuation value exceeds 8℃, the grain boundaries of polysilicon become disordered, a large number of holes appear on the surface, and the electrical performance is significantly reduced. Taking into account the temperature monitoring error of the experimental equipment (±1℃) and the slight fluctuations that may occur during the process, the preset maximum temperature fluctuation value is set to 6℃.

[0085] The present invention determines whether to introduce AC heating based on the diameter or the maximum temperature fluctuation value according to the stability tendency type of the silicon core rod, and can more accurately control the heating according to the different states of the silicon core rod. For silicon core rods with strong stability tendency, AC can be introduced in time to optimize the deposition process when its diameter exceeds the normal range based on diameter judgment; for silicon core rods with weak stability tendency, measures can be taken in time when temperature fluctuations may affect the deposition quality based on maximum temperature fluctuation value judgment. The maximum temperature fluctuation value of the silicon core rod is determined through detailed steps, and the temperature changes of the silicon core rod during the heating process can be accurately monitored. Abnormal temperature fluctuations can be discovered in time so that corresponding measures can be taken to ensure the deposition quality of polysilicon. The present invention improves the polysilicon deposition efficiency by introducing AC and DC electric fields to comprehensively regulate the polysilicon deposition process.

[0086] Specifically, in step S4, when determining to obtain image data of the gas diffusion area in the confined space during the deposition process or to start the air inlet preheating device, the determination of obtaining image data of the gas diffusion area in the confined space during the deposition process or to start the air inlet preheating device is made based on the degree of fluctuation in the uniformity of growth of the silicon core rods within a preset time period after the introduction of the alternating current and / or the minimum distance between the silicon core rods and the air inlet;

[0087] When the fluctuation degree of the uniformity of the growth of the silicon core rods within the preset time after the introduction of the alternating current is greater than the preset fluctuation degree and the minimum distance between the silicon core rods and the air inlet is less than the preset distance, it is determined to start the air inlet preheating device;

[0088] When the fluctuation degree of the uniformity of the growth of the silicon core rods within the preset time period after the introduction of the alternating current is greater than the preset fluctuation degree and the minimum distance between the silicon core rods and the gas inlet is greater than or equal to the preset distance, it is determined to obtain image data of the gas diffusion area in the confined space during the deposition process;

[0089] When the fluctuation degree of the growth uniformity of the silicon core rod within the preset time period after the alternating current is introduced is less than or equal to the preset fluctuation degree, it is determined to maintain the original state.

[0090] The air inlet preheating device described in the embodiment of the present invention includes but is not limited to "resistance preheating device, induction preheating device and heat exchange preheating device". For example, the gas at the air inlet is heated by a resistance element such as a resistance wire. When the resistance wire is energized, heat is generated, causing the passing gas to heat up.

[0091] The preset time length in the embodiment of the present invention can be determined through a large number of experiments. During the experiment, different preset time lengths are set respectively to observe the fluctuation of the uniformity of silicon core rod growth and its correlation with the actual production situation. After multiple experiments, the time length that can most accurately reflect the growth state of silicon core rods and has practical guiding significance for the production process is selected as the preset time length. For example, after multiple experiments on a certain production line, it was found that when the preset time length is 15 minutes, the fluctuation data of the uniformity of silicon core rod growth is highly correlated with the quality indicators of the final product (the high correlation includes but is not limited to "synchronization of change trend, closeness of data correlation and and significance of causal effects"), which can promptly identify potential problems in the production process. Therefore, 15 minutes is determined as the preset duration. The synchronization of the changing trend includes that when the fluctuation data of the uniformity of silicon core rod growth changes, the quality indicators of the final product will subsequently show a predictable trend of change. The closeness of the data correlation includes that the relationship between the two can be quantified through mathematical statistical methods (such as calculating the correlation coefficient). A high correlation means that the absolute value of the correlation coefficient is close to 1. The significance of the causal effect includes that the unstable growth uniformity will directly affect the deposition process of silicon atoms, thereby affecting the formation of crystal structure, impurity distribution, etc., and ultimately leading to changes in product quality.

