Patent Publication Number: US-11642751-B2

Title: Polishing method and polishing apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This document claims priorities to Japanese Patent Application Number 2019-108387 filed Jun. 11, 2019 and Japanese Patent Application Number 2020-093103 filed May 28, 2020, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     A CMP (chemical mechanical polishing) apparatus is used in a process of polishing a surface of a wafer in manufacturing of a semiconductor device. The CMP apparatus is configured to press the wafer against a polishing pad on a polishing table by a polishing head, while rotating the polishing table, to thereby polish the surface of the wafer. During polishing of the wafer, slurry is supplied onto the polishing pad. The surface of the wafer is planarized by the chemical action of the slurry and the mechanical action of abrasive grains contained in the slurry. 
     The CMP apparatus is a composite machine that performs polishing, cleaning, and drying of a wafer. Specifically, the wafer is polished by a polishing unit, and then the polished wafer is transported to a cleaning unit and the wafer is cleaned by the cleaning unit. Further, the cleaned wafer is transported to a drying unit, so that the wafer is dried in the drying unit. In this manner, polishing, cleaning, and drying of the wafer are sequentially performed. 
     A plurality of wafers stored in a wafer cassette are carried to the CMP apparatus, and these wafers are sequentially polished, cleaned, and dried by the CMP apparatus. A plurality of wafers (i.e., wafers to be polished) stored in one wafer cassette have the same film structure. Generally, polishing of each wafer is terminated when a thickness of a film that forms the surface of the wafer reaches a target thickness. 
     However, an initial film thickness varies slightly from wafer to wafer. As a result, a polishing time from the start of polishing to the end of polishing also varies slightly from wafer to wafer. If the polishing time of each wafer varies, a throughput becomes unstable. In particular, in a composite process of sequentially polishing, cleaning, and drying a plurality of wafers, polishing of the wafers becomes a rate-determining factor, and a processing time of the entire wafers becomes unstable. 
     SUMMARY OF THE INVENTION 
     Therefore, there are provided a polishing method and a polishing apparatus capable of terminating polishing of a substrate, such as a wafer, at a preset polishing time. 
     Embodiments, which will be described below, relate to a polishing method and a polishing apparatus for polishing a substrate, such as a wafer, while pressing the substrate against a polishing surface of a polishing pad, and more particularly to a polishing method and a polishing apparatus for polishing a substrate on a polishing surface of a polishing pad while adjusting a temperature of the polishing surface. 
     In an embodiment, there is provided a polishing method comprising: polishing a substrate by pressing the substrate against a polishing surface of a polishing pad, while regulating a temperature of the polishing surface by a heat exchanger; calculating a target polishing rate required for an actual polishing time to coincide with a target polishing time, the actual polishing time being a time duration from start of polishing the substrate until a film thickness of the substrate reaches a target thickness; determining a target temperature of the polishing surface that can achieve the target polishing rate; and during polishing of the substrate, changing a temperature of the polishing surface to the target temperature by the heat exchanger. 
     In an embodiment, calculating the target polishing rate comprises: calculating a remaining film thickness by subtracting the target thickness from a film thickness of the substrate at a present point in time; calculating a remaining time by subtracting an elapsed time from the target polishing time, the elapsed time being a period of time from start of polishing the substrate to the present point in time; and dividing the remaining film thickness by the remaining time, thereby calculating the target polishing rate. 
     In an embodiment, determining the target temperature of the polishing surface comprises determining the target temperature of the polishing surface corresponding to the target polishing rate based on a relational expression indicating a correlation between polishing rate and temperature of the polishing surface. 
     In an embodiment, the relational expression is a relational expression produced by: polishing one of sample substrates on the polishing surface of the polishing pad while keeping the temperature of the polishing surface constant by the heat exchanger; calculating a polishing rate of the one sample substrate; repeating polishing of one of the sample substrates and calculation of a polishing rate of the one sample substrate, while changing the sample substrate to be polished from one to another of the plurality of sample substrates and while changing the temperature of the polishing surface to another temperature, thereby obtaining a plurality of polishing rates corresponding to a plurality of temperatures of the polishing surface; and determining the relational expression indicating a correlation between the plurality of temperatures of the polishing surface and the plurality of polishing rates. 
     In an embodiment, the relational expression is a relational expression produced by: polishing a sample substrate on the polishing surface of the polishing pad while measuring a temperature of the polishing surface; calculating a plurality of polishing rates of the sample substrate corresponding to a plurality of temperatures of the polishing surface, respectively; and determining the relational expression indicating a correlation between the plurality of temperatures of the polishing surface and the plurality of polishing rates. 
     In an embodiment, there is provided a polishing method comprising: polishing a substrate by pressing the substrate against a polishing surface of a polishing pad, while regulating a temperature of the polishing surface by a heat exchanger; calculating a target polishing rate required for an actual polishing time to coincide with a target polishing time, the actual polishing time being a time duration from start of polishing the substrate until a film thickness of the substrate reaches a target thickness; and during polishing of the substrate, adjusting a temperature of the polishing surface by the heat exchanger such that a current polishing rate of the substrate is maintained at the target polishing rate. 
     In an embodiment, calculating the target polishing rate comprises: calculating a remaining film thickness by subtracting the target thickness from a film thickness of the substrate at a present point in time; calculating a remaining time by subtracting an elapsed time from the target polishing time, the elapsed time being a period of time from start of polishing the substrate to the present point in time; and dividing the remaining film thickness by the remaining time, thereby calculating the target polishing rate. 
     In an embodiment, adjusting the temperature of the polishing surface is performed within a temperature range that does not exceed a predetermined upper limit temperature, the upper limit temperature being determined based on a temperature of the polishing surface that maximizes a polishing rate of the substrate. 
     In an embodiment, there is provided a polishing apparatus comprising: a polishing table for supporting a polishing pad; a polishing head configured to polish a substrate by pressing the substrate against a polishing surface of the polishing pad; a heat exchanger having a heating flow passage and a cooling flow passage therein, the heat exchanger being arranged above the polishing table; a pad-temperature measuring device configured to measure a temperature of the polishing surface; a fluid supply system having a heating-fluid supply pipe and a cooling-fluid supply pipe coupled to the heating flow passage and the cooling flow passage, respectively; a film-thickness sensor attached to the polishing table; and an operation controller having a memory and a processing device, the memory storing a program therein, the processing device being configured to perform an arithmetic operation according to an instruction contained in the program, the operation controller being configured to calculate a target polishing rate required for an actual polishing time to coincide with a target polishing time, the actual polishing time being a time duration from start of polishing the substrate until a film thickness of the substrate reaches a target thickness, determine a target temperature of the polishing surface that can achieve the target polishing rate, and operate the fluid supply system during polishing of the substrate to change a temperature of the polishing surface to the target temperature by the heat exchanger. 
