JPH05238877A - Melt level control unit in cz process - Google Patents

Abstract

PURPOSE:To provide the subject control unit designed to detect in high accuracy the level of a melt irrespective of melt surface vibration and, based on the result, maintain the melt at a specified level at all times. CONSTITUTION:(A) A position detector 4 to measure the distance between a melt surface 3 and a light-intercepting surface using the regular reflection of laser beams and (B) a light shutter 5 actuating synchronously with the vibration frequency of the melt surface 3 are installed outside an oven to be put to vertical motion together with a pull shaft 6. A control section 13 operates the difference between the detection data from the position detector 4 and a specified melt level data set in advance, and then gives instruction signals to the servo-motor 9 for the pull shaft's vertical motion and the servo-motor 11 for the crucible shaft's vertical motion to control these drivings, thus maintaining the melt at a specified level at all times.

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 used in a single crystal manufacturing apparatus by the CZ method.

[0002]

2. Description of the Related Art When a single crystal to be a substrate of a semiconductor device is manufactured by the CZ method, the melt level in the crucible decreases 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, the melt level must first be measured. 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]

SUMMARY OF THE INVENTION In the above measuring device, since the reflected light of the light projected on the melt surface is scattered in each direction by the vibration of the melt surface due to the heating of the crucible, the detection accuracy becomes low, and the melt It is difficult to control the level accurately. Further, in the measuring devices according to JP-A-1-83595 and JP-A-60-42294, it is necessary to dispose a reference position detector or a reflecting mirror in the chamber, and the light receiving surface of these is contaminated by adhesion of amorphous substance or the like. If so, the intensity of the detection light is attenuated, and the melt level detection accuracy is significantly reduced. Therefore, the present invention focuses on the above conventional problems, always detects the melt level with high accuracy regardless of the vibration of the melt surface,
An object of the present invention is to provide a melt level control device in the CZ method that can be controlled.

[0004]

In order to achieve the above object, a melt level control device in the CZ method according to the present invention moves up and down as a seed shaft moves up and down in a single crystal manufacturing device using the CZ method. Provided in the outside of the furnace, a position detection unit that measures the distance between the melt surface and the light-receiving surface using specular reflection of laser light, and is provided between the position detection unit and the melt surface, and any cycle Calculates the difference between the optical shutter that shutters the laser beam and the preset melt surface position and the melt surface position detected by the position detector, and moves the seed axis and crucible axis up and down based on this calculation result. A servo motor and a control unit for outputting a control signal to each servo motor may be provided. In such a configuration, the position detection unit and the optical shutter may be provided at an absolutely fixed position outside the furnace.

[0005]

According to the above construction, the position detecting section for measuring the distance between the melt surface and the light receiving surface by using the regular reflection of the laser light is provided in the outer portion of the furnace which is elevated as the seed shaft is elevated. Since the optical shutter for shuttering the laser light at an arbitrary cycle is provided between the position detection unit and the melt surface, the vibration of the melt surface is synchronized by synchronizing the vibration cycle of the melt surface and the shuttering cycle. It is possible to eliminate variations in the intensity of reflected light due to. Therefore, by detecting stable reflected light, it is possible to obtain highly accurate melt surface position data. Then, in the control unit, after calculating the difference between the detection data by the position detection unit and the preset melt surface position data, it is decided to control the drive of the seed shaft lifting servomotor and the crucible shaft lifting servomotor. Therefore, the melt surface position can always be maintained at a predetermined position. Also, when the position detector and the optical shutter are provided at an absolutely fixed position above the outside of the furnace, it is possible to obtain highly accurate melt surface position data as in the above case.

