JPH0369876B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for controlling the bottom shape of a pulled single crystal, which is suitable for use in controlling the bottom shape of a silicon single crystal, for example.

"Prior Art" FIG. 2 is a sectional view showing the configuration of a general single crystal manufacturing apparatus. In this figure, 1 is a furnace body, and a quartz crucible 2 is provided approximately in the center of the furnace body 1. This quartz crucible 2 is held by a graphite susceptor 3, and the lower end of the graphite susceptor 3 is attached to the upper end of a shaft 4 by a predetermined joining member. In this case, a crucible rotating motor 32 and a crucible lifting motor 3 are connected to the lower end of the shaft 4.
1 is transmitted through a transmission mechanism 33, so that the crucible 2 can rotate in a predetermined direction and can move up and down in the vertical direction. 6, 6 are heaters that control the temperature of the molten metal (silicon polycrystalline molten metal) 7 in the crucible 2, and are provided at a predetermined distance apart from the outside of the crucible 2; Insulating material 8 in the gap
is provided.

Next, reference numeral 10 denotes a hollow cylindrical upper casing joined to the upper end of the furnace body 1, and a lifting head 11 is provided at the upper end of the upper casing so as to be horizontally pivotable. A wire pulling mechanism 12 is provided in the pulling head 11, and a wire cable 13 extends from the wire lifting mechanism 12 toward the center of rotation of the crucible 2. The driving force of a pulling motor 15 is transmitted to the wire pulling mechanism 12, and depending on the direction of rotation of the pulling motor 15, the wire cable 13 can be pulled up or
They are starting to lower their prices. Further, the lifting head 11 is configured to rotate in the direction of arrow A when the driving force of the head rotation motor 16 is transmitted.

Next, 20 is a seed holder attached to the lower end of the wire cable 13, which holds a seed (single crystal seed) 21 as shown.

In the above configuration, when the head rotation motor 16 is driven and the pulling motor 15 is driven in the lifting direction after the seed 21 is immersed in the molten metal 7, the wire cable 13 is driven upward in the direction of arrow A. As the seed 21 is pulled up, single crystal silicon 22 grows at the lower end of the seed 21 as shown in the figure. In addition, in this single crystal growth process,
The shaft 4 is rotated in the opposite direction to arrow A, so that
The single crystal silicon 22 and the molten metal 7 are configured to rotate in opposite directions.

In addition, in FIG. 2, 29 is the pulling motor 15.
A speed detector 30 detects the rotational speed of the apparatus, and 30 is a control section that controls each part of the apparatus. In this case, the detection signal S ₁ (corresponding to the pulling speed) of the speed detector 29 and the video signal of the television camera 25 are each supplied to the control section 30. And the control section 3
0's functions include detecting the crystal pulling speed based on the signal _S1 , measuring the diameter of the growing single crystal based on the image signal of the television camera 25, controlling the amount of heat generated by the heater 6, controlling the rotation of the motors 15 and 16, and rotating the crucible. This includes rotation control of the motor 32 and the crucible lifting/lowering motor 31, etc. Various controls of this control section 30 are performed according to a predetermined program in the built-in ROM.

Now, single crystal silicon 22 is being pulled up.
It is desirable that the growth shape of the upper end (hereinafter referred to as "top") and lower end (hereinafter referred to as "bottom") correspond to the desired shape.
Further, it is desirable that the straight body portion and the seed portion have a uniform diameter equal to the target value. Since the growth shape is determined by the pulling speed, the temperature of the molten metal, the relative rotational speed of the single crystal silicon 22, the liquid level of the molten metal, etc., the diameter of the single crystal silicon 22 is determined by adjusting these parameters. It is necessary to perform control so that the size and shape become the desired size.

In this case, in controlling the diameter of the seed part and the straight body part, the upper surface of the molten metal 7 is photographed by the television camera 25 through the window part 1a provided in the upper end part of the furnace body 1,
Furthermore, the image data of the television camera 25 is analyzed to detect the boundary position between the single crystal silicon 22 and the molten metal liquid surface, and based on this detection result, the diameter of the single crystal silicon 22 is adjusted to a predetermined size. Controls each parameter. Furthermore, as the single crystal silicon 22 grows, the liquid level of the molten metal in the crucible 2 decreases;
Since changing the diameter of the tube 2 would have an adverse effect on the growth shape, the shaft 4 is raised to keep the liquid level constant.

