Patent Publication Number: US-2022228924-A1

Title: Method of calibrating radiation thermometer and system thereof

Description:
TECHNICAL FIELD 
     The present invention relates to a method of calibrating a radiation thermometer and a system thereof, particularly relates to a method and a system of automatically calibrating a radiation thermometer disposed in a polishing apparatus. 
     BACKGROUND ART 
     A CMP (Chemical Mechanical Polishing) apparatus is used in a process of polishing a surface of a substrate, such as a wafer, in the manufacturing of a semiconductor device. The CMP apparatus has at least one polishing unit, and the polishing unit is configured to hold and rotate the substrate with a polishing head, and press the wafer against a polishing pad on a rotating polishing table to polish the surface of the substrate. During polishing, a polishing liquid (or slurry) is supplied onto the polishing pad, so that the surface of the substrate is planarized by the chemical action of the polishing liquid and the mechanical action of abrasive grains contained in the polishing liquid. 
     A polishing rate of the substrate depends not only on a polishing load on the substrate pressed against the polishing pad, but also on a surface temperature of the polishing pad. This is because the chemical action of the polishing liquid on the substrate depends on the temperature. Therefore, in the manufacturing of a semiconductor device, it is important to maintain an optimum surface temperature of the polishing pad during polishing of the substrate in order to increase the polishing rate of the substrate, and to keep the increased polishing rate constant. 
     From this viewpoint, a pad-temperature regulating apparatus is conventionally used to regulate a surface temperature of a polishing pad (for example, see Patent Document  1 ). The pad-temperature regulating apparatus typically includes a heat exchanger capable of contacting a surface of the polishing pad, a liquid supply system for supplying a heating liquid having a regulated temperature and a cooling liquid having a regulated temperature into the heat exchanger, a radiation thermometer for measuring a surface temperature of the polishing pad, and a controller for controlling the liquid supply system based on the surface temperature of the polishing pad measured by the radiation thermometer, The controller controls flow rates of the heating liquid and the cooling liquid based on the surface temperature of the polishing pad measured by the radiation thermometer so that the surface temperature of the polishing pad is maintained at a predetermined target temperature. 
     The polishing apparatus may include a radiation thermometer that is different from the radiation thermometer of the pad-temperature regulating apparatus. This other radiation thermometer is, for example, a thermometer for monitoring whether or not the surface temperature of the polishing pad in the vicinity of the polishing head is maintained at a predetermined set temperature during polishing of the substrate. The other radiation thermometer is also connected to the above-mentioned controller. When measured values of the surface temperature of the polishing pad transmitted from the other radiation thermometer exceed an allowable range stored in advance in the controller, the controller stops an operation of the polishing apparatus, and issues an alarm. This prevents a polishing abnormality from occurring in the substrate. 
     In order to maintain the polishing rate of the substrate constant, and to effectively prevent the polishing abnormalities from occurring in the substrate, the radiation thermometer is required to output an accurate measurement of the pad surface temperature to the controller. For this reason, the manufacturer of the polishing apparatus performs calibrations of the radiation thermometer before shipping the polishing apparatus. 
     The calibration of a conventional radiation thermometer is performed as follows. First, an operator who calibrates the radiation thermometer prepares a heating device, such as a hot plate, and a portable radiation thermometer. Next, a heat radiation surface of the heating device is heated to a predetermined target temperature, and a temperature of the heat radiation surface is measured by both the radiation thermometer placed in the polishing apparatus, and the portable radiation thermometer. The operator then calibrates the radiation thermometer so that measured values of the radiation thermometer match measured values of the portable radiation thermometer. 
     Patent Literature 
     Patent document 1: Japanese laid-open patent publication No. 2018-027582 
     SUMMARY OF INVENTION 
     Technical Problem 
     After a certain amount of time has passed since the radiation thermometer has been in use, the measured value of the radiation thermometer (i.e, the temperature output value of the radiation thermometer) may deviate from the actual surface temperature of the polishing pad. Accordingly, it is preferable that the radiation thermometer be calibrated periodically at the customer&#39;s site even after delivery of the polishing apparatus. 
     However, the conventional calibration work of radiation thermometer is a work that requires some large amount of labor, and it is practically difficult to calibrate the radiation thermometer periodically because the polishing apparatus is stopped during the calibration work. Further, in the conventional calibration work of radiation thermometer, a portable radiation thermometer handled by the operator is used as a. standard for calibrating the radiation thermometer of the polishing apparatus. In this case, calibration results of radiation thermometer may vary depending on a skill level of the operator. For example, if an angle at which the operator points the portable thermometer to the heat radiation surface of the heating device, and the distance between the portable thermometer and the heat radiation surface of the heating device change, the calibration results of the radiation thermometer may vary. Therefore, there is a need tier a method and a system that can automatically calibrate the radiation thermometer, and in particular, a method and a system that can perform the calibration of radiation thermometer in a short time and automatically. 
     It is therefore an object of the present invention to provide a method and a system of automatically calibrating a radiation thermometer disposed in a polishing apparatus. 
     Solution to Problem 
     In an of embodiment, there is provided a method of automatically calibrating a radiation thermometer disposed in a polishing apparatus, comprising: placing a heating device, to which a measurement body is attached, below the radiation thermometer; and using a controller of the polishing apparatus coupled to the heating device to heat a temperature of the measurement body to a plurality of target temperatures, to measure the temperatures of the measurement body at each target temperature with the radiation thermometer, to calculate temperature deviation amounts which are differences between each of the target temperatures and temperature output values of the radiation thermometer corresponding to each target temperature, and to calibrate the radiation thermometer so that all the temperature deviation amounts are within a preset reference range. 
     In an embodiment, there is provided a method of automatically calibrating a radiation thermometer disposed in a polishing apparatus, comprising: preparing a plurality of heating devices each of which has a measurement body attached thereto; and using a controller of the polishing apparatus coupled to the plurality of heating devices to heat a temperature of each measurement body to a predetermined target temperature, to move each measurement body below the radiation thermometer to measure a temperature of each measurement body at the target temperature with the radiation thermometer, to calculate temperature deviation amounts which are differences between each of the target temperatures and temperature output values of the radiation thermometer corresponding to each target temperature, and to calibrate the radiation thermometer so that all the temperature deviation amounts are within a preset reference range. 
     In an embodiment, calibrating the radiation thermometer is correcting a conversion parameter stored in an analog-digital converter of the radiation thermometer. 
     In an embodiment, the method further comprises: after calibrating the radiation thermometer, heating again the temperature of the measurement body to the plurality of target temperatures; measuring the temperature of the measurement body at each target temperature with the radiation thermometer; calculating again the temperature deviation amounts; and checking whether or not all the temperature deviation amounts are within the preset reference range. 
     In an embodiment, the measurement body is made of a material haying an emissivity similar to an emissivity of the polishing pad. 
     In an embodiment, there is provided A method of automatically calibrating a radiation thermometer disposed in a polishing apparatus, comprising: placing a heating device to which a plurality of measurement bodies having known emissivities different from each other are attached, below the radiation thermometer; and using a controller of the polishing apparatus coupled to the heating device to heat temperatures of the plurality of measurement bodies to a predetermined target temperature, to measure the temperatures of the plurality of measurement bodies heated to the predetermined target temperature with the radiation thermometer, respectively, to calculate temperature deviation amounts which are differences between each of the temperature expectation values to be output from the radiation thermometer when the measurement bodies heated to the predetermined target temperature are measured by the radiation thermometer, and each of the temperature output values of the radiation thermometer, and to calibrate the radiation thermometer so that all the temperature deviation amounts are within a preset reference range. 
     In an embodiment, calibrating the radiation thermometer is correcting a conversion parameter stored in an analog-digital converter of the radiation thermometer. 
     In an embodiment, the method further comprises: after calibrating the radiation thermometer, measuring again the temperatures of the plurality of measurement bodies whose temperature are maintained at the target temperature, with the radiation thermometer; calculating again the temperature deviation amounts; and checking whether or not all the temperature deviation amounts are within the preset reference range. 
     In an embodiment, there is provided a calibration system for calibrating a radiation thermometer disposed in a polishing apparatus, comprising: a heating device to which a measurement body is attached, and which is placed below the radiation thermometer; and a temperature regulator coupled to the heating device, wherein the temperature regulator is coupled to a controller disposed in the polishing apparatus, and the controller is configured: to heat a temperature of the measurement body to a plurality of target temperatures through the temperature regulator, to measure the temperatures of the measurement body at each target temperature with the radiation thermometer, to calculate temperature deviation amounts which are differences between each of the target temperatures and temperature output values of the radiation thermometer corresponding to each target temperature, and to calibrate the radiation thermometer so that all the temperature deviation amounts are within a preset reference range. 
     In an embodiment, there is provided a calibration system for calibrating a radiation thermometer disposed in a polishing apparatus, comprising: a plurality of heating devices each of which has a measurement body attached thereto; a temperature regulator coupled to the plurality of heating devices, and a heating-device moving mechanism configured to move each of the plurality of heating devices below the radiation thermometer, wherein the temperature regulator and the heating-device moving mechanism are coupled to a controller disposed in the polishing apparatus, and the controller is configured to heat a temperature of each measurement body to a predetermined target temperature, to use the heating-device moving mechanism to each measurement body below the radiation thermometer, to measure the temperature of each measurement body at the target temperature with the radiation thermometer, to calculate temperature deviation amounts which are differences between each of the target temperatures and temperature output values of the radiation thermometer corresponding to each target temperature, and to calibrate the radiation thermometer so that all the temperature deviation amounts are within a preset reference range. 
     In an embodiment, the controller is configured to correct a conversion parameter stored in an analog-digital converter of the radiation thermometer. 
     In an embodiment, the controller is configured to, after calibrating the radiation thermometer, heat again the temperature of the measurement body to the plurality of target temperatures; to measure the temperature of the measurement body at each target temperature with the radiation thermometer; to calculate again the temperature deviation amounts; and to check whether or not all the temperature deviation amounts are within the preset reference range. 