     In an embodiment, the operation controller is configured to: calculate a remaining film thickness by subtracting the target thickness from a film thickness of the substrate at a present point in time; calculate a remaining time by subtracting an elapsed time from the target polishing time, the elapsed time being a period of time from start of polishing the substrate to the present point in time; and divide the remaining film thickness by the remaining time to calculate the target polishing rate. 
     In an embodiment, the operation controller stores, in the memory, a relational expression indicating a correlation between polishing rate and temperature of the polishing surface, and the operation controller is configured to determine the target temperature of the polishing surface corresponding to the target polishing rate based on the relational expression. 
     In an embodiment, the relational expression is a relational expression produced by: polishing one of sample substrates on the polishing surface of the polishing pad while keeping the temperature of the polishing surface constant by the heat exchanger; calculating a polishing rate of the one sample substrate; repeating polishing of one of the sample substrates and calculation of a polishing rate of the one sample substrate, while changing the sample substrate to be polished from one to another of the plurality of sample substrates and while changing the temperature of the polishing surface to another temperature, thereby obtaining a plurality of polishing rates corresponding to a plurality of temperatures of the polishing surface; and determining the relational expression indicating a correlation between the plurality of temperatures of the polishing surface and the plurality of polishing rates. 
     In an embodiment, the relational expression is a relational expression produced by: polishing a sample substrate on the polishing surface of the polishing pad while measuring a temperature of the polishing surface; calculating a plurality of polishing rates of the sample substrate corresponding to a plurality of temperatures of the polishing surface, respectively; and determining the relational expression indicating a correlation between the plurality of temperatures of the polishing surface and the plurality of polishing rates. 
     In an embodiment, there is provided a polishing apparatus comprising: a polishing table for supporting a polishing pad; a polishing head configured to polish a substrate by pressing the substrate against a polishing surface of the polishing pad; a heat exchanger having a heating flow passage and a cooling flow passage therein, the heat exchanger being arranged above the polishing table; a pad-temperature measuring device configured to measure a temperature of the polishing surface; a fluid supply system having a heating-fluid supply pipe and a cooling-fluid supply pipe coupled to the heating flow passage and the cooling flow passage, respectively; a film-thickness sensor attached to the polishing table; and an operation controller having a memory and a processing device, the memory storing a program therein, the processing device being configured to perform an arithmetic operation according to an instruction contained in the program, the operation controller being configured to calculate a target polishing rate required for an actual polishing time to coincide with a target polishing time, the actual polishing time being a time duration from start of polishing the substrate until a film thickness of the substrate reaches a target thickness, and operate the fluid supply system during polishing of the substrate to adjust a temperature of the polishing surface by the heat exchanger such that a current polishing rate of the substrate is maintained at the target polishing rate. 
     In an embodiment, the operation controller is configured to: calculate a remaining film thickness by subtracting the target thickness from a film thickness of the substrate at a present point in time; calculate a remaining time by subtracting an elapsed time from the target polishing time, the elapsed time being a period of time from start of polishing the substrate to the present point in time; and divide the remaining film thickness by the remaining time to calculate the target polishing rate. 
     In an embodiment, the operation controller is configured to allow the heat exchanger to adjust the temperature of the polishing surface within a temperature range that does not exceed a predetermined upper limit temperature, the upper limit temperature being determined based on a temperature of the polishing surface that maximizes a polishing rate of the substrate. 
     According to the present invention, the film thickness of the substrate reaches the target thickness, and at the same time, the preset target polishing time is reached. Therefore, polishing of a plurality of substrates can be terminated at a constant polishing time, and as a result, the throughput can be stable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic view showing an embodiment of a polishing apparatus; 
         FIG.  2    is a horizontal cross-sectional view showing an embodiment of a heat exchanger; 
         FIG.  3    is a plan view showing a positional relationship between the heat exchanger and a polishing head on a polishing pad; 
         FIG.  4    is a graph showing an example of a relational expression indicative of a correlation between polishing rate and temperature of a polishing surface; 
         FIG.  5    is a diagram illustrating a graph showing an example of a change in the polishing rate with polishing time, and a graph showing an example of a change in film thickness with polishing time; 
         FIG.  6    is a diagram illustrating a graph showing another example of a change in the polishing rate with polishing time, and a graph showing another example of a change in film thickness with polishing time; 
         FIG.  7    is a graph showing a plurality of data points specified by respective polishing rates of a plurality of sample wafers and corresponding temperatures of the polishing surface; 
         FIG.  8    is a diagram illustrating an example of creating the relational expression indicative of the correlation between the polishing rate and the temperature of the polishing surface shown in  FIG.  4   ; 
         FIG.  9    is a schematic cross-sectional view of a polishing apparatus having a dresser; and 
         FIG.  10    is a schematic view showing an example of a configuration of an operation controller. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments will now be described with reference to the drawings. 
       FIG.  1    is a schematic view showing an embodiment of a polishing apparatus having a temperature regulation device. As shown in  FIG.  1   , the polishing apparatus 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 slurry supply nozzle  4  for supplying slurry onto a surface of the polishing pad  3 , and a temperature regulation device  5  for regulating a temperature of a polishing surface  3   a  of the polishing pad  3 . The surface (upper surface) of the polishing pad  3  provides the polishing surface  3   a  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 wafer W is held on a lower surface of the polishing head  1  by, for example, vacuum suction. A table motor  6  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 the upper surface of the polishing table  2 . 
     The polishing apparatus includes an operation controller  40  for controlling operations of the polishing head  1 , the table motor  6 , the slurry supply nozzle  4 , and the temperature regulation device  5 . The operation controller  40  is constituted by at least one computer. The operation controller  40  includes a memory  110  storing programs therein, and an arithmetic device  120  that performs arithmetic operations according to instructions contained in the programs. The arithmetic device  120  includes a CPU (central processing unit) or GPU (graphics processing unit) that performs the arithmetic operations according to the instructions contained in the programs. The memory  110  includes a main memory (for example, a random-access memory) accessible by the arithmetic device  120 , and an auxiliary memory (for example, a hard disk drive or a solid-state drive) that stores data and programs therein. 
