Abstract:
In a conventional method, it is difficult to reject a stray light component with certainty, so that it is difficult to accurately measure the temperature of the melt surface. Since a temperature measuring device and a computing means are expensive, the cost of the measurement tends to be high. Modifications to an existing apparatus for pulling a single crystal are required, which is an inconvenience. In order to solve the above problems, a CCD camera is used for detecting the radiation light luminance distribution of the melt surface, the minimum radiation light luminance L min  is determined based on the radiation light luminance distribution data measured using the CCD camera, and the temperature T S  of the melt surface within an apparatus for pulling a single crystal is computed based on the minimum radiation light luminance L min .

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to methods and a device for measuring the temperature of the melt surface within an apparatus for pulling a single crystal and, more particularly, to methods for measuring the temperature of the melt surface within an apparatus for pulling a single crystal wherein non-contact temperature measurement is performed and a device is used for the methods. 
     2. Description of the Relevant Art 
     Keeping the temperature of the melt surface in optimum condition during single crystal growth is needed in order to ensure the quality of the single crystal. As a precondition, it is required that the temperature of the melt surface be accurately measured. A dip-type thermocouple, a non-contact radiation thermometer, and the like have been used for measuring the temperature of the melt surface. However, in a temperature measuring method wherein the thermocouple is used, the thermocouple easily wears and has a short life span, or constituents of the thermocouple contaminate the melt, resulting in a bad influence upon the quality of a single crystal to be pulled. Therefore, it is difficult to continuously measure the temperature of the melt surface for a long period of time. 
     In order to cope with the problem, recently a method wherein non-contact temperature measurement of the melt surface is performed using the radiation thermometer has been frequently used. The temperature measuring method wherein the radiation thermometer is used is based on the luminance of a thermal radiation light radiated from an object of measurement being determined from the temperature and the emissivity of the object of measurement. The temperature is obtained based on the luminance of the thermal radiation light measured by non-contact measurement and the emissivity obtained on a different occasion. Therefore, in the temperature measuring method wherein the radiation thermometer is used, there is no probability that impurities will contaminate a melt. The temperature of the melt surface can be continuously measured during the pulling of a single crystal. 
     FIG. 1 is a diagrammatic sectional view showing an apparatus  40  for pulling a single crystal incorporating a conventional temperature measuring device  42  wherein a radiation thermometer is used, and reference numeral  11  in the figure represents a crucible. The crucible  11  is cylindrical, and is supported with an ascent/descent means (not shown) by which the crucible  11  is moved up and down while being rotated. The vertical position of the crucible  11  can be adjusted by driving the ascent/descent means. An almost cylindrical heater  12  is arranged around the crucible  11  and an electric power supply regulator  12   a  is connected thereto. An almost cylindrical heat insulating mold  13  is arranged around the heater  12 , and a lower chamber&#39;s wall  14  is arranged around the heat insulating mold  13  so as to surround the heat insulating mold  13 . An upper chamber&#39;s wall  15  stands on a lower chamber&#39;s upper wall  14   a  having the shape of a ring. 
     Inside the upper chamber&#39;s wall  15 , a pulling shaft  16   a  is suspended. A seed crystal  16   b  is held by a holder  16   c  at the lower end of the pulling shaft  16   a , which is wound while being rotated by a driving means  16 . A window  41  is formed in a vertical position on a lower chamber&#39;s side wall  14   b  where the melt surface  17   a  is located, and is sealed with a quartz glass member  41   a  or the like. 
     The crucible  11  is charged with a melt  17  of melted polycrystal silicon (Si) or the like. By bringing the seed crystal  16   b  into contact with the melt surface  17   a  and pulling the pulling axis  16   a  while rotating it, a single crystal  18  can be grown from the melt surface  17   a.    
     On the other hand, a radiation thermometer  43  is placed outside the window  41  in the almost horizontal direction, and is connected to a computing means  44  which is further connected to the electric power supply regulator  12   a  . The non-contact temperature measuring device  42  includes the radiation thermometer  43  and the computing means  44 . The luminance of a thermal radiation light radiated from the heat insulating mold  13  in the vicinity of the melt surface  17   a  is measured using the radiation thermometer  43 . The temperature is computed and detected based on the measured luminance of the thermal radiation light in the computing means  44 . In the electric power supply regulator  12   a , the quantity of electric power supplied to the heater  12  is regulated based on the computed and detected temperature so as to keep the melt surface  17   a  at a prescribed temperature. As a result, the melt surface  17   a  is kept at a prescribed temperature. 