"Problems to be Solved by the Invention" By the way, the shape control of the bottom is carried out by gradually reducing the diameter of the crystal in order to maintain the straight body part after being pulled in a dislocation-free state. .

In conventional bottom shape control, a skilled worker visually inspects the bottom part and controls the pulling speed and molten metal temperature, thereby controlling the bottom shape. In other words, the diameter of the single crystal 22 becomes smaller when the pulling speed is faster, becomes larger when the pulling speed is slower, becomes smaller when the molten metal surface temperature is higher, and becomes larger when the molten metal surface temperature is lower, so these values are By controlling the bottom shape, the bottom shape was manually controlled.

However, in the conventional manual method, the bottom shape is not constant, requires skill, and has problems such as deformation of the shape due to human error.

This invention was made in view of the above-mentioned circumstances, and is a method for producing a pulled single crystal that can fully automate bottom shape control without the need for human labor and can match the bottom shape to the target shape with high precision. The present invention aims to provide a bottom shape control method.

"Means for Solving the Problems" In order to solve the above-mentioned problems, this invention
a diameter detection unit that detects the diameter of the growing single crystal;
In a method for controlling the bottom shape of a pulled single crystal in a single crystal pulling apparatus having a pulling part for pulling up the single crystal and a pulling speed detection part for detecting a pulling speed of the pulling part, In the pulling process of the part, controlling the pulling speed of the pulling part so that the deviation between the diameter of the straight body part and a predetermined target value becomes 0,
In the step of pulling up the bottom portion of the single crystal, an average value of the pulling speed during a specified time immediately before this step is calculated, and the pulling operation of the bottom portion of the single crystal is performed based on the average value. That's what I do. Note that the calculation of the average value of the pulling speed in the specified time period immediately before the bottom part pulling process is performed by dividing the specified time period immediately before the lifting process into a plurality of parts,
This is performed by calculating the average pulling speed for each of these divided times and calculating the average value from these average pulling speeds.

``Function'' Since the pulling speed and molten metal temperature in the bottom process are calculated based on the average value of the pulling speed during the specified time immediately before the bottom process, it is adapted to the current single crystal pulling situation. The bottom process is performed automatically.

"Embodiments" Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a flowchart showing a bottom shape control method to which an embodiment of the present invention is applied. The configuration of the single crystal pulling apparatus used in this example is the same as the above-described pulling apparatus shown in FIG. 2.

First, once the seed 21 is immersed in the molten metal 7, the control unit 30 reverses the rotation direction of the pulling motor 15, thereby entering the seed part pulling process. The torso will be pulled up one by one. Here, among the processes shown in FIG.
SP10 uses conventional processing and steps.
Steps SP11 to SP15 are processes that are particularly performed in this embodiment. These processes will be explained below.

First, the process at step SP10 is a process for making the diameter of the straight body portion match a target value. This process is
so that the diameter value of the straight body part obtained by analyzing the image signal of the television camera 25 matches the target value,
The pulling speed, surface temperature of the molten metal 2, etc. are controlled.
In this case, the pulling speed control is performed by, for example, detecting the deviation between the detected diameter and the target value, and setting the pulling speed so that this deviation becomes 0 using PID (proportional, integral, differential).
This is determined by calculation, etc., and the lifting is performed at the newly determined lifting speed. Furthermore, in controlling the molten metal surface temperature, control is performed to keep the temperature constant by controlling the heater supply power and the crucible rotation speed. Therefore, although the diameter of the straight body portion is controlled to be constant through the process of step SP10, the pulling speed varies depending on the conditions at that time.

Next, the processing of steps SP11 to SP15 will be explained.

Step SP11 is a process for determining whether the time for pulling up the straight body has reached the specified time T1,
If the specified time has been reached, move on to step SP12,
If it has not been reached, move to step SP14. The specified time T1 in this case is set in units of several minutes corresponding to a pulling length of approximately several mm.