     Polishing of the wafer W is performed as followings. The wafer W, to be polished, is held by the polishing head  1 , and is then rotated by the polishing head  1 . The polishing table  2  is rotated together with the polishing pad  3  by the table motor  6 . While the wafer W and the polishing pad  3  are rotating, the slurry is supplied from the slurry supply nozzle  4  onto the polishing surface  3   a  of the polishing pad  3 , and the surface of the wafer W is pressed by the polishing head  1  against the polishing surface  3   a  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 slurry. The surface of the wafer W is planarized by the chemical action of the slurry and the mechanical action of abrasive grains contained in the slurry. 
     The polishing apparatus further includes a film-thickness sensor  7  configured to measure a film thickness of the wafer W. The film-thickness sensor  7  is fixed to the polishing table  2  and rotates together with the polishing table  2 . The film-thickness sensor  7  is configured to generate a film-thickness signal that changes according to the film thickness of the wafer W. The film-thickness sensor  7  is arranged in the polishing table  2  and generates film-thickness signals indicating film thicknesses of a plurality of areas including a central portion of the wafer W each time the polishing table  2  makes one rotation. Examples of the film-thickness sensor  7  include an optical sensor and an eddy current sensor. 
     During polishing of the wafer W, the film-thickness sensor  7  rotates together with the polishing table  2 , and generates the film-thickness signal while sweeping across the surface of the wafer W. This film-thickness signal comprises an index value that directly or indirectly indicates the film thickness of the wafer W. The film-thickness signal varies as the film thickness of the wafer W decreases. The film-thickness sensor  7  is coupled to the operation controller  40 , so that the film-thickness signal is sent to the operation controller  40 . When the film thickness of the wafer W, indicated by the film-thickness signal, reaches a predetermined target thickness, the operation controller  40  instructs the polishing head  1  and the polishing table  2  to terminate polishing of the wafer W. 
     The temperature regulation device  5  includes a heat exchanger  11  configured to regulate the temperature of the polishing surface  3   a  of the polishing pad  3  by performing heat exchange with the polishing pad  3 . The temperature regulation device  5  further includes a fluid supply system  30  for supplying a heating fluid having a regulated temperature and a cooling fluid having a regulated temperature into the heat exchanger  11 . The temperature regulation device  5  further includes an elevating mechanism  20  coupled to the heat exchanger  11 . The heat exchanger  11  is located over the polishing table  2  and the polishing surface  3   a  of the polishing pad  3 . The heat exchanger  11  has a bottom surface facing the polishing surface  3   a  of the polishing pad  3 . The elevating mechanism  20  is configured to raise and lower the heat exchanger  11 . More specifically, the elevating mechanism  20  is configured to move the bottom surface of the heat exchanger  11  in a direction toward the polishing surface  3   a  of the polishing pad  3  and in a direction away from the polishing surface  3   a  of the polishing pad  3 . The elevating mechanism  20  includes an actuator (not shown), such as a motor or an air cylinder. The operation of the elevating mechanism  20  is controlled by the operation controller  40 . 
     The fluid supply system  30  includes a heating-fluid supply tank  31  as a heating-fluid supply source for holding the heating fluid having a regulated temperature therein. The fluid supply system  30  further includes a heating-fluid supply pipe  32  and a heating-fluid return pipe  33 , each coupling the heating-fluid supply tank  31  to the heat exchanger  11 . Ends of the heating-fluid supply pipe  32  and the heating-fluid return pipe  33  are coupled to the heating-fluid supply tank  31 , and the other ends are coupled to the heat exchanger  11 . 
     The heating fluid having a regulated temperature is supplied from the heating-fluid supply tank  31  to the heat exchanger  11  through the heating-fluid supply pipe  32 , flows in the heat exchanger  11 , and is returned from the heat exchanger  11  to the heating-fluid supply tank  31  through the heating-fluid return pipe  33 . In this manner, the heating fluid circulates between the heating-fluid supply tank  31  and the heat exchanger  11 . The heating-fluid supply tank  31  has a heater (not shown in the drawings), so that the heating fluid is heated by the heater to have a predetermined temperature. 
     The fluid supply system  30  includes a first on-off valve  41  and a first flow-rate control valve  42  attached to the heating-fluid supply pipe  32 . The first flow-rate 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 controlling function, whereas the first flow-rate control valve  42  is a valve having a flow rate controlling function. 
     The fluid supply system  30  further includes a cooling-fluid supply pipe  51  and a cooling-fluid discharge line  52 , both coupled to the heat exchanger  11 . The cooling-fluid supply pipe  51  is coupled to a cooling-fluid supply source (e.g., a cold water supply source) provided in a factory in which the polishing apparatus is installed. The cooling fluid is supplied to the heat exchanger  11  through the cooling-fluid supply pipe  51 , flows in the heat exchanger  11 , and is drained from the heat exchanger  11  through the cooling-fluid discharge line  52 . In one embodiment, the cooling fluid that has flowed through the heat exchanger  11  may be returned to the cooling-fluid supply source through the cooling-fluid discharge line  52 . 
     The fluid supply system  30  further includes a second on-off valve  55  and a second flow-rate control valve  56  attached to the cooling-fluid supply pipe  51 . The second flow-rate control valve  56  is located between the heat exchanger  11  and the second on-off valve  55 . The second on-off valve  55  is a valve not having a flow rate controlling function, whereas the second flow-rate control valve  56  is a valve having a flow rate controlling function. 
     The first on-off valve  41 , the first flow-rate control valve  42 , the second on-off valve  55 , and the second flow-rate control valve  56  are coupled to the operation controller  40 , so that the operations of the first on-off valve  41 , the first flow-rate control valve  42 , the second on-off valve  55 , and the second flow-rate control valve  56  are controlled by the operation controller  40 . 