     However, in the temperature measurement using the above temperature measuring device  42 , the temperature of the heat insulating mold  13  and that of the melt surface  17   a  have not been the same, as the diameter of the seed crystal  18  and the apparatus for pulling a single crystal  40  have been larger in order to manufacture an LSI more efficiently. As a result, it has been difficult to accurately measure the temperature of the melt surface  17   a . Since the heat capacity of the melt  17  is relatively large, there is a difference in temperature between the melt  17  in the vicinity of the crucible  11  close to the heater  12  and the melt  17  in the vicinity of the single crystal  18  away from the heater  12 . As a result, it is difficult to accurately measure the required temperature of the melt surface  17   a  in the vicinity of the single crystal  18 . Since convection is caused in the melt  17  by the difference in temperature, the temperature of the melt surface  17   a  easily varies with time. As a result, it is difficult to accurately measure the temperature of the melt surface  17   a  following the variations. 
     In order to cope with the above problems, it is desirable that the temperature of the melt surface  17   a  in the vicinity of the single crystal  18  be directly measured using the radiation thermometer. Radiation lights having radiants such as the upper portion of the side wall of the crucible  11 , the heater  12 , the heat insulating mold  13 , and the lower chamber&#39;s upper wall  14   a , which surround the melt surface  17   a  and are hot, provide a specular reflection on the melt surface  17   a . Therefore, even when the temperature of the melt surface  17   a  in the vicinity of the single crystal  18  is directly measured using the radiation thermometer, the radiation lights caused by specular reflection (hereinafter, referred to as the stray lights) are incident on the radiation thermometer, in addition to the thermal radiation light from the melt surface  17   a  itself, so that an error in the measured temperature is easily caused. 
     In order to reduce the influence of the stray light and improve the measurement precision, various kinds of temperature measuring devices were proposed. 
     FIG. 2 is a diagrammatic sectional view showing an apparatus  50  for pulling a single crystal incorporating a conventional temperature measuring device  55  (Japanese Kokai No. 58-168927), and reference numeral  14   a  represents a lower chamber&#39;s upper wall. A window  19  facing the melt surface  17   a  in the vicinity of a single crystal  18  is formed at a prescribed place on the lower chamber&#39;s upper wall  14   a , and is sealed with a quartz glass member  19   a  or the like. 
     On the other hand, a polarizing filter  51  and an optical detecting means (silicon electromotive force device)  52  are arranged above the window  19  in a slanting direction on the axis  54  of a radiation light. The optical detecting means  52  is connected through an amplifier  53  to an electric power supply regulator  12   a . The temperature measuring device  55  includes the polarizing filter  51 , the optical detecting means  52 , and the amplifier  53 . 
     In the temperature measuring device  55  having the above construction, a stray light component is rejected by separating to measure a component S 1  polarized in parallel to the melt surface  17   a  and a component S 2  polarized vertically (neither of them shown) and performing a computation of (S 1 +S 2 ) −α(S 1 −S 2 ). Here, α is a function related to a measurement wavelength region, an angle of reflection, and the like. Practically, the value is experientially selected. 
     Since the other constituents are almost the same as those of the apparatus for pulling a single crystal  40  shown in FIG. 1, detailed descriptions thereof are omitted here. 
     FIG. 3 is a diagrammatic sectional view showing an apparatus  60  for pulling a single crystal incorporating a temperature measuring device  62  which was previously proposed by the present inventors (Japanese Kokai No. 06-129911), and reference numeral  15  in the figure represents an upper chamber&#39;s wall. A window  61  facing downward in a slanting direction is formed at a prescribed place on the side wall  15   a  of the upper chamber&#39;s wall  15 , and is sealed with a quartz glass member  61   a  or the like. 
     A temperature measuring auxiliary plate  63  is held at a prescribed place on the inner surface of the lower chamber&#39;s upper wall  14   a . The temperature measuring auxiliary plate  63  is made of a graphite material or the like whose emissivity is known and has low angle-dependence. On the other hand, a radiation thermometer  64  and a dichroic radiation thermometer  65  are arranged above the windows  19  and  61  in a slanting direction, respectively. The radiation thermometer  64  is placed on the axis of a thermal radiation light  67   a  radiated from a measurement point A on the melt surface  17   a , while the dichroic radiation thermometer  65  is placed on the axis of a radiation light  67   b  radiated from a radiant B on the temperature measuring auxiliary plate  63 . The mounting positions and angles of the temperature measuring auxiliary plate  63 , the radiation thermometer  64 , and the dichroic radiation thermometer  65  are selected respectively so that the radiation light  67   c  radiated from the radiant B is reflected from the measurement point A and that the reflected light (stray light)  67   d  is incident on the radiation thermometer  64  in conjunction with the thermal radiation light  67   a . The radiation thermometer  64  and the dichroic radiation thermometer  65  are connected to a computing means  66  which is connected to an electric power supply regulator  12   a . The temperature measuring device  62  includes the temperature measuring auxiliary plate  63 , the radiation thermometer  64 , the dichroic radiation thermometer  65 , and the computing means  66 . 
