Czochralski single crystal growth method based on PID control and single crystal furnace

Abstract

The invention provides a straight pulling single crystal growth method based on PID control and a single crystal furnace. The method comprises the following steps: selecting any one of decisive parameters of a shouldering shape as a PID control independent variable, and taking a shouldering diameter growth rate as a PID control dependent variable; inputting the independent variable value of each node and the corresponding dependent variable value into a control system to serve as a set value in a control process; establishing a diameter growth rate measurement algorithm for calculating an actual value in a control process; in the shouldering process, the PID control system calculates the actual value of the diameter growth rate in the shouldering process according to the established algorithm, the actual value is compared with the set value of the corresponding node, the pulling process is adjusted according to the difference value of the actual value and the set value, and the diameter growth rate is adjusted and controlled. According to the method, the diameter growth rate is adopted to replace the diameter to serve as a parameter of PID regulation and control, compared with the diameter change range, the change amplitude of the diameter growth rate is very small, and stable PID control is facilitated. In addition, the diameter growth rate is adopted as a regulation and control parameter, the diameter and the diameter change trend of each position in the shouldering process can be accurately controlled, and accurate control over the shouldering shape is considered.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a Czochralski single crystal growth method and a single crystal furnace based on PID control. Background Art

[0002] Silicon single crystals are the basis for manufacturing semiconductor integrated circuit chips and solar photovoltaic cells. They are irreplaceable key materials in high-tech fields such as microelectronics, photovoltaics, communications, and aerospace.

[0003] The main growth methods of silicon single crystals include the Czochralski method and the zone melting method. The silicon single crystals produced by the Czochralski method have a higher oxygen content and therefore have higher strength. They are not prone to defects such as dislocations and slip lines and deflection due to factors such as thermal stress during the manufacturing process of high-temperature electronic components. Compared with the zone melting method, it has shown obvious advantages and is therefore widely adopted by major silicon single crystal manufacturers around the world.

[0004] The manufacturing process of the Czochralski method mainly includes the processes of material preparation, seeding, shoulder release, shoulder rotation, equal diameter and finishing. Among them, shoulder release is the process of gradually increasing the crystal diameter by reducing the pulling speed and heater power until the process requirements are met. As a key stage to ensure that the crystal enters equal diameter growth without dislocation, its smooth progress largely determines whether the crystal rod can grow smoothly without breaking, which is related to the quality of crystal rod growth.

[0005] The existing shouldering process mostly adopts the PID (proportional integral differential) control method, with the real-time diameter measured by the CCD camera as the input signal, and uses the "length-diameter" parameter control method for adjustment, that is, the crystal diameter corresponding to different shouldering lengths is set in advance, and the PID is adjusted according to the difference between the actual diameter corresponding to the shouldering length and the set diameter during growth. The main adjustment means is to change the crystal pulling speed. However, this technology has obvious disadvantages. The crystal diameter is in a continuous increase process during the shouldering process, from about 5mm to 200mm or even more than 300mm (depending on the target crystal rod diameter required by the process). In the early stage of shouldering, the basic diameter of the crystal is small, and the difference with the set value is also small. At this time, the effect of PID is small. In the later stage of shouldering, the crystal diameter increases by dozens of times, and the difference between the real-time value and the set value increases accordingly, and the PID control effect is enhanced. This makes it difficult for PID regulation to achieve stable regulation at different stages of shouldering, and insufficient or over-regulation occurs frequently, resulting in shouldering fluctuations, a large difference from the set value, and even shouldering breakage.

[0006] Based on the above background, the actual shoulder release operation in the industry is highly dependent on the operator's manual observation and manual adjustment. The "length-diameter" PID adjustment can only play an auxiliary role and cannot be fully automated. Manual shoulder release increases labor costs and has low production efficiency, which is not conducive to the automated development of industrial production. In addition, the quality of shoulder release is highly dependent on the worker's observation accuracy and operational proficiency, resulting in uneven quality of crystal rod shoulder release and difficulty in unification. It is urgent to develop a fully automatic and easy-to-manage shoulder release method to solve the above problems. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a Czochralski single crystal growth method and a single crystal furnace based on PID control, which can more accurately regulate the shoulder release program.