     The temperature regulation device  5  further includes a pad-temperature measuring device  39  for measuring a temperature of the polishing surface  3   a  of the polishing pad  3  (which may hereinafter be referred to as pad surface temperature). The pad-temperature measuring device  39  is coupled to the operation controller  40 . The operation controller  40  is configured to operate the first flow-rate control valve  42  and the second flow-rate control valve  56  based on the pad surface temperature measured by the pad-temperature measuring device  39 . The first on-off valve  41  and the second on-off valve  55  are usually open. The pad-temperature measuring device  39  may be a radiation thermometer configured to measure the temperature of the polishing surface  3   a  of the polishing pad  3  in a non-contact manner. The pad-temperature measuring device  39  is disposed above the polishing surface  3   a  of the polishing pad  3 . 
     The pad temperature measuring device  39  measures the pad surface temperature in a non-contact manner and sends the measured value of the pad surface temperature to the operation controller  40 . The operation controller  40  operates the first flow-rate control valve  42  and the second flow-rate control valve  56  based on the measured pad surface temperature to regulate the flow rates of the heating fluid and the cooling fluid such 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 operation controller  40 , and regulate the flow rate of the heating fluid and the flow rate of the cooling fluid to be supplied to the heat exchanger  11 . The heat exchange is performed between the polishing pad  3  and the heating fluid and cooling fluid flowing through the heat exchanger  11 , whereby the pad surface temperature changes. 
     Such a feedback control allows the temperature of the polishing surface  3   a  of the polishing pad  3  (i.e., the pad surface temperature) to be maintained at the predetermined target temperature. PID control can be used as the feedback control. The target temperature of the polishing pad  3  is determined based on the type of film forming the surface of the wafer W or the polishing process. The determined target temperature is input in advance into the operation controller  40  and stored in the memory  110 . 
     A heating liquid, such as hot water, may be used as the heating fluid supplied to the heat exchanger  11 . The heating fluid is heated by a heater (not shown) of the heating-fluid supply tank  31  to have a temperature of about, for example, 80° C. In order to increase the surface temperature of the polishing pad  3  more quickly, silicone oil may be used as the heating fluid. When silicone oil is used as the heating fluid, the silicone oil is heated by the heater of the heating-fluid supply tank  31  to have a temperature of 100° C. or more (e.g., about 120° C.). 
     A cooling liquid, such as cold water or silicone oil, may be used as the cooling fluid supplied to the heat exchanger  11 . In the case of using silicone oil as the cooling fluid, a chiller, which is the cooling-fluid supply source, may be coupled to the cooling-fluid supply pipe  51  so as to cool the silicone oil to 0° C. or less, so that the heat exchanger  11  can quickly cool the polishing pad  3 . Pure water may be used as the cold water. A chiller may be used as the cooling-fluid supply source to cool the pure water to produce the cold water. In this case, the cold water that has flowed through the heat exchanger  11  may be returned to the chiller through the cooling-fluid discharge pipe  52 . 
     The heating-fluid supply pipe  32  and the cooling-fluid supply pipe  51  are completely independent pipes. Therefore, the heating fluid and the cooling fluid are supplied to the heat exchanger  11  without being mixed with each other. The heating-fluid return pipe  33  and the cooling-fluid discharge line  52  are also completely independent pipes. Accordingly, the heating fluid is returned to the heating fluid supply tank  31  without being mixed with the cooling fluid, and the cooling fluid is drained or is returned to the cooling fluid supply source without being mixed with the heating fluid. 
     Next, the heat exchanger  11  will be described with reference to  FIG.  2   .  FIG.  2    is a horizontal cross-sectional view showing the heat exchanger  11 . As shown in  FIG.  2   , the heat exchanger  11  includes a flow-passage structure  70  having a heating flow passage  61  and a cooling flow passage  62  formed therein. In the present embodiment, the entire heat exchanger  11  has a circular shape. The bottom surface of the heat exchanger  11  is flat and circular. The bottom surface of the heat exchanger  11  is constituted by a bottom surface of the flow-passage structure  70 . The flow-passage structure  70  is made of a material having excellent wear resistance and high thermal conductivity, which may be ceramic, such as dense SiC. 
     The heating flow passage  61  and the cooling flow passage  62  are arranged next to each other (or side by side), and extend in a spiral shape. Further, the heating flow passage  61  and the cooling flow passage  62  have a shape of point symmetry, and have the same length. Each of the heating flow passage  61  and the cooling flow passage  62  basically comprises a plurality of arc flow passages  64  having a constant curvature and a plurality of inclined flow passages  65  coupling the arc flow passages  64 . Two adjacent arc flow passages  64  are coupled by each inclined flow passage  65 . 
     Such constructions make it possible to locate the outermost portions of the heating flow passage  61  and the cooling flow passage  62  at an outermost portion of the heat exchanger  11 . Specifically, the entire bottom surface of the heat exchanger  11  lies under the heating flow passage  61  and the cooling flow passage  62 . Therefore, the heating fluid and the cooling fluid can quickly heat and cool the polishing surface  3   a  of the polishing pad  3 . The heat exchange between the polishing pad  3  and the heating fluid and cooling fluid is performed in a state such that the slurry is present between the polishing surface  3   a  of the polishing pad  3  and the bottom surface of the heat exchanger  11 . It should be noted that the shapes of the heating flow passage  61  and the cooling flow passage  62  are not limited to the embodiment shown in  FIG.  2   , and the heating flow passage  61  and the cooling flow passage  62  may have other shapes. 
     The heating-fluid supply pipe  32  (see  FIG.  1   ) is coupled to an inlet  61   a  of the heating flow passage  61 , and the heating-fluid return pipe  33  (see  FIG.  1   ) is coupled to an outlet  61   b  of the heating flow passage  61 . The cooling-fluid supply pipe  51  (see  FIG.  1   ) is coupled to an inlet  62   a  of the cooling flow passage  62 , and the cooling-fluid discharge pipe  52  (see  FIG.  1   ) is coupled to an outlet  62   b  of the cooling flow passage  62 . The inlets  61   a  and  62   a  of the heating flow passage  61  and the cooling flow passage  62  are located at the peripheral portion of the heat exchanger  11 , and the outlets  61   b  and  62   b  of the heating flow passage  61  and the cooling flow passage  62  are located at the central portion of the heat exchanger  11 . Therefore, the heating fluid and the cooling fluid flow spirally from the peripheral portion toward the central portion of the heat exchanger  11 . The heating flow passage  61  and the cooling flow passage  62  are completely separated, so that the heating fluid and the cooling fluid are not mixed in the heat exchanger  11 . 