     In the temperature measuring device  62  having the above construction, the luminance of a radiation light  67  which is the reflected light  67   d  integrated with the thermal radiation light  67   a  radiated from the measurement point A is measured using the radiation thermometer  64 , and the luminance signal  68  is transmitted to the computing means  66 . At the same time, the temperature signal  69  of the radiant B measured using the dichroic radiation thermometer  65  is transmitted to the computing means  66 . In the computing means  66 , the luminance of the radiation light  67   b  radiated from the radiant B is computed with the data of the temperature signal  69 , and the luminance of the radiation light  67   b  is subtracted from that of the radiation light  67  to obtain that of the thermal radiation light  67   a . The temperature of the measurement point A on the melt surface  17   a  is detected by computation with the luminance data of the thermal radiation light  67   a.    
     Since the other constituents are almost the same as those of the apparatus for pulling a single crystal  50  shown in FIG. 2, detailed descriptions thereof are omitted here. 
     FIG. 4 is a diagrammatic sectional view showing an apparatus for pulling a single crystal  70  incorporating a temperature measuring device  71  which was previously proposed by the present inventors (Japanese Kokai No. 08-74979), and reference numeral  14   a  in the figure represents a lower chamber&#39;s upper wall. A stray light rejecting plate  72  is held at a prescribed place on the under surface of the lower chamber&#39;s upper wall  14   a . The stray light rejecting plate  72  is made of a graphite material or the like, which has a relatively low emissivity and does not easily contaminate a melt  17  as an impurity. A cooling means (not shown) is mounted near the mounting place of the stray light rejecting plate  72  on the lower chamber&#39;s upper wall  14   a . By operating the cooling means, the temperature of the stray light rejecting plate  72  is kept at a prescribed temperature or below at all times. 
     On the other hand, a radiation thermometer  73  is arranged above a window  19  in a slanting direction, and is placed on the axis of a thermal radiation light  75   a  radiated from a measurement point A on the melt surface  17   a . The mounting positions and angles of the stray light rejecting plate  72  and the radiation thermometer  73  are respectively selected so that a radiation light  75   b  radiated from a radiant B on the stray light rejecting plate  72  is reflected from the measurement point A and so that the reflected light (stray light)  75   c  is incident on the radiation thermometer  73  in conjunction with the thermal radiation light  75   a . The radiation thermometer  73  is connected to a computing means  74  which is connected to an electric power supply regulator  12   a . The temperature measuring device  71  includes the stray light rejecting plate  72 , the radiation thermometer  73 , and the computing means  74 . 
     In the temperature measuring device  71  having the above construction, the luminance of the radiation light  75  which is the reflected light  75   c  integrated with the thermal radiation light  75   a  radiated from the measurement point A, is measured using the radiation thermometer  73 , and the luminance signal  76  is transmitted to the computing means  74 . At that time, by cooling the radiant B beforehand to a prescribed temperature (e.g. 800° C. when the melt  17  is Si) or below, the luminance of the reflected light  75   c  becomes so small that it can be neglected. Therefore, even if the luminance of the radiation light  75  is used for a computation in the computing means  74 , a quite accurate temperature of the measurement point A on the melt surface  17   a  can be obtained. 
     Since the other constituents are almost the same as those of the apparatus  50  for pulling a single crystal shown in FIG. 2, detailed descriptions thereof are omitted here. 
     In the temperature measuring device  55  shown in FIG. 2. a function α is experientially selected, so that it is difficult to certainly reject a stray light component to accurately measure the temperature of the melt surface  17   a.    
     In the temperature measuring device  62  shown in FIG.  3 . both of the radiation thermometer  64  and the dichroic radiation thermometer  65  are required for an apparatus for pulling a single crystal  60 , leading to a high cost. 