[0008] In order to solve the above problems, the present invention provides a method for growing a single crystal by pulling it vertically based on PID control, comprising: selecting any one of the decisive parameters of the shoulder shape as the PID control independent variable, and taking the shoulder diameter growth rate as the PID control dependent variable; inputting the independent variable value and the corresponding dependent variable value of each node into the control system as the set value in the control process; establishing a measurement algorithm for the diameter growth rate to calculate the actual value in the control process; in the shoulder release process, the PID control system calculates the actual value of the diameter growth rate of the shoulder release process according to the established algorithm, and compares it with the set value of the corresponding node, and adjusts the pulling process according to the difference between the two to achieve diameter growth rate regulation.

[0009] Optionally, the determining parameters of the shoulder release shape include shoulder release time, shoulder release diameter and shoulder release length.

[0010] Optionally, the independent variable value and the corresponding dependent variable value of each node are input into the control system as set values ​​in the control process, which is selected from one of the following: setting the diameter growth rate as the shoulder release length changes, as the set value in the control process; and setting the diameter growth rate as the shoulder release time changes, as the set value in the control process.

[0011] Optionally, the calculation formula for setting the growth rate of the diameter as the shoulder length changes is:

[0012] Δd ls =(d ls -d 0s ) / (l ts -l 0s ),

[0013] Where:

[0014] Δd ls Set a value for the diameter growth rate;

[0015] d lsSet the value for the current shoulder diameter;

[0016] d 0s Set a value for the shoulder diameter of the previous node;

[0017] l ts Set a value for the current shoulder length;

[0018] l 0s Sets a value for the shoulder length of the previous node.

[0019] Optionally, the calculation formula for setting the growth rate of the diameter as the shoulder release time changes is:

[0020] Δd ts =(d ts -d 0s ) / (t s -t 0s ),

[0021] Where:

[0022] Δd ts Set a value for the diameter growth rate;

[0023] d ts Set the value for the current diameter;

[0024] d 0s Set a value for the diameter of the previous node;

[0025] t s is the time corresponding to the current node;

[0026] t 0s is the time corresponding to the previous node.

[0027] Optionally, the measurement algorithm for establishing the diameter growth rate is used to calculate the actual value during the control process, and is selected from one of the following: calculating the diameter growth rate based on the change in the shoulder release length as the actual value during the control process; and calculating the diameter growth rate based on the change in the shoulder release time as the actual value during the control process.

[0028] Optionally, the diameter growth rate is calculated based on the change in the shoulder length as the calculation formula for the actual value in the control process:

[0029] Δd la =(d la -d 0a ) / (l ta -l 0a ),

[0030] Where:

[0031] Δd lais the actual value of the diameter growth rate with the shoulder length as the independent variable;

[0032] d la The actual value of the current diameter is obtained by real-time measurement by the CCD camera during the shoulder release process;

[0033] d 0a is the actual diameter value of the previous data collection node, obtained by real-time measurement by the CCD camera;

[0034] l ta The actual value of the current shoulder length is automatically calculated by the machine lifting system;

[0035] l 0a It is the actual value of the shoulder length at the previous data collection node, which is automatically calculated by the machine lifting system.

[0036] Optionally, the diameter growth rate is calculated based on the change in the shoulder release time as the calculation formula for the actual value in the control process:

[0037] Δd ta =(d ta -d 0a ) / (t a -t 0a ), where:

[0038] Δd ta is the actual value of the diameter growth rate with the shoulder release time as the independent variable;

[0039] d ta The actual value of the current diameter is obtained by real-time measurement by the CCD camera during the shoulder release process;

[0040] d 0a is the actual diameter value of the previous data collection node, obtained by real-time measurement by the CCD camera;

[0041] t a is the time corresponding to the current node;

[0042] t 0a is the time corresponding to the previous node.

[0043] Optionally, the adjusting the pulling process includes adjusting one or more of the crystal pulling speed, heater power and melt surface temperature.

[0044] In order to solve the above problems, the present invention provides a single crystal furnace, including a pulling device and a control device, and the control device is configured to perform the following steps to control the pulling device: select any one of the decisive parameters of the shoulder shape as a PID control independent variable, and calculate the diameter growth rate as a PID control dependent variable; input the independent variable value and the corresponding dependent variable value of each node into the control system as the set value in the control process; establish a measurement variable algorithm for the diameter growth rate in the system as the actual value in the control process; in the shoulder release program, the PID control system calculates the actual value of the diameter growth rate of the square shoulder process, and compares it with the target value of the corresponding node, and adjusts the pulling process according to the difference between the two to achieve diameter growth rate regulation.