       FIG.  3    is a plan view showing a positional relationship between the heat exchanger  11  and the polishing head  1  on the polishing pad  3 . The heat exchanger  11  has a circular shape when viewed from above, and has a diameter smaller than the diameter of the polishing head  1 . A distance from the rotating center O of the polishing pad  3  to the center P of the heat exchanger  11  is equal to a distance from the rotating center O of the polishing pad  3  to the center Q of the polishing head  1 . Since the heating flow passage  61  and the cooling flow passage  62  are adjacent to each other, the heating flow passage  61  and the cooling flow passage  62  are arranged not only along the radial direction of the polishing pad  3 , but also along the circumferential direction of the polishing pad  3 . Therefore, while the polishing table  2  and the polishing pad  3  are rotating, the polishing pad  3  performs the heat exchange with both of the heating fluid and the cooling fluid. 
     Referring back to  FIG.  1   , the operation controller  40  obtains, from the film-thickness sensor  7 , the film-thickness signal that directly or indirectly indicates the film thickness of the wafer W during polishing of the wafer W. The operation controller  40  instructs the polishing head  1 , the polishing table  2 , etc. to terminate polishing of the wafer W when the film thickness of the wafer W has reached a preset target thickness. The target thickness is a numerical value that directly or indirectly indicates a target value of the film thickness of the wafer W. Furthermore, the operation controller  40  controls the temperature of the polishing surface  3   a  of the polishing pad  3  (i.e., the pad surface temperature) via the heat exchanger  11  such that an actual polishing time coincides with a preset target polishing time. The actual polishing time is a period of time from the start of polishing the wafer W until the film thickness of the wafer W reaches the target thickness. 
     More specifically, the operation controller  40  is configured to calculate a target polishing rate required for the actual polishing time (i.e., a time duration from the start of polishing the wafer W until the film thickness of the wafer W reaches the target thickness) to coincide with the preset target polishing time. The operation controller  40  is further configured to determine a target temperature of the polishing surface  3   a  that can achieve the calculated target polishing rate, and operate the fluid supply system  30  during polishing of the wafer W to change the temperature of the polishing surface  3   a  to the target temperature by the heat exchanger  11 . 
     The operation controller  40  calculates the target polishing rate during polishing of the wafer W as follows. The operation controller  40  calculates a remaining film thickness by subtracting the target thickness from a film thickness of the wafer W at a present point in time. This present point in time is a certain point in time during polishing of the wafer W. The film thickness of the wafer W at the present point in time can be determined from the film-thickness signal transmitted from the film-thickness sensor  7 . Next, the operation controller  40  calculates a remaining time by subtracting an elapsed time (i.e., a period of time from the start of polishing the wafer W to the present point in time) from the target polishing time. The operation controller  40  then divides the remaining film thickness by the remaining time, thereby calculating the target polishing rate. 
     The operation controller  40  determines the target temperature of the polishing surface  3   a  of the polishing pad  3  that can achieve the calculated target polishing rate. More specifically, the operation controller  40  determines the target temperature of the polishing surface  3   a  corresponding to the calculated target polishing rate based on a relational expression indicating a correlation between polishing rate and temperature of the polishing surface  3   a . The relational expression showing the correlation between polishing rate and temperature of the polishing surface  3   a  is produced in advance based on measurement data of the polishing rate and the temperature of the polishing surface  3   a . The measurement data can be obtained by an actual polishing process, such as experiments, polishing of a product wafer (or product substrate), or polishing of a sample wafer (or sample substrate). The operation controller  40  stores this relational expression in the memory  110  in advance. 
       FIG.  4    is a graph showing an example of the relational expression showing the correlation between the polishing rate and the temperature of the polishing surface  3   a . As shown in  FIG.  4   , the polishing rate of the wafer W changes depending on the temperature of the polishing surface  3   a  of the polishing pad  3 . Therefore, the operation controller  40  can determine, from the relational expression, the temperature of the polishing surface  3   a  (i.e., the target temperature) corresponding to the calculated target polishing rate. The operation controller  40  is configured to determine, during polishing of the wafer W, the target temperature of the polishing surface  3   a  of the polishing pad  3  that can achieve the target polishing rate. 
     Further, during polishing of the wafer W, the operation controller  40  operates the fluid supply system  30  to cause the heat exchanger  11  to change the temperature of the polishing surface  3   a  to the target temperature. More specifically, the operation controller  40  is configured to operate or manipulate the first flow-rate control valve  42  and the second flow-rate control valve  56  based on a difference between a current temperature of the polishing surface  3   a  and the target temperature. For example, when the current temperature of the polishing surface  3   a  is lower than the target temperature, the operation controller  40  increases the opening degree of the first flow-rate control valve  42  and decreases the opening degree of the second flow-rate control valve  56 . The flow rate of the heating fluid flowing in the heat exchanger  11  increases, while the flow rate of the cooling fluid flowing in the heat exchanger  11  decreases. As a result, the temperature of the heat exchanger  11  itself rises, and the temperature of the polishing surface  3   a  rises. In this way, the operation controller  40  controls the temperature of the polishing surface  3   a  via the heat exchanger  11  by operating the first flow-rate control valve  42  and the second flow-rate control valve  56 , so that the polishing rate of the wafer W can be adjusted. 
       FIG.  5    is a graph showing an example of a change in the polishing rate with polishing time and a graph showing an example of a change in the film thickness with polishing time. The temperature of the polishing surface  3   a  of the polishing pad  3  is maintained at a set temperature by the heat exchanger  11 . When polishing of the wafer W is started (polishing time 0), the wafer W is polished at a first polishing rate R 1 . As the wafer W is polished, the film thickness of the wafer W gradually decreases from its initial film thickness P 1 . 
