JPH05194080A - Apparatus for controlling molten liquid level in cz process and controlling method - Google Patents

Abstract

PURPOSE:To provide an apparatus and a method for controlling the molten liquid level in CZ process by detecting the molten liquid level in high accuracy independent of the oscillation of the liquid level and maintaining the position of the liquid level at a definite state relative to a heater. CONSTITUTION:A laser beam from a laser beam oscillator 2 placed above a chamber 1 is converted to a scanning light having a specific frequency and a specific scanning angle with a light scanner 3 and the scanning light is projected to a molten liquid surface 6. The scanning width of the scanning light formed on the molten liquid surface is detected by a CCD camera 7. A controller 8 compares the detected scanning width Lf with a target scanning width L0 and drives a crucible shaft driving servo-motor 12 until the difference falls within a limit range. Since the scanning width is remarkably large compared with the projected light spot diameter used in conventional molten liquid level measuring apparatus, the apparatus is insusceptible to the oscillation of the molten liquid surface to enable the control of the molten liquid level in high accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a melt level control device and control method for use in a CZ single crystal production apparatus.

[0002]

2. Description of the Related Art When a single crystal to be a substrate of a semiconductor element is manufactured by the CZ method, the melt level in the crucible drops as the single crystal grows, but the crucible shaft is driven to obtain a good quality single crystal. It is necessary to raise the crucible and control the position of the melt level relative to the heater to be constant.
In controlling the melt level, it is necessary to measure the melt level first, and the following measuring devices are known. (1) As shown in Japanese Utility Model Laid-Open No. 3-18171, a detection light is projected obliquely toward the melt surface, the reflected light from the melt surface is detected by a light-receiving element, and the melt level is calculated. apparatus. (2) As disclosed in JP-A-1-83595, after measuring the distance between the reference position detector and the melt surface, the crucible shaft is set so that the distance between the image sensor of the TV camera and the melt surface becomes a set value. A device for moving up and down. (3) As disclosed in JP-A-60-42294, a device for detecting the reflected light intensity of light projected perpendicularly to the melt surface with a photodiode and controlling the crucible axis so that the output becomes constant.

[0003]

Since the melt surface constantly vibrates due to the heating of the crucible, the reflected light of the light projected on the melt surface is scattered in each direction. On the other hand, since all the measuring devices described above have a light flux with a diameter of about 1 mm, the scattering lowers the detection accuracy, and it is difficult to accurately control the melt level. Therefore, the present invention focuses on the above-mentioned conventional problems, and a melt level control device and control method in the CZ method capable of always detecting and controlling the melt level with high accuracy regardless of the vibration of the melt surface. The purpose is to provide.

[0004]

In order to achieve the above object, a melt level control apparatus in the CZ method according to the present invention is a single crystal manufacturing apparatus using the CZ method, in which coherent light is emitted at a predetermined frequency by an optical scanner. An optical system for converting the scanning light of a predetermined scanning angle and projecting it onto the melt surface from above the chamber; a detection system for detecting the scanning width of the scanning light on the melt surface and inputting it to the control unit; and a predetermined crucible. A crucible position command unit that outputs a position command signal to the control unit, the width of the scanning light detected by the detection system, and a target value of the width of the scanning light based on a predetermined crucible position command signal are compared, and the result is obtained. And a control system for outputting a drive speed command signal to a power amplifier for a servomotor based on the above, and the melt level control method using the melt level control device is such that the melt surface is projected from above the chamber onto the melt surface. The scanning width Lf of the scanning light on the melt surface is compared with the target value L0 of the scanning width based on the crucible position command signal X0 output from the crucible position command section. Crucible position command signal X
When the driving speed command signal v0 of the crucible shaft lifting servomotor based on 0 is output to the servomotor power amplifier and the difference exceeds the limit value, the crucible position command signal X
After calculating the correction value ΔX of 0, the servomotor drive speed command signal v1 based on X0 ± ΔX is output to the servomotor power amplifier, and the crucible position Xf calculated from the rotation angle of the servomotor and the X0 was compared and the difference was controlled to be below the limit value.

