JPH09263486A - Apparatus for pulling single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus for pulling a single crystal capable exactly measuring the surface temp. of a fused liquid. SOLUTION: A quartz window 8 is disposed on the upper wall of a chamber 5 existing above a crucible 1 and a radiation thermometer 7 for measuring the temp. at the approximate center of the fused liquid boundary between the single crystal 6 and the fused liquid 2 through the quartz window 8 is installed on the outer side of the quartz window 8. An arithmetic section 10 for calculating the measured value of the temp. from the signal outputted by the radiation thermometer 7 is connected to the radiation thermometer. Further, an electric power supply control section 11 for controlling the output of the heater 3 is connected to the arithmetic section 10. A stray light removing plate 9 is disposed in the position of a radiation source (or the position of a reflection source) of the incident stray light on the position where the stray light is measured by the radiation thermometer 7 in the upper wall of the chamber 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal pulling apparatus equipped with means for measuring the surface temperature of a melt in a crucible.

[0002]

2. Description of the Related Art There are various crystal growth methods,
One of them is the Czochralski method (CZ method). CZ
In the method, the seed crystal is immersed in the molten raw material filled in the crucible,
By pulling the seed crystal upward, the melt contacting the lower end of the seed crystal is solidified and the crystal grows.

During crystal growth, it is necessary to maintain the melt at an optimum temperature in order to maintain its quality. In particular, since the temperature of the surface of the melt has a great influence on the growth and quality of crystals, various crystal pulling apparatuses capable of measuring the temperature have been proposed. Therefore, as a first proposal, there is a device using a thermocouple. However, when a thermocouple is used, the life of the thermocouple is short because the temperature of the melt is high (about 1400 ° C in the case of silicon). Since the thermocouple is a contact-type measuring means, impurities are not mixed in the melt. There is a problem that crystal quality is adversely affected. Therefore, it is practically impossible to continuously measure the melt temperature during crystal pulling using a thermocouple.

Next, the use of a radiation thermometer, which is a non-contact type measuring means, has been proposed. The radiation thermometer measures the temperature by utilizing a phenomenon in which the luminance of thermal radiation emitted from the measurement target is determined by the temperature of the measurement target and its emissivity. When this radiation thermometer is used for measuring the melt temperature, the problem that impurities are mixed in the melt is solved, and continuous measurement can be performed even during crystal pulling.

FIG. 4 is a schematic vertical sectional view showing a conventional crystal pulling apparatus using a radiation thermometer. Reference numeral 5 in the drawing denotes a chamber having a circular shape in cross section, and a pull chamber 12 having a diameter smaller than that of the chamber 5 is connected thereabove at the same axis. A crucible 1 is arranged in the chamber 5, and the crucible 1
A heater 3 having a cylindrical shape concentric with the crucible 1 is provided around the outside of the. Further, a heat insulating cylinder 4 is arranged on the outer circumference of the heater 3. Also, a seed crystal is attached to the tip of the seed chuck.
A lifting shaft (wire) 14 capable of attaching and detaching 13 is exposed above the center of the crucible 1.

A window 5a is provided on the side wall of the chamber 5 at a position corresponding to the surface of the melt 2 in the crucible 1, and a window 5a is provided outside the window 5a for the heat insulating cylinder 4 located near the surface of the melt 2. A radiation thermometer 7 for measuring the temperature from the lateral direction is installed. The radiation thermometer 7 is connected to a calculation unit 10 which calculates a temperature measurement value from a signal output from the radiation thermometer 7, and a power supply control unit 11 which controls the output of the heater 3 is connected to the calculation unit 10.

The radiation thermometer 7 measures the brightness of thermal radiation light incident on the radiation thermometer 7 and outputs the result to the arithmetic unit 10. Arithmetic unit
Reference numeral 10 converts the input signal into a measured temperature and supplies it to the power supply controller 11. As a result, the power supply controller 11 causes the heater 3 to
Is controlled to maintain the temperature of the melt 2 at a predetermined temperature.

However, with the increase in size of the crystal pulling apparatus, as shown in FIG. 4, the measured temperature measured from the outside through the heat-retaining cylinder 4 includes an error from the actual melt surface temperature,
Accurate measurement is difficult. Further, in a large-sized apparatus, since the heat capacity of the high temperature portion is extremely large, the temperature difference between the melt 2 and the vicinity of the heater 3 is large, and thermal convection of the melt 2 occurs. Therefore, the surface temperature of the melt 2 changes with time, and it is very difficult to accurately measure the temperature by following the change.