     In an embodiment, the measurement body is made of a material having an emissivity similar to an emissivity of the polishing pad, 
     In an embodiment, there is provided a calibration system for calibrating a radiation thermometer disposed in a polishing apparatus, comprising: a heating device to which a plurality of measurement bodies having known emissivities different from each other are attached, and which is placed below the radiation thermometer; and a temperature regulator coupled to the heating device, wherein the temperature regulator is coupled to a controller disposed in the polishing apparatus, and the controller is configure to heat temperatures of the plurality of measurement bodies to a predetermined target temperature, to measure the temperatures of the plurality of measurement bodies heated to the predetermined target temperature with the radiation thermometer, respectively, to calculate temperature deviation amounts which are differences between each of the temperature expectation values to be output from the radiation thermometer when the measurement bodies heated to the predetermined target temperature are measured by the radiation thermometer, and each of the temperature output values of the radiation thermometer, and to calibrate the radiation thermometer so that all the temperature deviation amounts are within a preset reference range. 
     In an embodiment, the controller is configured to correct a conversion parameter stored in an analog-digital converter of the radiation thermometer. 
     In an embodiment, the controller is configured to, after calibrating the radiation thermometer, heat the temperatures of the plurality of measurement bodies to the plurality of target temperatures; to measure again the temperatures of the plurality of measurement bodies whose temperature are maintained at the target temperature, with the radiation thermometer; to calculate again the temperature deviation amounts; and checking whether or not all the temperature deviation amounts are within the preset reference range. 
     Advantageous Effects of Invention 
     According to the present invention, simply by placing the heating device, to which the measurement body is attached, below the radiation thermometer, and. connecting the controller of the polishing apparatus to the heating device, the controller automatically performs the calibration of the radiation thermometer. Therefore, the burden on the operator and the downtime of the polishing apparatus are reduced, and thus it can be expected that the calibration process of the radiation thermometer is periodically performed.. As a result, it is possible to polish the substrate at the desired polishing rate, and furthermore, the substrate can be polished at a desired polishing rate, and further, the occurrence of polishing abnormalities on the substrate can be effectively prevented. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view showing a polishing apparatus according to one embodiment; 
         FIG. 2  is a schematic view showing a radiation thermometer for measuring a pad surface temperature in the vicinity of the polishing head; 
         FIG. 3  is an enlarged schematic view showing a sensor unit of the radiation thermometer shown in  FIG. 2 ; 
         FIG. 4  is a schematic view showing a configuration of calibration system according to one embodiment; 
         FIG. 5A  is a top view schematically showing a calibration tool of the calibration system shown in  FIG. 4 ; 
         FIG. 5B  is a side view of the calibration tool shown in  FIG. 5A ; 
         FIG. 6  is a schematic view showing an example of internal structure of the radiation thermometer; 
         FIG. 7  is a flowchart showing a first half of a method of calibrating the radiation thermometer according to one embodiment; 
         FIG. 8  is a flowchart showing a latter half of the method of calibrating the radiation thermometer according to one embodiment; 
         FIG. 9  is a graph illustrating an example of a function that shows a relationship between each target temperature and a temperature output value of the radiation thermometer corresponding to this target temperature; 
         FIG. 10  is a graph illustrating an example in which a y-intercept of the function shown in  FIG. 9  has been corrected; 
         FIG. 11  is a graph illustrating an example in which a slope of the function shown in  FIG. 10  has been corrected.; 
         FIG. 12  is a schematic view showing an example of calibration sheet; 
         FIG. 13  is a perspective view schematically showing the calibration tool according to another embodiment; 
         FIG. 14  is a schematic view showing a state in which a heating device is moved below the radiation thermometer by a heating-device moving mechanism shown in  FIG. 13 ; 
         FIG. 15  is a schematic view showing a protective cover for the heating device; 
         FIG. 16  is a flowchart showing a first half of a method for checking the temperature output values of the radiation thermometer according to one embodiment; 
         FIG. 17  is a flowchart showing a latter half of the method for checking the temperature output values of the radiation thermometer according to one embodiment; 
         FIG. 18A  is a top view schematically showing the calibration tool according to still another embodiment; 
         FIG. 18B  is a perspective view schematically showing a moving mechanism for moving a heating plate shown in  FIG. 18A ; 
         FIG. 19A  is a schematic view illustrating a measurement error of a. temperature output value output from the radiation thermometer When temperatures of a plurality of measurement bodies heated to a target temperature of 100° C. is measured by the radiation thermometer, respectively; 
         FIG. 19B  is a schematic view illustrating a measurement error of a temperature output value output from the radiation thermometer When temperatures of a plurality of measurement bodies heated to a target temperature of 100° C. is measured by the radiation thermometer, respectively; 
         FIG. 19C  is a schematic view illustrating a measurement error of a. temperature output value output from the radiation thermometer when temperatures of a plurality of measurement bodies heated to a target temperature of 100° C. is measured by the radiation thermometer, respectively; 
         FIG. 19D  is a schematic view illustrating a measurement error of a temperature output value output from the radiation thermometer when temperatures of a plurality of measurement bodies heated to a target temperature of 100° C. is measured by the radiation thermometer, respectively; 
         FIG. 20  is a flowchart showing a first half of a method of performing the calibration of the radiation thermometer in a calibration system with the calibration tool shown in  FIG. 18A ; and 
         FIG. 21  is a flowchart showing a latter half of the method of performing the calibration of the radiation thermometer in the calibration system with the calibration tool shown in  FIG. 18A . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will now be described with reference to the drawings. 
       FIG. 1  is a schematic view showing a polishing apparatus according to one embodiment. The polishing apparatus shown in  FIG. 1  includes a polishing head  1  for holding and rotating a wafer W which is an example of a substrate, a polishing table  2  that supports a polishing pad  3 , a polishing-liquid supply nozzle  4  for supplying a polishing liquid (e.g. a slurry) onto a surface of the polishing pad  3 , and a pad-temperature regulating apparatus  5  for regulating a surface temperature of the polishing pad  3 . The surface (upper surface) of the polishing pad  3  provides a polishing surface for polishing the wafer W. 
     The polishing head  1  is vertically movable, and is rotatable about its axis in a direction indicated by arrow. The water W is held on a lower surface of the polishing head  1  by, for example, vacuum suction. A motor (not shown) is coupled to the polishing table  2 , so that the polishing table  2  can rotate in a direction indicated by arrow. As shown in  FIG. 1 , the polishing head  1  and the polishing table  2  rotate in the same direction. The polishing pad  3  is attached to an upper surface of the polishing table  2 . 
     Polishing of the wafer W is performed in the following manner. The wafer W, to be polished, is held by the polishing head I, and is then rotated by the polishing head  1 . The polishing pad  3  is rotated together with the polishing table  2 . In this state, the polishing liquid is supplied from the polishing-liquid supply nozzle  4  onto the surface of the polishing pad  3 . and the surface of the wafer W is then pressed by the polishing head I against the surface (i.e. polishing surface) of the polishing pad  3 . The surface of the wafer W is polished by the sliding contact with the polishing pad  3  in the presence of the polishing liquid. The surface of the wafer W is planarized by the chemical action of the polishing liquid and the mechanical action of abrasive grains contained in the polishing liquid. 
     The pad-temperature regulating apparatus  5  includes a heat exchanger  11  which can contact the surface of the polishing pad  3 , and a liquid supply system  30  for supplying a heating liquid having a regulated temperature and a cooling liquid having a regulated temperature into the heat exchanger  11 . This liquid supply system  30  includes a heating-liquid supply tank  31  as a heating-liquid supply source for storing the heating liquid having a regulated temperature, and a heating-liquid supply pipe  32  and a heating-liquid return pipe  33 , each coupling the heating-liquid supply tank  31  to the heat exchanger  11 . One ends of the heating-liquid supply pipe  32  and the heating-liquid return pipe  33  are coupled to the heating-liquid supply tank  31 , while the other ends are coupled to the heat exchanger I I. 
     The heating liquid having a regulated temperature is supplied from the heating-liquid supply tank  31  to the heat exchanger  11  through the heating-liquid supply pipe  32 , flows in the heat exchanger  11 , and is retuned from the heat exchanger  11  to the heating-liquid supply tank  31  through the heating-liquid return pipe  33 . In this manner, the heating liquid circulates between the heating-liquid supply tank  31  and the heat exchanger  11 . The heating-liquid supply tank  31  has a heater (not shown) disposed therein, this heater heating the heating liquid to a predetermined temperature. 
     A first on-off valve  41  and a first flow control valve  42  are attached to the heating-liquid supply pipe  32 . The first flow control valve  42  is located between the heat exchanger  11  and the  - first on-off valve  41 . The  - first on-off valve  41  is a valve not having a flow rate regulating function, whereas the first flow control valve  42  is a valve having a flow rate regulating function. 
     The liquid supply system  30  further includes a cooling-liquid supply pipe  51  and a cooling-liquid discharge pipe  52 , both coupled to the exchanger  11 . The cooling-liquid supply pipe  51  is coupled to a cooling-liquid supply source (e.g. a cold water supply source) provided in a factory in which the polishing apparatus is installed. The cooling liquid is supplied to the heat exchanger  11  through the cooling-liquid supply pipe  51 , flows in the heart exchanger  11 , and is drained from the heat exchanger  11  through the cooling-liquid discharge pipe  52 . In one embodiment, the cooling liquid that has flowed through the heat exchanger  11  may he returned to the cooling-liquid supply source through the cooling-liquid discharge pipe  52 . 
     A second on-off valve  55  and a second flow control valve  56  are attached to the cooling-liquid supply pipe  51 . The second flow control valve  56  is located between the pad contact member  11  and the second on-off valve  55 . The second on-off valve  55  is a valve not having a flow rate regulating function, whereas the second flow control valve  56  is a valve having a flow rate regulating function. 
     The pad-temperature regulating system  5  further includes a radiation thermometer  39  for measuring a surface temperature of the polishing pad  3  (which may hereinafter be referred to as pad surface temperature), and a controller  40  which operates the first flow control valve  42  and the second flow control valve  56  based on the pad surface temperature measured by the radiation thermometer  39 , The first on-off valve  41  and the second on-off valve  55  are usually open. 