[0045] The present invention adopts the diameter growth rate instead of the diameter as the parameter of PID control. Compared with the diameter change range, the diameter growth rate has a small change range, which is convenient for PID to perform stable control. In addition, the diameter growth rate is adopted as the control parameter, so that the diameter and the diameter change trend at each position in the shoulder release process can be accurately controlled, and the accurate control of the shoulder release shape can be taken into account. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Attached Figure 1 Shown is a schematic diagram of the implementation steps of a specific implementation method of the Czochralski single crystal growth method based on PID control described in the present invention.

[0047] Attached Figure 2 The Δd calculated in Example 1 of the present invention is shown as ls Schematic diagram of the values ​​and the corresponding curves.

[0048] Attached Figure 3 The Δd calculated in Example 2 of the present invention is shown as ls Schematic diagram of the values ​​and the corresponding curves.

[0049] Attached Figure 4 The Δd calculated in Example 3 of the present invention is shown as ls Schematic diagram of the values ​​and the corresponding curves. DETAILED DESCRIPTION

[0050] The specific implementation methods of the Czochralski single crystal growth method based on PID control and the single crystal furnace provided by the present invention are described in detail below with reference to the accompanying drawings.

[0051] Attached Figure 1The figure shows a schematic diagram of the implementation steps of a specific embodiment of the Czochralski single crystal growth method based on PID control according to the present invention, including: step S10, selecting any one of the decisive parameters of the shoulder shape as the PID control independent variable, and taking the shoulder diameter growth rate as the PID control dependent variable; step S11, inputting the independent variable value and the corresponding dependent variable value of each node into the control system as the set value in the control process; step S12, establishing a measurement algorithm for the diameter growth rate to calculate the actual value in the control process; step S13, in the shoulder release process, the PID control system calculates the actual value of the diameter growth rate in the shoulder release process according to the established algorithm, and compares it with the set value of the corresponding node, and adjusts the pulling process according to the difference between the two to achieve diameter growth rate regulation.

[0052] Referring to step S10, any one of the decisive parameters of the shoulder release shape is selected as the PID control independent variable, and the shoulder release diameter growth rate is used as the PID control dependent variable. The decisive parameters of the shoulder release shape include shoulder release time, shoulder release diameter and shoulder release length.

[0053] Referring to step S11, the independent variable value and the corresponding dependent variable value of each node are input into the control system as the set value in the control process. This step is further selected from one of the following: setting the growth rate of the diameter as the shoulder length changes, as the set value in the control process; and setting the growth rate of the diameter as the shoulder time changes, as the set value in the control process.

[0054] If the shoulder length is selected as the independent variable, the calculation formula for setting the growth rate of the diameter as the shoulder length changes is:

[0055] Δd ls =(d ls -d 0s ) / (l ts -l 0s ),

[0056] Where:

[0057] Δd ls Set a value for the diameter growth rate;

[0058] d ls Set the value for the current shoulder diameter;

[0059] d 0s Set a value for the shoulder diameter of the previous node;

[0060] l ts Set a value for the current shoulder length;

[0061] l 0s Sets a value for the shoulder length of the previous node.

[0062] If the shoulder release time is selected as the independent variable, the calculation formula for setting the growth rate of the diameter with the change of the shoulder release time is:

[0063] Δd ts =(d ts -d 0s ) / (t s -t 0s ),

[0064] Where:

[0065] Δd ts Set a value for the diameter growth rate;

[0066] d ts Set the value for the current diameter;

[0067] d 0s Set a value for the diameter of the previous node;

[0068] t s is the time corresponding to the current node;

[0069] t 0s is the time corresponding to the previous node.

[0070] The purpose of the above steps is to set an expected growth rate value, which is used to control the shoulder release speed during the actual pulling process.

[0071] Referring to step S12, a measurement algorithm for the diameter growth rate is established to calculate the actual value during the control process. Further, the measurement algorithm for establishing the diameter growth rate to calculate the actual value during the control process is selected from one of the following: calculating the diameter growth rate according to the change of the shoulder release length as the actual value during the control process; and calculating the diameter growth rate according to the change of the shoulder release time as the actual value during the control process.

[0072] Correspondingly, if the shoulder length is selected as the independent variable in step S11, this step should calculate the growth rate of the diameter according to the change of the shoulder length as the calculation formula of the actual value in the control process:

[0073] Δd la =(d la -d 0a ) / (l ta -l 0a ),

[0074] Where:

[0075] Δd la is the actual value of the diameter growth rate with the shoulder length as the independent variable;

[0076] d laThe actual value of the current diameter is obtained by real-time measurement by the CCD camera during the shoulder release process;

[0077] d 0a is the actual diameter value of the previous data collection node, obtained by real-time measurement by the CCD camera;

[0078] l ta The actual value of the current shoulder length is automatically calculated by the machine lifting system;

[0079] l 0a It is the actual value of the shoulder length at the previous data collection node, which is automatically calculated by the machine lifting system.