In order to overcome such a problem, it is necessary to directly measure the surface of the melt 2 with the radiation thermometer 7 from above. However, in this case, the following problems newly arise. That is, the inner surface of the apparatus (chamber 5) is formed of a material having a relatively high reflectance, and heat radiation from the wall surface of the crucible 1 in contact with the melt 2 or a high temperature portion such as the heater 3 is generated in the furnace. And is incident on the radiation thermometer 7 (FIG. 5). Then, this reflected light is measured by the radiation thermometer 7 together with the heat radiation light from the melt surface, so that an error occurs between the actual melt surface temperature and the measured value. The emitted light that causes such a measurement error is called stray light. If the reflectance inside the furnace is lowered, the effect of stray light can be reduced, but if the state of the entire furnace inner surface is changed, the crystal quality is greatly affected.

A melt temperature measuring device for a single crystal growth furnace for reducing the influence of stray light and improving the measurement accuracy is disclosed in Japanese Patent Laid-Open No. 58-16.
It is disclosed in Japanese Patent No. 8927. In this device, the polarizing film and the optical detector are arranged above the melt with their optical axes being the same so that the heat radiation light from the surface of the melt enters in this order. Light emitted from the melt passes through a polarizing filter and then strikes an optical detector. The optical detector detects the thermal radiation spectrum of the thermal radiation from the melt and measures its temperature, and based on the measurement result, the heating power of the heater is adjusted and the melt temperature is controlled. The optical detector used here is one that detects only a wavelength component shorter than the wavelength corresponding to the maximum spectral emissivity at the melting point of the melt. As a result, the signal-to-noise ratio is significantly improved as compared with the case where the measurement is performed using a normal radiation thermometer. Further, since the heat radiation light passes through the polarizing filter, stray light reflected and incident on the surface of the melt can be removed.

[0011]

However, even in this conventional apparatus, it is difficult to completely remove the stray light reflected by the surface of the melt and incident on the optical detector, and it cannot be inferred from the measurement results. . The inventors of the present invention have proposed a method for measuring the surface temperature of a melt in a single crystal furnace, which is improved in this respect, in Japanese Patent Application No. 6-1299
Proposed in No. 11 publication. In this method, the radiation light from the melt is measured with a radiation thermometer during the single crystal growth process, while the temperature of the radiation source of the reflected light (stray light) from the high temperature part inside the furnace that enters the radiation thermometer is measured. Then, correct the value measured by the radiation thermometer. Therefore, the stray light component is removed from the luminance of the thermal radiation incident on the radiation thermometer, and the temperature of the melt surface can be measured with good followability and high accuracy. Further, since the melt surface is directly measured, the temperature followability and the measurement accuracy are improved as compared with the case where the temperature is measured from the outside of the heat retaining tube, and the temperature control during pulling of the single crystal can be more accurately performed.

When the surface temperature of the melt is measured by using the radiation thermometer which utilizes the heat radiation light from the high temperature melt as described above, the heat radiation light from the high temperature part in the furnace is inside the furnace body. Stray light is also measured because it is diffusely reflected at the point B, reflected on the surface of the melt to be measured, and enters the radiation thermometer as stray light. However, since the surface of the melt is a mirror surface, it is known that the radiation source of stray light is limited to an extremely narrow portion reflected on the surface of the melt, and the temperature at this portion (radiation source of stray light) is measured and If corrected, the accuracy of the melt surface temperature measurement will be greatly improved. In this case, the position of the stray light radiation source that fluctuates due to fluctuations in the liquid surface is measured in real time using an image processing device that uses laser light, and by measuring the temperature at the position of the detected stray light radiation source, A method for highly accurately correcting stray light components from the thermal radiance incident on the radiation thermometer is also proposed (Japanese Patent Application No. 7-243911).
issue). However, this device has the drawback of being bulky.

The present invention has been made in view of such circumstances, and by providing a stray light removing plate for removing the stray light incident on the radiation thermometer or its influence, the surface temperature of the melt can be accurately measured. It is an object of the present invention to provide a single crystal pulling apparatus capable of performing various measurements.

[0014]

According to the first and second aspects of the present invention, in a single crystal pulling apparatus equipped with means for measuring the surface temperature of the melt in the crucible, the heat radiation light from the surface of the melt is measured. It is provided with a radiation thermometer and a stray light removing plate provided at a radiation source position or a reflection source position of stray light incident on the melt surface position to be measured. For example, the stray light removing plate is provided on the inner surface of the chamber ceiling wall.