If the lifting time has not reached the specified time, the process moves from step SP11 to step SP14.
Here, processing is performed to accumulate the pulling speed. This pulling speed accumulation process is a process in which the current pulling speed is entered into a register SUM prepared in advance, and the current pulling speed is added to the register SUM every time this step SP14 is executed thereafter. When the processing of this step SP14 is completed, the step
Proceeding to SP15, the contents of the averaging counter COUNT are incremented. In this case, the counter
The contents of COUNT are cleared in the initial state. When the process of step SP15 is completed, the process moves to step SP16, and it is determined whether the process of controlling the bottom shape has started, that is, whether the process of pulling up the straight body part has been completed. The determination in step SP16 is, for example, whether the bottom control start button has been pressed by the operator;
Alternatively, this is performed by determining whether the cumulative total of the pulling length of the straight body portion has reached a preset target value. When the determination is "NO" at step SP16, the process returns to step SP10 again, and from then on, the process continues from step SP10 to SP11→SP14→SP15→
A loop l1 of SP16→SP10 is circulated. Therefore, the contents of the register SUM at the time of exiting from this loop l1 are the sum of the pulling speeds in the specified time T1, and the contents of the register SUM are the sum of the pulling speeds in the specified time T1, and the contents of the register
The count contents are the number of times step SP15 is executed,
In other words, it corresponds to the number of additions.

Next, when the judgment is ``YES'' at step SP11 and the process moves to step SP12, the cumulative value in the register SUM is divided by the count value of the counter COUNT, and thereby the average value of the pulling speed within the specified time T1 is calculated. Find this average lifting speed and register AVE.
〓Stored in SE. Further, in step SP12, the contents of the register SUM and the counter COUNT are cleared, and a timer for measuring the pulling time is also cleared. Next, in step SP13, the average speed data in the register AVE SE is stored in the shift register. In this case, the shift register consists of about 10 to 100 registers, and the
Each time data is stored in SP13, the data is sequentially shifted, and the data stored in the terminal register is discarded at the next data storage timing.

When the processing of step SP13 is completed, step SP13 is completed.
Proceeding to SP16, it is determined whether or not the bottom process has been entered, and if it has not entered, the process returns to step SP11 via step SP10. Steps in this case
The determination at SP11 is "NO" because the timer has been cleared by the process at step SP12, and as a result, the process of circulating through the loop I1 is started again.

As can be seen from the above, before entering the bottom step, the average pulling speed is calculated every prescribed time T1, and this average pulling speed is sequentially stored in the shift register.

Next, when the bottom process is started, the step
When the judgment in SP16 is “YES”, proceed to the step.
Proceeding to SP17, all the data in the shift register is divided by the number of registers to calculate the average pulling speed for the specified time T2. The specified time T2 in this case is the specified time immediately before the bottom part pulling process (bottom process), and as is clear from the above, the specified time T1 x the number of registers, so it is approximately 1 The value is from hours to several hours, and the pulling length is a number.
It corresponds to about 10 cm to 10 cm. That is, the process in step 17 is a process for calculating the average value of the pulling speed (average pulling speed) during the specified time immediately before the bottom part pulling process.

Next, in step 18, the average pulling speed obtained in step 17 is used as reference data, and a predetermined calculation is performed on this reference data to calculate an initial value of the pulling speed at the bottom portion. For example, if the initial value of the bottom pulling speed is set to 1.2 times the average pulling speed obtained in step SP17, then if the average pulling speed is 1 mm/min, it is set to 1.2 mm/min. , average pulling speed is 1.2mm/min
When , the calculation is performed to set the speed to 1.44mm/min.

In addition, in step SP18,
The molten metal temperature in the bottom part pulling process is also controlled using the average pulling speed calculated in SP17 as molten metal temperature feedback information. This is a process that utilizes the fact that the pulling speed corresponds to fluctuations in molten metal temperature, and the reason for this correspondence is as follows. In other words, the lifting process (step
SP10~SP15) increases the pulling speed to suppress the diameter increase when the molten metal temperature is lower than the set value, and increases the pulling speed to suppress the diameter decrease when the molten metal temperature is higher than the set value. Since the process slows down the molten metal temperature, fluctuations in the molten metal temperature will be reflected in fluctuations in the pulling speed. Then, in step SP18, the average molten metal temperature is analyzed from the average pulling speed calculated in step SP17, and based on this analysis result, an initial value of the molten metal temperature in the bottom part pulling process is calculated.