[0092] Specifically, in step S4, the step of determining the degree of fluctuation of the growth uniformity of the silicon core rods within a preset time period after the alternating current is introduced includes:

[0093] Step S4401: selecting a number of cross sections at equal intervals along the axial direction of the silicon core rod, and selecting a number of points at equal angles in the circumferential direction on each cross section as growth uniformity monitoring points;

[0094] Step S4402, recording the diameter data of the monitoring point at each time point to form a three-dimensional data set;

[0095] Step S4403: for the measurement data at each time point, calculate the standard deviation of the inner diameter of each cross section, and then average the standard deviations of all cross sections to obtain the growth uniformity at that time point;

[0096] Step S4404: calculating the absolute values ​​of the differences in growth uniformity at adjacent time points, and averaging the absolute values ​​of the differences to obtain the degree of fluctuation in the growth uniformity of the silicon core rod within a preset time period.

[0097] In the embodiment of the present invention, if the length of the silicon core rod is 1000 mm, five cross sections are selected at equal intervals along the axial direction of the silicon core rod, that is, cross sections are selected at 200 mm, 400 mm, 600 mm, 800 mm, and 1000 mm from the starting end of the silicon core rod, respectively. Eight points are selected at equal angles in the circumferential direction on each cross section as growth uniformity monitoring points, that is, one point is selected every 45°, and the diameter data of the monitoring point at each time point is recorded. Assuming that the preset time length is 60 minutes, data is recorded every 5 minutes to form a three-dimensional data set. For example, at the first 5-minute time point, the diameter data of the eight monitoring points in each of the five cross sections are recorded, and the monitoring data of 12 time points are recorded. Assuming that at the first time point (5 minutes), the diameters of the eight monitoring points in the first cross section are: 10.2 mm, 10.1 mm, 10.3 mm, 10.0 mm, 10.1 mm, 10.2 ... The diameters of the 8 monitoring points in the second section are: 10.5mm, 10.4mm, 10.6mm, 10.3mm, 10.7mm, 10.4mm, 10.5mm, 10.6mm, and so on. The data of 5 sections are recorded to complete the measurement data recording of the first time point. The measurement data of the subsequent 11 time points are recorded in the same way to form a three-dimensional data set. For the measurement data at the first time point, the standard deviation of the diameter in each section is calculated, and the standard deviations of all sections are averaged to obtain the growth uniformity at the time point. The growth uniformity of the subsequent 11 time points is calculated in the same way, and the absolute value of the difference in growth uniformity between adjacent time points is calculated. The absolute value of these difference absolute values ​​is averaged to obtain the fluctuation degree of the growth uniformity of the silicon core rod within the preset time length.

[0098] The preset distance described in the embodiment of the present invention can be determined by the following method: through experiments and simulations, the variation pattern of gas temperature at different distances is studied. After the gas is ejected from the air inlet, as the distance increases, the gas temperature will change due to heat exchange with the surrounding environment and the diffusion of the gas itself. The effect of this temperature change on gas diffusion is analyzed. For example, a decrease in temperature may cause a change in gas viscosity, which in turn affects the diffusion rate and range of the gas. The gas temperature requirements of the silicon core rod at different growth stages are understood. According to the growth requirements of the silicon core rod, the appropriate gas temperature range is determined. The structure of the equipment, such as the shape of the reaction chamber, the position and shape of the air inlet and other factors that affect the gas flow are considered. The equipment structure will cause the gas flow path in the reaction chamber to change. Different gas velocity distributions affect gas temperature and diffusion. The relationship between gas temperature and diffusion and distance is determined by combining equipment structure and gas flow characteristics. Taking these factors into account, through experiments and data analysis, a distance is found where the gas temperature meets the requirements for silicon mandrel growth and gas diffusion ensures uniform growth that meets quality standards. This distance is the preset distance. For example, in a polysilicon deposition system, the gas inlet is located at the top center of the reaction chamber, and the silicon mandrel is placed vertically within the reaction chamber. In a gas temperature and diffusion experiment, the gas temperature and gas concentration distribution are measured at different distances (e.g., 50mm, 70mm, 90mm, 110mm, 130mm, etc.). Temperature and gas concentration sensors are used to record temperature and gas concentration data at different distances. Experiments have shown that when the distance from the gas inlet is less than 70 mm, the gas temperature is high and the concentration distribution is uneven, resulting in excessively high silicon core rod surface temperatures, excessively fast polysilicon deposition rates, and large fluctuations in growth uniformity. When the distance from the gas inlet is greater than 90 mm, the gas temperature is too low, the chemical reaction rate on the silicon core rod surface decreases, the polysilicon deposition rate slows, and localized insufficient deposition may occur. Silicon core rod growth experiments: Polysilicon deposition experiments were conducted at different distances. Based on the growth of the silicon core rods, the effect of gas temperature on polysilicon growth was evaluated. The appropriate gas temperature range was determined by measuring indicators such as the diameter, crystal structure, and electrical properties at different locations on the silicon core rods. Experimental results show that when the gas temperature is within a certain range (e.g., 800°C-850°C), the growth uniformity of polysilicon is good, and the crystal structure and electrical properties meet quality requirements. Combined with equipment structure analysis: considering the shape of the reaction chamber and the shape of the gas inlet, the flow path of the gas in the reaction chamber is analyzed. The diameter of the gas inlet is 20mm, and the diameter of the reaction chamber is 300mm. After the gas is ejected from the gas inlet, a certain flow pattern is formed in the reaction chamber.Through simulation and experiments, the flow velocity and temperature changes of the gas at different distances were determined; the preset distance was determined: Based on the above experiments and analysis, it was found that when the distance between the silicon core rod and the air inlet was 80mm, the gas temperature was within the appropriate range (800℃-850℃), the gas diffusion was uniform, the growth uniformity of the silicon core rod fluctuated slightly, and the quality of the polysilicon met the requirements. Therefore, the preset distance was set to 80mm.