As a result, for example, the stray light that enters the measurement region by using the chamber wall surface as the radiation source is reduced, so that the thermal radiation brightness measured by the radiation thermometer is mostly derived from the surface temperature of the melt. . Therefore, the surface temperature of the melt can be accurately measured without requiring a large-scale device as in the conventional case.

According to the inventions of claims 3 and 4, in claim 1, the stray light removing plate has a switchable plate made of a plurality of materials having different reflectances, and a switching means for switching the plurality of plates. And a calculating means for calculating the surface temperature of the melt by correcting the stray light component from the value measured by the radiation thermometer when each plate is installed. For example, the switching means includes a frame portion that holds the plurality of plates in a horizontal direction, a rail portion that slides the frame portion in the horizontal direction, and a drive that moves the frame portion along the rail portion. And a means for operating the driving means externally.

Even when stray light originating from an object having a high emissivity and a high temperature, such as a heater, has a great influence, the measured value by the radiation thermometer is accurately corrected to remove the stray light component. be able to.

According to a fifth aspect of the present invention, in the third and fourth aspects, a means for controlling the output of the heater for heating the melt based on the value obtained from the calculating means is provided.

Since the output of the heater is automatically controlled by this, it becomes easy to always maintain the surface temperature of the melt at a predetermined temperature.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. Embodiment 1 FIG. 1 is a schematic vertical cross-sectional view showing a crystal pulling apparatus according to Embodiment 1. Reference numeral 5 in the drawing denotes a chamber having a circular shape in cross section, and a pull chamber 12 having a diameter smaller than that of the chamber 5 is connected thereabove at the same axis. A crucible 1 is arranged in the chamber 5, and the crucible 1 is provided outside the crucible 1.
A heater 3 having a concentric cylindrical shape is provided around. Further, a heat insulating cylinder 4 is arranged on the outer circumference of the heater 3. Further, a pulling shaft (wire) 14 capable of detaching the seed crystal 13 at the tip of the seed chuck faces the upper center of the crucible 1.

A quartz window 8 is provided on the upper wall of the chamber 5 located above the crucible 1, and outside the quartz window 8, a quartz window 8 is provided.
A radiation thermometer 7 for measuring the temperature at the approximate center of the melt interface between the single crystal 6 and the melt 2 through a quartz window 8 is installed. The radiation thermometer 7 is connected to a calculation unit 10 which calculates a temperature measurement value from a signal output from the radiation thermometer 7, and a power supply control unit 11 which controls the output of the heater 3 is connected to the calculation unit 10.

A stray light removing plate 9 is provided at the radiation source position (or the reflection source position) on the upper wall of the chamber 5 for the stray light incident on the position measured by the radiation thermometer 7. The stray light removing plate 9 is preferably made of a material such as a graphite plate which does not contain impurities in the melt 2 and has a low reflectance (for example, about 0.9).

Further, the stray light removing plate 9 is attached to the cooled furnace body portion or cooling means so that the stray light removing plate 9 becomes high in temperature due to radiant heat and does not affect the measurement value of the radiation thermometer 7. Shall be provided. Since the crucible 1 is raised as the melt 2 decreases due to the growth of the single crystal 6, the relative positions of the stray light removal plate 9, the surface of the melt 2 and the radiation thermometer 7 do not change significantly. Therefore, the size of the stray light removing plate 9 may be determined by the installation positions of the stray light removing plate 9 and the radiation thermometer 7, and the fluctuation of the melt.

Next, a temperature measuring method for pulling a single crystal by the single crystal pulling apparatus according to the present invention will be described. Seed crystals in the molten raw material (melt 2) filled in the crucible 1.
By soaking 13 and pulling the seed crystal 13 upward, the melt 2 in contact with the lower end of the seed crystal 13 solidifies to grow the crystal 6. The radiation thermometer 7 measures the brightness of thermal radiation light incident on the interface between the crystal 6 and the melt 2 and outputs the result to the calculation unit 10. When the emissivity of the melt surface is ε _S , the reflectivity of the melt surface is 1-ε _S. Therefore, when the stray light removal plate 9 is installed, the radiant light luminance L measured by the radiation thermometer 7 is (1) It can be expressed as an expression.

