Patent Publication Number: US-2021170545-A1

Title: System for adjusting pad surface temperature and polishing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority of Japan patent application serial no. 2019-221931, filed on Dec. 9, 2019. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     Technical Field 
     The present invention relates to a system for adjusting a pad surface temperature and a polishing apparatus. 
     Description of Related Art 
     A wafer polishing rate depends not only on a polishing load on a wafer polishing pad but also on a surface temperature of the polishing pad. This is because chemical actions of a polishing solution on a wafer depend on the temperature. Therefore, it is important to maintain the surface temperature of the polishing pad at an optimal value during wafer polishing in order to increase and also maintain a constant wafer polishing rate in manufacturing of a semiconductor device. 
     Thus, a pad temperature adjustment system for adjusting a surface temperature of a polishing pad is known. The pad temperature adjustment system includes a pad contact member that comes into contact with the surface of the polishing pad and a liquid supply line that is connected to the pad contact member. 
     PATENT DOCUMENTS 
     [Patent Document 1] Japanese Patent Laid-Open No. 2017-148933 
     There may be a case in which a liquid supply line is connected to a liquid supply source provided in a plant where a polishing apparatus is placed. In such a case, various devices are disposed between the liquid supply line and the liquid supply source, the flow amount of the liquid flowing through the liquid supply line being thus affected by a back pressure of a plant facility. Therefore, an apparatus that adjusts the flow amount of the liquid flowing through the liquid supply line (that is, a flow amount adjustment apparatus) is affected by the back pressure, and as a result, there is a concern that it may not be possible to precisely control the flow amount of the liquid to be supplied to a pad contact member. 
     Such a phenomenon may occur due to not only the influence of a back pressure but also the type of flow amount adjustment apparatus which is applied. In other words, although it is desirable that the flow amount of the liquid flowing through the liquid supply line be precisely controlled between a small flow amount region and a large flow amount region, there is a concern that it may not be possible to precisely control the flow amount of the liquid to be supplied to the pad contact member depending on the flow amount adjustment apparatus to be applied. 
     Thus, according to an aspect of the invention, there is provided a system capable of precisely controlling the flow amount of a liquid flowing through a liquid supply line. 
     According to another aspect of the invention, there is provided a polishing apparatus provided with a system capable of precisely controlling the flow amount of a liquid flowing through a liquid supply line. 
     SUMMARY 
     According to an aspect of the present invention, there is provided a system including: a heat exchanging member that is capable of exchanging heat with a surface of a pad; and a liquid supply unit that supplies a liquid to the heat exchanging member, in which the liquid supply unit includes a pump device that adjusts a flow amount of a liquid flowing through a heating liquid supply line, a needle valve that is attached to a cooling liquid supply line, and a control device that controls operations of the pump device and the needle valve. 
     According to an aspect, the liquid supply unit includes a flow amount switching unit that switches a flow amount of a liquid flowing through the cooling liquid supply line. 
     According to an aspect, the flow amount switching unit includes a pressure regulator and a first opening/closing valve that are attached to the cooling liquid supply line, a bypass line that bypasses the pressure regulator and the first opening/closing valve, and a second opening/closing valve that is attached to the bypass line. 
     According to an aspect, the liquid supply unit includes a pulsation attenuator disposed on an upstream side of the needle valve in a flowing direction of the liquid flowing through the cooling liquid supply line. 
     According to an aspect, the pump device includes at least one pump, and a pump controller that controls operations of the pump. 
     According to an aspect, there is provided a system including: a heat exchanging member that is capable of exchanging heat with a surface of a pad; and a liquid supply unit that supplies a liquid to the heat exchanging member, in which the liquid supply unit includes a pump device that adjusts a flow amount of a liquid flowing through a heating liquid supply line, a pump unit that is capable of operating on the basis of a pressure difference between a pressure of a liquid flowing through a cooling liquid supply line and a pressure of a liquid flowing through a cooling liquid returning line, and a control device that controls operations of the pump device and the pump unit. 
     According to an aspect, the liquid supply unit includes a supply-side pressure sensor that is attached to the cooling liquid supply line, and a returning-side pressure sensor that is attached to the cooling liquid returning line, and the control device calculates a pressure difference on the basis of a pressure measured by the supply-side pressure sensor and a pressure measured by the returning-side pressure sensor, and controls operations of the pump unit such that the calculated pressure difference reaches a target pressure on the basis of a correlation between the flow amount of the liquid flowing through the cooling liquid supply line and the pressure difference between the pressure of the liquid flowing through the cooling liquid supply line and the pressure of the liquid flowing through the cooling liquid returning line. 