[0080] Correspondingly, if the shoulder release time is selected as the independent variable in step S11, this step calculates the growth rate of the diameter according to the change of the shoulder release time as the calculation formula of the actual value in the control process:

[0081] Δd ta =(d ta -d 0a ) / (t a -t 0a ), where:

[0082] Δd ta is the actual value of the diameter growth rate with the shoulder release time as the independent variable;

[0083] d ta The actual value of the current diameter is obtained by real-time measurement by the CCD camera during the shoulder release process;

[0084] d 0a is the actual diameter value of the previous data collection node, obtained by real-time measurement by the CCD camera;

[0085] t a is the time corresponding to the current node;

[0086] t 0a is the time corresponding to the previous node.

[0087] The measurement interval of the actual values ​​of the diameter and length is determined by a given time period t, that is, the diameter and length data are collected once every time t.

[0088] The purpose of the above steps is to establish an algorithm for the growth rate value, which is used to calculate the shoulder release speed during the actual pulling process and compare it with the preset value, so as to adjust the pulling process.

[0089] Referring to step S13, in the shoulder release process, the PID control system calculates the actual value of the diameter growth rate of the shoulder release process according to the established algorithm, and compares it with the set value of the corresponding node, and adjusts the pulling process according to the difference between the two to achieve diameter growth rate regulation. After the seeding and necking processes are completed, automatic shoulder release is turned on. The adjustment of the pulling process includes adjusting one or more of the crystal pulling speed, heater power and melt surface temperature. This step uses the growth rate expectation to control the shoulder release process, which can avoid the situation where the absolute rate of shoulder release changes dramatically with the shoulder release distance or time when the crystal diameter changes, and more effectively and stably controls the shoulder release program.

[0090] The implementation of the present invention is further described below with specific implementation cases:

[0091] Embodiment 1:

[0092] In this embodiment, the shoulder release diameter is selected as the independent variable, and the diameter growth rate that changes with the shoulder release length is selected as the dependent variable for PID control to complete the shoulder release process of the silicon single crystal with a target diameter of 310 mm.

[0093] According to the shoulder shape required by the process, determine the shoulder diameter corresponding to different shoulder lengths, and set the PID control parameter nodes. Calculate the diameter growth rate of each node as the shoulder length changes, Δd ls =(d ls -d 0s ) / (l ts -l 0s ), where: Δd ls Set the value for the diameter growth rate; d ls Set the current diameter; d 0s Set the diameter value of the previous node; l ts Set the current shoulder length; d 0s is the shoulder length setting value of the previous node. The control parameter nodes and corresponding data set in this embodiment are shown in Table 1 below. The calculated Δd ls The values ​​and corresponding curves are Figure 2 Given in.

[0094] Table 1 Shoulder release parameters determined according to process requirements in Example 1

[0095]

[0096] The shoulder diameter setting value is used as the independent variable, and the shoulder diameter growth rate Δd is calculated. ls The node diameter and the corresponding diameter growth rate setting value are input into the PID control system, and the diameter growth rate is used as the PID control logic parameter.

[0097] Add the actual diameter growth rate variable Δd to the control system variables la,This variable is calculated in real time by the machine system program during the shoulder release process based on the measured values ​​of length and diameter, Δd la =(d la -d 0a ) / (l ta -l 0a ). Where: Δd la is the actual value of diameter growth rate; d ta is the actual value of the current diameter, d 0a is the actual value of the diameter of the previous node, measured in real time by the CCD camera; ta is the actual value of the current shoulder length, l 0a The actual value of the shoulder length of the previous node is calculated in real time by the machine lifting system. The data collection interval t is 60s, that is, the system calculates the data once every 60s and obtains Δd la The real-time value of .

[0098] After the seeding is completed, the program jumps to the shoulder release stage, and the set control program starts to run. The PID control system compares the actual value of the diameter growth rate with the set value, and feeds back to the pulling speed adjustment based on the size and difference. The program presets the shoulder release end diameter of 310mm. When the shoulder release diameter reaches 310mm, the program automatically ends, the shoulder release is completed, and the step jumps to the equal diameter.