[0025]

[Equation 1]

The first term ε _S L _b (T _S ) is the heat radiation component from the melt surface point A, and the second term (1-ε _S ) {ε _c
L _b (T _c ) + (1−ε _c ) L _b (T _H )} indicates the component from the stray light elimination plate 9. Among them, the term of ε _c L _b (T _c ) is the component of the radiation term from the stray light elimination plate 9, and (1-
The term ε _c ) L _b (T _H ) represents the component of the reflected light from the high temperature part in the furnace which is diffused and reflected on the stray light removing plate 9. Here, when the temperature of the stray light removing plate 9 is 800 ° C. or less, the influence of the former term on the melt temperature measurement value is 1 ° C. or less and can be ignored. Therefore, the stray light removing plate 9 is attached to the cooled furnace body portion or has a cooling means.
Then, by actually installing a thermocouple and measuring the temperature of the stray light removing plate 9, it was confirmed that the temperature did not exceed 800 ° C. In the latter term, if the brightness temperature of stray light is 1000 ° C or less and the reflectance of the stray light removal plate 9 is 0.9 or more, the influence on the measured melt temperature is 1 ° C.
It is below and can be ignored. Under such conditions, there is no effect of stray light on the radiant light luminance measured by the radiation thermometer, and it is possible to directly convert L in equation (1) into temperature.

As described above, since the surface of the melt is a mirror surface, the stray light incident on the measurement point A is reflected by the point B.
It is possible to limit to points. Therefore, by installing the stray light removing plate 9 having a low reflectance at the point B, it is possible to reduce the stray light entering the radiation thermometer 7 without affecting the crystal quality. In addition, since the surface of the melt fluctuates due to the effects of heat convection, its tilt angle changes, and
The positions of the dots are also changing. However, stray light removal plate 9
Has a size including point B when the melt surface fluctuates, so that a sufficient stray light removing effect can be obtained.

Second Embodiment Even if only the stray light removing plate 9 is provided as in the first embodiment,
Although the effect of removing stray light is obtained, the radiated light from the heater 3 may be the main cause of stray light depending on the furnace body structure and the installation position of the thermometer. Since the heater 3 has a high emissivity and a high temperature, even if the reflectance of the stray light removing plate 9 satisfies the above-mentioned conditions, the brightness temperature T _H becomes very large and the influence of stray light cannot be ignored. is there.

Therefore, in this embodiment, the stray light removing plate 9 having plates made of two kinds of materials having different reflectances is used. FIG. 2 is a schematic vertical sectional view showing a single crystal pulling apparatus according to the second embodiment. These two types of plates are attached by a slide mechanism so that they can be switched during temperature measurement. By operating an operating unit 15 provided outside the device, the drive unit of the slide mechanism is controlled to control the plates. You can switch between. The reflectance of one of the two types of plates forming the stray light removal plate 9 does not need to be 0.9 or more, but the scattering characteristics of the two types of stray light removal plate 9 need to be the same. In this embodiment, one is a graphite plate (reflectance 0.9) and the other is a SiC plate (reflectance 0.8).
And The other configurations are the same as those in the first embodiment, and the same reference numerals are given and the description thereof is omitted.

The sliding mechanism of the stray light removing plate 9 will be described with reference to FIG. 3, which is a bottom view thereof. Graphite plate 9a (150
mm × 150 mm) and the SiC plate 9b (150 mm × 150 mm) are held in parallel by a frame 21, and the frame 21 has a rail 22 having a width corresponding to the frame 22 fitted to a rail plate 23 attached to the back side. Are held together. The rail 22 has a belt-like shape, and the drive unit 24 connects the rail 22 to the rear surface of the rail plate 23.
By rotating on the surface, the frame 21 slides in the arrow direction.

A coolant passage is provided inside the frame 21 and the rail plate 23. A refrigerant pipe 26 is provided at the inlet and outlet of the refrigerant passage of the frame 21 via a flexible tube 25.
Are connected. A refrigerant pipe 27 is connected to the inlet and outlet of the refrigerant passage of the rail plate 23. Refrigerant such as cooling water is supplied to the refrigerant pipes 26 and 27 from the outside of the device, and the refrigerant that circulates in the frame 21 and the rail plate 23 to cool them is discharged to the outside through the refrigerant pipes 26 and 27. It has been done. Since the flexible tube 25 is connected to the frame 21, it does not hinder the movement of the frame 21.

Further, a thermocouple 28 is attached to the surface of the frame 21, and is connected by a conductor 29 to a temperature measuring device 16 provided outside the device.

Although FIG. 3 shows a configuration in which two types of plates are switched by sliding on a straight line, the present invention is not limited to this, and for example, a configuration in which two types of plates are installed in the circumferential direction and rotated to switch Good.