     According to an aspect, the liquid supply unit includes a pressure regulator that is attached to the cooling liquid supply line. 
     According to an aspect, the liquid supply unit includes a needle valve that is attached to the cooling liquid supply line, a bypass line that bypasses the needle valve, and an opening/closing valve that is attached to the bypass line. 
     According to an aspect, the liquid supply unit includes a pulsation attenuator disposed on an upstream side of the needle valve in a flowing direction of the liquid flowing through the cooling liquid supply line. 
     According to an aspect, the pump device includes at least one pump, and a pump controller that controls operations of the pump. 
     According to an aspect, there is provided a polishing apparatus including: a polishing head that holds a substrate and causes the substrate to rotate; a polishing table that supports a polishing pad; a polishing solution supply nozzle that supplies a polishing solution to a surface of the polishing pad; and the aforementioned system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  a schematic diagram illustrating an embodiment of a polishing apparatus. 
         FIG. 2  is a diagram illustrating comparison between a flow amount control range of a pump device and a flow amount control range of an air operation-type pressure regulator. 
         FIG. 3  is a diagram illustrating another embodiment of a pump device. 
         FIG. 4  is a diagram illustrating comparison between a flow amount control range of a needle valve and a flow amount control range of an air operation-type pressure regulator. 
         FIG. 5  is a diagram illustrating another embodiment of a liquid supply unit. 
         FIG. 6  is a diagram illustrating yet another embodiment of a liquid supply unit. 
         FIG. 7  is a diagram illustrating yet another embodiment of a liquid supply unit. 
         FIG. 8  is a diagram illustrating yet another embodiment of a liquid supply unit. 
         FIG. 9  is a diagram illustrating yet another embodiment of a liquid supply unit. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Each of the pump device and the needle valve controls the flow amount of the liquid such that it is within a flow amount control range that is a wide range from a small flow amount region to a large flow amount region. The pad temperature adjustment system can thus precisely control the flow amount of the liquid to be supplied to the heat exchanging member. 
       FIG. 1  is a schematic diagram illustrating an embodiment of a polishing apparatus. As illustrated in  FIG. 1 , a polishing apparatus PA includes a polishing head  1  that holds a wafer W as an example of a substrate and causes the wafer W to rotate, a polishing table  2  that supports a polishing pad  3 , a polishing solution supply nozzle  4  that supplies a polishing solution (for example, a slurry) to a surface  3   a  of the polishing pad  3 , and a pad temperature adjustment system  5  that adjusts a surface temperature of the polishing pad  3 . The surface (upper surface)  3   a  of the polishing pad  3  configures a polishing surface to polish the wafer W. 
     The polishing head  1  is capable of moving in the vertical direction and is capable of rotating about the axial center thereof in the direction indicated by the arrow. The wafer W is held at the lower surface of the polishing head  1  using vacuum adsorption or the like. A motor (not illustrated) is coupled to the polishing table  2 , and the polishing table  2  is capable of rotating in the direction indicated by the arrow. As illustrated 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 . 
     Polishing of the wafer W is performed as follows. The wafer W to be polished is held by the polishing head  1  and is further rotated by the polishing head  1 . The polishing pad  3  is rotated along with the polishing table  2 . The polishing solution is supplied from the polishing solution supply nozzle  4  to the surface  3   a of the polishing pad  3 , and further, the surface of the wafer W is pressed against the surface  3   a of the polishing pad  3 , that is, the polishing surface by the polishing head  1 . The surface of the wafer W is polished through rubbing contact with the polishing pad  3  in the presence of the polishing solution. The surface of the wafer W is flattened by a chemical action of the polishing solution and a mechanical action of abrasive grains contained in the polishing solution. 
     The pad temperature adjustment system  5  includes a heat exchanging member  11  with a flow path through which a liquid for adjusting the surface temperature of the polishing pad  3  flows formed therein and a liquid supply unit  30  that supplies liquids (more specifically, a heating liquid and a cooling liquid) with adjusted temperatures to the heat exchanging member  11 . 
     The heat exchanging member  11  is a member that is capable of exchanging heat with the surface  3   a  of the polishing pad  3 . The heat exchanging member  11  may be configured to come into contact with the surface  3   a of the polishing pad  3  to adjust the temperature of the surface  3   a or may be configured to adjust the temperature of the surface  3   a without any contact with the surface  3   a of the polishing pad  3 . 