     In the temperature measuring device  71  shown in FIG. 4, the cooling means need be mounted on the lower chamber&#39;s upper wall  14   a . An existing apparatus for pulling a single crystal would need to be extensively modified, which is an inconvenience. 
     SUMMARY OF THE INVENTION 
     The present invention was developed in order to solve the above problems, and it is an object of the present invention to provide methods for measuring the temperature of the melt surface within an apparatus for pulling a single crystal and a device used for the methods. In the methods, an existing apparatus for pulling a single crystal is used as it is without the necessity of making modifications thereon. The temperature of the melt surface can be accurately measured at low cost normally using one temperature measuring means. 
     The below symbols are defined as follows. 
     L: Luminance of a radiation light radiated from the melt surface toward the outside of a crucible 
     L b (T): Luminance of a radiation light on a black body having a temperature of T 
     L n ′: Luminance of a stray light 
     n: Number of times of reflection of a stray light on a chamber&#39;s wall 
     T S : Temperature of the melt surface 
     T H : Temperature of a radiant of a stray light (chamber&#39;s wall) 
     ε s : Emissivity of the melt surface (a decimal below 1) 
     ε c : Emissivity of the chamber&#39;s wall (a decimal below 1) 
     τ w : Transmittance of a quartz glass member (a decimal below 1) 
     FIG. 5 is a diagrammatic sectional view showing an apparatus  10  for pulling a single crystal in order to describe a temperature measuring method of the melt surface according to the present invention. The parts thereof except a temperature measuring device are the same as those of an apparatus  50  for pulling a single crystal shown in FIG. 2. A radiation thermometer  73  shown in FIG. 4 or the like is arranged above a quartz glass member  19   a  in a slanting direction. The axis of incident light of the radiation thermometer  73  can be set at any time in the direction of measurement points A 1 -A 3  or the like on the melt surface  17   a.    
     In this case, each luminance L of radiation lights  81 - 83  radiated outward from the measurement points A 1 -A 3  through a window  19  is obtained by Formula 1. 
     
       
         L=τ w {ε s L b (T S )+(1−ε s )L′}  Formula 1 
       
     
     The first term of the Formula 1 τ w ·ε s  L b  (T S ) is a component of a thermal radiation light radiated from the measurement points A 1 -A 3  on the melt surface  17   a , while the second term τ w ·(1−ε s )L′ is a component of a stray light which is radiated from reflection points B 1 -B 3  and is reflected on the measurement points A 1 -A 3  on the melt surface  17   a.    
     On the other hand, the luminance L 1 ′ of a stray light  81   a , which is radiated from a heater  12  or the like whose temperature T H  is higher than that of the melt surface  17   a  and is once reflected on the reflection point B 1 , is obtained by Formula 2. 
     
       
         L 1 ′=(1−ε c )L b (T H )  Formula 2 
       
     
     In this case, since the luminance L 1 ′ of the stray light  81   a  is large (bright), it is not desired that the luminance L 1 ′ of the stray light  81   a  be neglected. Neglecting it causes an error in the detected temperature. 
     On the other hand, the luminance L n ′ of a stray light  82   a  or  83   a , which is radiated from the heater  12 , a crucible  11 , or the like, is (n−1) times reflected on chamber&#39;s walls  14  and  15 , and has the n th reflection on the reflection point B 2  or B s , is obtained by Formula 3. 
     
       
         L n ′=(1−ε c ) n L b (T H )  Formula 3 
       
     
     In this case, since the luminance L n ′ of the stray light  82   a  or  83   a  is attenuated to be small (dark) as the number of times of reflection n increases, the luminance L n ′ of the stray light  82   a  or  83   a  can be neglected. Even if it is neglected, error is not often to caused by the detected temperature. 
     For example, where the emissivity ε c  of the upper chamber&#39;s wall  15  is 0.5, the luminance L n=3 ′ of a stray light  82   a , whose number of times of reflection n on the upper chamber&#39;s wall  15  is 3, decreases to about a quarter of the luminance of a stray light  81   a  whose number of times of reflection n is 1. 
     FIG. 6 comprises curves schematically showing the relationship of the Formulas 1-3. In the figure, C, D, and E represent the luminances of radiation lights from the melt surface  17   a , those of stray lights, and the measured luminances of radiation lights, respectively. The luminances C of the radiation lights from the melt surface  17   a  are almost uniform at any measurement point on the melt surface  17   a . On the other hand, the luminances D of the stray lights are different, depending on the measurement points on the melt surface  17   a , and the luminance L n ′ becomes a minimum value D o  at the point where the number of times of reflection n is maximum. Since the relationship E=C+D holds, the temperature of the melt surface  17   a  can be calculated with a minimum error by obtaining the minimum reading E o  from the measured luminances E of the radiation lights. 