[0005]

According to the above construction, since the coherent light is converted into the scanning light having the predetermined frequency and the predetermined scanning angle and projected onto the melt surface from above the chamber, the melt surface is formed by the conventional detection light. It is possible to form an optical scanning width that is significantly longer than the spot diameter that is generated. Therefore, such an optical scanning width can be made less susceptible to the vibration of the melt surface due to heating of the crucible, and the melt level measurement accuracy can be improved. Then, by measuring the scanning width of the scanning light formed on the melt surface, by controlling the driving of the crucible shaft lifting servomotor so that this scanning width always maintains a constant value, to the heater The crucible position can be controlled so that the melt level is always at the optimum position.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a melt level control device in the CZ method according to the present invention will be described below with reference to the drawings. In FIG. 1, for example, a laser light oscillator 2 that oscillates coherent detection light outside the upper part of a chamber 1, and an optical scan below the laser light oscillator 2 that drives a mirror at a predetermined swing angle θ and at a predetermined frequency. Is provided with
A bender mirror 4 is provided in the chamber 1. Further, a light transmission window 1a is attached to the outer wall of the chamber 1, and the laser light emitted from the laser light oscillator 2 is
The light is refracted by the bender mirror 4 through the optical scanner 3 and the light transmission window 1a and projected onto the melt surface 6 in the crucible 5.

The CCD camera 7 for detecting the optical scanning width formed on the melt surface 6 is fixed to the outside of the light transmission window 1b provided in the chamber 1, and the output wiring 7 of the CCD camera 7 is provided.
a is connected to the control unit 8. The output wiring 9a of the crucible position command unit 9 is also connected to the control unit 8.
The output wiring 8a of the control unit 8 is the power amplifier 1 for the optical scanner.
0 is connected to the optical scanner 3, and the output wiring 3a of the optical scanner 3 is connected to the power amplifier 10. The output wiring 8b of the control unit 8 is connected to a crucible shaft raising / lowering servomotor 12 via a servomotor power amplifier 11, and a crucible shaft 13 for raising / lowering the crucible 5 is connected to the crucible shaft via an elevator mechanism (not shown). Servo motor for lifting 1
Move up and down by 2. The output wiring 12 a of the encoder that detects the rotation angle of the servo motor 12 and converts it into a pulse value is connected to the control unit 8.

The optical scanning width L on the melt surface 6 of the scanning laser light projected on the melt surface 6 via the optical scanner 3 and the bender mirror 4 is as shown in FIGS. It becomes long over a plurality of vibration waveforms formed on the liquid surface, and is significantly larger than the spot diameter formed on the melt surface by the conventional melt level measuring device. Also, the frequency of the melt surface is 2
The predetermined frequency of the scanning laser light is set to, for example, 20 Hz with respect to about Hz. The CCD camera 7 detects this scanning width L and outputs it to the control unit 8.

FIG. 4 is a block diagram showing the structure of the melt level control device in this embodiment. The crucible position command signal X0 output means, that is, the command signal X0 output from the crucible position command section 9 shown in FIG. 1 is input to the target value L0 setting / storing means 21 of the optical scanning width in the control section 8, and the target scanning width is set. A limit value of the difference between L0 and the actual scanning width Lf, that is, the control limit value Δl storage means 22 stores the limit value Δl.

On the other hand, the scanning mirror swing angle θ and the frequency ω, the command signal output from the command signal output means 20 to the optical scanning power amplifier 10 causes the scanning mirror of the optical scanner 3 to swing at the swing angle θ and the frequency ω. To drive. Then, the scanning width Lf formed on the melt surface 6 of the scanning laser light projected on the melt surface 6 via the bender mirror 4 is detected by the light scanning width Lf detecting means, that is, the CCD camera 7, and | L0 − Lf
| Is input to the calculating means 23. Based on the calculation result and the output of the control limit value Δl storage means 22, Δl and | L0
-Lf │comparison / determination means 24 for Δl and │L 0 -Lf
Compare with |. If | L0-Lf | is less than .DELTA.l, the servo motor drive speed command signal v0 output means 25
Outputs v0 based on X0 to the servomotor power amplifier 11, and when | L0-Lf | exceeds .DELTA.l, the servo motor drive speed command is sent via the correction value. +-.. DELTA.X calculating means 26 of X0. The signal v1 output means 27 uses the X0 ±
V1 based on ΔX is output to the servomotor power amplifier 11. The crucible shaft lifting servomotor 12 is driven by the servomotor power amplifier 11, and the crucible shaft 13 moves up and down.

Further, the crucible position Xf calculating means 28 calculates Xf on the basis of the output of the servo motor rotation angle detecting means for detecting the rotation angle of the servo motor 12 and converting it into a pulse value, that is, | X0 -Xf | Limit value ΔXL of the difference between the calculation result of the calculation means 29 and the crucible position
Limit value ΔX of the difference between X0 and Xf output by the storage means 30
From L and .DELTA.XL and .vertline.X0 -Xf.vertline., The comparison / determination means 31 compares the two. The result is fed back to the servo motor drive speed command signal v0 output means 25 or the servo motor drive speed command signal v1 output means 27.