     The radiation thermometer  39  measures the pad surface temperature in a non-contact manner, and sends a measured value of the pad surface temperature to the controller  40 . The controller  40  operates the first flow-rate control valve  42  and the second flow-rate control valve  56  to control the flow rates of the heating fluid and the cooling fluid based on the measured pad surface temperature so that the pad surface temperature is maintained at a preset target temperature. The first flow-rate control valve  42  and the second flow-rate control valve  56  operate according to control signals from the controller  40  to regulate the flow rate of the heating liquid and the flow rate of the cooling liquid to be supplied to the heat exchanger  11 . The heat exchange is performed between the heating and cooling liquids flowing through the heat exchanger H and the polishing pad  3 . As a result, the pad surface temperature changes. 
     By such feedback control, the surface temperature of the polishing pad  3  (i.e, the pad surface temperature) is maintained at a predetermined target temperature. In this embodiment, the controller  40  is configured to control operations of the polishing apparatus as a whole, including the pad-temperature regulating apparatus  5  and the polishing head  1 . The target temperature of the polishing pad  3  is determined based on a type of the wafer W or a polishing process. The determined target temperature is input in advance to the controller  40 . 
     In order to maintain the pad surface temperature at the predetermined target temperature, the heat exchanger  11  is placed in contact with the surface (i.e. the polishing surface) of the polishing pad  3  during polishing of the wafer W. In this specification, the manner of contact of the heat exchanger  11  with the surface of the polishing pad  3  includes not only direct contact of the heat exchanger  11  with the surface of the polishing pad  3 , but also contact of the heat exchanger I I with the surface of the polishing pad  3  in the presence of a polishing liquid (or slurry) between the heat exchanger  11  and the surface of the polishing pad  3 . In either case, heat exchange occurs between the polishing pad  3  and the heating liquid and cooling liquid, flowing in the heat exchanger  11 , whereby the pad surface temperature is controlled. 
     Hot water may be used as the heating liquid to be supplied to the heat exchanger  11 , When it is intended to raise the surface temperature of the polishing pad  3  more quickly, a silicone oil may be used as the heating liquid. Cold water or a silicone oil may be used as the cooling liquid to be supplied to the heat exchanger  11 . In the case of using a silicone oil as the cooling liquid, the polishing pad  3  can be cooled quickly by coupling a chiller as a cooling-liquid supply source to the cooling-liquid supply pipe  51 , and by cooling the silicone oil to a temperature of not more than 0° C. Pure water can be used as the cold water. In order to cool pure water to produce cold water, a chiller may be used as a cooling-liquid supply source. In this case, cold water that has flowed through the heat exchanger H may be returned to the chiller through the cooling-liquid discharge pipe  52 . 
     The heating-liquid supply pipe  32  and the cooling-liquid supply pipe  51  are completely independent pipes. Thus, the heating liquid and the cooling liquid can be simultaneously supplied to the heat exchanger H without mixing with each other, The heating-liquid return pipe  33  and the cooling-liquid discharge pipe  52  are also completely independent pipes. Thus, the heating liquid is returned to the heating-liquid supply tank  31  without mixing with the cooling liquid, while the cooling liquid is either drained or returned to the cooling-liquid supply source without mixing with the heating liquid. 
     The polishing apparatus according to this embodiment has a radiation thermometer for measuring the surface temperature (pad surface temperature) of the polishing pad  3  in the vicinity of the polishing head  1 ,  FIG. 2  is a schematic view showing a radiation thermometer for measuring the pad surface temperature in the vicinity of the polishing head  1 , As shown in  FIG. 2 , the polishing head  1  is coupled to a rotation shaft  15  which rotates the polishing head  1 , and the rotation shaft  15  is surrounded by a cover  16 . The cover  16  has a flange portion  16 a protruding from an outer surface thereof, and a radiation thermometer  48  is attached to a lower surface of the flange portion  16 a. In the following description, the radiation thermometer  39  may be referred to as a “first radiation thermometer  39 ”, and the radiation thermometer  48  may be referred to as a “second radiation thermometer  48 ”, 
     The second radiation thermometer  48  measures the pad surface temperature in the vicinity of the polishing head  1  that is polishing the wafer W. The second radiation thermometer  48  is also connected to the controller  40 , and the pad surface temperature measured by the second radiation thermometer  48  is sent to the controller  40 . The controller  40  stores in advance an allowable range of the pad surface temperature with respect to the target temperature which is preset according to each of polishing processes. While the wafer W is being polished, the controller  40  monitors whether or not the measured values of the pad surface temperature sent from the second radiation thermometer  48  are within the allowable range. When the measured value of the pad surface temperature deviates from the allowable range, the controller  40  issues an alarm. 
     In one embodiment, the controller  40  may issue an alarm and together stop polishing of the wafer W. During polishing of the wafer W, the controller  40  monitors the pad surface temperature measured by the second radiation thermometer  48 , thereby preventing a polishing abnormality from occurring in the wafer W. 
       FIG. 3  is an enlarged schematic view showing a sensor unit of the second radiation thermometer  48  shown in  FIG. 2 . Configuration of a sensor unit of the first radiation thermometer  39  is the same as the configuration of the sensor unit of the second radiation thermometer  48 , and thus duplicate descriptions thereof are omitted. 
     Typically, a radiation thermometer measures an intensity (an amount of energy) of electromagnetic wave, such as ultraviolet rays, infrared rays, or visible rays, emitted from an object to be measured, and converts the intensity into temperature to thereby measure the temperature of the object to be measured. As shown in  FIG. 3 , the sensor unit  48   a  of the second radiation thermometer  48  faces the surface of the polishing pad  3  so that the electromagnetic waves emitted from the surface of the polishing pad  3 , which is the object to he measured, effectively reach the sensor unit  48   a . A tip of the sensor unit  48   a  is surrounded by a barrier  49 , which is a member that prevents electromagnetic waves emitted from objects other than the polishing pad  3  from reaching the sensor unit  48   a . The barrier  49  protects the second radiation thermometer  48  from disturbances, allowing accurate pad surface temperature to be measured. 
     After a certain period of time has passed since the start of use of the radiation thermometers  39  and  48 , each of the output values of the radiation thermometers  39 ,  48  may deviates from the actual pad surface temperature. Therefore, the radiation thermometers  39 ,  48  are periodically calibrated using a. calibration system, which will be described below. For example, the calibration process for each of radiation thermometers  39 ,  48  is performed during maintenance of the polishing apparatus, or after replacing of the polishing pad  3 . 
       FIG. 4  is a schematic view showing a configuration of calibration system according to one embodiment. The calibration system shown in  FIG. 4  is used to calibrate the first radiation thermometer  39  and the second radiation thermometer  48 .  FIG. 5A  is a top view schematically showing a calibration tool of the calibration system shown in  FIG. 4 . and FIG. SB is a side view of the calibration tool shown in  FIG. 5A , 
     The calibration system shown in  FIG. 4  includes a calibration tool  60  placed below the second radiation thermometer  48 , and a temperature regulator  66  coupled to the calibration tool  60 .  FIG. 4  illustrates an example in which the calibration tool  60  of the calibration system is placed below the second radiation thermometer  48 . When performing the calibration process of the first radiation thermometer  39 , the calibration tool  60  is placed below the first radiation thermometer  39 . 
     As shown in  FIGS. 5A and 5B , the calibration tool  60  includes a heating device  61 , such as a hot plate, and a platform  63  for supporting the heating device  61 . The heating device  61  includes a heating plate  61   a , a heater  61   b  disposed under the heating plate  61   a , and a temperature sensor  61   c  capable of measuring a temperature of the heating plate  61   a , The heater  51   b  has an upper surface disposed so as to be in contact with lower surface of the heating plate  61   a , and a lower surface secured to the platform  63 . In one embodiment, the heater  61   b  may be arranged inside the heating plate  61   a . In this case, a lower surface of the heating plate  61   a  is secured to the platform  63 . 
     The calibration tool  60  is coupled to the temperature regulator  66  (see  FIG. 4 ), The temperature regulator  66  controls operation of the heater  61   b  based on a temperature of the heating plate  61   a  output from the temperature sensor  61   c  of the heating device  61  (for example, PID control), thereby maintaining the temperature of the heating plate  61   a  at a predetermined target temperature. The temperature sensor  61   c  shown in  FIG. 5B  is a thermocouple. However, the type of the temperature sensor  61   c  is free-selected. For example, the temperature sensor  61   c  may be a platinum resistance thermometer, a thermistor thermometer, or a bimetal thermometer. 
     As shown in  FIG. 5B , the platform  63  includes a main frame  63   a  having a substantially C-shaped cross section, and a reinforcing rib  63   b . The main frame  63   a  is constructed of a main plate extending in a vertical direction, and two plate-shaped arms connected to both ends of the main plate and extending in a horizontal direction. The reinforcing rib  63   b  extends from one arm to the other arm, and the heating device  61  is secured to an upper surface of one ann. A lower surface of the other ann comes into contact with the polishing pad  3  when the platform  63  is placed on the polishing pad  3 . The reinforcing rib  63   b  is a member for preventing the main frame  63   a  of the platform  63  from being bent by parts of the calibration tool  60 , such as the heating device  61 . When the platform  63  is placed on the polishing pad  3 , the reinforcing rib  63   b  keeps the upper surface of the heating plate  61   a  horizontal. Further, the calibration tool  60  includes a frame body  71  which is secured to the platform  63  so as to surround the heating plate  61   a  of the heating device  61 . The frame body  71  is a member for preventing the heating plate  61   a  from colliding with members for example, the polishing head  1 ) disposed in the polishing apparatus. 
     As described above, the conventional calibration of the radiation thermometer has been performed using the portable radiation thermometer held by an operator. In this embodiment, when the platform  63  is placed on the upper surface of the polishing pad  3  so that the upper surface of the heating plate  61   a  of the heating device  61  faces the second radiation thermometer  48 , a distance between the heating device  61  and the second radiation thermometer  48  is always kept constant. Further, the upper surface of the heating plate  61   a  faces the sensor unit  48   a  of the second radiation thermometer  48  so as to be parallel to each other. Therefore, it is possible to avoid a problem that the calibration result varies depending on the skill level of operator. 