     The present inventors studied a method for measuring the temperature of the melt surface within an apparatus for pulling a single crystal and found that the temperature of the melt surface  17   a  can be obtained accurately and easily by measuring the smallest luminance L on the melt surface  17   a  and calculating the temperature based on the luminance L, leading to the completion of the present invention. 
     The method for measuring the temperature of the melt surface within an apparatus for pulling a single crystal (1) according to the present invention is characterized by measuring the luminance distribution of radiation lights radiated from the melt surface within an apparatus for pulling a single crystal using a temperature distribution measuring means, computing and detecting a point having a minimum radiation light luminance using a computing means with the radiation light luminance distribution data, and measuring the surface temperature at the point using a radiation temperature measuring means. 
     In the method for measuring the temperature of the melt surface within an apparatus for pulling a single crystal ( 1 ), after the point on which a stray light component has the smallest influence is computed and detected using the temperature distribution measuring means and the computing means, the surface temperature at the point can be accurately measured using relatively cheap radiation temperature measuring means. Even when plural apparatuses for pulling a single crystal are installed, only one unit of the temperature distribution measuring means and the computing means need be prepared. The radiation temperature measuring means is relatively cheap, a modifications and additional equipment to the main unit of the apparatus for pulling a single crystal are not needed at all. As a result, the cost can be largely reduced. 
     The method for measuring the temperature of the melt surface within an apparatus for pulling a single crystal ( 2 ) according to the present invention is characterized by using a monochromatic radiation thermometer as the radiation temperature measuring means in the method for measuring the temperature of the melt surface ( 1 ). 
     In the method for measuring the temperature of the melt surface within an apparatus for pulling a single crystal ( 2 ), since the cheap monochromatic radiation thermometer is used as the radiation temperature measuring means, the cost can be reduced. 
     The method for measuring the temperature of the melt surface within an apparatus for pulling a single crystal ( 3 ) according to the present invention is characterized by measuring the luminance distribution of radiation lights radiated from the melt surface within an apparatus for pulling a single crystal using a temperature distribution measuring means, and obtaining the surface temperature at a point having a minimum radiation light luminance as computing and detecting the point of the minimum luminance, using a computing means with the radiation light luminance distribution data. 
     In the method for measuring the temperature of the melt surface within an apparatus for pulling a single crystal ( 3 ), even if the operation conditions substantially vary during the pulling of a single crystal, a point on which a stray light component has the smallest influence can be accurately found using the temperature distribution measuring means and the computing means, and the surface temperature at the point can be accurately measured at all times. Since modifications and additional equipment to the main unit of the apparatus for pulling a single crystal are not needed at all, an increase in cost is not caused. 
     The method for measuring the temperature of the melt surface within an apparatus for pulling a single crystal ( 4 ) according to the present invention is characterized by using a CCD camera as the temperature distribution measuring means in one of the methods for measuring the temperature of the melt surface ( 1 )-( 3 ). 
     In the method for measuring the temperature of the melt surface within an apparatus for pulling a single crystal ( 4 ), since the CCD camera is used as the temperature distribution measuring means, the surface temperature distribution can be accurately measured by a relatively simple operation. 
     The method for measuring the temperature of the melt surface within an apparatus for pulling a single crystal ( 5 ) according to the present invention is characterized by using a thermal image measuring device as the temperature distribution measuring means in one of the methods for measuring the temperature of the melt surface ( 1 )-( 3 ). 
     In the method for measuring the temperature of the melt surface within an apparatus for pulling a single crystal ( 5 ), since the thermal image measuring device is used as the temperature distribution measuring means, the surface temperature distribution and the surface temperature can be more accurately measured. 
     The temperature measuring device of the melt surface within an apparatus for pulling a single crystal ( 1 ) according to the present invention is characterized by having a temperature distribution measuring means by which the radiation light luminance distribution on the melt surface is detected, and a computing means by which the minimum radiation light luminance is determined based on the radiation light luminance distribution data measured using the temperature distribution measuring means and the temperature is computed based on the minimum radiation light luminance. 