[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. 1 is attached to a shaft type Si single crystal manufacturing apparatus for pulling a single crystal by raising a pulling shaft.
It is explanatory drawing which shows schematic structure of the melt level control apparatus of Claim 1. In the figure, outside the upper end of the chamber 1,
A position detecting unit 4 and an optical shutter 5 each including a laser light oscillator that projects laser light perpendicularly to the melt surface 3 in the crucible 2 and a light receiver that receives reflected light of the laser light from the melt surface 3. Is provided. The position detector 4 and the optical shutter 5 move up and down as the pulling shaft 6 moves up and down. A screw shaft 7 for raising and lowering the pulling shaft 6 is provided outside the chamber 1, and a servomotor 9 for raising and lowering the pulling shaft is installed via a timing belt 8. Crucible shaft 10 for raising and lowering the crucible 2
Is moved up and down by a crucible shaft up / down servomotor 11 via an up / down mechanism (not shown).

The output wiring 12a of the command unit 12 is connected to the control unit 13
And transmits a command signal relating to a predetermined melt surface position and optical shutter timing to the control unit 13. Also,
The output wiring 13a of the controller 13 is connected to the optical shutter 5, the output wiring 13b is connected to the pull-up shaft lifting servomotor 9 via a power amplifier 14, and the output wiring 13c is connected to a power amplifier 15. It is connected to the crucible shaft lifting servomotor 11. In addition, the output wiring 4a of the position detector 4 and the output wiring 16 of the encoder 16 mounted on the lifting shaft lifting servomotor 9
The output wiring 17a of the encoder 17 mounted on the servo motor 11 for moving the crucible shaft up and down is connected to the control unit 13. Since the laser beam projected onto the melt surface 3 is synchronized with the vibration of the melt surface 3, for example, when the vibration frequency of the melt surface 3 is about 2 Hz, the operating frequency of the optical shutter 5 is also set to 2 Hz. To be done.

FIG. 2 is a block diagram showing the structure of the control unit of the melt level control device in this embodiment. Predetermined melt surface position command signal Xmc, optical shutter timing command signal VDC
The command signal Xmc output by the output unit, that is, the command unit 12 shown in FIG. 1 is input to and stored in the predetermined melt surface position Xmc storage unit 21 in the control unit 13, and the command signal VDC is the optical shutter drive command signal VD output. It is input to the means 22 and then output to the optical shutter 5. Further, the current melt surface position Xmf detecting means, that is, the melt surface position detection data by the position detecting section 4 in FIG. 1 is inputted to the average value calculating means 23 of Xmf, and Xmf is calculated.
The average value xmf of is calculated. The detection data P1 by the servo motor encoder 16 for raising and lowering the lifting shaft is input to the seed moving distance (P1-P10) k1 calculating means 24,
The detection data P2 by the crucible shaft raising / lowering servomotor encoder 17 is input to the crucible movement distance (P2-P20) k2 computing means 25. Here, P10 is a servo motor pulse value for raising / lowering shaft corresponding to Xmc at the time of completion of melting, that is, immediately before the start of raising the seed axis, and P20 is a servo motor for raising / lowering the crucible axis corresponding to Xmc at the time of completion of melting. It is a motor pulse value. Then, the calculation means 24, 2
5, the constants k1 and k set and stored in advance are stored.
2 The constants k1 and k2 of the setting / storing means 26 are output, and the seed moving distance (P1-P10) k1 and the crucible moving distance (P2-P20) k2 are calculated.

The above xmf, (P1-P10) k1, and (P2-
The respective values of P20) k2 and Xmc are input to the difference ΔX calculating means 27 between the predetermined melt surface position and the current melt surface position, and Δ
The calculated value of X is input to the comparison / determination means 28 for ΔX and 0. When .DELTA.X = 0, the pulling shaft raising / lowering servo motor rotation speed v1 command signal output means 29 and the crucible shaft raising / lowering servo motor rotation speed v2 command signal output means 30 are used to pull up shaft raising / lowering servo motors 9 and A command signal v is sent to each of the crucible shaft lifting servomotors 11.
1 and v2 are output. Further, when ΔX ≠ 0, the pulling shaft lifting servo motor rotation speed correction value v1 ′ calculating means 31 and the crucible shaft lifting servo motor rotation speed correction value v2 ′ calculating means 32, and the speed correction coefficients k3 and k4 are set. V1 ', v2' are calculated by the storage means 33,
The correction rotation speed v1 'command signal output means 34 and the correction rotation speed v2' command signal output means 35 output command signals v1 ', v2' to the lifting shaft lifting servomotor 9 and the crucible shaft lifting servomotor 11, respectively. To be done.

