JPH02279584A - Diameter control device for single crystal pulling-up device - Google Patents

Abstract

PURPOSE:To rapidly extricate a diameter control from upper and lower limit regions with a device for making PID control of the diameter control by a speed control of a motor for pulling-up a single crystal from a melt by detecting the arrival at an upper/lower limit circuit and increasing and decreasing the set value of a temp. control. CONSTITUTION:The motor 3 for pulling up a single crystal is controlled in speed by a speed controller 4. The controller 4 controls the speed by the feedback of a revolving power generator 5. The diameter control is executed by the PID control in a PID computing circuit 7 for the diameter control and the measured value PV is obtd. by subjecting the image inputted with an industrial camera 8 to an image processing. The manipulated variable MV of the diameter control passes the upper/lower limit circuit 6 and provides the speed reference of the controller 4. The arrival of the manipulated variable (pulling-up speed reference) of the arithmetic circuit 7 at the upper and lower limits is detected by a limit detecting circuit 12 and the specified value is added and subtracted to from the temp. set value in a temp. compensating circuit 13, by which the diameter is increased or decreased.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a diameter control device for a single crystal pulling device.

(Prior art) A conventional single crystal pulling device has a silicon melt in a crucible, and uses a pulling motor to gradually pull the crystal.
It manufactures silicon single crystals, and the speed of the electric motor is controlled by a speed control device.

The speed control device is speed controlled by the feedback of the rotary generator (tacho generator), the diameter control is PID controlled by the diameter control PID calculation circuit, and the measured values are obtained by image processing input with an industrial camera. The manipulated variable for diameter control passes through the upper and lower limit circuits and becomes the speed base of the speed control device, and the temperature control is PID controlled by the temperature control PID calculation circuit, the measured value is given by the temperature sensor, and the manipulated variable for temperature control controls the current flowing through the heater, and the temperature control set point is given by a parameter as a function of the pulled length of the crystal.

When the temperature is constant, the diameter becomes smaller as the pulling speed increases, and the diameter becomes thicker as the pulling speed becomes lower.

Also, when the speed is constant, the diameter becomes smaller as the temperature increases, and the diameter becomes larger as the temperature decreases.

(Problem to be solved by the invention) If the pulling speed becomes higher or lower than a certain upper or lower limit value during diameter control, crystal breakage may occur or the characteristics may become uneven, so diameter control fal
Although upper and lower limit circuits are provided for the operation amount value of the lPID calculation circuit, if the upper and lower limit circuits are applied during diameter control, the diameter cannot be fully controlled by speed control and diameter control becomes uncontrolled.

If this state continues for a long time, it will not be possible to obtain a product with a predetermined diameter, and the product will not be of good quality.

The object of the present invention is to detect that the upper and lower limit circuits are involved, increase or decrease the set value of the temperature control PID calculation circuit, quickly escape from the upper and lower limit regions, and return to diameter control based on the pulling speed.

[Structure of the invention]

(Means for Solving the Problems) The present invention uses a diameter control device for a single crystal pulling device to detect when the diameter reaches a region where it cannot be controlled only by controlling the pulling speed, and to compensate by using a temperature of $I1ga. This is a diameter control device for a single crystal pulling device, which is characterized by pulling the diameter back from an uncontrollable region to a controllable region.

That is, this is a diameter control device for a single crystal pulling device that detects that the upper and lower limit circuits are connected and increases or decreases the temperature control set value.

(Function) When the upper and lower limits are reached, it becomes impossible to control the diameter by the pulling speed, so when the speed reference reaches the upper limit, it is desired to make the diameter thinner, but the set temperature SV is in a region that cannot be controlled by speed control. make it higher. As a result, what was within the upper limit is returned to within the upper and lower limits. On the other hand, if the speed standard reaches the lower limit, you would like to make the diameter thicker, but since it is in an area that cannot be controlled by speed control, lower the set temperature.

The temperature compensation at this time is the temperature compensation amount ΔT given in a pulsed manner.
and the time for the next temperature compensation amount can be set as parameters.

In other words, since the temperature time constant is large, the temperature compensation amount ΔT is not given as a ramp function with respect to time, and if the time applied to the upper and lower limits continues for more than a predetermined time, temperature compensation is further performed in a pulsed manner. Let it be a circuit that gives a quantity ΔT.

Letting T be the temperature set value when there is no temperature compensation, the temperature set value Tset for temperature control is expressed by the following formula.

TsetmT+ΔT (t) (Example) The present invention will be described below with reference to an embodiment shown in FIG.

There is a silicon melt 2 in a crucible 1, and a crystal is gradually pulled up by a pulling electric motor 3 to produce a silicon single crystal. The speed of the electric motor 3 is controlled by a speed control device 4, and the speed control device 4 controls the speed by feedback from a rotary generator 5. Diameter control is performed by diameter $l control PID calculation circuit 7
The measured value PV is obtained by image processing the inputted value with the industrial camera 8, and the manipulated variable MV for diameter control passes through the upper and lower limit circuit 6 and becomes the speed reference for the speed control device 4.

A limit detection circuit 12 that detects whether the upper or lower limits are reached, and a temperature compensation circuit 13 that increases or decreases the set temperature when the limits are reached are provided.

Temperature control is PID controlled by a temperature control PID calculation circuit 9, and the measured value PV is given by a temperature compensation circuit 13.

Diameter control PID calculation circuit 7 by limit detection circuit 12
It is detected that the operation m (pulling speed standard) has reached the upper limit or the lower limit. As shown in Fig. 2, a constant value is added to the temperature set value to increase the set temperature and make the diameter thinner.

Note that the addition amount is not given as a ramp function with respect to time, but is given in one shot because the time constant that actually affects the temperature is large. Similarly, when the lower limit is reached, the diameter is too small, but it is in an area that cannot be controlled by the pulling speed control, so the temperature compensation circuit 12 subtracts a constant value from the temperature set value as shown in Figure 2, and sets the temperature. lower the temperature,
Make the diameter thicker.

As a result of the above, it quickly escapes from the upper and lower limit areas,
Diameter control becomes possible by returning to diameter control based on pulling temperature.

〔Effect of the invention〕

According to the present invention, the temperature setting value is increased or decreased in steps, so that it is possible to return to diameter control based on the pulling rate and continue diameter control.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a diameter control device showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram of temperature compensation. 7...Diameter control PID calculation circuit 9...Temperature control PID calculation circuit lO...Heater 11...Temperature sensor 12...Limit detection circuit 13...Temperature compensation circuit agent Patent attorney Nori Ogo husband

Claims (1)

[Claims] An electric motor that pulls up a single crystal from a melt, a speed control device that controls the speed of this motor, an industrial camera device that monitors the melt section, and a measured value obtained by image processing the industrial camera device. PI from predetermined diameter setting value
A diameter control device for a single crystal pulling device comprising a diameter control PID calculation circuit that performs D control and outputs a manipulated variable; an upper and lower limit circuit that provides a speed reference to the speed control device based on the manipulated variable; Diameter control of a single crystal pulling device comprising a limit detection circuit that detects whether the upper and lower limits of the upper and lower limit circuits have been reached, and a temperature compensation circuit that increases or decreases the set temperature based on the signal from this limit detection circuit. Device.