[0099] Embodiment 2:

[0100] In this embodiment, the shoulder release time is selected as the independent variable, and the diameter growth rate that changes with the shoulder release time is selected as the dependent variable for PID control to complete the shoulder release process of the silicon single crystal with a target diameter of 310 mm.

[0101] According to the shoulder shape required by the process, determine the shoulder diameter corresponding to different shoulder lengths, and set the PID control parameter nodes. Calculate the diameter growth rate of each node as the shoulder time changes, Δd ts =(d ts -d 0s ) / (t s -t 0s ), where: Δd ts Set the value for the diameter growth rate; d ts Set the current diameter; d 0s Set the value for the diameter of the previous node; t s is the time corresponding to the current node; t 0s is the time corresponding to the previous node. Calculated Δd ts The values ​​and corresponding curves are Figure 3 The control parameter nodes and corresponding data set in this embodiment are shown in Table 2.

[0102] Table 2 Shoulder release parameters determined according to process requirements in Example 2

[0103]

[0104] The shoulder diameter setting value is used as the independent variable, and the shoulder diameter growth rate Δd is calculated. ls The node diameter and the corresponding diameter growth rate setting value are input into the PID control system, and the diameter growth rate is used as the PID control logic parameter.

[0105] Add the actual diameter growth rate variable Δd to the control system variables la ,This variable is calculated in real time by the machine system program during the shoulder release process based on the measured values ​​of length and diameter, Δd ta =(d ta -d 0a ) / (t a -t 0a ). Where: Δd ta is the actual value of the diameter growth rate with the shoulder release time as the independent variable; d ta is the actual value of the current diameter; d 0a is the actual diameter value of the previous data collection node, measured in real time by the CCD camera; t a is the time corresponding to the current node; t 0a is the time corresponding to the previous node.

[0106] The data collection interval t is 5s, that is, the system calculates data every 5s and obtains Δd once. la The real-time value of .

[0107] After the seeding is completed, the program jumps to the shoulder release stage, and the set control program starts to run. The PID control system compares the actual value of the diameter growth rate with the set value, and feeds back to the pulling speed adjustment based on the size and difference. The program presets the shoulder release end diameter of 310mm. When the shoulder release diameter reaches 310mm, the program automatically ends, the shoulder release is completed, and the step jumps to the equal diameter.

[0108] Embodiment 3:

[0109] In this embodiment, the shoulder release length is selected as the independent variable, and the diameter growth rate that changes with the shoulder release length is selected as the dependent variable for PID control to complete the shoulder release process of the silicon single crystal with a target diameter of 210 mm.

[0110] According to the shoulder shape required by the process, determine the shoulder diameter corresponding to different shoulder lengths, and set the PID control parameter nodes. Calculate the diameter growth rate of each node as the shoulder length changes, Δd ls =(d ls -d 0s ) / (l ts -l 0s ), where: Δdls Set the value for the diameter growth rate; d ls Set the current diameter; d 0s Set the diameter value of the previous node; l ts Set the current shoulder length; d 0s is the shoulder length setting value of the previous node. The control parameter nodes and corresponding data set in this embodiment are shown in Table 3. The calculated Δd ls The values ​​and corresponding curves are Figure 4 Given in.

[0111] Table 3 Shoulder release parameters determined according to process requirements in Example 3

[0112]

[0113] The shoulder length setting value is used as the independent variable, and the shoulder diameter growth rate Δd is calculated. ls The node diameter and the corresponding diameter growth rate setting value are input into the PID control system, and the diameter growth rate is used as the PID control logic parameter.

[0114] Add the actual diameter growth rate variable Δd to the control system variables la ,This variable is calculated in real time by the machine system program during the shoulder release process based on the measured values ​​of length and diameter, Δd la =(d la -d 0a ) / (l ta -l 0a ). Where: Δd la is the actual value of diameter growth rate; d ta is the actual value of the current diameter, d 0a is the actual value of the diameter of the previous node, measured in real time by the CCD camera; ta is the actual value of the current shoulder length, l 0a The actual value of the shoulder length of the previous node is calculated in real time by the machine lifting system. The data collection interval t is 60s, that is, the system calculates the data once every 60s and obtains Δd la The real-time value of .

[0115] After the seeding is completed, the program jumps to the shoulder release stage, and the set control program starts to run. The PID control system compares the actual value of the diameter growth rate with the set value, and feeds back to the pulling speed adjustment based on the size and difference. The program presets the shoulder release end diameter of 210mm. When the shoulder release diameter reaches 210mm, the program automatically ends, the shoulder release is completed, and the step jumps to the equal diameter.