     The liquid supply unit  30  includes a heating liquid supply tank  31  that stores the heating liquid with an adjusted temperature, a heating liquid line HL, which is connected to the heating liquid supply tank  31 , through which the heating liquid flows, and a cooling liquid line CL through which the cooling liquid flows. 
     The heating liquid line HL includes a heating liquid supply line HSL and a heating liquid returning line HRL that couple the heating liquid supply tank  31  and the heat exchanging member  11 . One end of each of the heating liquid supply line HSL and the heating liquid returning line HRL is connected to the heating liquid supply tank  31  while the other ends thereof are connected to the heat exchange member  11 . 
     The liquid supply unit  30  includes a pump device  32  that adjusts the flow amount of the heating liquid flowing through the heating liquid supply line HSL and a control device  40  that controls operations of the pump device  32 . The pump device  32  is configured to circulate the heating solution between the heating liquid supply tank  31  and the heat exchanging member  11 . 
     The pump device  32  includes a pump  33  that is connected to the heating liquid supply line HSL and a pump controller  34  that controls operations of the pump  33 . The pump  33  is a pump that is capable of operating at a low speed and at a high speed to supply a small flow amount of heating liquid and a large flow amount of heating liquid to the heat exchanging member  11 . The pump controller  34  is electrically connected to the control device  40  and controls operations of the pump  33  on the basis of commands from the control device  40 . 
     If the pump device  32  is driven, then the heating liquid with an adjusted temperature is supplied from the heating liquid supply tank  31  to the heat exchanging member  11  through the heating liquid supply line HSL and is then returned from the heat exchanging member  11  to the heating liquid supply tank  31  through the heating liquid returning line HRL. The heating liquid supply tank  31  includes a heater (not illustrated) disposed therein, and the heating liquid is heated to a predetermined temperature by the heater. 
     In the embodiment illustrated in  FIG. 1 , the flow amount of the heating liquid to be supplied to the heat exchanging member  11  is controlled by the pump device  32 . The pump device  32  connected to the heating liquid supply line HSL can control the flow amount of heating liquid within a flow amount control range that is a wide range from a small flow amount region to a large flow amount region. The pad temperature adjustment system  5  can thus precisely control the flow amount of heating liquid flowing through the heating liquid supply line HSL. 
       FIG. 2  is a diagram illustrating comparison between a flow amount control range of the pump device and a flow amount control range of an air operation-type pressure regulator. Hereinafter, problems in a case in which the pressure regulator is provided instead of the pump device  32  will be described with reference to  FIG. 2 . 
     In  FIG. 2 , the horizontal axis represents the amount of operation [%] while the vertical axis represents the flow amount [L/min]. The air operation-type pressure regulator controls the flow amount of liquid on the basis of compressed air supplied to the pressure regulator. As is obvious from the graph representing a correlation between the amount of operation of the pressure regulator and the flow amount of liquid, the flow amount of liquid significantly changes with a small amount of operation of the pressure regulator in the small flow amount region. 
     On the other hand, as is obvious from the graph representing a correlation between the amount of operation of the pump device  32  and the flow amount of liquid, the flow amount of liquid has a small change with a small amount of operation of the pump device  32  in both the small flow amount region and the large flow amount region. The pump device  32  can thus precisely control the flow amount of liquid from the small flow amount region to the large flow amount region. 
     In this embodiment, since the pad temperature adjustment system  5  includes the pump device  32 , it is possible to precisely control the flow amount of liquid to be supplied to the heat exchanging member  11  in a wide range from the small flow amount region to a large flow amount region. With such a configuration, the pad temperature adjustment system  5  can precisely adjust the surface temperature of the polishing pad  3 . 
       FIG. 3  is a diagram illustrating another embodiment of a pump device. Since configurations and operations of this embodiment that will not be described in particular are the same as those in the aforementioned embodiment, repeated description thereof will be omitted. As illustrated in  FIG. 3 , the pump device  32  may include a plurality (two in the embodiment illustrated in  FIG. 3 ) pumps  33 A and  33 B disposed in series in the flowing direction of the liquid flowing through the heating liquid supply line HSL and a pump controller  34  that controls operations of the pumps  33 A and  33 B. The number of pumps  33  is not limited in the embodiments illustrated in  FIGS. 1 and 3 . Three or more pumps  33  may be provided. 