[0099] The preset degree of fluctuation in the embodiment of the present invention can be determined by the following method: under the premise of fixing other process parameters, artificially create different degrees of fluctuation in the uniformity of silicon core rod growth (such as by adjusting the current, gas flow, etc.), conduct multiple groups of deposition experiments, and use XRD, SEM, electrical performance testing and other means to comprehensively evaluate the key indicators such as crystal structure, surface quality, and electrical performance of the polysilicon products obtained in each group of experiments. According to the application requirements of the polysilicon products, each quality indicator is given a weight, and a comprehensive quality evaluation function is constructed. For example, the crystal structure weight of polysilicon for photovoltaic use can be set to 40%, the surface quality weight to 30%, and the electrical performance weight to 30%. Calculate the comprehensive quality score of polysilicon products under different fluctuation levels and determine the quality qualification threshold: Based on the product quality standards, determine the minimum comprehensive quality score that meets the quality requirements, find the growth uniformity fluctuation value corresponding to the score, and on this basis, combine the stability requirements of the production process and the acceptable quality fluctuation range to determine the preset fluctuation level. This value should ensure that when the growth uniformity fluctuation is less than this value, the product quality is likely to meet the standard; when it is greater than this value, measures need to be taken to optimize the deposition process. For example, in a series of polysilicon deposition experiments, by adjusting the DC and AC power supply parameters, the fluctuation level of the silicon core rod growth uniformity varies between 0.01-0.15mm. After the experiment, the polysilicon was tested: when the fluctuation degree was 0.05mm, the average grain size of the polysilicon was 5μm, the surface roughness Ra was 0.2μm, the resistivity was 8500Ω・cm, and the comprehensive quality score was 85 points (out of 100 points), which met the quality standards for polysilicon for photovoltaic cells. When the fluctuation degree increased to 0.07mm, the average grain size dropped to 4μm, a small number of microcracks appeared on the surface, the resistivity rose to 9500Ω・cm, and the comprehensive quality score dropped to 75 points, close to the lower limit of quality. Taking into account the measurement error of ±0.01mm and process fluctuations in the production process, the preset fluctuation degree was set to 0.06mm.

