JPH06316484A - Melt level controller in cz process - Google Patents

Abstract

PURPOSE:To keep the surface of a melt at 9L desired position in the production of a single crystal by the CZ process by detecting the melt surface position without being affected by the fluctuation of the melt surface. CONSTITUTION:The surface 2 of a melt is irradiated with a laser beam as the expanded parallel rays 3 from the upper part of a chamber 1. The melt surface 2 is caught by a CCD camera 4 from the oblique upper part, and the position of the center of gravity of the laser spotlight is outputted as a present value Vf. The command value Vc outputted from a command part 11 as a melt surface position and the present value Vf are compared by a controller, a driving speed command signal is outputted to the power amplifier of a servomotor for lifting a crucible shaft up and down, when the difference exceeds an allowable value, and the driving of the crucible shaft is adjusted. Since the spotlight diameter on the melt surface is large, the position of the center of gravity of the spotlight is detected by the CCD camera 4, the melt surface position is controlled with high precision regardless of the fluctuation of the melt surface 2.

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 CZ single crystal production apparatus.

[0002]

2. Description of the Related Art When a single crystal serving as a substrate of a semiconductor device 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 heater so that the melt surface is always maintained at a constant position. In controlling the melt level, first, the melt surface position must be measured, and the following means are known as such means. (1) As shown in Japanese Utility Model Laid-Open No. 3-18171, the detection light is projected obliquely from above toward the melt surface, and the reflected light from the melt surface is detected by the light receiving element to calculate the melt surface position. . (2) As shown in JP-A-2-102187, the position of the fusion ring generated in the single crystal growth portion is measured by a CCD camera to control the melt surface position. (3) As shown in Japanese Utility Model Laid-Open No. 3-96356, the melt surface position is measured by looking through the reflection image of the member provided above the melt surface with a telescope or the like provided outside the chamber.

[0003]

The above-mentioned conventional melt level measuring devices have the following problems, respectively. (1) Since the reflected light of the light projected on the melt surface is scattered in each direction due to the fluctuation of the melt surface, the detection accuracy becomes low, and the melt level is detected when the fluctuation is large. Can not do it. Therefore, it is difficult to accurately control the melt level. (2) In Japanese Patent Application Laid-Open No. 2-102187, the measurement accuracy deteriorates when the single crystal during pulling shakes. (3) In Kaikaihei 3-96356, since the reflection image of the member provided above the melt surface cannot be seen stably due to the fluctuation of the melt surface, the melt level control becomes inaccurate and the member adheres to the member. When the amorphous silicon falls, the melt is contaminated and the single crystallization rate is lowered. Therefore, the present invention pays attention to such a conventional problem, and a CZ that can always detect the melt surface position with high accuracy and control it to a desired position without being affected by the fluctuation of the melt surface. It aims at providing the melt level control device in the method.

[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 by the CZ method, in which laser light is applied as an expanded spot light to the melt surface. An optical system for irradiation, a detection system for capturing the irradiation position of the expanded spot light on the melt surface and its periphery with a CCD camera, and inputting it to a control unit, and outputting a predetermined melt surface position command signal to the control unit Command unit, and the spot position detected by the detection system and the target value of the melt surface position based on a predetermined melt surface position command signal are compared, and based on the result, the power amplifier for driving the crucible lifting motor is driven. A control system including a control unit that outputs a speed command signal is provided, and in such a configuration, the measured coordinates of the center of gravity of the expanded spot light with which the melt surface is irradiated and the predetermined melt surface position Compares the reference coordinates corresponding to the center of gravity of the definitive spot light was assumed to control the melt surface position by vertically moving the crucible so that the measured coordinate matches the reference coordinates.

[0005]

According to the above construction, since the laser light is applied to the melt surface as an enlarged spot light, the spot diameter on the melt surface becomes large, and the image is CCD regardless of the fluctuation of the melt surface. It can be captured by a camera.
Since the CCD camera detects the position of the center of gravity of the captured spot light and inputs it to the control unit, even if the spot light image fluctuates constantly due to fluctuations in the melt surface, the melt surface position is always kept under constant conditions. Can be detected. Then, the barycentric position is compared with a preset barycentric position,
By adjusting the driving of the crucible raising / lowering motor so that they match each other, the melt surface can be maintained at a predetermined 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. FIG. 1 is an explanatory view showing a schematic configuration of a melt level control device, which is not shown above the chamber 1, for example, He-
An oscillator such as a Ne laser and a beam expander are provided. The laser light oscillated vertically from the laser light oscillator toward the melt surface 2 becomes a parallel light beam 3 expanded to an arbitrary spot diameter by a beam expander,
The melt surface 2 is irradiated. A CCD camera 4 is installed diagonally above the chamber 1 and observes the melt surface 2 through the light transmission window 1a. 5 crucibles, 6 crucible shafts,
Reference numeral 7 is a crucible lifting motor, 8 is a rotation → linear motion conversion unit, and 10 is a control device body. The control device body 10 sets and outputs a value Vc of the spot position at a predetermined melt surface height, and compares the command value Vc with the current value Vf of the spot position output by the CCD camera 4. The comparison unit 12 outputs the deviation ΔV, the control unit 13 outputs the command signal Vout based on the magnitude of the ΔV, and the motor driving power amplifier 14.