     In the embodiment illustrated in  FIG. 3 , each of the pumps  33 A and  33 B is a pump that can operate at a low speed. In a case in which a small flow amount of heating liquid is supplied to the heat exchanging member  11 , either the pump  33 A or  33 B is operated. In a case in which a large flow amount of heating liquid is supplied to the heat exchanging member  11 , both the pumps  33 A and  33 B are operated. With such a configuration, the pump device  32  can more precisely control the flow amount of liquid to be supplied to the heat exchanging member  11 . 
     Returning to  FIG. 1 , a heating liquid supply valve HSV and a pressure sensor HPM are attached to the heating liquid supply line HSL. The heating liquid supply valve HSV is an opening/closing valve that opens and closes the flow path of the heating liquid supply line HSL and is disposed on a downstream side of the pump device  32 . The pressure sensor HPM is disposed on a downstream side of the heating liquid supply valve HSV. 
     A heating liquid returning valve HRV that opens and closes the flow path of the heating liquid returning line HRL and a flow amount sensor HFM that measures the flow amount of the liquid flowing through the heating liquid returning line HRL are attached to the heating liquid returning line HRL. The flow amount sensor HFM is disposed on an upstream side of the heating liquid returning valve HRV. 
     The heating liquid supply valve HSV, the pressure sensor HPM, the heating liquid returning valve HRV, and the flow amount sensor HFM are electrically connected to the control device  40 . 
     The cooling liquid line CL includes a cooling liquid supply line CSL and a cooling liquid returning line CRL that are coupled to the heat exchanging member  11 . The cooling liquid supply line CSL is connected to a cooling liquid supply source (for example, a cooling water supply source) provided in a plant where the polishing apparatus PA is placed. Note that illustration of the cooling liquid supply source is omitted. The cooling liquid is supplied to the heat exchanging member  11  through the cooling liquid supply line CSL and is then returned from the heat exchanging member  11  to the cooling liquid supply source through the cooling liquid returning line CRL. 
     A cooling liquid supply valve CSV, a motor needle valve MNV, and a pressure sensor CPM are attached to the cooling liquid supply line CSL. The cooling liquid supply valve CSV is an opening/closing valve that opens and closes the flow path of the cooling liquid supply line CSL. 
     Hereinafter, the motor needle valve may simply be referred to as a needle valve. The needle valve MNV is disposed on a downstream side of the cooling liquid supply valve CSV while the pressure sensor CPM is disposed on a downstream side of the needle valve MNV. The control device  40  is electrically connected to the needle valve MNV and can control operations of the needle valve MNV. 
     In the embodiment illustrated in  FIG. 1 , the flow amount of cooling liquid to be supplied to the heat exchanging member  11  is controlled by the needle valve MNV (and the control device  40 ). The needle valve MNV connected to the cooling liquid supply line CSL can control the flow amount of cooling liquid in a flow amount control range that is a wide range from a small flow amount region to a large flow amount region. The pad temperature adjustment system  5  can thus precisely control the flow amount of cooling liquid flowing through the cooling liquid supply line CSL. 
       FIG. 4  is a diagram illustrating comparison between a flow amount control range of the needle valve and a flow amount control range of the air operation-type pressure regulator. In  FIG. 4 , the horizontal axis represents the amount of operation [%] while the vertical axis represents the flow amount [L/min]. As is obvious from the graph representing a correlation between the amount of operation of the pressure regulator and the flow amount of liquid, the flow amount control range of the pressure regulator is 55 to 80%. 
     On the other hand, as is obvious from the graph representing a correlation between the amount of operation of the needle valve MNV and the flow amount of liquid, the flow amount control range of the needle valve MNV is 0 to 100%, and the needle valve MNV can precisely control the flow amount of liquid from the small flow amount region to the large flow amount region. 
     In this embodiment, since the liquid supply unit  30  includes the needle valve MNV, the flow amount of liquid to be supplied to the heat exchanging member  11  can precisely be controlled in a wide range from the small flow amount region to the large flow amount region. With such a configuration, the pad temperature adjustment system  5  can precisely adjust the surface temperature of the polishing pad  3 . 