     As shown in  FIG. 4 . the temperature regulator  66  is connected to the controller  40  of the polishing apparatus, and is configured to be able to change the set temperature of the temperature regulator  66  based on an instruction from the controller  40 . In other words, the controller  40  can regulate the temperature of the heating plate  61   a  of the heating device  61  to a desired target temperature through the temperature regulator  66 . 
     The calibration tool  60  may have a cooling device capable of cooling the heating plate  61   a  of the heating device  61 . In this embodiment, the cooling device of the calibration tool  60  is a cooling fan  65  capable of sending air to the heating plate  61   a  of the heating device  61 . The cooling fan  65  is connected to the temperature regulator  66 , and the temperature regulator  66  controls the operations of the heater  61   b  and the cooling fan  65  to regulate the temperature of the heating plate  61   a  to the desired target temperature. The air sent from the cooling fan  65  to the heating plate  61   a  enables the temperature of the heating plate  61   a  to be regulated more precisely. Further, in the initial stage of heating of the heating plate  61   a , a so-called “overshoot phenomenon” may occur, in which the temperature of the heating plate  61   a  rises significantly above the target temperature. However, the air sent from the cooling fan  65  can quickly converge the overshoot phenomenon of the heating plate  61   a , so that the time required to calibrate the second radiation thermometer  48  can be reduced. 
       FIG. 6  is a schematic view showing an example of internal structure of the second radiation thermometer  48 . The first radiation thermometer  39  also has the same internal structure as the internal structure shown in  FIG. 6 , and thus duplicate descriptions thereof are omitted. As shown in  FIG. 6 , the second radiation thermometer  48  has a sensor unit  48   a  for measuring an intensity (an amount of energy) of electromagnetic wave. such as ultraviolet rays, infrared rays, or a visible rays, emitted from an object to be measured, an amplifier  48   b  for amplifying an analog signal value output from the sensor unit  48   a , an analog-digital converter (AD converter)  48   c  for converting the analog signal value amplified by the amplifier  48   b  into a digital signal value, an emissivity correction unit  48   d  for correcting a digital signal value output from an analog-digital converter  48   c  based on an emissivity of the object to be measured, and a conversion unit  48   e  for converting the corrected digital signal value output from the emissivity correction unit  48   d  into a temperature of the object to be measured. In the second radiation thermometer  48  shown in  FIG. 6 , the sensor unit  48   a , the amplifier  48   b , the AD converter  48   c , the emissivity correction unit  48   d , and the conversion unit  48   e  are arranged in this order. However, this embodiment is not limited to this example. For example, in the second radiation thermometer  48 , the sensor unit  48   a , the amplifier  48   b , the emissivity correction unit  48   d , the AD converter  48   c , and the conversion unit  48   e  may be arranged in this order. 
     In order for the second radiation thermometer  48  to accurately measure a temperature of the object to be measured, it is preferable to input in advance an emissivity of the object to be measured into the emissivity correction unit  48   d  of the second radiation thermometer  48 . Therefore, in this embodiment, a measurement body  68  having a predetermined emissivity is attached to the upper surface of the heating plate  61   a  of the heating device  61  (see  FIGS. 5A and 5B ). When the heating plate  61   a  of the heating device  61  is heated by the heater  61   b , a temperature of the measurement body  68  becomes the same as a temperature of the heating plate  61   a . When calibrating the second radiation thermometer  48 , a position of the calibration tool  60  is adjusted so that the measurement body  68  is located directly under the second radiation thermometer  48 , and the second radiation thermometer  48  measures the temperature of the measurement body  68  having the same temperature as the heating plate  61   a . In this case, the heat radiation surface of the heating device  61  measured by the second radiation thermometer  48  is a surface of the measurement body  68 . Examples of the measurement body  68  include a blackbody tape having a known emissivity. In one embodiment, a blackbody paint having a known emissivity may be applied to the upper surface of the heating plate  61   a  to form the measurement body  68 . The known emissivity of the blackbody tape or the blackbody paint is input to the emissivity correction unit  48   d  in advance. The emissivity correction mit  48   d  corrects the digital signal value output from the analog-digital converter  48   c  into a digital signal value that is a case where the emissivity of the measurement body  68  is a predetermined value (e.g, 1.0), based on the input emissivity of the measurement body  68 . 
     In one embodiment, the emissivity of the measurement body  68  may be unknown. In this case, the emissivity correction unit  48   d  outputs the digital signal value output from the analog-digital converter  48   c  to the conversion unit  48   e  without any correction. 
     The measurement body  68  may be made of a material having an emissivity similar to that of the polishing pad  3 . For example, the measurement body  68  made of the same resin as the polishing pad  3  may be attached to the upper surface of the heating plate  61   a . Alternatively, the measurement body  68  may be omitted, and the heating plate  61   a  may be used as the measurement body whose temperature is measured by the second radiation thermometer  48 . In this case, the heat radiation surface of the measurement body measured by the second radiation thermometer  48  is the surface (upper surface) of the heating plate  61   a . Further, it is preferable that the heating plate  61   a  is made of the same resin as the polishing pad  3 . 
     Next, a method of calibrating the second radiation thermometer  48  will be described. A method of calibrating the first radiation thermometer  39  is the same as the method of calibrating the second radiation thermometer  48 , and thus duplicate descriptions thereof are omitted. 
       FIG. 7  is a flowchart showing a first half of a method of calibrating the second radiation thermometer  48  according to one embodiment, and  FIG. 8  is a flowchart showing a latter half of the method of calibrating the second radiation thermometer  48  according to one embodiment. As shown in  FIG. 4 , first, the calibration tool  60  is placed on the upper surface of the polishing pad  3  so that the measurement body  68  faces the sensor unit  48   a  of the second radiation thermometer  48  (step  1  in  FIG. 7 ). Further, the temperature regulator  66  of the calibration system is connected to the controller  40  of the polishing apparatus (step  2  in  FIG. 7 ). 
     The controller  40  stores in advance a plurality of target temperatures set for performing calibration of the second radiation thermometer. The plurality of target temperatures are, for example, constructed of a group of temperatures that are shifted every predetermined temperature interval (e.g, 10° C.), and this group includes, for example, temperatures of 30° C., 40° C., 50° C., 60° C., 70° C., and 80° C. Next, the controller  40  sends one target temperature Ta selected from the plurality of target temperatures to the temperature regulator  66  to heat the heating plate  61   a  and the measurement body  68  of the heating device  61  to the target temperature Ta (step  3  in  FIG. 7 ). In this embodiment, the controller  40  firstly sends the smallest target temperature (for example, 30° C.) Ta among the plurality of target temperatures to the temperature regulator  66 . 
     When the temperature of the measurement body  68  reaches the target temperature Ta and the measured value of the temperature sensor  61   c  stabilizes at the target temperature Ta, the second radiation thermometer  48  measures the temperature of the measurement body  68  (step  4  in  FIG. 7 ), and sends the measured value to the controller  40 . The controller  40  stores the temperature output value (the measured value of temperature) of the measurement body  68  sent from the second radiation thermometer  48  (step  5  in  FIG. 7 ). 
     Next, the controller  40  determines whether or not the temperature measurements of the measurement body  68  by the second radiation thermometer  48  have been performed for all the target temperatures (step  6  in  FIG. 7 ). In this embodiment, the controller  40  determines whether or not the target temperature Ta used in step  3  is the highest target temperature (for example, 80° C.) among the plurality of target temperatures, When the target temperature Ta used in step  3  is not the highest target temperature (“No” in step  6  of  FIG. 7 ), the controller  40  selects a target temperature Tb (for example, 40° C.), which is next higher than the target temperature Ta, among the plurality of target temperatures as a next target temperature Ta (step  7  in  FIG. 7 ), and repeats the steps  3  to  5 . 
     When the temperature measurement of the measurement body  68  by the second radiation thermometer  48  is performed for all the target temperatures (“Yes” in step  6  of  FIG. 7 ). the controller  40  calculates a difference between each target temperature Ta and the temperature output value of the second radiation thermometer  48  corresponding to the target temperature Ta, respectively (step  8  in  FIG. 7 ). The difference between the target temperature Ta and the temperature output value of the second radiation thermometer  48  corresponding to the target temperature Ta is an error of the measured value of the second thermometer  48  with respect to the target temperature Ta. In this embodiment, the difference between each target temperature Ta and the temperature output value of the second radiation thermometer  48  corresponding to the target temperature Ta is referred to as “temperature deviation amount”. Next, the controller  40  determines whether or not all the temperature deviation amounts are within a reference range (step  9  in  FIG. 7 ). The reference range for the temperature deviation amounts is preset, and stored in the controller  40  in advance, 
     When there is any temperature deviation amount that exceeds the reference range (“No” in step  9  of  FIG. 7 ), the controller  40  corrects the temperature output values from the second radiation thermometer  48  so that all the temperature deviation amounts are within the reference range (step  10  in  FIG. 8 ). In this embodiment, in order to correct the temperature output values from the second radiation thermometer  48 , the controller  40  corrects (i.e, changes) conversion parameters stored in the analog-digital converter  48   c  of the second radiation thermometer  48 . 
       FIGS. 9 through 11  are graphs for illustrating an example of a method of correcting the temperature output values of the second radiation thermometer  48 , More specifically,  FIG. 9  is a graph illustrating an example of a function that shows a relationship between each target temperature Ta and the temperature output value of the second radiation thermometer  48  corresponding to this target temperature Ta,  FIG. 10  is a graph illustrating an example in which a v-intercept of the function shown in  FIG. 9  has been corrected, and  FIG. 11  is a graph illustrating an example in which a slope of the function shown in  FIG. 10  has been corrected. In the graphs shown in  FIGS. 9 through 11 , a vertical axis (y-axis) represents the temperature output value of the second radiation thermometer  48 , and a horizontal axis (x-axis) represents the target temperature Ta. Further, in the graphs shown in  FIGS. 9 through 11 , an upper limit line UL corresponding to an upper limit, and a lower limit line LL corresponding to a lower limit in the reference range for the temperature deviation amounts are shown by virtual lines (dated lines), respectively. 