     The temperature measuring device of the melt surface within an apparatus for pulling a single crystal ( 1 ) need not be used in combination with another radiation thermometer and the operation thereof is extremely simple. As a result, the measurement precision can certainly be improved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic sectional view showing an apparatus for pulling a single crystal incorporating a conventional temperature measuring device wherein a radiation thermometer is used; 
     FIG. 2 is a diagrammatic sectional view showing an apparatus for pulling a single crystal incorporating another conventional temperature measuring device; 
     FIG. 3 is a diagrammatic sectional view showing an apparatus for pulling a single crystal incorporating still another conventional temperature measuring device; 
     FIG. 4 is a diagrammatic sectional view showing an apparatus for pulling a single crystal incorporating still another conventional temperature measuring device; 
     FIG. 5 is a diagrammatic sectional view showing an apparatus for pulling a single crystal in order to describe the function of a temperature measuring device according to the present invention; 
     FIG. 6 comprises curves schematically showing the relationship shown by Formulas 1-3; 
     FIG. 7 is a diagrammatic sectional view showing a device used in a method for measuring the temperature of the melt surface within an apparatus for pulling a single crystal (the first process) according to Embodiment (1) of the present invention, and a device used in a method of measuring the temperature of the melt surface within an apparatus for pulling a single crystal according to Embodiment (2); 
     FIG. 8 is a diagrammatic sectional view showing a device used in a method of measuring the temperature of the melt surface within an apparatus for pulling a single crystal (the second process) according to the Embodiment (1); 
     FIG. 9 comprises flow charts schematically expressing the operation of a temperature measuring device of the melt surface within an apparatus for pulling a single crystal according to the Embodiment (1), and FIG.  9 ( a ) shows the first process thereof and FIG.  9 ( b ) shows the second process thereof; and 
     FIG. 10 comprises flow charts schematically expressing the operation of a temperature measuring device of the melt surface within an apparatus for pulling a single crystal according to the Embodiment (2). 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the methods of measuring the temperature of the melt surface within an apparatus for pulling a single crystal and the device used in the methods according to the present invention are described below by reference to the Figures of the drawings. Here, the same marks are affixed to the components that have the same functions as those of a conventional apparatus. 
     FIG. 7 is a diagrammatic sectional view showing an apparatus for pulling a single crystal  10  which is used in the first process of a method for measuring the temperature of the melt surface within an apparatus for pulling a single crystal according to Embodiment (1), and reference numeral  11  in the figure represents a crucible. The crucible  11  is cylindrical, and is supported with an ascent/descent means (not shown) by which the crucible  11  is moved up and down while being rotated. The vertical position of the crucible  11  can be adjusted by driving the ascent/descent means. An almost cylindrical heater  12  is arranged around the crucible  11 , and an electric power supply regulator  12   a  is connected thereto. An almost cylindrical heat insulating mold  13  is arranged around the heater  12 , and a lower chamber&#39;s wall  14  is arranged around the heat insulating mold  13  so as to surround the heat insulating mold  13 . An upper chamber&#39;s wall  15  stands on a lower chamber&#39;s upper wall  14   a  having the shape of a ring. 
     Inside the upper chamber&#39;s wall  15 , a pulling axis  16   a  is suspended. A seed crystal  16   b  is held by a holder  16   c  at the lower end of the pulling axis  16   a , which is wound while being rotated by a driving means  16 . A window  19  facing the melt surface  17   a  is formed at a prescribed place on the lower chamber&#39;s upper wall  14   a , and is sealed with a quartz glass member l 9   a  or the like. 
     The crucible  11  is charged with a melt  17  of melted polycrystal silicon (Si) or the like. By bringing and the seed crystal  16   b  into contact with the melt surface  17   a  and pulling the pulling axis  16   a  while rotating it, a single crystal  18  can be grown from the melt surface  17   a.    
     On the other hand, a CCD camera  21  is placed above the window  19  in a slanting direction as a temperature distribution measuring means. The mounting angle of the CCD camera  21  is selected so that a part of the upper chamber&#39;s wall  15  reflected by the melt surface  17   a  comes within the visual field D thereof. The CCD camera  21  is connected to a computing means  22 . A temperature measuring device  20  includes the CCD camera  21  and the computing means  22 . The computing means  22  is further connected to the electric power supply regulator  12   a , wherein the quantity of electric power supplied to the heater  12  is regulated based on the computed temperature so as to keep the melt surface  17   a  at a prescribed temperature. 
     FIG.  9 ( a ) is a flow chart schematically expressing the operation of the computing means  22  in the temperature measuring device  20 . 