     The pressure regulator includes a large number of components (for example, a DA unit, an electropneumatic regulator, and a regulator body). On the other hand, the needle valve MNV includes a small number of components (for example, a DA unit and a needle valve body). Therefore, in a case in which the control device  40  controls operations of the needle valve MNV, responsiveness of the needle valve MNV to the control device  40  is higher than responsiveness of the pressure regulator. Further, since the number of components of the needle valve MNV is small, the needle valve MNV can reduce the probability of failure of the needle valve MNV itself. It is thus possible to enhance safety of the liquid supply unit  30 . 
     Returning to  FIG. 1 , a cooling liquid returning valve CRV and a flow amount sensor CFM that measures the flow amount of liquid flowing through the cooling liquid returning line CRL are attached to the cooling liquid returning line CRL. The flow amount sensor CFM is disposed on an upstream side of the cooling liquid returning valve CRV. 
     The cooling liquid supply valve CSV, the pressure sensor CPM, the cooling liquid returning valve CRV, and the flow amount sensor CFM are electrically connected to the control device  40 . 
     The pad temperature adjustment system  5  further includes a pad temperature measurement tool  39  that measures the surface temperature of the polishing pad  3 . The pad temperature measurement tool  39  is disposed above the surface  3   a of the polishing pad  3  and is configured to measure the surface temperature of the polishing pad  3  in a non-contact manner. The pad temperature measurement tool  39  is electrically connected to the control device  40 . The control device  40  controls the pump device  32  and the needle valve MNV such that the surface temperature of the polishing pad  3  reaches an optimal temperature, on the basis of the pad surface temperature measured by the pad temperature measurement tool  39 . 
     As illustrated in  FIG. 1 , the liquid supply unit  30  may include a pulsation attenuator  45  (that is, a damper) that is disposed on an upstream side of the needle valve MNV in the flowing direction of the liquid flowing through the cooling liquid supply line CSL. The pulsation attenuator  45  is configured to curb variations in pressure of the liquid flowing through the cooling liquid supply line CSL. By providing the pulsation attenuator  45 , the needle valve MNV can precisely control the flow amount of liquid, in particular, the flow amount of liquid in the large flow amount region without being affected by the variations in pressure of the liquid. 
       FIG. 5  is a diagram illustrating another embodiment of a liquid supply unit. Since configurations and operations of this embodiment that will not be described in particular are the same as those in the aforementioned embodiments, repeated description will be omitted. As illustrated in  FIG. 5 , the liquid supply unit  30  may include a flow amount switching unit  50  that switches the flow amount of liquid flowing through the cooling liquid supply line CSL. The flow amount switching unit  50  includes a pressure regulator R 1  and a first opening/closing valve V 1  that are attached to the cooling liquid supply line CSL, a bypass line BPL that bypasses the pressure regulator R 1  and the first opening/closing valve V 1 , and a second opening/closing valve V 2  that is attached to the bypass line BPL. 
     The flow amount switching unit  50  switches the flow amount of liquid to be supplied to the heat exchanging member  11  through the cooling liquid supply line CSL between a first flow amount (large flow amount) and a second flow amount (small flow amount) that is smaller than the first flow amount through opening and closing operations of the first opening/closing valve V 1  and opening and closing operations of the second opening/closing valve V 2 . 
     More specifically, the flow amount switching unit  50  supplies liquid to the heat exchanging member  11  through the bypass line BPL (and the cooling liquid supply line CSL) by closing the first opening/closing valve V 1  and opening the second opening/closing valve V 2 . Through such operations, the needle valve MNV precisely controls the flow amount of the liquid in the large flow amount region that passes through the needle valve MNV itself. 
     The flow amount switching unit  50  supplies the liquid to the heat exchanging member  11  only through the cooling liquid supply line CSL by opening the first opening/closing valve V 1  and closing the second opening/closing valve V 2 . The flow amount of liquid flowing through the cooling liquid supply line CSL is controlled to be the second flow amount by the pressure regulator R 1 . Through such operations, the needle valve MNV precisely controls the flow amount of liquid in the small flow amount region that passes through the needle valve MNV itself. 
     More specifically, the pressure regulator R 1  controls the flow amount of liquid flowing through the cooling liquid supply line CSL while the needle valve MNV controls the flow amount of liquid restricted to the small flow amount by the pressure regulator R 1 . The needle valve MNV can thus precisely control the flow amount of liquid flowing through the cooling liquid supply line CSL. 
       FIG. 6  is a diagram illustrating yet another embodiment of a liquid supply unit. Since configurations and operations of this embodiment that will not be described in particular are the same as those in the aforementioned embodiments, repeated description thereof will be omitted. 