     When the polishing time reaches a correction point T 1  for the polishing rate, the operation controller  40 , as described above, determines a target polishing rate required for an actual polishing time (i.e., a time duration from the start of polishing the wafer W until the film thickness of the wafer W reaches a target thickness PT) to coincide with a target polishing time EP. Specifically, the operation controller  40  calculates a remaining film thickness SP by subtracting the target thickness PT from a film thickness P 1 ′ of the wafer W at the present point in time T 1 , calculates a remaining time RT by subtracting an elapsed time (i.e., a time duration from the start of polishing the wafer W to the present point in time T 1 ) from the target polishing time EP, and divides the remaining film thickness SP by the remaining time RT to determine a target polishing rate R 2  (=SP/RT). Further, the operation controller  40  determines the target temperature of the polishing surface  3   a  that can achieve the target polishing rate R 2  from the relational expression shown in  FIG.  4   , and operates the fluid supply system  30  during polishing of the wafer W to allow the heat exchanger  11  to change the temperature of the polishing surface  3   a  to the target temperature. As a result, the polishing rate of the wafer W changes from the first polishing rate R 1  to the target polishing rate R 2 . 
     The wafer W is polished at the target polishing rate R 2 . When the film thickness of the wafer W reaches the target thickness PT, polishing of the wafer W is terminated. At this time, the polishing time (i.e., the actual polishing time) of the wafer W coincides with the target polishing time EP. Specifically, at the same time that the film thickness of the wafer W reaches the target thickness PT, the elapsed time from the start of polishing the wafer W reaches the target polishing time EP. 
       FIG.  6    is a graph showing another example of the change in the polishing rate with polishing time and a graph showing another example of the change in the film thickness with polishing time. The temperature of the polishing surface  3   a  of the polishing pad  3  is maintained at a set temperature by the heat exchanger  11 . When the polishing of the wafer W is started (polishing time 0), the wafer W is polished at a first polishing rate R 1 . As the wafer W is polished, the film thickness of the wafer W gradually decreases from its initial film thickness P 2 . The initial film thickness P 2  is smaller than the initial film thickness P 1  shown in  FIG.  5   . 
     When the polishing time reaches a correction point T 2  for the polishing rate, the operation controller  40 , as described above, determines a target polishing rate required for an actual polishing time (i.e., a time duration from the start of polishing the wafer W until the film thickness of the wafer W reaches the target thickness PT) to coincide with the target polishing time EP. Specifically, the operation controller  40  calculates a remaining film thickness SP by subtracting the target thickness PT from a film thickness P 2 ′ of the wafer W at the present point in time T 2 , calculates a remaining time RT by subtracting an elapsed time (i.e., a time duration from the start of polishing the wafer W to the present point in time T 2 ) from the target polishing time EP, and divides the remaining film thickness SP by the remaining time RT to determine a target polishing rate R 3  (=SP/RT). Further, the operation controller  40  determines a target temperature of the polishing surface  3   a  that can achieve the target polishing rate R 3  from the relational expression shown in  FIG.  4   , and operates the fluid supply system  30  during polishing of the wafer W to allow the heat exchanger  11  to change the temperature of the polishing surface  3   a  to the target temperature. As a result, the polishing rate of the wafer W changes from the first polishing rate R 1  to the target polishing rate R 3 . 
     The wafer W is polished at the target polishing rate R 3 . When the film thickness of the wafer W reaches the target thickness PT, the polishing of the wafer W is terminated. At this time, the polishing time (i.e., the actual polishing time) of the wafer W coincides with the target polishing time EP. Specifically, at the same time that the film thickness of the wafer W reaches the target thickness PT, the elapsed time from the start of polishing the wafer W reaches the target polishing time EP. 
     The target thickness PT and the target polishing time EP shown in  FIG.  6    are the same as the target thickness PT and the target polishing time EP shown in  FIG.  5   , respectively. The correction point T 2  for the polishing rate shown in  FIG.  6    is the same as the correction point T 1  for the polishing rate shown in  FIG.  5   , but may be different. In one embodiment, a plurality of correction points may be set within the target polishing time EP. The operation controller  40  may calculate target polishing rates at these correction points, determine target temperatures of the polishing surface  3   a , and change the temperature of the polishing surface  3   a  to each target temperature. 
     According to this embodiment, the time when the film thickness of the wafer W reaches the target thickness coincides with the time when the elapsed time from the start of polishing the wafer W reaches the target polishing time. Specifically, when a plurality of wafers having different initial film thicknesses are polished, the actual polishing times of the plurality of wafers are the same and coincide with the target polishing time. The polishing apparatus according to the present embodiment can terminate polishing of a plurality of wafers at a fixed polishing time, and as a result, can stabilize a throughput. 
     Next, an example of creating the relational expression showing the correlation between the polishing rate and the temperature of the polishing surface  3   a  shown in  FIG.  4    will be described. While the temperature of the polishing surface  3   a  of the polishing pad  3  is kept constant by the heat exchanger  11 , one of sample wafers (sample substrates) prepared in advance is polished on the polishing surface  3   a  of the polishing pad  3 . Each of these sample wafers has a surface composed of the same type of film as the film that forms the surface of the wafer W (which is a product wafer or a product substrate) shown in  FIG.  1   . For example, the sample wafer may be a blanket wafer (blanket substrate) having a surface composed of a single film. Polishing of the sample wafer is performed under the same polishing conditions as those for the wafer W shown in  FIG.  1   . 
     When the one sample wafer is polished, the operation controller  40  calculates the polishing rate of that sample wafer. The polishing rate can be calculated by dividing a difference between an initial film thickness of the sample wafer and a film thickness after polishing by a polishing time. 
     Further, while changing the sample wafer to be polished from one to another of the plurality of sample wafers and while changing the temperature of the polishing surface  3   a  of the polishing pad  3  from one to another temperature, polishing of a sample wafer and calculation of a polishing rate are repeated. As a result, a plurality of polishing rates corresponding to a plurality of temperatures of the polishing surface  3   a  are obtained. 
       FIG.  7    is a graph showing a plurality of data points specified by the respective polishing rates of the plurality of sample wafers and the corresponding temperatures of the polishing surface  3   a . Each data point DP indicates a temperature of the polishing surface  3   a  of the polishing pad  3  when each sample wafer is polished and a polishing rate of that sample wafer. The operation controller  40  plots the plurality of data points DP on a coordinate system. This coordinate system has a vertical axis representing the polishing rate and a horizontal axis representing the temperature of the polishing surface  3   a . The vertical axis may represent the temperature of the polishing surface  3   a , and the horizontal axis may represent the polishing rate. The operation controller  40  determines an approximate line representing the plurality of data points DP by performing curve fitting or regression analysis on the plurality of data points DP on the coordinate system. This approximate line corresponds to a relational expression representing the correlation between the plurality of temperatures of the polishing surface  3   a  and the plurality of polishing rates. 