     The switch (not shown) of the temperature measuring device  20  is turned on to start the operation. In the step (hereinafter, referred to as S)  1 , a determination is made as to whether a radiation light luminance signal L is output from the CCD camera  21  or not. A determination that it is not yet output leads to a return to S 1 . On the other hand, if a determination that the output has started is made, data of radiation light luminance signals L at each of plural points (radiation light luminance L distribution data) within the visual field D is captured and is stored in a memory (not shown) of the computing means  22  (S 2 ). 
     In S 3 , a determination is made as to whether all the data of the radiation light luminance signals L at each of the plural points is captured and is stored or not is made. A determination that the data is not yet perfect leads to a return to S 2 . On the other hand, if a determination is made that all the data is captured and is stored, the stored radiation light luminance signals L at each point are called up (S 4 ), and the minimum radiation light luminance signal L min  is extracted from the radiation light luminance signals L in S 5 . 
     The point A which radiates the minimum radiation light luminance signal L min  is stored in the memory and a command to show it on a display (not shown) or the like is output (S 6 ). In S 7 , a determination as to whether the switch of the CCD camera  21  is on or not is made. A determination that the switch is on leads to a return to S 1 , and the radiation point A of the radiation light luminance signal L min  is confirmed again. On the other hand, if a determination is made that the switch is not on, the operation of the computing means  22  is finished. 
     Then, the temperature measuring device  20  is taken off, leading to the completion of the first process of the method of measuring the temperature of the melt surface. 
     FIG. 8 is a diagrammatic sectional view showing an apparatus for pulling a single crystal  10 A which is used in the second process of the method of measuring the temperature of the melt surface within an apparatus for pulling a single crystal according to the Embodiment (1). The only point different from the apparatus for pulling a single crystal  10  shown in FIG. 7 is that a temperature measuring device  30  is mounted in place of the temperature measuring device  20 . A monochromatic radiation thermometer  31  is placed outside the window  19  of the apparatus for pulling a single crystal  10 A as a radiation temperature measuring means. The mounting angle of the monochromatic radiation thermometer  31  is selected so that a point A which radiates a radiation light luminance signal L min  comes within the relatively narrow visual field E thereof The monochromatic radiation thermometer  31  is connected to a computing means  32 . A temperature measuring device  30  includes the monochromatic radiation thermometer  31  and the computing means  32 . The computing means  32  is further connected to the electric power supply regulator  12   a , wherein the quantity of electric power supplied to heater  12  is regulated so as to keep the melt surface  17   a  at a prescribed temperature. 
     FIG.  9 ( a ) is a flow chart schematically expressing the operation of the computing means  32  in the temperature measuring device  30 . 
     The switch (not shown) of the computing means  32  is turned on to start the operation. In S 8 , a determination as to whether a radiation light luminance signal L min  is output from the monochromatic radiation thermometer  31  or not is made. A determination that is not yet output leads to a return to S 8 . On the other hand, if a determination is made that the output is started, the temperature T S  of the melt surface  17   a  is computed based on the radiation light luminance signal L min  (S 9 ). The temperature T S  is shown on a display (not shown) and the temperature T S  is transmitted to the electric power supply regulator  12   a  (S 10 ). In S 11 , a determination as to whether the switch of the monochromatic radiation thermometer  31  is on or not is made. A determination that the switch is on leads to a return to S 8 , and the temperature T S  of the melt surface  17   a  is repeatedly measured. On the other hand, upon determining that the switch is not on, the operation of the computing means  32  is finished. 
     After detecting the point A which radiates the minimum radiation light luminance signal L min  the first process, ordinarily, the temperature of the melt surface  17   a  is measured only through the second process wherein the temperature measuring device  30  is used. At that time, even if the quantity of the melt  17  decreases as the single crystal  18  is pulled, the vertical position of the crucible  11  is regulated at all times by driving the ascent/descent means so as to keep the radiation point A in almost the same position. 
     As is obvious from the above descriptions, in the method of measuring the temperature of the melt surface within an apparatus for pulling a single crystal according to the Embodiment (1), even when plural main units of the apparatus for pulling a single crystal  10  are installed, only one unit of the CCD camera  21  and the computing means  22  need be prepared. After computing and detecting the point A on which a stray light component has the smallest influence using the temperature measuring device  20 , the surface temperature of the point A can be measured accurately and at low cost using the relatively cheap monochromatic radiation thermometer  31  and the computing means  32 . Since modifications and additional equipment to the main unit of the apparatus for pulling a single crystal  10  are not required at all, the cost can be largely reduced. 