     As illustrated in  FIG. 6 , the liquid supply unit  30  includes a pump unit (pressure boosting unit)  60  that can operate on the basis of a pressure difference between a pressure of the liquid flowing through the cooling liquid supply line CSL and a pressure of the liquid flowing through the cooling liquid returning line CRL. 
     Although the liquid supply unit  30  includes the needle valve MNV in the aforementioned embodiment, the liquid supply unit  30  includes a pressure regulator Ra instead of the needle valve MNV in the embodiment illustrated in  FIG. 6 . 
     The pump unit  60  includes a pump  63  that is connected to the cooling liquid supply line CSL and a pump controller  64  that controls operations of the pump  63 . The pump controller  64  is electrically connected to the control device  40  and controls operations of the pump  63  on the basis of commands from the control device  40 . 
     In the embodiment illustrated in  FIG. 6 , the pump unit  60  includes a pressure regulator Ra, and the pressure regulator Ra is adjacent to the pump  63  and is disposed on a downstream side of the pump  63 . The pressure regulator Ra is electrically connected to the pump controller  64 , and the pump controller  64  can control operations of the pressure regulator Ra. In one embodiment, the pressure regulator Ra is electrically connected to the control device  40 , and the control device  40  can control operations of the pressure regulator Ra. 
     The liquid supply unit  30  includes a supply-side pressure sensor CPMa that is attached to the cooling liquid supply line CSL and a returning-side pressure sensor CPMb that is attached to the cooling liquid returning line CRL. The control device  40  calculates a pressure difference on the basis of a pressure measured by the supply-side pressure sensor CPMa and a pressure measured by the returning-side pressure sensor CPMb and controls operations of the pump unit  60  such that the calculated pressure difference reaches a target pressure on the basis of a correlation between the flow amount of liquid flowing through the cooling liquid supply line CSL and the pressure difference between the pressure of the liquid flowing through the cooling liquid supply line CSL and the pressure of the liquid flowing through the cooling liquid returning line CRL. 
     As illustrated in  FIG. 6 , the control device  40  includes a storage device  40   a  that stores a program and a processing device  40   b  that executes arithmetic operations in accordance with the program. The control device  40  configured of a computer operates in accordance with the program electrically stored in the storage device  40   a . The program includes at least commands for causing the pump unit  60  to operate. 
     The aforementioned program is stored in a non-transitory tangible computer-readable recording medium and is then provided to the control device  40  via the recording medium. Alternatively, the program may be input from a communication device (not illustrated) to the control device  40  via a communication network such as the Internet or a local area network. 
     The supply-side pressure sensor CPMa and the returning-side pressure sensor CPMb may be electrically connected to the control device  40 . In the embodiment illustrated in  FIG. 6 , the supply-side pressure sensor CPMa and the returning-side pressure sensor CPMb are electrically connected to the pump controller  64 . Therefore, the pump controller  64  calculates the pressure difference on the basis of the pressure measured by the supply-side pressure sensor CPMa and the pressure measured by the returning-side pressure sensor CPMb and controls operations of the pump  63  such that the calculated pressure difference reaches the target pressure on the basis of the aforementioned correlation. The pump controller  64  may have a configuration that is similar to that of the control device  40  and can operate in accordance with commands from the control device  40 . During operations of the pump  63 , the pump controller  64  fully opens the pressure regulator Ra. 
     A correlation is present between the pressure difference and the flow amount. More specifically, the flow amount and the pressure difference increase depending on the amount of operation as the amount of operation increases, and the flow amount and the pressure difference decreases depending on the amount of operation as the amount of operation decreases. The control apparatus  40  controls the flow amounts of liquids (the heating liquid and the cooling liquid) to be supplied to the heat exchanging member  11  to satisfy the following expression. 
       The amount of operation of the cooling liquid [%]=(100−the amount of operation of the heating liquid) [%]
 
     In other words, on the assumption that the flow amount of liquid (including the heating liquid and the cooling liquid) when the amount of operation is 100% is 6 L/min, the flow amount [L/min] of cooling liquid satisfies the following expression. 