Next, a melt level control method by this melt level control device will be described with reference to the flow chart of FIG. The numbers on the left shoulder of each step in FIG. 3 are step numbers. In step 1, command signals of the pull shaft raising / lowering servo motor rotation speed v1 and the crucible shaft raising / lowering servo motor rotation speed v2 are output, and in step 2, the optical shutter drive instruction signal VD is output. In step 3, melt surface position data Xmf, servo motor encoder data P1 and P2, and constants k1 and k2 are read,
Based on this, in step 4, the average value xmf of Xmf, the seed axis moving distance (P1-P10) k1, and the crucible moving distance (P2
-P20) k2 is calculated. In step 5, the predetermined melt surface position Xmc is read, and in step 6, the difference between the predetermined melt surface position and the current melt surface position ΔX = Xmc- {xmf + (P
2−P20) k2− (P1−P10) k1} is calculated. Then, in step 7, it is judged whether or not ΔX is equal to 0. If ΔX = 0, the process returns to step 1,
The servomotor rotation speed v1 for raising and lowering the pulling shaft and the servomotor rotation speed v2 for raising and lowering the crucible shaft are maintained as they are. If .DELTA.X.noteq.0, the speed correction coefficients k3 and k4 are read in step 8 and the correction value v1 '= v1. +-.. DELTA.
X · k3 and a correction value v2 ′ = v2 ± ΔX · k4 of the rotation speed of the crucible shaft lifting servomotor are calculated. next,
In step 10, the command signals for the corrected rotational speeds v1 'and v2' are output, and the process returns to step 2.

FIG. 4 is an explanatory view showing a schematic structure of the melt level control device according to the second aspect. In the figure, a position detector 4 including a laser light oscillator that projects laser light perpendicularly to the melt surface 3 in the crucible 2 and a light receiver that receives the reflected light from the melt surface 3 of the laser light. The optical shutter 5 is installed above the chamber 1 at an absolute fixed position that does not interfere even when the pulling shaft 6 is maximally extended.
The output wiring 4 a of the position detection unit 4 and the output wiring 17 a of the encoder 17 mounted on the crucible shaft lifting servomotor 11 are connected to the control unit 13. The rest of the configuration is the same as that of claim 1, and therefore its explanation is omitted.

FIG. 5 is a block diagram showing the structure of the control unit of the melt level control device according to the second embodiment. Although the configuration of this block diagram has many parts in common with FIG. 2, it is simpler than the block diagram shown in FIG. 2 because there is no data input for the servomotor for raising and lowering the shaft.
That is, the average value calculating means 23 of Xmf calculates xmf by the input from the current melt surface position Xmf detecting means 4, and the input from the crucible shaft lifting servomotor encoder 17 and the constant k2 setting / storing means 26a. Based on the output, the crucible movement distance (P2-P20) k2 calculating means 25 calculates (P2-P20) k2. These values are input to the difference ΔX calculation means 27 between the predetermined melt surface position and the current melt surface position, and the calculated value of ΔX is input to the comparison / determination means 28 between ΔX and 0. If .DELTA.X = 0, the crucible shaft raising / lowering servomotor rotation speed v2 command signal output means 30
From the command signal v2 to the servomotor 11 for raising and lowering the crucible axis.
Is output. When ΔX ≠ 0, the crucible shaft ascending / descending servo motor rotation speed correction value v2 ′ calculating means 32 and the speed correction coefficient k4 setting / storing means 33a produce v2 ′.
Is calculated, and the corrected rotational speed v2 'command signal output means 35 is calculated.
From the command signal v2 to the servomotor 11 for raising and lowering the crucible axis.
'Is output. A command signal v1 is output from the lifting shaft lifting servo motor rotation speed v1 command signal output means 29 to the lifting shaft lifting servo motor 9.