       FIG.  8    is a diagram for explaining another example of creating the relational expression showing the correlation between the polishing rate and the temperature of the polishing surface  3   a  shown in  FIG.  4   . In this example, a single sample wafer prepared in advance is polished on the polishing surface  3   a  of the polishing pad  3  while the temperature of the polishing surface  3   a  is measured by the pad-temperature measuring device  39 . The heat exchanger  11  is not used. During polishing of the sample wafer, the film thickness of the sample wafer is measured by the film-thickness sensor  7 . 
     In this example, the adjustment of the temperature of the polishing surface  3   a  by the heat exchanger  11  is not performed. Therefore, as shown in  FIG.  8   , the temperature of the polishing surface  3   a  rises with the polishing time of the sample wafer. Typically, the polishing rate of the sample wafer changes depending on the temperature of the polishing surface  3   a . Therefore, the operation controller  40  calculates a plurality of polishing rates of the sample wafer corresponding to a plurality of temperatures of the polishing surface  3   a . Specifically, the operation controller  40  calculates amounts of change in film thickness in film-thickness measurement periods MP, and divides the amounts of change in film thickness by the corresponding film-thickness measurement periods MP, respectively, to thereby calculate multiple polishing rates. The temperature of the polishing surface  3   a  within each film-thickness measurement period MP is assumed to be constant. 
     The operation controller  40  obtains a plurality of measured values of the temperature of the polishing surface  3   a  at the film-thickness measurement periods MP from the pad-temperature measuring device  39 . Further, the operation controller  40  plots, on a coordinate system, a plurality of data points specified by the plurality of measured values of the temperature of the polishing surface  3   a  and the corresponding polishing rates. This coordinate system is the same as the coordinate system shown in  FIG.  7   . The operation controller  40  determines an approximate line representing the plurality of data points by performing curve fitting or regression analysis on the plurality of data points on the coordinate system. This approximate line corresponds to a relational expression representing the correlation between the plurality of temperatures of the polishing surface  3   a  and the plurality of polishing rates. 
     Measurement data of the polishing surface  3   a  and film-thickness data of the wafer W obtained when the wafer W, which is a product wafer (product substrate), is polished may be used for creating and/or updating the above-described relational expression. 
     As shown in  FIG.  4   , the polishing rate of the wafer W changes depending on the temperature of the polishing surface  3   a  of the polishing pad  3  (i.e., the pad surface temperature). The polishing rate may also be affected by consumables of the polishing apparatus. The polishing apparatus generally has a plurality of consumables. Specific examples of the consumables include the polishing pad  3 , a dresser, and an elastic membrane and a retainer ring of the polishing head  1 . 
       FIG.  9    is a schematic cross-sectional view of a polishing apparatus including a dresser  80 . For simplification of descriptions, the temperature regulation device  5  including the heat exchanger  11  described above is not shown in  FIG.  9   . The dresser  80  is a device for dressing (or regenerating) the polishing surface  3   a  of the polishing pad  3  after polishing of the wafer W or during polishing of the wafer W. The dresser  80  has a dressing surface  80   a  made of abrasive grains, such as diamond particles. The dresser  80  presses the dressing surface  80   a  against the polishing surface  3   a  of the polishing pad  3  while the dresser  80  is rotating about its axis. The polishing surface  3   a  is slightly scraped off by the dresser  80 , whereby the polishing surface  3   a  is regenerated. 
     As dressing of the polishing pad  3  is repeated, the abrasive grains (diamond particles or the like) forming the dressing surface  80   a  gradually wear. As the wear of the abrasive grains progresses, the dresser  80  cannot properly dress the polishing surface  3   a  of the polishing pad  3 , and as a result, a polishing rate of a wafer changes. Moreover, as dressing of the polishing pad  3  is repeated, the polishing pad  3  also wears (i.e., the thickness of the polishing pad  3  decreases). As the wear of the polishing pad  3  progresses, the properties of the polishing pad  3  change, and as a result, a polishing rate of a wafer changes. 
     As shown in  FIG.  9   , the polishing head  1  includes an elastic membrane (or a membrane)  91  that forms a pressure chamber  90  in the polishing head  1 . During polishing of the wafer W, the pressure chamber  90  is filled with a pressurized gas. A lower surface of the elastic membrane  91  is in contact with the upper surface of the wafer W. The pressurized gas in the pressure chamber  90  presses the wafer W against the polishing surface  3   a  of the polishing pad  3  via the elastic membrane  91 . The pressing force of the wafer W against the polishing pad  3  can be adjusted by the pressure of the gas in the pressure chamber  90 . The elastic membrane  91  is made of a material such as silicone rubber. When the elastic membrane  91  is used for a long period of time, responsiveness (expansion and contraction) of the elastic membrane  91  deteriorates. As a result, a polishing rate of a wafer changes. 
     As shown in  FIG.  9   , the polishing head  1  further includes a retainer ring  92  arranged around the elastic membrane  91 . The retainer ring  92 , arranged around the wafer W, presses the polishing surface  3   a  of the polishing pad  3  while the retainer ring  92  is rotating together with the wafer W. The retainer ring  92  has not only a function of retaining the position of the wafer W being polished, but also a function of controlling a polishing rate of an edge portion of the wafer W. Since the retainer ring  92  is brought into sliding contact with the polishing surface  3   a , the retainer ring  92  gradually wears, as polishing of a wafer is repeated. As the wear of the retainer ring  92  progresses, the force with which the retainer ring  92  presses the polishing pad  3  changes, and as a result, a polishing rate of a wafer changes. 
     As described above, the polishing rate may change due to the change (for example, wear) of the consumables, such as the polishing pad  3 , with time. Therefore, in one embodiment, the operation controller  40  calculates a target polishing rate required for an actual polishing time (i.e., a time duration from the start of polishing the wafer W until the film thickness of the wafer W reaches a target thickness) to coincide with a target polishing time. During polishing of the wafer W, the operation controller  40  operates the fluid supply system  30  to allow the heat exchanger  11  to adjust the temperature of the polishing surface  3   a  such that a current polishing rate of the wafer W is maintained at the target polishing rate. 