[0100] The present invention decides whether to obtain image data of the gas diffusion area, turn on the air inlet preheating device, or maintain the original state based on the degree of fluctuation in the growth uniformity of the silicon core rod within a preset time after the introduction of alternating current and the minimum distance between the silicon core rod and the air inlet. This decision-making method can accurately handle different production conditions. For example, when the growth uniformity fluctuates greatly and the silicon core rod is close to the air inlet, it means that the air inlet is close to the silicon core rod, causing the gas to react before reaching the reaction temperature, resulting in uneven generation. At this time, turning on the air inlet preheating device can improve the air intake conditions, optimize the gas distribution, and thereby improve the uniformity of silicon core rod growth; when the growth uniformity fluctuates greatly but the silicon core rod is far from the air inlet, obtaining image data of the gas diffusion area is helpful for in-depth analysis of the gas diffusion situation. The present invention improves the polysilicon deposition efficiency by introducing AC and DC electric fields to comprehensively regulate the polysilicon deposition process.

[0101] Specifically, in step S5, when determining whether to adjust the parameters affecting the growth of the silicon mandrel, it is determined whether to adjust the parameters affecting the growth of the silicon mandrel based on the comparison result of the average interval of the gas pixels in the gas diffusion area with the preset average interval;

[0102] When the average interval of the gas pixels in the gas diffusion area is greater than or equal to the preset average interval, determining to adjust the gas introduction speed;

[0103] When the average interval of the gas pixels in the gas diffusion area is less than the preset average interval, it is determined to adjust the alternating current intensity.

[0104] The average spacing of gas pixels in the gas diffusion area in the embodiment of the present invention is the average value of the average spacing of gas pixels in the gas diffusion area obtained from several image data of the gas diffusion area in the confined space during the deposition process. In the process from the introduction of the AC electric field to the reaching of the initial AC electric field strength, the image acquisition system is used to capture images of the gas diffusion area at certain time intervals (such as 10 seconds). Assuming that a total of 5 image data are collected, each collected image is processed, the gas pixels are identified by an image recognition algorithm, and the average spacing of the gas pixels in the gas diffusion area in the image is calculated. Assuming that the average spacing of gas pixels in the five collected images is 4 pixel units, 6 pixel units, 5 pixel units, 7 pixel units, and 5 pixel units, respectively, and the average of these five average spacings is calculated, the average spacing of gas pixels in the gas diffusion area is 5.4 pixel units. The preset average spacing can be determined by the following method: collecting previous experimental data under the same or similar deposition process conditions, including image data of the gas diffusion area and corresponding silicon core rod growth quality data; processing these image data, calculating the average spacing of gas pixels in each experiment, and analyzing the relationship between the average spacing of gas pixels and the growth quality of silicon core rods; finding the value range of the average spacing of gas pixels when the growth quality of silicon core rods is good; for example, in the past 100 experiments, when the growth quality of silicon core rods reached the high-quality standard, the average spacing of gas pixels was mostly concentrated between 4.5 and 5.5 pixel units. This range can be used as an important reference for determining the preset average spacing, and finally the preset average spacing is determined to be 5 pixel units. However, the above value is not limited to this, and those skilled in the art can also adjust the value according to actual needs.

[0105] In the embodiments of the present invention, the parameters influencing silicon mandrel growth include gas injection rate and AC current intensity. Acquiring image data of the gas diffusion region within a confined space during deposition involves selecting a high-resolution, high-frame-rate high-speed camera, such as the Phantom v711 high-speed camera, which has a resolution of up to 1280 × 800 pixels and a frame rate of up to 10,000 frames per second, capable of clearly capturing the instantaneous state of gas diffusion. The appropriate frame rate is set based on the gas diffusion rate and experimental requirements. For gas diffusion during polysilicon deposition, a frame rate of 100-500 frames per second is generally sufficient. For example, when the gas diffusion rate is fast, a frame rate of 300 frames per second can be selected to capture detailed changes in gas diffusion. The appropriate exposure time is determined through experimental testing to ensure sufficient image brightness while avoiding overexposure that may result in loss of image detail. Typically, the exposure time can be set between 10 and 100 microseconds. For example, in good lighting conditions, the exposure time can be set to 20 microseconds. The sensitivity is appropriately set based on the lighting intensity and camera performance. Generally, set the ISO between 100 and 800. If the lighting intensity is low, the ISO value can be increased appropriately, but be careful to avoid excessive noise introduced by excessively high ISO values. Use the acquisition software that comes with the high-speed camera and set parameters such as the image save path and file name format. You can set the system to automatically save a set of images at regular intervals for subsequent analysis. For example, you can set the system to save a 100-frame image sequence every 10 seconds. Start the high-speed camera and capture images from the moment the AC electric field is introduced until the initial AC field intensity is reached. Ensure stable operation and no interruptions during the acquisition process. The captured images may contain some noise and background interference, requiring preprocessing. First, use a median filter algorithm to remove salt and pepper noise from the images. Then, use background subtraction to subtract the background image from the captured images, highlighting the image information of the gas diffusion region and thus obtaining image data.

