JP2844032B2 - Melt level controller in CZ method - Google Patents

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 serving as 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 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, and the following measuring devices are known. (1) As shown in Japanese Utility Model Application Laid-Open No. 3-18171, measurement in which detection light is projected obliquely toward the melt surface, and light reflected from the melt surface is detected by a light receiving element to calculate the melt level. apparatus. (2) As shown 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 television camera and the melt surface becomes a set value. A device to move up and down. (3) As disclosed in JP-A-60-42294, a device that detects the intensity of reflected light of light projected perpendicularly to the surface of a melt with a photodiode and controls the crucible axis so that the output is constant.

[0003]

In the above measuring apparatus, the reflected light of the light projected on the melt surface is scattered in each direction due to the vibration of the melt surface due to the heating of the crucible. It is difficult to control the level accurately. Further, in the measuring devices disclosed in 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 surfaces of these measuring devices are contaminated by amorphous adhesion or the like. Then, the intensity of the detection light is attenuated, and the accuracy of detecting the melt level is significantly reduced. Therefore, the present invention focuses on the above conventional problems, and always detects the melt level with high accuracy regardless of the vibration of the melt surface,
It is an object of the present invention to provide a melt level control device in a CZ method that can control the melt level.

[0004]

In order to achieve the above-mentioned object, a melt level control apparatus in a CZ method according to the present invention is a single crystal manufacturing apparatus using the CZ method, which moves up and down with the raising and lowering of a seed shaft. A position detection unit that is provided outside the furnace and measures the distance between the melt surface and the light receiving surface using regular reflection of laser light; and a position detection unit that is provided between the position detection unit and the melt surface and has an arbitrary period. Calculates the difference between a preset melt surface position and the melt surface position detected by the position detector, and moves the seed shaft and crucible shaft up and down based on the calculation result. In this configuration, the position detection unit and the optical shutter may be provided at an absolute fixed position above the outside of the furnace.

[0005]

According to the above construction, a position detecting section for measuring the distance between the melt surface and the light receiving surface by using regular reflection of a laser beam is provided on an outer portion of the furnace which moves up and down as the seed shaft moves up and down. Since an optical shutter for shuttering the laser light at an arbitrary cycle is provided between the position detection unit and the melt surface, the vibration period of the melt surface is synchronized with the oscillation period of the melt surface to oscillate the vibration of the melt surface. This makes it possible to eliminate the variation in the reflected light intensity due to the light. Therefore, by detecting stable reflected light, highly accurate melt surface position data can be obtained. Then, the control unit calculates the difference between the data detected by the position detection unit and the preset melt surface position data, and then controls the driving of the seed shaft elevating servomotor and the crucible shaft elevating servomotor. Therefore, the melt surface position can always be maintained at a predetermined position. Also, when the position detecting section and the optical shutter are provided at an absolute fixed position above the furnace, highly accurate melt surface position data can be obtained as described above.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a melt level control apparatus in the CZ method according to the present invention will be described below with reference to the drawings. FIG. 1 shows a shaft type Si single crystal manufacturing apparatus that pulls a single crystal by raising a pulling shaft.
FIG. 2 is an explanatory diagram illustrating a schematic configuration of a melt level control device according to claim 1. In the same figure, outside the upper end of the chamber 1,
A position detector 4 and an optical shutter 5 each including a laser light oscillator for projecting a laser beam perpendicular to the melt surface 3 in the crucible 2, and a light receiver for receiving the 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 with the up and down movement of the pulling shaft 6. A screw shaft 7 for raising and lowering the lifting shaft 6 is provided outside the chamber 1, and a servomotor 9 for raising and lowering the lifting shaft is provided via a timing belt 8. Crucible shaft 10 for raising and lowering crucible 2
Is moved up and down by a crucible shaft elevating servomotor 11 via an elevating mechanism (not shown).

The output wiring 12a of the command section 12 is connected to the control section 13
And transmits a command signal relating to a predetermined melt surface position and an optical shutter timing to the control unit 13. Also,
The output wiring 13a of the control unit 13 is connected to the optical shutter 5, the output wiring 13b is connected to the lifting shaft elevating servomotor 9 via the power amplifier 14, and the output wiring 13c is connected to the power amplifier 15 via the power amplifier 15. The crucible shaft elevating servomotor 11 is connected. Further, the output wiring 4a of the position detecting section 4 and the output wiring 16 of the encoder 16 mounted on the servomotor 9 for raising and lowering the pull-up shaft.
a, the output wiring 17 a of the encoder 17 mounted on the crucible shaft elevating servomotor 11 is connected to the control unit 13. Since the laser light projected on 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. Is done.