Next, a melt level control method by the melt level control device will be described with reference to the flow chart of FIG. 5 and FIG. The numbers on the upper left of each step in FIG. 5 are step numbers. First, step 1
The crucible position command signal X0 is read, and in step 2, the target scan width L0 based on the command signal X0, the actual scan width Lf detected by the CCD camera 7, and the control limit value Δl of the difference between L0 and Lf are read. Be done. In step 3, | L
The calculation result of 0-Lf | is compared with the control limit value Δl. If Δl ≧ | L0-Lf |
Output to. Also, in step 3, Δl <| L0-Lf |
In the case of 1, the crucible position command signal X0 is corrected to X0 ± ΔX, and the servomotor drive speed command signal v1 based on the X0 ± ΔX is output to the servomotor power amplifier 11.

In step 6, the crucible position displaced by the servo motor drive speed command signal v0 or v1 is
It is detected by the rotation angle of the crucible shaft elevating / lowering servo motor 12, calculated by the pulse signal output from the encoder 14, and read as the crucible position Xf. Then in step 7, X0 and X
The difference between f and the limit value ΔXL of the difference is compared. If .DELTA.XL.gtoreq..vertline.X0-Xf.vertline., The melt level determination is started and the process returns to step 2. Also, ΔXL <| X0
If -Xf |, return to step 5.

In this embodiment, the bender mirror is installed above the inside of the chamber. However, the present invention is not limited to this. May be projected onto the melt surface.

[0015]

As described above, according to the present invention, when controlling the melt level in the single crystal manufacturing apparatus, the coherent light is converted into the scanning light having the predetermined frequency and the predetermined scanning angle by the optical scanner, and the coherent light is emitted above the chamber. From the projection on the melt surface, because it was a melt level control device and control method for controlling the raising and lowering of the crucible by detecting the scanning width of the scanning light formed on the melt surface, unlike conventional measuring devices, The melt level can be controlled with high accuracy without being affected by the vibration of the melt surface. Therefore, it becomes possible to easily maintain the melt level to the heater constant, it is possible to reduce the fluctuation of the Oi concentration taken into the grown crystal, and it is possible to obtain a high-quality single crystal. .

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of a melt level control device.

FIG. 2 is a side view of scanning light projected on the melt surface.

FIG. 3 is an explanatory plan view of an optical scanning width formed on a melt surface.

FIG. 4 is a block diagram showing a configuration of a melt level control device.

FIG. 5 is a flowchart for executing control of a melt level control device.

[Explanation of symbols]

 1 Chamber 2 Laser Light Oscillator 3 Optical Scanner 6 Melt Surface 7 CCD Camera 8 Control Unit 9 Crucible Position Command Unit 11 Servo Motor Power Amplifier 12 Crucible Axis Lifting Servo Motor 13 Crucible Axis

Claims (2)

[Claims] 1. An optical system for converting a coherent light into a scanning light having a predetermined frequency and a predetermined scanning angle by an optical scanner, and projecting the coherent light onto a melt surface from above the chamber in a single crystal manufacturing apparatus using the CZ method; A detection system that detects the scanning width of the melt surface of light and inputs it to the control unit, a crucible position command unit that outputs a predetermined crucible position command signal to the control unit, and the width of the scanning light detected by the detection system. And a target value of the width of the scanning light based on a predetermined crucible position command signal, and based on the result, a control system that outputs a drive speed command signal to the power amplifier for the servo motor, A melt level control device for the CZ method. 2. A scanning width Lf of the scanning light projected onto the melt surface from above the chamber on the melt surface is compared with a target value L0 of the scan width based on the crucible position command signal X0 output from the crucible position command section. , If the difference is less than the control limit value,
When the driving speed command signal v0 of the crucible shaft lifting servomotor based on the crucible position command signal X0 is output to the servomotor power amplifier and the difference exceeds the limit value,
After calculating the correction value ΔX of the crucible position command signal X0, the driving speed command signal v1 of the servo motor based on X0 ± ΔX is output to the power amplifier for the servo motor and calculated from the rotation angle of the servo motor. 2. The melt level control method using the melt level control apparatus according to claim 1, wherein the crucible position Xf is compared with the X0 and the difference is controlled to be equal to or less than a limit value.