[0106] The gas diffusion region described in the embodiments of the present invention can be determined by the following method: The gas diffusion region is determined by extending a certain range in the axial and radial directions from the silicon mandrel as the center. For example, in the axial direction, a certain length (e.g., 10% of the length of the silicon mandrel) is extended upward and downward from the bottom of the silicon mandrel in each direction. In the radial direction, a region is extended outward by a certain multiple (e.g., twice the radius of the silicon mandrel) based on the radius of the silicon mandrel as the gas diffusion region. CFD simulation software combined with an electric field simulation module is used to simulate the gas flow field, electric field distribution, and silicon mandrel growth under different extension lengths and multiples. Changes in parameters such as gas concentration and velocity in the simulation results are observed to determine the optimal range of the gas diffusion region. For example, simulations have found that when the axial extension length is 10% of the silicon mandrel length and the radial extension length is twice the radius of the silicon mandrel, the gas concentration distribution on the silicon mandrel surface is most uniform and the growth quality is optimal. This value can be used as a reference value. However, the above values ​​are not limited to this, and those skilled in the art may adjust the values ​​according to actual needs.

[0107] Specifically, in step S5, when it is determined to adjust the gas introduction speed, it is determined to adjust the gas introduction speed with a first adjustment coefficient, and when it is determined to adjust the alternating current intensity, it is determined to adjust the alternating current intensity with a second adjustment coefficient.

[0108] In the embodiment of the present invention, the first adjustment coefficient can be obtained by conducting multiple groups of experiments at different gas introduction speeds, recording data such as the average spacing of gas pixels in the gas diffusion area, the uniformity of silicon core rod growth, the crystal structure and electrical properties of polysilicon in each group of experiments, and performing statistical analysis on the experimental data. For example, the rate of change of each parameter at different gas introduction speeds is calculated, and the relationship between the gas introduction speed adjustment amount and the deviation of the average spacing of gas pixels is determined by regression analysis and other methods, thereby obtaining a value range of the first adjustment coefficient; the value range of the first adjustment coefficient is set to 1.05-0.21, and the value of the first adjustment coefficient is preferably 1.12. The adjustment amount of the gas injection rate is positively correlated with the average spacing of the gas pixels in the gas diffusion area. The value of the first adjustment coefficient is to reasonably adjust the gas injection rate when the average spacing of the gas pixels in the gas diffusion area is greater than or equal to the preset average spacing, so as to make the gas diffusion more uniform, thereby optimizing the growth conditions of the silicon core rod. If the value is too large, the gas injection rate may be over-adjusted, causing the gas concentration on the surface of the silicon core rod to change too much, affecting the deposition quality; if the value is too small, the average spacing of the gas pixels in the gas diffusion area may not be effectively adjusted, and the purpose of optimizing growth cannot be achieved. However, the above value is not limited to this, and technical personnel in this field can also adjust the value according to actual needs.

[0109] In an embodiment of the present invention, the second adjustment coefficient can be obtained by conducting multiple groups of experiments under different alternating current intensities, recording data such as the average spacing of gas pixels in the gas diffusion area, the uniformity of silicon core rod growth, the crystal structure and electrical properties of polysilicon in each group of experiments, and performing statistical analysis on the experimental data. For example, the rate of change of each parameter under different alternating current intensities is calculated, and the relationship between the adjustment amount of the alternating current intensity and the deviation of the average spacing of gas pixels is determined through regression analysis and other methods, thereby obtaining a value range of the second adjustment coefficient; the value range of the second adjustment coefficient is preferably 0.81-0.96, and the value of the second adjustment coefficient is preferably 0.89. The adjustment amount of the alternating current intensity is negatively correlated with the degree of fluctuation of the uniformity of silicon core rod growth. The value of the second adjustment coefficient is to reasonably adjust the alternating current intensity and optimize the gas diffusion and silicon core rod growth conditions when the average spacing of gas pixels in the gas diffusion area is less than the preset average spacing. If the value is too large, the AC intensity may be over-adjusted, causing the surface temperature of the silicon core rod to change too much, affecting the deposition quality; if the value is too small, the average spacing of the gas pixels in the gas diffusion area may not be effectively adjusted, and the purpose of optimizing growth cannot be achieved. However, the above value is not limited to this, and technical personnel in this field can also adjust the value according to actual needs.