     As described above, the controller  40  stores in advance the plurality of target temperatures Ta to be output to the temperature regulator  66 , and the second radiation temperature  48  sends the measured values of temperature of the measurement body  68  heated to each target temperature Ta to the controller  40 . Therefore, the controller  40  can plot the temperature output values of the second radiation thermometer  48  corresponding to each target temperature Ta on a graph as shown in  FIG. 9 . Further, the controller  40  calculates a function RF based on all the plot points. For example, the controller  40  calculates an approximate straight line based on all the plot points by the least square method, and uses this approximate straight line as the function RF. 
     In the example shown in  FIG. 9 , a plot point Px exceeds the upper limit line UL. In this case, the controller  40  determines in step  9  shown in  FIG. 7  that there is a temperature deviation amount exceeding the reference range, and corrects the slope (i.e, gain) and y-intercept (i.e, offset) of the function RF so that all the temperature deviation amounts are within the reference range. 
     In this embodiment, the conversion parameters stored in the analog-digital converter  48   c  of the second radiation thermometer  48  are corrected to thereby change the slope and the y-intercept of the function RF. The v-intercept of the function RF corresponds to the temperature output value of the second radiation thermometer  48  in the function RF when the target temperature Ta is zero. The controller  40  calculates a correction amount in v-intercept based on all the temperature deviation amounts, and moves the function RF up and down along the y-axis based on this correction amount. In the example shown in  FIG. 10 , the function RF shown in  FIG. 9  is moved up along the y-axis so that the y-intercept of the function RF becomes zero. The function RF may be moved down alone the v-axis so that all the temperature deviation amounts are in the reference range. Further, the corrected y-intercept may be different from zero. 
     Next, the controller  40  calculates a correction amount in slope of the function RF based on all the temperature deviation amounts, and changes the slope of the function RF based on this correction amount.  FIG. 11  shows an example of reducing the slope of the function RF which passes through the corrected y-intercept (origin in the graph shown in  FIG. 11 ) so that all the temperature deviation amounts are within the reference range. Of course, the slope of the correlation function RF may be increased so that all the temperature deviation amounts are within the reference ranee. 
     In one embodiment, the controller  40  may correct the y-intercept of the function RF after correcting the slope of the function RF, or may simultaneously correct the slope and the y-intercept of the function RF. Further, if all the temperature deviation amounts are within the reference range after correcting the v-intercept (or the slope) of the function RF, the controller  40  may omit the correction of the slope (or y-intercept) of the function RF. 
     As described above, the conversion unit  48   e  of the second radiation thermometer  48  converts the corrected digital signal value output from the emissivity correction unit  48   d  into the temperature of the object to be measured. Specifically, the conversion unit  48   e  stores in advance a conversion formula for converting the corrected digital signal value into the pad surface temperature. In one embodiment, the controller  40  may correct (i.e., change) parameters of the conversion formula stored in the conversion unit  48   e  in order to correct the slope and y-intercept of the function RF (i.e, to calibrate the second radiation thermometer  48 ). For example, when the conversion formula is a linear function, a slope and a. y-intercept of the conversion formula may be corrected, and when the conversion formula is a quadratic function, coefficients of the conversion formula may be corrected. 
     In this embodiment, the calibration operation of the second radiation thermometer performed by the controller  40  corresponds to the operation shown in steps  3  through  10  described above. The controller  40  measures the temperature of the measurement body  68  at each target temperature Ta with the second radiation thermometer  48  while changing the temperatures of the heating plate  61   a  and the measurement body  68  of the heating device  61  to each of the plurality of target temperatures Ta, and calculates the temperature deviation amounts. Further, the controller  40  corrects the conversion parameters stored in the analog-digital converter  48   c  of the second radiation thermometer  48  (or the parameters of the conversion formula stored in the conversion unit  48   e ) so that all the temperature deviation amounts are within the reference range. 
     The controller  40  preferably checks whether or not all the temperature deviation amounts after correction at each target temperature Ta are within the above reference range (step  11  in  FIG. 8 ). Specifically, the controller  40  changes the temperatures of the heating plate  61   a  and the measurement body  68  of the heating device  61  to each target temperature Ta again, treasures the temperature of the measurement body  68  at each target temperature Ta with the second radiation thermometer  48 . calculates the temperature deviation amount at each target temperature Ta, and checks whether or not all the temperature deviation amounts are within the reference range. The operation shown in step  11  is a checking operation for determining whether or not the second radiation thermometer  48  has been reliably calibrated. 
     Before performing the checking operation, the temperatures of the heating plate  61   a  and the measurement body  68  of the heating device  61  have been heated by the calibration operation described above to the highest target temperature among the plurality of target temperatures, Accordingly, the controller  40  operates the cooling fan  65  to cool the temperatures of the heating plate  61   a  and the measurement body  68  in stages to each target temperature Ta from the highest target temperature to the lowest target temperature. In this case, a time required for the checking operation can be reduced, and thus a downtime of the polishing apparatus can be shortened. 
     In one embodiment, immediately after the calibration operation is completed, the controller  40  may operate the cooling fan  65  to cool the temperatures of the heating plate  61   a  and the measurement body  68  to room temperature (normal temperature). In this case, the checking operation is performed while heating the temperatures of the heating plate  61   a  and the measurement body  68  in stages to each target temperature Ta from the lowest target temperature to the highest target temperature. 
     When all the corrected temperature deviation amounts are within the reference range, the controller  40  generates a signal for indicating that the calibration process of the second radiation thermometer  48  is completed (step  12  in  FIG. 7 ). This completion signal is, for example, used as a trigger for activating a buzzer of the polishing apparatus. By sounding the buzzer of the polishing apparatus, an operator of the polishing apparatus can quickly recognize that the calibration of the second radiation thermometer  48  is completed. In a case also where all the temperature deviation amounts are within the reference range in step  9  of  FIG. 7  (“Yes” in step  9  of  FIG. 7 ), the controller  40  determines that it is not necessary to perform the calibration of the second radiation thermometer  48 , and generates the completion signal of the calibration process of the second radiation thermometer  48  (step  12  in  FIG. 7 ). 
     If, in the checking operation shown in step  11 , there is any temperature deviation amount that exceeds the reference range (“No” in step  11  of  FIG. 8 ), the controller  40  repeats the calibration operation shown in steps  3  through 10  described above, and the checking operation shown in step  11  described above. Specifically, the controller  40  adds one to the number of repetitions N of the combination of the calibration operation and the checking operation (step  13  in  FIG. 8 ). An initial value of the number of repetitions N is zero, and the controller  40  stores an upper limit NA of the number of repetitions N in advance. 
     The controller  40  compares the number of repetitions N with the upper limit NA (step  14  in  FIG. 8 ). When the number of repetitions N is smaller than the upper limit NA (“Yes” in step  14  of  FIG. 8 ), the controller  40  returns step  3  to repeat the calibration operation and the checking operation. When the number of repetitions N reaches the upper limit NA (“No” in step  14  of  FIG. 8 ), the controller  40  generates a signal for prompting a replacement of the second radiation thermometer  48  (step  15  in  FIG. 8 ). This replacement signal is, for example, used as a trigger for issuing an alarm for the polishing apparatus. In a. case where, even when the calibration operation is repeated until the number of repetitions N reaches the upper limit NA, there is at least one temperature deviation amount that exceeds the reference range in the checking operation, the second radiation thermometer  48  can be considered to be faulty, or to have reached the end of life thereof. Therefore, the controller  40  issues an alarm to thereby prompt the replacement of the second radiation thermometer  48 , preventing a polishing abnormality from occurring in the wafer W. 
     The upper limit NA may be one. In this case, if there is any temperature deviation amount that exceeds the reference range in step l l of  FIG. 8 , the controller  40  immediately generates the replacement signal for the second radiation thermometer  48  without repeating the calibration operation and the checking operation. 
     According to this embodiment, simply by placing the calibration tool  60  of the calibration system below the second radiation thermometer  48  (or the first radiation thermometer  39 ), and connecting, the temperature regulator  66  to the controller  40  of the polishing apparatus, the controller  40  automatically performs the calibration of the second radiation thermometer  48  (or the first radiation thermometer  39 ). Therefore, the burden on the operator and the downtime of the polishing apparatus are reduced, so that it can he expected that the calibration processes of the first radiation thermometer  39  and the second radiation thermometer  48  are periodically performed. As a result, the wafer W can be polished at a desired polishing rate, and further, the occurrence of polishing abnormalities on the wafer W can be effectively prevented. 
     As shown in  FIG. 4 , the calibration system may have an output device  43 , such as a printer. The output device  43  shown in  FIG. 4  is provided outside the polishing apparatus, and is configured to wirelessly communicate with the controller  40 . In one embodiment, the output device  43  may be configured to connect to the controller  40  by wire. Alternatively, the output device  43  connected to the controller  40  by wire or wirelessly may be provided inside the polishing apparatus. 
     The output device  43  reads out the calibration results of the second radiation thermometer  48  (or the first radiation thermometer  39 ) from the controller  40 . and outputs a calibration sheet as shown in  FIG. 12 . On the calibration sheet, at least the date when the radiation thermometer was calibrated, the slope (i.e, gain) and y-intercept (i.e, offset) of the function RF before and after the correction, and the temperature deviation amounts of the radiation thermometer obtained during the checking operation (see step  11  in  FIG. 8 ) are preferably indicated. Storing such calibration sheets enables the life (that is, replacement time) of each of the radiation thermometer  39 ,  48  to be estimated. 
       FIG. 13  is a perspective view schematically showing the calibration tool of the calibration system according to another embodiment. Configuration of this embodiment, which is not specifically described, is the same as the configuration of the above-described embodiments, and thus duplicate descriptions thereof are omitted. 