     Since the monochromatic radiation thermometer  31  is used as a radiation temperature measuring means, the cost of the temperature measurement of the melt surface can be further reduced. 
     Since the CCD camera  21  is used as a temperature distribution measuring means, the surface temperature distribution can be measured by a simple operation. 
     The method for measuring the temperature of the melt surface within an apparatus for pulling a single crystal according to Embodiment (2) is described below. Since an apparatus used for the method for measuring the temperature of the melt surface within an apparatus for pulling a single crystal according to the Embodiment (2) is the same as one shown in FIG.  7 . except for a computing means  26 , the method according to the Embodiment (2) is described by reference to FIG.  7 . 
     Reference numeral  21  in the figure represents a CCD camera, and the CCD camera  21  is connected to a computing means  26  which is connected to an electric power supply regulator  12   a . A temperature measuring device  25  includes the CCD camera  21  and the computing means  26 . Since the other constituents are the same as those of the apparatus described in the Embodiment (1), detailed descriptions thereof are omitted here. 
     FIG. 10 is a flow chart schematically expressing the operation of the computing means  26  in the temperature measuring device  25 . Since S 21 -S 25  in FIG. 10 are the same as S 1 -S 5  of the flow chart shown in FIG.  9 ( a ), the descriptions of S 21 -S 25  are omitted here. 
     In S 25 , when a radiation light luminance signal L is determined as being the minimum radiation light luminance signal. L min , the temperature T S  of the melt surface  17   a  is computed based on the radiation light luminance signal L min  (S 26 ). The temperature T S  is shown on a display (not shown) and the temperature T S  signal is transmitted to the electric power supply regulator  12   a  (S 27 ). In S 28 , a determination as to whether the switch of the CCD camera  21  is on or not is made. A determination that the switch is on leads to a return to S 21 , and the temperature T S  of the melt surface  17   a  is continuously computed. On the other hand, upon determining that the switch is not on, the operation of the computing means  26  is finished. 
     As is obvious from the above descriptions, in the method for measuring the temperature of the melt surface within an apparatus for pulling a single crystal according to the Embodiment (2), even if the operation conditions substantially vary during the pulling of a single crystal  18 , a point A on which a stray light component has the smallest influence can be accurately found using the CCD camera  21  and the computing means  26 , and the surface temperature of the point A can be accurately measured at all times. Since modifications and additional equipment to the main unit of the apparatus for pulling a single crystal  10 A are not required at all, an increase in cost is not caused. 
     Since the CCD camera  21  is used as a temperature distribution measuring means, the surface temperature distribution can be accurately measured by a simple operation. 
     In the temperature measuring device  25  according to the Embodiment (2), it is not necessary to use the temperature distribution measuring means in combination with another radiation thermometer. As a result, the operation is extremely simple, so that the measurement precision can certainly be improved. 
     In the methods for measuring the temperature of the melt surface within an apparatus for pulling a single crystal according to the Embodiments (1) and (2). the cases wherein the CCD camera  21  is used as a temperature distribution measuring means constituting the temperature measuring device  20  or  25  are described, but the temperature distribution measuring means is not limited to the CCD camera  21 . In another embodiment, a thermal image measuring device may be used as a temperature distribution measuring means. In this case, the surface temperature can be more accurately measured. 
     EXAMPLES 
     The results of the temperature measurement of the melt surface within an apparatus for pulling a single crystal by the methods according to the embodiments of the present invention are described below. 
     Example 1 
     A temperature measuring method according to the Embodiment (1) was adopted. A monochromatic radiation thermometer  31  having a visual field E of about 2 mm was used. The mounting angle (angle of incidence) thereof was set to about 20°. A point A on which a stray light component had the smallest influence was set in position about 75 mm sideward and about 90 mm forward from the center of a crucible  11 , and the temperature T S  of the melt surface  17   a  was measured. When the range of the variation of the distance between the point A and the monochromatic radiation thermometer  31  was within ±5 mm, the measurement error in the temperature T S  could be reduced to about 30° C. and less. 
     Example 2 
     A temperature measuring method according to the Embodiment (2) was adopted. Using a CCD camera  21  whose mounting angle (angle of incidence) was set to about 20°, the temperature T S  of the melt surface  17   a  was measured. As a result, a point A on which a stray light component had the smallest influence was detected in the position about 75 mm sideward and about 90 mm forward from the center of a crucible  11 . The mean number of times of reflection n of the stray lights reaching the point A was 3, and the measurement error in the temperature T S  could be reduced to about 30° C. or less at all times.