[0110] The present invention precisely controls the gas diffusion state and silicon core rod growth by specifically adjusting the gas introduction rate or AC current intensity based on a comparison of the average spacing of gas pixels in the gas diffusion region with a preset average spacing. By properly adjusting these two parameters, the gas distribution within the confined space can be optimized, allowing the gas to diffuse more evenly onto the silicon core rod surface, thereby improving the uniformity of silicon core rod growth and the quality of polysilicon deposition. For example, when the average spacing of gas pixels is greater than the preset average spacing, adjusting the gas introduction rate can accelerate mass transfer, allowing the gas to be distributed more quickly around the silicon core rod, ensuring that all parts of the silicon core rod receive sufficient reactive gas and avoiding uneven growth due to uneven gas distribution. By combining CFD simulation software with an electric field simulation module, the gas flow field, electric field distribution, and silicon core rod growth at different expansion lengths and multiples can be simulated. The optimal gas diffusion region can be determined, and the gas diffusion region with the most uniform gas concentration distribution and optimal growth quality on the silicon core rod surface can be found. This helps optimize the polysilicon deposition process and improve product quality. The present invention improves polysilicon deposition efficiency by introducing AC and DC electric fields to comprehensively regulate the polysilicon deposition process.

[0111] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

Claims

1. A polysilicon deposition method based on AC / DC integrated control, characterized in that: include: Preheating the silicon core rod with direct current to make the temperature of the silicon core rod reach the initial reaction temperature, and monitoring in real time the temperature data after the preheating is completed and the silicon core rod begins to grow to meet the growth standard and the growth data of the silicon core rod; Calculating a stability tendency value of the silicon core rod based on an average temperature fluctuation value during the process of the silicon core rod starting to grow until it meets the growth standard and a maximum time difference during the process of the silicon core rod growing until it meets the growth standard, and determining a stability tendency type of the silicon core rod based on the stability tendency value of the silicon core rod; Calculation of the stability tendency value of the silicon core rod includes: Acquire temperature data when the silicon core rod starts to grow until it meets the growth standard, and calculate the average value of the difference between the temperature at different moments in the process when the silicon core rod starts to grow until it meets the growth standard and the average temperature to obtain an average temperature fluctuation value; Record the earliest time stamp and the latest time stamp at different positions of the silicon core rod from the start of growth to the time when the silicon core rod meets the growth standard, and obtain the maximum time difference; The weighted average sum of the average temperature fluctuation value and the maximum time difference is used to obtain the stability tendency value; Determine the type of stability tendency of silicon mandrels include: If the stability tendency value of the silicon core rod is less than the preset stability tendency value, the stability tendency type of the silicon core rod is determined to be a strong stability tendency type; If the stability tendency value of the silicon core rod is greater than or equal to the preset stability tendency value, the stability tendency type of the silicon core rod is determined to be a weak stability tendency type; Direct current is used to heat the silicon core rods, and based on the stable tendency type of the silicon core rods, based on the diameter of the silicon core rods and / or based on the maximum temperature fluctuation value of the silicon core rods, whether to introduce alternating current to heat the silicon core rods is determined; Based on the degree of fluctuation in the uniformity of silicon core rod growth within a preset time after the introduction of alternating current and the minimum distance between the silicon core rod and the gas inlet, image data of the gas diffusion area in the confined space during the deposition process is obtained, or the gas inlet preheating device is turned on; The average interval of gas pixels in the gas diffusion area is determined based on image data of the gas diffusion area in the confined space during the deposition process, and whether to adjust the parameters affecting the growth of the silicon core rod is determined based on a comparison result of the average interval with a preset average interval.