Next, when the process moves to step SP19, the bottom sequence is started. The bottom sequence in this case is a process of changing the pulling speed, molten metal temperature, etc. according to the bottom pulling length according to a pre-stored program. However, step SP19
The initial values of the pulling speed and molten metal temperature in step SP18 are set to the values calculated in step SP18.
An example of the pulling speed control in step SP19 is, for example, until the bottom part is pulled up to the distance L1, the bottom part is pulled up at the initial value of the pulling speed calculated in step 18, and the distance is L2 (L1<L2). The initial value of the pulling speed is sequentially set to a predetermined value, such as pulling at a speed of 1.2 times the initial value until reaching distance L3 (L2<L3), and then pulling at a speed of 1.4 times the initial value until reaching distance L3 (L2<L3). Control is performed to increase the rate of increase. Furthermore, control of the molten metal temperature is performed in the same manner as the speed control described above.

In this way, if the pulling speed and molten metal temperature in the bottom part pulling process are set according to the average value of the pulling speed during the specified time immediately before the bottom process, it will be possible to obtain the most suitable for the current single crystal pulling situation. A suitable bottom lifting process can be performed, and the transition from the straight body part lifting process to the bottom part lifting process can be performed extremely quickly and smoothly. Therefore, the bottom part lifting process can be efficiently automated.

On the other hand, in this case, if the initial value of the pulling speed and the initial value of the molten metal temperature in the bottom sequence are set to fixed values, the pulling conditions may differ from the expected conditions at the time the bottom pulling process is started. In this case, the bottom shape may not be as expected. Also, in order to avoid this inconvenience, if we perform intermediate processing to match the assumed lifting conditions before processing the bottom part,
A problem arises in that it takes a lot of time to match the conditions. In particular, it takes a long time (1 to 2 hours) to adjust the temperature of the molten metal to the set value, which is extremely disadvantageous in terms of work efficiency.

"Effects of the Invention" As explained above, according to the present invention, in the step of pulling a straight body of a single crystal, the straight body is pulled so that the deviation between the diameter of the straight body and a predetermined target value becomes 0. The pulling speed of the upper part is controlled, and in the pulling process of the bottom part of the single crystal, the pulling speed is not fixed in advance.
The average value of the pulling speed during the specified time immediately before this step was calculated, and the pulling operation of the bottom part of the single crystal was performed based on the average value, so that during the straight body part pulling process, Regardless of the fluctuations in the pulling conditions, etc., the bottom pulling process can be the most suitable for the single crystal pulling situation, and the transition from the straight body part pulling process to the bottom part pulling process can be made in an extremely short time. This has the effect that the bottom part lifting process can be efficiently automated.

[Brief explanation of drawings]

FIG. 1 is a flow chart showing a control method in an embodiment of the present invention, and FIG. 2 is a schematic diagram showing the structure of a general single crystal pulling apparatus. 2... Crucible, 4... Shaft, 10... Upper casing, 13... Wire cable, 15... Pulling motor (pulling part), 20... Seed holder, 21
...Seed, 22...Single crystal silicon, 25...
Television camera (diameter detection section), 29... speed detector (pulling speed detection section), 30... control section (diameter detection section: pulling speed detection section).

Claims (1)

[Scope of Claims] 1. A single crystal having a diameter detection section that detects the diameter of a growing single crystal, a pulling section that pulls up the single crystal, and a pulling speed detection section that detects the pulling speed of the pulling section. In the method for controlling the bottom shape of a pulled single crystal in a crystal pulling apparatus, in the step of pulling the straight body part of the single crystal, the diameter of the straight body part and a predetermined target value are set to zero. The pulling speed of the pulling part is controlled, and in the pulling process of the bottom part of the single crystal, the average value of the pulling speed for a specified time immediately before this process is calculated, and the pulling speed of the single crystal is controlled based on the average value. A method for controlling the bottom shape of a pulled single crystal, comprising performing a pulling operation of the bottom portion. 2. Calculation of the average value of the pulling speed in the specified time immediately before the bottom part pulling process is performed by dividing the specified time immediately before the lifting process into a plurality of parts,
The single crystal pulling apparatus according to page 1 of the claims is characterized in that the method is carried out by calculating an average pulling speed for each of these divided times and calculating an average value from these average pulling speeds. control method.