     The radiation thermometers  39 ,  48  may become dirty due to an adhesion of the polishing liquid or the like to the radiation thermometers  39 ,  48 . Further, the radiation thermometers  39 ,  48  may be failed. In these cases, since the radiation thermometers  39 ,  48  cannot accurately measure the pad surface temperature, there is a risk that polishing abnormalities may occur in the wafer W, or a yield may be decreased. Therefore, it is desirable to check whether or not the radiation thermometers  39 ,  48  are accurately measuring the pad surface temperature every time a predetermined number of wafers W are polished (for example, every time one wafer W is polished). For this purpose, in this embodiment, the calibration tool  60  is placed in the vicinity of the radiation thermometers to check the temperature output values of the radiation thermometers  39 ,  48  each time the predetermined number of wafers W are polished. 
       FIG. 13  illustrates a calibration tool  60  disposed in the vicinity of the first radiation thermometer  39 . Although not shown, a calibration tool having the same configuration as the calibration tool  60  shown in  FIG. 13  is also disposed in the vicinity of the second radiation thermometer  48 . In one embodiment, the calibration tool  60  shown in  FIG. 13  may be placed in the vicinity of either one of the first radiation thermometer  39  and the second radiation thermometer  48 . 
     The calibration tool  60  shown in  FIG. 13  includes a plurality of heating devices  61 A,  61 B (two heating devices in the illustrated example), the temperature regulator  66  connected to the heating devices  61 A,  61 B, and a moving mechanism (heating-device moving mechanism)  80  for moving each of the heating devices  61 A,  61 B below the first radiation thermometer  39 . In this embodiment, each of the heating devices  61 A and  61 B has the same configuration as the heating device  61  described with reference to  FIGS. 4 to 6 . Accordingly, each of the heating devices  61 A,  61 B has the measurement body  68  (see  FIGS. 5A and 5B ) described above. In one embodiment, each of the heating devices  61 A,  61 B may have a Peltier element as a heating source for the heating plate  61   a  and the measurement body  68 , instead of a heater  61   b.    
     In this embodiment, although the heating devices  61 A,  61 B are connected to the common temperature regulator  66 , individual temperature regulators  66  corresponding to each of the plurality of heating devices  61 A,  61 B may be provided. The controller  40  heats each of the plurality of heating devices  61 A,  61 B to the predetermined target temperatures through the temperature regulator  66 . The predetermined target temperatures set with respect to the heating devices  61 A,  61 B may be the same or different from each other. The controller  40  stores the predetermined target temperatures of the heating devices  61 A,  61 B in advance. 
     The moving mechanism  80  shown in  FIG. 13  has the platform  63  for supporting the heating devices  61 A,  61 B, and an actuator  82  for rotating the platform  63 . In this embodiment, the platform  63  is a plate member having a semicircular shape, and the actuator  82  is a motor. The moving. mechanism  80  further has a support arm  84  for supporting the actuator  82 , and the support arm  84  is secured to the first radiation thermometer  39 . The support arm  84  can be secured to any stationary member as long as it is capable of supporting the movement mechanism  80 . For example, the support arm  84  may be secured to a frame structure (not shown) of the polishing apparatus. Further, a rotation axis  82   a  of the actuator  82  is coupled to the platform  63 . When the actuator  82  is set in motion, the platform  63  rotates around the rotation axis  82   a . The actuator  82  is configured to allow the platform  63  to rotate at any desired rotation angle. 
       FIG. 14  is a schematic view showing a state in which one heating device  61 A is moved below the first radiation thermometer  39 .  FIG. 14  illustrates a first measurement position where the platform  63  has been moved so that one heating device  61 A is positioned below the first radiation thermometer  39 . Although not shown, a position of the platform  63  when the other heating device  61 B is positioned below the first radiation thermometer  39  is referred to as a second measurement position.  FIG. 13  illustrates a standby position where the platform  63  is moved away from the first radiation thermometer  39 . When the platform  63  is moved to the standby position, the first radiation thermometer  39  can measure the surface temperature of the polishing pad  3 . 
     When checking the temperature output values of the first radiation thermometer  39 , the controller  40  operates the actuator  82  to move the platform  63  from the standby position to each of the first and second measurement positions. The controller  40  further obtains from the first radiation thermometer the temperature output values of the measurement bodies  68  of the heating devices  61 A and  61 B, which are heated to the predetermined target temperatures, respectively. The distance from the first radiation thermometer  39  to the heating devices  61 A,  61 B is preferably as small as possible so as to avoid large errors in the temperature output values of the first radiation thermometer  39  due to disturbances. For example, the distance between the first radiation thermometer  39  and the heating devices  61 A,  61 B is set so that the surface area of the measurement body  68  is less than 1.5 times a field of view of the first radiation thermometer  39 . 
     As described above, the type of the temperature sensor  61   c  is free-selected. For example, the temperature sensor  61   c  may be a thermocouple, a platinum resistance thermometer, a thermistor thermometer, a bimetal thermometer, or IC temperature sensor. Since the platinum resistance thermometer has high measurement accuracy, it is preferable that the temperature sensor  61   c  is the platinum resistance thermometer. 
       FIG. 15  is a schematic view showing a protective cover for the heating devices  61 A and  61 B. If dirt (e.g, polishing liquid) adheres to the measurement bodies  68  of the heating devices  61 A,  61 B, the first radiation thermometer  39  cannot measure the accurate temperatures of the measurement bodies  68 . Therefore, the protective cover  85  may be provided, which covers the heating devices  61 A,  61 B that have been moved to the standby position. The protective cover  85  shown in  FIG. 15  has an approximate semicircular shape, and has a housing space formed therein, which provides accommodation for the heating devices  61 A,  61 B together with a part of the platform  63 . The protective cover  85  is secured to a stationary member, such as a frame structure of the polishing apparatus, through a secure member (not shown), such as a bracket. 
     Next, a method of checking the temperature output values of the first radiation thermometer  39  will be described. A method of checking the temperature output values of the second radiation thermometer  48  is the same as the method of checking the temperature output values of the first radiation thermometer  39 , and thus duplicate descriptions thereof are omitted. As described below, if the temperature output values of the radiation thermometers  39 ,  48  deviate from the allowable range set for the predetermined target temperature, the radiation thermometers  39 ,  48  are calibrated. 
       FIG. 16  is a flowchart showing a first half of the method for checking the temperature output values of the first radiation thermometer  39  according to one embodiment, and  FIG. 17  is a flowchart showing a latter half of the method for checking the temperature output values of the first radiation thermometer  39  according to one embodiment. 
     As shown in  FIG. 16 , the controller  40  performs the polishing process of the wafer W (step  1  in  FIG. 16 ). Next, the controller  40  determines whether or not the number of wafers Nw to be polished reaches a predetermined number of wafers NB (step  2  in  FIG. 16 ). The controller  40  stores the predetermined number of wafers NB in advance. The predetermined number of wafers NB may be “one”. If the number of wafers Nw to be polished has not reached the predetermined number of wafers NB (see “Yes” in step  2  of  FIG. 16 ), the controller  40  returns to step  1  to perform the polishing process for the next wafer W. 
     The controller  40  stores in advance a plurality of target temperatures Tb, Tc set for each measurement body  68  of the plurality of heating devices  61 A,  61 B in order to check the temperature output values of the first radiation thermometer  39 . These target temperatures Tb and Tc may be the same as each other or may be different from each other. When the number of wafers NW to be polished reaches a predetermined number of wafers NB (see “No” in step  2  of  FIG. 16 ), the controller  40  heats the measurement bodies  68  of the heating devices  61 A and  61 B to the target temperatures Tb and Tc, respectively, through the temperature regulator  66  (step  3  of  FIG. 16 ). 
     Next, the first radiation thermometer  39  measures the temperature of each measurement body  68  (step  4  in  FIG. 16 ), and sends those measured values to the controller  40 . Further, the controller  40  stores the temperature output values (temperature measurement values) of each measurement body  68  sent from the first radiation thermometer  39  (step  5  in  FIG. 16 ). 
     Next, the controller  40  calculates differences between the target temperatures Tb, Tc and the temperature output values of the first radiation thermometer  39  corresponding to each target temperatures Tb, Tc, respectively (step  6  in  FIG. 16 ). In other words, the controller  40  calculates “temperature deviation amounts”, which are the differences between each of the target temperatures Tb, Tc and the temperature output values of the first radiation thermometer  39  corresponding to the target temperatures Tb and Tc, respectively. Next, the controller  40  determines whether or not all the temperature deviation amounts are within the reference range (step  8  in  FIG. 16 ), The reference range for the temperature deviation amounts is preset, and stored in the controller  40  in advance. 
     If there is any temperature deviation amount that exceeds the reference range (“No” in step  8  of  FIG. 16 ), the controller  40  corrects the temperature output values from the first radiation thermometer  39  so that all the temperature deviation amounts are within the reference range (step  10  of  FIG. 17 ). In this embodiment also, the controller  40  corrects (i.e, changes) the conversion parameters stored in the analog-digital converter  48   c  of the first radiation thermometer  39  in order to correct the temperature output values from the first radiation thermometer  39 . For example, the controller  40  corrects, using the method described with reference to  FIGS. 9 through 11  the slope (i.e, gain) and the y-intercept (i.e, offset) of the function RF so that all temperature deviation amounts are within the reference range. Alternatively, the correction of the temperature output values may he performed by the correction of the parameters of the conversion formula stored in the conversion unit  48   e  of the first radiation thermometer  39 . 
     In this manner, if any temperature output value of the first radiation thermometer  39  exceeds the allowable range when the measurement bodies  68  of the plurality of heating devices  61 A,  61 B are measured with the first radiation thermometer  39 , the calibration of the first radiation thermometer  39  is performed. As a result, the wafer W can be polished at a desired polishing rate, and further, the occurrence of polishing abnormalities on the wafer W can be effectively prevented. 