The CCD camera 4 captures the condition of the melt surface including the expanded spot light irradiated onto the melt surface 2 from vertically above from an obliquely upper position. Then, the barycentric position of the image of the spot light is calculated and output. By having a large spot diameter and calculating the position of the center of gravity of the spot, it is possible to almost eliminate the influence of fluctuations in the melt surface.

FIG. 2 is a flow chart for executing the melt level control, and the numbers in the upper left of each step indicate the step number. In step 1, the preset melt level surface, that is, the command value Vc relating to the spot position on the melt surface, is read, and in step 2, the current melt surface height, that is, the spot detected by the CCD camera. The current value Vf of the center of gravity is read. Next, in step 3, the deviation ΔV = Vc-Vf between the command value and the current value is calculated, and in step 4, | ΔV | is compared with the preset allowable deviation value Ve. Be seen. If | ΔV | ≦ Ve, it is determined that the current melt surface height is within the predetermined range, and the process returns to step 2. Also, |
If ΔV |> Ve, proceed to step 5. In step 5, the operation output signal Vout = k1ΔV (where k1 is a gain constant) is output to the motor driving power amplifier. Upon receiving the operation output signal Vout, the motor driving power amplifier outputs Vd = k2.Vout (where k2 is a gain constant) to the crucible lifting motor in step 6, and in step 7, the rotation-to-linear motion conversion section operates. By vertically moving the crucible shaft, the melt surface height is adjusted to a predetermined position. Then return to step 2.

FIG. 3 is an explanatory view showing an example of image output from a CCD camera. FIG. 3A shows a state in which the current value of the melt surface position matches the melt surface height command value, and spot light on the melt surface is shown. The barycentric position of is coincident with the coordinate (0,0). (B) shows the case where the current value of the melt surface position is 20 mm above the melt surface height command value, and the center of gravity of the spot light on the melt surface is at the position of coordinates (20, 0). Further, (c) shows the case where the current value of the melt surface height is 20 mm below the melt surface height command value, and the center of gravity of the spot light on the melt surface is the position of coordinates (−20, 0). It is in. In this embodiment, the fluctuation range of the melt surface height can be up to ± 20 mm, and the control accuracy can be ± 1 mm or less.

[0010]

As described above, according to the present invention, a laser beam is irradiated as a magnified spot light on the melt surface, and the center of gravity of the magnified spot light is determined by a CCD camera installed obliquely above. Therefore, the melt surface position can always be detected with high accuracy without being affected by the fluctuation of the melt surface. Then, the calculated actual magnified spot light barycentric position is compared with a preset barycentric position, and by adjusting the driving of the crucible shaft lifting servomotor so that they coincide with each other, the melt surface can be easily adjusted to a predetermined value. It is possible to maintain the position.

[Brief description of drawings]

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

FIG. 2 is a flowchart for executing melt level control.

FIG. 3 is an explanatory diagram showing an image output example of a CCD camera,
(A) is a state in which the current value of the melt surface height matches the melt surface height command value, (b) is a state in which the current value is higher than the command value, (c) is the current value in the command Each value is lower than the value.

[Explanation of symbols]

 2 Melt surface 4 CCD camera 7 Crucible lifting motor 11 Command unit 12 Comparison unit 13 Control unit 14 Crucible lifting motor driving power amplifier

Claims (2)

[Claims] 1. A single crystal production apparatus using the CZ method,
An optical system that irradiates the melt surface with laser light as expanded spot light, a detection system that captures the irradiation position of the expanded spot light on the melt surface and its periphery with a CCD camera, and inputs it to the control unit, A command unit that outputs a liquid surface position command signal to the control unit, compares the spot position detected by the detection system and a target value of the melt surface position based on a predetermined melt surface position command signal, and 2. A melt level control device in the CZ method, comprising a control system including a control unit for outputting a drive speed command signal to a power amplifier for driving a crucible raising / lowering motor. 2. The measured coordinates of the center of gravity of the expanded spot light irradiated on the melt surface are compared with the reference coordinates corresponding to the center of gravity of the spot light at a predetermined melt surface position, and the measured coordinates are set to the reference coordinates. 2. The melt level control device according to claim 1, wherein the melt surface position is controlled by moving the crucible up and down so as to coincide with each other.