FIG. 2 is a block diagram showing the configuration of the control unit of the melt level control device in the present embodiment. Predetermined melt surface position command signal Xmc, light shutter timing command signal VDC
The output signal, that is, the command signal Xmc output from the command unit 12 shown in FIG. 1 is input and stored in the predetermined melt surface position Xmc storage means 21 in the control unit 13, and the command signal VDC is the optical shutter drive command signal VD output. After being input to the means 22, it is output to the optical shutter 5. Further, the current melt surface position Xmf detection means, that is, the melt surface position detection data by the position detection unit 4 in FIG.
Is calculated. The data P1 detected by the servomotor encoder 16 for raising and lowering the pulling shaft is input to the seed moving distance (P1 -P10) k1 calculating means 24,
The detection data P2 from the crucible shaft raising / lowering servomotor encoder 17 is input to the crucible moving distance (P2-P20) k2 calculating means 25. Here, P10 is a servo motor pulse value for raising and lowering the lifting shaft corresponding to Xmc at the time of completion of melting, that is, immediately before the start of raising the seed shaft. This is the motor pulse value. And the calculating means 24, 2
5, constants k1 and k set and stored in advance
2 The constants k1 and k2 of the setting and storage means 26 are output, and the seed moving distance (P1-P10) k1 and the crucible moving distance (P2-P20) k2 are calculated.

The above-mentioned xmf, (P1−P10) k1, (P2−
P20) The numerical values of k2 and Xmc are input to the difference ΔX calculating means 27 between the predetermined melt surface position and the current melt surface position,
The calculated value of X is input to the comparing / determining means 28 for comparing ΔX and 0. Here, when ΔX = 0, the lifting shaft elevating servomotor rotation speed v1 command signal output means 29 and the crucible shaft elevating servomotor rotation speed v2 command signal output means 30 output the lifting shaft elevating servomotor 9 and A command signal v is sent to the crucible shaft elevating servomotor 11 respectively.
1 and v2 are output. When ΔX ≠ 0, the servomotor rotational speed correction value v1 ′ calculating means 31 for raising and lowering the shaft and the servomotor rotational speed correction value v2 ′ calculating means 32 for raising and lowering the crucible shaft, and the speed correction coefficients k3 and k4 are set. V1 'and v2' are calculated by the storage means 33,
Command signals v1 ', v2' are output from the corrected rotation speed v1 'command signal output means 34 and the corrected rotation speed v2' command signal output means 35 to the lifting shaft elevating servomotor 9 and the crucible shaft elevating servomotor 11, respectively. Is done.

Next, a method for controlling the melt level by the present melt level control device will be described with reference to the flowchart of FIG. In FIG. 3, the numbers described at the left shoulder of each step are step numbers. In step 1, a command signal of a servomotor rotation speed v1 for raising and lowering the shaft and a rotation speed v2 of servomotor for raising and lowering the crucible shaft is output. In step 2, an optical shutter drive command signal VD is output. In step 3, the melt surface position data Xmf, servo motor encoder data P1, P2 and constants k1, k2 are read.
On the basis of this, in step 4, the average value xmf of Xmf, the seed axis moving distance (P1-P10) k1, the crucible moving distance (P2)
-P20) The operation of k2 is performed. In step 5, the predetermined melt surface position Xmc is read, and in step 6, the difference ΔX 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 determined whether or not ΔX is equal to 0. If ΔX = 0, the process returns to step 1, and
The rotation speed v1 of the servomotor for raising and lowering the lifting shaft and the rotation speed v2 of the servomotor for raising and lowering the crucible shaft are maintained. If .DELTA.X.noteq.0, the speed correction coefficients k3 and k4 are read in step 8, and in step 9, the correction value v1 '= v1. ± ..DELTA.
X · k3 and a correction value v2 '= v2 ± ΔX · k4 of the crucible shaft lifting / lowering servomotor rotation speed are calculated. next,
In step 10, command signals for the corrected rotational speeds v1 'and v2' are output, and the process returns to step 2.

FIG. 4 is an explanatory diagram showing a schematic configuration of the melt level control device according to the second aspect. In FIG. 1, a position detecting unit 4 including a laser light oscillator for projecting a laser beam perpendicular to a melt surface 3 in a crucible 2 and a light receiving device for receiving a laser beam reflected from the melt surface 3. The optical shutter 5 is installed at an absolutely fixed position above the chamber 1 so as not to interfere even when the lifting shaft 6 is fully extended.
The output wiring 4a of the position detector 4 and the output wiring 17a of the encoder 17 mounted on the crucible shaft elevating servomotor 11 are connected to the controller 13. The other configuration is the same as that of the first aspect, and the description is omitted.