     In this embodiment also, the controller  40  preferably checks whether all the temperature deviation amounts after the correction are within the reference range (step  11  in  FIG. 17 ). Specifically, the controller  40  again measures the temperatures of the measurement bodies  68  of the heating devices  61 A and  61 B, which are maintained at the predetermined target temperatures Tb, Tc, respectively, with the first radiation thermometer  39 , calculates the temperature deviation amounts with respect to the target temperatures Tb,Tc, respectively, and checks whether all the temperature deviation amounts are within the reference range. The operation shown in step  11  is a checking operation for determining whether or not the first radiation thermometer  39  has been reliably calibrated. 
     If all the corrected temperature deviation amounts are within the reference ranee, the controller  40  returns to step  1  to perform the polishing process for the next wafer W. 
     In a case also where all the temperature deviation amounts are within the reference ranee in step  8  of  FIG. 16 , the controller  40  performs the polishing process for the next wafer W without performing the calibration of the first radiation thermometer  39 . 
     If, in the checking operation shown in step  11 , there is any temperature deviation amount that exceeds the reference range (“No” in step  11  of  FIG. 17 ), the controller  40  repeats the calibration operation shown in steps  3  through  10  and the checking operation shown in step  11 . Specifically, the controller  40  adds one to the number of repetitions N of the combination of the calibration operation and the checking operation (step  13  in  FIG. 17 ). The initial value of the number of repetitions N is zero, and the controller  40  stores the upper limit NA of the number of repetitions N in advance. 
     The controller  40  compares the number of repetitions N with the upper limit NA (step  13  in  FIG. 17 ). When the number of repetitions N is smaller than the upper limit NA (“Yes” in step  14  of  FIG. 8 ), the controller  40  returns step  3  of  FIG. 16  to repeat the calibration operation and the checking operation. When the number of repetitions N reaches the upper limit NA (“No” in step  13  of  FIG. 17 ), the controller  40  generates a signal for prompting a maintenance of the first radiation thermometer  48  (step  14  in  FIG. 17 ). This maintenance signal is, for example, used as a trigger for issuing an alarm for the polishing apparatus. In a case where, even when the calibration operation is repeated until the number of repetitions N reaches the upper limit NA, there is at least one temperature deviation amount that exceeds the reference range in the checking operation, it can be considered that dirt is attached to the first radiation thermometer  39 . or that the first radiation thermometer  39  is faulty. Therefore, the controller  40  issues an alarm to thereby prompt the maintenance of the first radiation thermometer  39 , preventing polishing abnormality from occurring in the wafer W. 
     The upper limit NA may be one. In this case, if there is any temperature deviation amount that exceeds the reference range in step  11  of  FIG. 17 , the controller  40  immediately generates the maintenance signal for the first radiation thermometer  39  without repeating the calibration operation and the checking operation. 
       FIG. 18A  is a top view schematically showing the calibration tool  60  of a calibration system according to still another embodiment, and  FIG. 1813  is a perspective view schematically showing a moving mechanism for moving the heating plate  61   a  shown in  FIG. 18A . Configuration of this embodiment, which is not specifically described, is the same as the configuration of the above-described calibration systems, and thus duplicate descriptions thereof are omitted. 
     As shown in  FIG. 18A , a plurality of measurement bodies (four measurement bodies in the illustrated example)  68 A,  68 B,  68 C,  68 D are attached to an upper surface of the heating plate  61   a  of the heating device  61 . The plurality of measurement bodies  68 A through  68 D have different emissivities from each other, and the emissivity of one measurement body (e.g, measurement body  68 A) selected from the plurality of measurement bodies  68 A through  68 D is input to the emissivity correction unit  48   d  (see  FIG. 6 ) of the second radiation thermometer  48 . The emissivities of each measurement bodies  68 A through  68 D are known, and stored in advance in the controller  40 . 
     Further, the calibration tool  60  has a moving mechanism (measurement-body moving mechanism)  74  for moving the heating plate  61   a  in a horizontal direction with respect to the platform  63 . In this embodiment, the moving mechanism  74  is constructed of a combination of an X-axis moving mechanism  75  and a Y-axis moving mechanism  76  that move the heating plate  61   a  horizontally. The X-axis moving mechanism  75  is configured to move the heating plate  61   a  along the X-axis, and the Y-axis moving mechanism  76  is configured to move the heating plate  61   a  along the Y-axis perpendicular to the X-axis. Each of these X-axis movement mechanism  75  and Y-axis movement mechanism  76  is, for example, constituted by a ball screw mechanism and a servomotor for driving the ball screw mechanism. In one embodiment, each of the X-axis movement mechanism  75  and the Y-axis movement mechanism  76  may be a piston-cylinder mechanism, The X-axis movement mechanism  75  and the Y-axis movement mechanism  76  are connected to the controller  40 , and the controller  40  can control operations of the X-axis movement mechanism  75  and the Y-axis movement mechanism  76 , i.e, an operation of the movement mechanism  74 . 
     The controller  40  can operate the X-axis moving mechanism  75  and the Y-axis moving mechanism  76  to thereby move the heating plate  61   a  in the X-axis and Y-axis directions relative to the second radiation thermometer  48  (or the first radiation thermometer  39 ). Thus, the controller  40  can control the operation of the moving mechanism  74  to thereby position each of the plurality of measurement bodies  68 A through  68 D attached to the upper surface of the heating plate  61 A directly under the second radiation thermometer  48  (or the first radiation thermometer  39 ). 
     In this embodiment, the temperature of each of the plurality of measurement bodies  68 A through  68 D heated to a predetermined target temperature is measured by the second radiation thermometer  48  (or the first radiation thermometer  39 ). As described above, the emissivity of one measurement body  68 A selected. front the plurality of measurement bodies  68 A through  68 D is input to the emissivity correction section  48   d  of the second radiation thermometer  48 . In this case, since the emissivities of the measurement bodies  68 B through  68 D is different from the emissivity input to the emissivity correction section  48   d  of the second radiation thermometer  48 , each of the temperature output values of the measurement bodies  68 B through  68 D output from the second radiation thermometer  48  includes a measurement error caused by the setting error of emissivity, This measurement error will he described below with reference to  FIGS. 19A through 19D . 
       FIGS. 19A through 191 ) are schematic views each of which illustrates a measurement error of a temperature output value output from the second radiation thermometer when temperatures of a plurality of measurement bodies  68 A through  68 D heated to a target temperature of 100° C. is measured by the second radiation thermometer  48 , respectively. More specifically,  FIG. 19A  is a schematic view showing a temperature output value Ma to be output from the second radiation thermometer  48  when the temperature of the measurement body  68 A heated to 100° C. and having an emissivity aa of  0 . 90  is measured by the second radiation thermometer  48 . and  FIG. 19B  is a schematic view showing a temperature output value Mb to be output from the second radiation thermometer  48  when the temperature of the measurement body  68 B heated to 100° C. and having an emissivity εb of  0 . 91  is measured by the second radiation thermometer  48 .  FIG. 19C  is a schematic view showing the temperature output value Mc to be output from the second radiation thermometer  48  when the temperature of the measurement body  68 C heated to 100° C. and having an emissivity εc of 0.92 is measured by the second radiation thermometer  48 , and  FIG. 19D  is a schematic view showing the temperature output value Md to be output from the second radiation thermometer  48  when the temperature of the measurement body  68 D heated to 100° C. and having an emissivity ad of 0.95 is measured by the second radiation thermometer  48 . 
     Typically, if an emissivity pre-input to the radiation thermometer differs from an emissivity of an object to be measured, the temperature output value (temperature measurement value) output from the radiation thermometer includes a measurement error caused by the emissivity setting error. The emissivity setting error is a ratio of the emissivity input to the radiation thermometer relative to the emissivity of the object to be measured, and is expressed by the following equation (1). 
         E (%)=(ε0/ε−1,00)·100   (1)
 
     where E represents the setting error of emissivity,  80  represents the emissivity input to the radiation thermometer, and  8  represents the emissivity of the object to be measured. 
     In this embodiment, the emissivity input to the second radiation thermometer  48  is 0.90, corresponding to the emissivity εa of the measurement body  68 A. Accordingly, when measuring the measurement body  68 A with the second radiation thermometer  48 , the emissivity setting error is 0%, and thus the temperature output value output from the second radiation thermometer  48  does not include the measurement error. In contrast, the emissivities εb-εd of the measurement bodies  68 B through  68 D are different from the emissivity εa of the measurement body  68 A, respectively. Therefore, when measuring each of the measurement bodies  68 B through  68 D with the second radiation thermometer  48 , each temperature output value output from the second radiation thermometer  48  includes a measurement error caused by the emissivity setting error. Specifically, when measuring the measurement body  68 B having the emissivity εb of 0.91, the emissivity setting error is 1%, and thus the temperature output value output from the second radiation thermometer  48  includes the measurement error caused by the emissivity setting error of 1%, Similarly, when measuring the measurement body  68 C having the emissivity εc of 0.92, the temperature output value output from the second radiation thermometer  48  includes the measurement error caused by the emissivity setting error of 2%, and when measuring the measurement body  68 D having the emissivity εd of 0.95, the temperature output value output from the second radiation thermometer  48  includes the measurement error caused by the emissivity setting error of 5%. 
     The relationship between the intensity (amount of energy) of the electromagnetic wave emitted from the object to be measured and the temperature of the object to be measured is not a linear relationship. Therefore, even though the emissivity setting error is multiplied by the temperature measurement value output from the radiation thermometer, the measurement error cannot be corrected. For example, when the emissivity setting error is 5%, multiplying the temperature measurement value output from the radiation thermometer by 1.05 does not obtain the actual temperature of the object to be measured. Further, the measurement error caused by the emissivity setting error depends on a wavelength of the electromagnetic wave used by the radiation thermometer and the temperature of the object to be measured. 
     However, if the emissivities of the plurality of measurement bodies  68 A to  68 D are known, each of the measurement errors occurring when the temperatures of the measurement bodies  68 A to  68 D heated to the predetermined target temperature Tx are measured h the second radiation thermometer can be obtained previously by experiments. In other words, expected values Ma-Md of the temperature output values to be output from the second radiation thermometer  48  when the measurement bodies  68 A to  68 D are measured by the second radiation thermometer  48 , respectively, can be obtained previously. In this specification, each of the expected values Ma-Md of the temperature output values to be output from the second radiation thermometer  48  is referred to as a “temperature expectation value. 