     Specifically, in the example shown in  FIG.  5   , when the polishing time reaches the correction point T 1  for the polishing rate, the operation controller  40  determines the target polishing rate R 2  (=SP/RT) required for an actual polishing time (i.e., a time duration from the start of polishing the wafer W until the film thickness of the wafer W reaches the target thickness PT) to coincide with the target polishing time EP. Then, the operation controller  40  calculates a current polishing rate at each of points in time during polishing of the wafer W, and operates the fluid supply system  30  to adjust the temperature of the polishing surface  3   a  via the heat exchanger  11  such that the current polishing rate coincides with the target polishing rate R 2 . The current polishing rate is a polishing rate per unit time during polishing of the wafer. The operation controller  40  can calculate the current polishing rate from an amount of change in the film-thickness signal received from the film-thickness sensor  7  and the unit time. 
     As can be seen from the graph shown in  FIG.  4   , the polishing rate changes depending on the temperature of the polishing surface  3   a  of the polishing pad  3 . Therefore, the operation controller  40  can maintain the target polishing rate by adjusting the temperature of the polishing surface  3   a  via the heat exchanger  11 . More specifically, the operation controller  40  regularly or irregularly calculates the current polishing rate during polishing of the wafer W after the correction point T 1  shown in  FIG.  5   , and controls the temperature regulation device  5 , including the fluid supply system  30  and the heat exchanger  11 , so as to minimize the difference between the current polishing rate and the target polishing rate R 2 . As a result of such feedback control operation, the polishing rate of the wafer W is maintained at the target polishing rate R 2 . 
     As a result, as shown in  FIG.  5   , when the film thickness of the wafer W reaches the target thickness PT, the polishing of the wafer W is terminated. The polishing time (i.e., the actual polishing time) of the wafer W at this time coincides with the target polishing time EP. Specifically, at the same time that the film thickness of the wafer W reaches the target thickness PT, the elapsed time from the start of polishing the wafer W reaches the target polishing time EP. The same operations are performed in the example shown in  FIG.  6   . 
     The polishing rate basically increases as the temperature of the polishing surface  3   a  of the polishing pad  3  increases. However, depending on slurry and/or material of a wafer surface to be polished, the polishing rate may decrease as shown in  FIG.  4    when the temperature of the polishing surface  3   a  is too high. Therefore, the operation controller  40  is configured to operate the fluid supply system  30  to adjust the temperature of the polishing surface  3   a  by the heat exchanger  11  within a temperature range that does not exceed a predetermined upper limit temperature. The upper limit temperature is determined based on a temperature of the polishing surface  3   a  that maximizes the polishing rate. In one example, the upper limit temperature is a temperature of the polishing surface  3   a  that maximizes the polishing rate. The determined upper limit temperature is stored in the memory  110 . 
     The previous embodiments described with reference to  FIGS.  1  to  8    may be appropriately combined with the embodiment described with reference to  FIG.  9   . For example, the operation controller  40  calculates the target polishing rate, determines the target temperature of the polishing surface  3   a  that can achieve the target polishing rate, operates the fluid supply system  30  during polishing of the wafer W to change the temperature of the polishing surface  3   a  to the target temperature by the heat exchanger  11 , then calculates a current polishing rate at each of a plurality of points in time during polishing of the wafer W, and operates the fluid supply system  30  to adjust the temperature of the polishing surface  3   a  via the heat exchanger  11  such that the current polishing rate coincides with the target polishing rate. 
     The operation controller  40  is constituted by at least one computer.  FIG.  10    is a schematic view showing an example of a configuration of the operation controller  40 . As shown in  FIG.  10   , the operation controller  40  includes the memory  110  in which a program and data are stored, the processing device  120 , such as CPU (central processing unit) or GPU (graphics processing unit), for performing arithmetic operation according to instructions contained in the program stored in the memory  110 , an input device  130  for inputting the data, the program, and various information into the memory  110 , an output device  140  for outputting processing results and processed data, and a communication device  150  for connecting to a communication network, such as the Internet or local area network. 
     The memory  110  includes a main memory  111  which is accessible by the processing device  120 , and an auxiliary memory  112  that stores the data and the program therein. The main memory  111  may be a random-access memory (RAM), and the auxiliary memory  112  is a storage device which may be a hard disk drive (HDD) or a solid-state drive (SSD). 
     The input device  130  includes a keyboard and a mouse, and further includes a storage-medium reading device  132  for reading the data from a storage medium, and a storage-medium port  134  to which a storage medium can be coupled. The storage medium is a non-transitory tangible computer-readable storage medium. Examples of the storage medium include optical disk (e.g., CD-ROM, DVD-ROM) and semiconductor memory (e.g., USB flash drive, memory card). Examples of the storage-medium reading device  132  include optical drive (e.g., CD-ROM drive, DVD-ROM drive) and memory reader. Examples of the storage-medium port  134  include USB port. The program and/or the data stored in the storage medium is introduced into the operation controller  40  via the input device  130 , and is stored in the auxiliary memory  112  of the memory  110 . The output device  140  includes a display device  141  and a printer  142 . 
     The operation controller  40  operates according to the instructions included in the program electrically stored in the memory  110 . In one embodiment, the operation controller  40  performs the steps of: calculating a target polishing rate required for an actual polishing time (i.e., a time duration from the start of polishing the wafer W until the film thickness of the wafer W reaches a target thickness) to coincide with a target polishing time; determining a target temperature of the polishing surface  3   a  that can achieve the calculated target polishing rate, and operating the fluid supply system  30  during polishing of the wafer W to change the temperature of the polishing surface  3   a  to the target temperature by the heat exchanger  11 . In another embodiment, the operation controller  40  performs the steps of: calculating a target polishing rate required for an actual polishing time (i.e., a time duration from the start of polishing the wafer W until the film thickness of the wafer W reaches a target thickness) to coincide with a target polishing time; and operating the fluid supply system  30  during polishing of the wafer W to adjust the temperature of the polishing surface  3   a  by the heat exchanger  11  such that a current polishing rate of the wafer W is maintained at the target polishing rate. 
     The program for causing the operation controller  40  to perform the above steps is stored in a non-transitory tangible computer-readable storage medium. The operation controller  40  is provided with the program via the storage medium. The operation controller  40  may be provided with the program via a communication network, such as the Internet or local area network. 
     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.