The measuring method in the second embodiment will be described. The measurement by the radiation thermometer 7 is performed by setting one plate, and then operating the operation unit 15 in the middle of pulling up to switch to the other stray light removing plate 9 having a different reflectance by the above-mentioned slide mechanism, and the brightness of the stray light is changed. check the temperature T _H to perform the correction. The measured brightness in each case using the two kinds of stray light removing plates 9 can be expressed as in equations (2) and (3). If the scattering characteristics are the same, the brightness temperature T _{H of the} stray light is the same, and if it is a short time, the melt surface temperature T _S is also the same. Therefore, the difference in the measured luminances obtained by using the two types of stray light removing plates 9 is given by equation (4).

[0035]

[Equation 2]

Here, the radiation from the stray light removing plate 9 is ignored.
The brightness L of the stray light source is_b(T_H) Is
 It can be calculated by equation (5). And from the melt surface
Thermal radiation component ε of_SL_b(T_S) Can be calculated using equation (6).
And the thermal radiation component ε _SL_b(T_S) From the melt table
Surface temperature T_SIs calculated.

[0037]

(Equation 3)

The calculation unit 10 includes the equations (5), (6), τ_W, Ε_S,
ε_c1, Ε_c2, And the temperature conversion formula are preset. Performance
The calculation unit 10 calculates the temperature of the two types of stray light removing plates 9 based on the equation (5).
Degree T _C1, T_C2, Output L of radiation thermometer 7₁, L_TwoFrom stray light
Radiance of radiation source L_b(T_H) Is calculated, and the
From the formula, melt surface temperature T_SAsk for. This value is the power supply
It is supplied to the control unit 11, which causes the power supply control unit 11 to be turned off.
The output of the rotor 3 is controlled to maintain the temperature of the melt 2 at a predetermined temperature.
I do.

[0039]

EXAMPLE An actual stray light removing plate 9 having two types of plates
The melt temperature was measured with and without (Embodiment 2) installed. In the present invention apparatus installed stray light removing plate 9, the brightness temperature T _H of the stray light by (5) 1200
℃, and the melt surface temperature T _S is 1500 ℃ according to the formula (6).
Was asked. Further, the melt surface temperature T _S by the conventional apparatus is
It was 1430 ° C., and there was an error of about 70 ° C. from the value measured by the device of the present invention. From this result, it was confirmed that the error of the device of the present invention due to the influence of stray light was eliminated.

[0040]

As described above, the single crystal pulling apparatus according to the present invention is provided with the stray light removing plate for removing the influence of the stray light incident on the radiation thermometer, so that the melt can be melted with a simple apparatus configuration. The surface temperature can be measured accurately. This makes it possible to control and improve the quality of the pulled single crystal, and the present invention has excellent effects.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view showing a single crystal pulling apparatus according to a first embodiment.

FIG. 2 is a schematic vertical sectional view showing a single crystal pulling apparatus according to a second embodiment.

FIG. 3 is a bottom view showing a sliding mechanism of a stray light removing plate.

FIG. 4 is a schematic vertical sectional view showing a conventional single crystal pulling apparatus equipped with a means for measuring the surface temperature of a melt.

FIG. 5 is a diagram showing stray light incident on a measurement position.

[Explanation of symbols]

 1 Crucible 2 Melt 5 Chamber 6 Single Crystal 7 Radiation Thermometer 9 Stray Light Removal Plate 10 Calculation Unit 11 Power Supply Control Unit 15 Operation Unit

Claims (5)

[Claims] 1. A single crystal pulling apparatus comprising means for measuring the surface temperature of a melt in a crucible, a radiation thermometer for measuring thermal radiation light from the melt surface, and a melt surface position to be measured. A single crystal pulling apparatus comprising: a stray light removing plate provided at a radiation source position or a reflection source position of incident stray light. 2. The single crystal pulling apparatus according to claim 1, wherein the stray light removing plate is provided on an inner surface of a ceiling wall of a chamber that houses the crucible. 3. The stray light removing plate has a switchable plate made of a plurality of materials having different reflectances, and a switching means for switching the plurality of plates and a radiation thermometer when each plate is installed. The single crystal pulling apparatus according to claim 1, further comprising: a calculating unit that corrects a stray light component from a value measured by calculating the surface temperature of the melt. 4. The switching means comprises a frame portion horizontally holding the plurality of plates in parallel, a rail portion for sliding the frame portion in the horizontal direction, and the frame portion along the rail portion. 4. The single crystal pulling apparatus according to claim 3, further comprising drive means for moving the single crystal, and the operation for the drive means can be performed externally. 5. The single crystal pulling apparatus according to claim 3, further comprising means for controlling an output of a heater for heating the melt based on a value obtained from the calculating means.