[0116] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A Czochralski single crystal growth method based on PID control, characterized in that: include: Select any one of the decisive parameters of the shoulder shape as the PID control independent variable, and use the shoulder diameter growth rate as the PID control dependent variable; Input the independent variable value and the corresponding dependent variable value of each node into the control system as the set value in the control process; Establish a measurement algorithm for diameter growth rate to calculate the actual value in the control process; During the shoulder release process, the PID control system calculates the actual value of the diameter growth rate of the shoulder release process according to the established algorithm, and compares it with the set value of the corresponding node. The pulling process is adjusted according to the difference between the two to achieve diameter growth rate control.

2. The method according to claim 1, characterized in that The decisive parameters of the shoulder release shape include shoulder release time, shoulder release diameter and shoulder release length.

3. The method according to claim 1, characterized in that The independent variable value and the corresponding dependent variable value of each node are input into the control system as the set value in the control process, which is selected from one of the following: Setting the diameter growth rate as the shoulder length changes as a set value in the control process; and The diameter growth rate is set as the shoulder release time changes, which serves as the set value in the control process.

4. The method according to claim 3, characterized in that The calculation formula for setting the growth rate of the diameter as the shoulder length changes is: Δd ls =(d ls -d 0s ) / (l ts -l 0s ), Where: Δd ls Set a value for the diameter growth rate; d ls Set the value for the current shoulder diameter; d 0s Set a value for the shoulder diameter of the previous node; l ts Set a value for the current shoulder length; l 0s Sets a value for the shoulder length of the previous node.

5. The method according to claim 3, characterized in that: The calculation formula for setting the growth rate of the diameter as the shoulder release time changes is: Δd ts =(d ts -d 0s ) / (t s -t 0s ), Where: Δd ts Set a value for the diameter growth rate; d ts Set the value for the current diameter; d 0s Set a value for the diameter of the previous node; t s is the time corresponding to the current node; t 0s is the time corresponding to the previous node.

6. The method according to claim 1, characterized in that The measurement algorithm for establishing the diameter growth rate, used to calculate the actual value during the control process, is selected from one of the following: The growth rate of diameter is calculated according to the change of shoulder length as the actual value in the control process; as well as The diameter growth rate is calculated according to the change of shoulder release time as the actual value in the control process.

7. The method according to claim 6, characterized in that The diameter growth rate is calculated based on the change in shoulder length, which is used as the calculation formula for the actual value in the control process: Δd la =(d la -d 0a ) / (l ta -l 0a ), Where: Δd la is the actual value of the diameter growth rate with the shoulder length as the independent variable; d la The actual value of the current diameter is obtained by real-time measurement by the CCD camera during the shoulder release process; d 0a is the actual value of the diameter of the previous data collection node, obtained by real-time measurement by the CCD camera; l ta The actual value of the current shoulder length is automatically calculated by the machine lifting system; l 0a It is the actual value of the shoulder length at the previous data collection node, which is automatically calculated by the machine lifting system.

8. The method according to claim 6, characterized in that The diameter growth rate is calculated according to the change of shoulder release time, which is used as the calculation formula of the actual value in the control process: Δd ta =(d ta -d 0a ) / (t a -t 0a ), where: Δd ta is the actual value of the diameter growth rate with the shoulder release time as the independent variable; d ta The actual value of the current diameter is obtained by real-time measurement by the CCD camera during the shoulder release process; d 0a is the actual value of the diameter of the previous data collection node, obtained by real-time measurement by the CCD camera; t a is the time corresponding to the current node; t 0a is the time corresponding to the previous node.

9. The method according to claim 1, characterized in that: The adjusting of the pulling process includes adjusting one or more of the crystal pulling speed, heater power and melt surface temperature.

10. A single crystal furnace, comprising a pulling device and a control device, characterized in that: The control device is configured to perform the following steps to control the lifting device: Select any one of the decisive parameters of the shoulder shape as the PID control independent variable, and calculate the diameter growth rate as the PID control dependent variable; Input the independent variable value and the corresponding dependent variable value of each node into the control system as the set value in the control process; Establish a measurement variable algorithm for the diameter growth rate in the system as the actual value in the control process; In the shoulder release procedure, the PID control system calculates the actual value of the diameter growth rate of the square shoulder process and compares it with the target value of the corresponding node. The pulling process is adjusted according to the difference between the two to achieve diameter growth rate control.

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