2. The polysilicon deposition method based on AC / DC integrated control according to claim 1, characterized in that: Determining whether to introduce alternating current to heat the silicon core rods based on the diameter of the silicon core rods and / or based on the maximum temperature fluctuation value of the silicon core rods includes: If the stability tendency type of the silicon core rod is a strong stability tendency type, determining whether to introduce alternating current to heat the silicon core rod based on the diameter of the silicon core rod; If the stability tendency type of the silicon core rod is a weak stability tendency type, whether to introduce alternating current to heat the silicon core rod is determined based on the diameter of the silicon core rod and the maximum temperature fluctuation value of the silicon core rod.

3. The polysilicon deposition method based on AC / DC integrated control according to claim 2, characterized in that: Determining whether to introduce AC heating for silicon core rods includes: If the stability tendency type of the silicon core rod is a strong stability tendency type, determining to introduce alternating current to heat the silicon core rod under the condition that the diameter of the silicon core rod is greater than a preset diameter; If the stability tendency type of the silicon core rod is a weak stability tendency type, it is determined to introduce AC to heat the silicon core rod under the conditions that the diameter of the silicon core rod is greater than the preset diameter and the maximum temperature fluctuation value of the silicon core rod is less than the preset maximum temperature fluctuation value.

4. The polysilicon deposition method based on AC / DC integrated control according to claim 3, characterized in that: Determine the maximum temperature fluctuation value of the silicon core rod including: Select several sections at equal intervals along the axial direction of the silicon core rod, and select multiple points at equal angles in the circumferential direction on each section as temperature monitoring points; Record the temperature value of each temperature monitoring point at different time points, average the temperature values ​​of the temperature monitoring points of each section, and obtain the average temperature value of each section at different time points to form a temperature data set; The absolute value of the difference between the average temperature value of each section in each time interval and the average temperature value of the adjacent time interval is calculated to obtain the temperature fluctuation value of each section in each time interval, and the largest temperature fluctuation value is taken as the maximum temperature fluctuation value of the silicon core rod.

5. The polysilicon deposition method based on AC / DC integrated control according to claim 4, characterized in that: Determining to obtain image data of a gas diffusion area in a confined space during a deposition process or to start a gas inlet preheating device includes: If the fluctuation degree of the growth uniformity of the silicon core rod within the preset time period after the introduction of the alternating current is greater than the preset fluctuation degree and the minimum distance between the silicon core rod and the air inlet is less than the preset distance, it is determined to start the air inlet preheating device; If the fluctuation degree of the uniformity of silicon core rod growth within a preset time after the introduction of alternating current is greater than a preset fluctuation degree and the minimum distance between the silicon core rod and the gas inlet is greater than or equal to a preset distance, it is determined that image data of the gas diffusion area in the confined space during the deposition process is obtained.

6. The polysilicon deposition method based on AC / DC integrated control according to claim 5, characterized in that: The degree of fluctuation of the growth uniformity of the silicon core rod within a preset time after the introduction of AC power includes: Select several sections at equal intervals along the axial direction of the silicon core rod, and select multiple points at equal angles in the circumferential direction on each section as growth uniformity monitoring points; Record the diameter data of the monitoring point at each time point to form a three-dimensional data set; For the measured data at each time point, the standard deviation of the inner diameter of each cross section was calculated, and then the standard deviations of all cross sections were averaged to obtain the growth uniformity at that time point; The absolute values ​​of the differences in the growth uniformity at adjacent time points are calculated, and the absolute values ​​are averaged to obtain the fluctuation degree of the growth uniformity of the silicon core rod within a preset time period.

7. The polysilicon deposition method based on AC / DC integrated control according to claim 6, characterized in that: Determining whether to adjust the parameters affecting silicon core rod growth includes: If the average interval of the gas pixels in the gas diffusion area is greater than or equal to the preset average interval, determining to adjust the gas introduction speed; If the average interval of the gas pixels in the gas diffusion area is smaller than the preset average interval, it is determined to adjust the alternating current intensity.

8. The polysilicon deposition method based on AC / DC integrated control according to claim 7, characterized in that: The adjustment amount of the gas introduction speed is positively correlated with the average interval of gas pixels in the gas diffusion area, and the adjustment amount of the alternating current intensity is negatively correlated with the fluctuation degree of the growth uniformity of the silicon core rod.

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