FIG. 5 is a block diagram showing the configuration of the control unit of the melt level control device according to the second embodiment. The configuration of this block diagram has many parts in common with FIG. 2, but is simpler than the block diagram shown in FIG. 2 because there is no data input to the servomotor for lifting the shaft.
That is, the average value calculating means 23 of Xmf calculates xmf based on the current input from the melt surface position Xmf detecting means 4 and the input from the crucible shaft elevating servomotor encoder 17 and the constant k2 setting / storage means 26a. Based on the output, the crucible moving distance (P2-P20) k2 calculating means 25 calculates (P2-P20) k2. These values are input to the difference ΔX calculating means 27 between the predetermined melt surface position and the current melt surface position, and the calculated value of ΔX is input to the comparing / determining means 28 for comparing ΔX and 0. Here, when ΔX = 0, the crucible shaft elevating servomotor rotation speed v2 command signal output means 30
Command signal v2 to the crucible shaft lifting servomotor 11
Is output. If ΔX ≠ 0, then the crucible shaft lifting / lowering servomotor rotational speed correction value v2 ′ calculation means 32 and the speed correction coefficient k4 setting / storage means 33a provide v2 ′.
Is calculated, and the corrected rotation speed v2 'command signal output means 35
Command signal v2 to the crucible shaft lifting servomotor 11
Is output. A command signal v1 is output from the servomotor 9 for raising and lowering the lifting shaft to the servomotor 9 for raising and lowering the shaft.

FIG. 6 is a flowchart for executing control in the melt level control device according to the second embodiment of the present invention. In FIG. 6, the numbers described at the left shoulder of each step are step numbers. In step 1, a command signal of the crucible shaft elevating servomotor rotation speed v2 is output, and in step 2, a command signal of the pulling shaft elevating servomotor rotation speed v1 and an optical shutter drive instruction signal VD are output. In step 3, the melt surface position data Xmf, the servo motor encoder data P2 and the constant k2 are read, and in step 4, the average value xmf of Xmf and the crucible movement distance (P2 -P20) k2 are calculated in step 4. 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.
An operation of {xmf + (P2-P20) k2} is performed. At step 7, it is determined whether or not the ΔX is equal to 0. If ΔX = 0, the process returns to the step 1, and 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 determined. Keep it as it is. Also,
If .DELTA.X.noteq.0, a speed correction coefficient k4 is read in step 8, and in step 9, a correction value v2 '= v2. ± ..DELTA.X.k4 of the crucible shaft elevating servomotor rotational speed is calculated. Next, at step 10, a command signal for the corrected rotational speed v2 'is output, and the process returns to step 2.

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

[0015]

As described above, according to the present invention, C
In a single crystal manufacturing apparatus using the Z method, an outer fixed part which rises and lowers together with a seed shaft or an absolute fixed part in an upper part outside the furnace,
A melt surface position detection unit based on regular reflection of laser light and an optical shutter are provided to enable measurement without the influence of the melt surface vibration. A highly accurate melt surface position can be detected. By controlling the moving speed of the seed axis and the crucible axis based on this 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, A single crystal of high quality can be obtained. Further, in the present invention, since the position detecting unit and the optical shutter are provided outside the furnace, contamination of the optical system due to amorphous adhesion or the like can be completely prevented.

[Brief description of the drawings]

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

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 flowchart for executing control in the melt level control device shown in FIG. 1;

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

FIG. 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. 4;

[Explanation of symbols]

 2 Crucible 3 Melt surface 4 Position detection unit 5 Optical shutter 6 Pull-up shaft 9 Servo motor for raising / lowering shaft 10 Crucible shaft 11 Servo motor for raising / lowering crucible shaft 13 Control unit

Claims (2)

(57) [Claims] In a single crystal manufacturing apparatus using a CZ method, a distance between a melt surface and a light receiving surface is measured using specular reflection of a laser beam, which is provided on an outer portion of the furnace that moves up and down as the seed axis moves up and down. A position detecting unit to be provided, provided between the position detecting unit and the melt surface, an optical shutter for shuttering the laser light at an arbitrary cycle, and a position of the melt surface set in advance and detected by the position detecting unit. And a controller for calculating a difference from the melt surface position and outputting a control signal to a servomotor for raising and lowering the seed shaft and the crucible shaft based on the calculation result. Control device. 2. The melt level control device according to claim 1, wherein the position detection unit and the optical shutter are provided at an absolute fixed position above the outside of the furnace.