FIG. 6 is a flow chart for executing control in the melt level control device according to the second embodiment. The numbers on the left shoulder of each step in FIG. 6 are step numbers. In step 1, a command signal of the crucible shaft raising / lowering servo motor rotation speed v2 is output, and in step 2, a command signal of the pulling shaft raising / lowering servo motor rotation speed v1 and an optical shutter drive command signal VD are output. At step 3, melt surface position data Xmf, servo motor encoder data P2 and constant k2 are read, and at step 4, the average value xmf of Xmf and crucible moving distance (P2-P20) k2 are calculated. In step 5, the predetermined melt surface position Xmc is read, and in step 6, the difference ΔX = Xmc− between the predetermined melt surface position and the current melt surface position.
The calculation of {xmf + (P2-P20) k2} is performed. Then, in step 7, it is judged whether or not ΔX is equal to 0. If ΔX = 0, the process returns to step 1, and the pulling shaft lifting servomotor speed v1 and the crucible shaft lifting servomotor speed v2 are set. Keep it as it is. Also,
If .DELTA.X.noteq.0, the speed correction coefficient k4 is read in step 8, and in step 9, the correction value v2 '= v2. +-.. DELTA.X.k4 of the crucible shaft lifting servomotor speed is calculated. Next, in step 10, the command signal of the corrected rotational speed v2 'is output, and the process returns to step 2.

In each of the above embodiments, the shaft type S is used.
Although the present invention relates to a single crystal manufacturing apparatus, the present invention is not limited to the shaft method, and claim 2 can also be applied to a winding single crystal manufacturing apparatus using a cable or the like.

[0015]

As described above, according to the present invention, C
In the single crystal manufacturing apparatus using the Z method, the outer part of the furnace that moves up and down together with the seed axis or the absolutely fixed part above the outer part of the furnace,
Since the melt surface position detection unit by specular reflection of laser light and an optical shutter are provided to enable measurement without influence of vibration of the melt surface, it is always possible to pull the single crystal regardless of vibration of the melt surface. It is possible to detect the melt surface position with high accuracy. By controlling the moving speeds of the seed axis and the crucible axis based on the detection result, the melt surface is maintained at a predetermined position, so that the fluctuation of the Oi concentration taken into the grown crystal can be reduced, It becomes possible to obtain a high quality single crystal. Further, in the present invention, since the position detector and the optical shutter are provided outside the furnace, it is possible to completely prevent the optical system from being contaminated due to adhesion of amorphous material.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a configuration of a control unit of the melt level control device shown in FIG.

FIG. 3 is a flow chart for executing control in the melt level control device shown in FIG.

FIG. 4 is an explanatory diagram showing a schematic configuration of a melt level control device according to claim 2;

5 is a block diagram showing a configuration of a control unit of the melt level control device shown in FIG.

FIG. 6 is a flowchart for executing control in the melt level control device shown in FIG.

[Explanation of symbols]

 2 crucible 3 melt surface 4 position detector 5 optical shutter 6 pulling shaft 9 pulling shaft up / down servo motor 10 crucible shaft 11 crucible shaft up / down servo motor 13 control unit

Claims (2)

[Claims] 1. In a single crystal manufacturing apparatus using the CZ method, the distance between the melt surface and the light receiving surface is measured by using specular reflection of laser light, which is provided in an outer portion of the furnace that moves up and down as the seed axis moves up and down. Position detector, an optical shutter provided between the position detector and the melt surface, for shuttering the laser light at an arbitrary cycle, and the preset melt surface position and the position detector detected A melt level in the CZ method, which comprises: a controller for calculating a difference from the melt surface position, and for outputting a control signal to each of servo motors for raising and lowering the seed axis and the crucible axis based on the result of the operation. Control device. 2. The melt level control device according to claim 1, wherein the position detector and the optical shutter are provided at absolutely fixed positions above the outside of the furnace.