     For example, the target temperature Tx used for calibration of the second radiation thermometer  48  has been previously determined as 100° C. In this case, an experiment is performed, in which the temperatures of the measurement bodies  68 B through  68 D heated to 100° C. are actually measured with the second radiation thermometer  48  in which the emissivity Ea of the measurement body  68 A is input. Then, the temperature output values of the measurement bodies  68 B through  68 D output from the second radiation thermometer  48  are determined as the temperature expectation values Mb-Md, respectively. When measuring the measurement body  68 A with the second radiation thermometer  48 , the emissivity setting error is 0%, and thus the temperature measurement value does not include the measurement error. Therefore, the temperature expectation value Ma of the measurement body  68 A to be output from the second radiation thermometer  48  is equal to the target temperature Tx (=100° C.). Examples of the temperature expectation values Ma-Md determined by such experiment are illustrated in  FIGS. 19B through 19D . 
     In one embodiment, a characteristic equation, which represents a relationship between the emissivity setting error at the predetermined target temperature Tx and the measurement error, may be determined in advance based on the temperature output values of each of the measurement bodies  68 A through  68 D output from the second radiation thermometer  48 . In this case, the temperature expectation values Ma through Md are determined from the characteristic equation. 
     In this manner, in a case where the calibration of the second radiation thermometer  48  is performed using the calibration tool  60  according to this embodiment, it is necessary to determine in advance the temperature expectation values Ma-Md which are output from the second temperature radiometer  48  when each of the plurality of measurement bodies  68 A through  68 D heated to the predetermined target temperature Tx is measured by the second temperature radiometer  48 . The same applies a case where the calibration of the first radiation thermometer  39  is performed using the calibration tool  60  according to this embodiment. The temperature expectation values Ma Md are stored in advance in the controller  40 . 
     Next, referring to  FIGS. 20 and 21 , a method of calibrating the second radiation thermometer  48  using the calibration tool  60  shown in  FIG. 18A  will be described. A method of calibrating the first radiation thermometer  39  using the calibration tool  60  shown in  FIG. 18A  is the same as the method of calibrating the second radiation thermometer  48  described below, and thus duplicate descriptions thereof are omitted. 
       FIG. 20  is a flowchart showing a first half of a method of performing the calibration of the second radiation thermometer  48  in a calibration system with the calibration tool  60  shown in  FIG. 18A , and  FIG. 21  is a flowchart showing a latter half of the method of performing the calibration of the second radiation thermometer  48  in the calibration system with the calibration tool  60  shown in  FIG. 18A . The steps, which are not specifically described in the flowcharts shown in  FIGS. 20 and 21 . are the same as the steps in the flowcharts shown in  FIGS. 7 and 8 . 
     As shown in  FIG. 20 , in this embodiment also, the calibration tool  60  is placed. on the upper surface of the polishing pad  3  so that the heating plate  61   a  of the heating device  61  faces the sensor unit  48   a  of the second radiation thermometer  48  (step  1  in  FIG. 20 ), and further the temperature regulator  66  of the calibration system is connected to the controller  40  of the polishing apparatus (step  2  in  FIG. 20 ). 
     The controller  40  stores in advance the predetermined target temperature Tx, which is set for performing the calibration of the second radiation thermometer  48 . Although the predetermined target temperature Tx can be set freely, it is preferable that the predetermined target temperature Tx is set to the target temperature of the polishing pad  3  in a frequently used polishing process. The controller  40  heats the temperatures of the heating plate  61   a  and the plurality of measurement bodies  68 A- 68 D of the calibration tool  60  placed on the polishing pad  3  to the predetermined target temperature Tx through the temperature regulator  66  (step  3  in  FIG. 20 ). 
     Next, the controller  40  operates the moving mechanism  74  to move one measurement body  68 A among the plurality of measurement bodies  68 A through  68 D below the second radiation thermometer  48 , and measures the temperature of the measurement body  68 A with the second radiation thermometer  48  (step  4  in  FIG. 20 ). Then, the controller  40  stores the temperature output value output from the second radiation thermometer  48  (step  5  in  FIG. 20 ). 
     Next, the controller  40  determines whether or not the temperatures of all the measurement bodies  68 A through  68 D are measured (step  6  in  FIG. 20 ). When the temperatures of all the measurement bodies  68 A through  68 D are not measured (“No” in step  6  of  FIG. 20 ), the controller  40  operates the moving mechanism  74  to move the next measurement body  68 B below the second radiation thermometer  48  (step  7  of  FIG. 20 ). Further, the controller  40  measures the temperature of the measurement body  68 B with the second radiation thermometer  48  (step  4  in  FIG. 20 ), and stores the temperature output value output from the second radiation thermometer  48  (step  5  in  FIG. 20 ). 
     When the measurement of the temperatures of all measurement bodies  68 A through  681 ) is completed (“Yes” in step  6  of  FIG. 20 ), the controller  40  calculates the temperature deviation amount in each of the plurality of measurement bodies  68 A through  681 ) (step  8  of  FIG. 20 ). In this embodiment, the temperature deviation amount is a difference between each temperature expectation value Ma through Md, and the temperature output value of each measurement body  68 A through  68 D output from the second radiation thermometer  48 . For example, the temperature deviation amount in the measurement body  68 A is the difference between the temperature expectation value Ma. (100° C. in  FIG. 19 ) and the temperature output value of the second radiation thermometer  48  for the measurement body  68 A, and the temperature deviation amount in the measurement body  68 A is the difference between the temperature expectation value Md (103.2° C. in  FIG. 19 ) and the temperature output value of the second radiation thermometer  48  for the measurement body  68 A. Next, the controller  40  determines whether or not all of the temperature deviation amounts are within the reference range (step  9  in  FIG. 20 ). The reference range for the temperature deviation amounts is preset, and stored in the controller  40  in advance. 
     When there is any temperature deviation amount that exceeds the reference range (“No” in step  9  of  FIG. 20 ), the controller  40  corrects the temperature output values from the second radiation thermometer  48  so that all the temperature deviation amounts are within the reference range (step  10  in  FIG. 21 ). The correction of the temperature output values may be performed by the correction of the conversion parameters stored in the analog-digital converter  48   c  of the second radiation thermometer  48 , or by the correction of the parameters of the conversion formula stored in the conversion unit  48   e  of the second radiation thermometer  48 . 
     In this embodiment also, the calibration operation of the second radiation thermometer performed by the controller  40  corresponds to the operation shown in step  3  through step  10 . The controller  40  measures the temperatures of the plurality of measurement bodies  68 A through  68 D heated to the predetermined target temperature Tx with the second radiation thermometer  48 , and calculates the temperature deviation amounts for each measurement body. Further, the controller  40  corrects the conversion parameters stored in the analog-digital converter  48   c  of the second radiation thermometer  48  (or the parameters of the conversion formula stored in the conversion unit  48   e ) so that all the temperature deviation amounts are within the reference range. 
     The controller  40  preferably checks whether all the temperature deviation amounts for each measurement bodies  68 A through  68 D after the correction are within the reference range (step  11  in  FIG. 21 ). Specifically, the controller  40  again measures all of the temperatures of the measurement bodies  68 A through  68 D, each of which is maintained at the predetermined target temperatures Tx, with the second radiation thermometer  48 , calculates the temperature deviation amounts for each of the measurement bodies  68 A through  68 D, and checks whether or not all the temperature deviation amounts are within the reference range. The operation shown in step  11  is a checking operation for determining whether or not the second radiation thermometer  48  has been reliably calibrated. 
     When all the corrected temperature deviation amounts are within the reference range, the controller  40  generates a signal for indicating that the calibration process of the second radiation thermometer  48  is completed (step  12  in  FIG. 20 ). in the checking operation shown in step I I, there is any temperature deviation amount that exceeds the reference range (“No” in step  11  of  FIG. 21 ), the controller  40  repeats the calibration operation shown in steps  3  through 10 , and the checking operation shown in step IL Further, when the number of repetitions N reaches the upper limit NA (“No” in step  14  of  FIG. 21 ), the controller  40  generates a signal for prompting a replacement of the second radiation thermometer  48  (step  15  in  FIG. 21 ). 
     In this embodiment, it is not necessary to heat the heating plate  61 A and the measurement bodies  68 A to  68 D to multiple target temperatures in order to perform the calibration of the second radiation thermometer  48 . In other words, it is only necessary to heat the heating plate  61  a and the measurement bodies  68 A to  68 D to one target temperature Tx, and then maintain them at the target temperature Tx. Therefore, a time required for the calibration of the second radiation thermometer  48  can be shortened, and. thus a downtime of the polishing apparatus can be greatly reduced. Further, the controller  40  maintains the temperatures of the measurement bodies  68 A to  68 D at the target temperature Tx until the checking operation is completed even after the calibration operation is completed. Therefore, the checking operation can be performed. immediately after the calibration operation is completed. 
     The previous description of embodiments is provided to enable a person skilled in the art to make and use the present invention. Moreover, various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles and specific examples defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the embodiments described herein but is to be accorded the widest scope as defined by limitation of the claims. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to a method and a system of automatically calibrating a radiation thermometer disposed in a polishing apparatus. 
     REFERENCE SIGNS LIST 
       1  polishing head 
       2  polishing table 
       3  polishing pad 
       5  pad-temperature regulating apparatus 
       11  heat exchanger 
       30  liquid supply system 
       39  (first) radiation thermometer 
       40  controller 
       48  (second) radiation thermometer 
       60  calibration tool 
       61  heating device 
       63  platform 
       65  cooling device 
       66  temperature regulator 
       68  measurement body 
       68 A, 68 B, 68 C, 68 D measurement body 
       74  moving mechanism (measurement-body moving mechanism) 
       75  X-axis moving mechanism 
       76  Y-axis moving mechanism 
       80  moving mechanism (heating-device moving mechanism) 
       82  motor