       The flow amount of the cooling liquid [L/min]=(6−the flow amount of heating liquid) [L/min]
 
     The control device  40  calculates a targeted pressure difference (target pressure) from a currently needed flow amount on the basis of the aforementioned correlation. The control device  40  controls the flow amount of cooling liquid to be supplied to the heat exchanging member  11  such that the pressure difference calculated on the basis of the pressure measured by the supply-side pressure sensor CPMa and the pressure measured by the returning-side pressure sensor CPMb reaches the target pressure. A database corresponding to the aforementioned correlation is stored in the storage device  40   a.    
     In this manner, the control device  40  controls the flow amount of cooling liquid on the basis of the pressure difference. Therefore, the liquid supply unit  30  can secure a constant flow amount with respect to the amount of operation even if the back pressure of the plant facility varies. As a result, the liquid supply unit  30  can enhance stability of the surface temperature of the polishing pad  3 . According to the embodiment illustrated in  FIG. 6 , the control device  40  can execute monitoring of abnormalities such as variations in pressure of the cooling liquid supply source, variations in back pressure, and blockage of the cooling liquid supply line CSL. 
     The pump controller  64  (or the control device  40 ) causes the pressure regulator Ra to operate and controls the flow amount of cooling liquid in a case in which driving of the pump unit  60  is stopped, that is, in a case in which the rotation speed of the pump  63  reaches 0 min −1 . 
     The case in which the rotation speed of the pump  63  reaches 0 min −1  is, for example, a following case. A supply pressure acts on a liquid introduced from a cooling liquid supply source provided in the plant to the cooling liquid supply line CSL. In a case in which a large flow amount of liquid is supplied, the pump unit  60  is caused to operate to boost the supply pressure of the liquid. On the other hand, the supply pressure of the liquid does not become lower than the supply pressure of the liquid introduced from the cooling liquid supply source even if the driving of the pump unit  60  is stopped. Therefore, in a case in which a small flow amount of liquid is supplied, the pump controller  64  stops the driving of the pump unit  60  and controls the flow amount of cooling liquid using the pressure regulator Ra. 
       FIG. 7  is a diagram illustrating yet another embodiment of a liquid supply unit. Since configurations and operations of this embodiment that will not be described in particular are the same as those in the aforementioned embodiments, repeated description thereof will be omitted. 
     Although the liquid supply unit  30  includes the pressure regulator Ra in the embodiment illustrated in  FIG. 6 , the liquid supply unit  30  includes the needle valve MNV instead of the pressure regulator Ra in the embodiment illustrated in  FIG. 7 . Even in this case, the control device  40  causes the needle valve MNV to operate to control the flow amount of cooling liquid in a case in which the driving of the pump unit  60  is stopped. As illustrated in  FIG. 7 , the liquid supply unit  30  may include the pulsation attenuator  45  disposed on an upstream side of the needle valve MNV. 
       FIG. 8  is a diagram illustrating yet another embodiment of a liquid supply unit. Since configurations and operations of this embodiment that will not be described in particular are the same as those in the aforementioned embodiment, repeated description will be omitted. As illustrated in  FIG. 8 , the liquid supply unit  30  includes the needle valve MNV attached to the cooling liquid supply line CSL, the bypass line BPL that bypasses the needle valve MNV, and an opening/closing valve Va that is attached to the bypass line BPL. 
     The needle valve MNV and the opening/closing valve Va are electrically connected to the control device  40 . If the control device  40  closes the opening/closing valve Va, then the liquid flowing through the cooling liquid supply line CSL passes through the cooling liquid supply line CSL to which the needle valve MNV is attached without passing through the bypass line BPL and is then supplied to the heat exchanging member  11 . If the control device  40  opens the opening/closing valve Va, then the liquid passes through both the bypass line BPL and the cooling liquid supply line CSL and is then supplied to the heat exchanging member  11 . 
     As illustrated in  FIG. 8 , the liquid supply unit  30  may include the pulsation attenuator  45  disposed on an upstream side of the needle valve MNV in the flowing direction of the liquid flowing through the cooling liquid supply line CSL. 
     The control device  40  may switch first control for controlling the flow amount of liquid in the small flow amount region and second control for controlling the flow amount of liquid in the large flow amount region in accordance with a needed flow amount. 
     In a case in which the control device  40  executes the first control, the control device  40  stops the driving of the pump unit  60  and closes the opening/closing valve Va. Then, the liquid passes only through the cooling liquid supply line CSL to which the needle valve MNV is attached without passing through the bypass line BPL. The control device  40  causes the needle valve MNV to operate to control the flow amount of the liquid to be supplied to the heat exchanging member  11  in the small flow amount region. 
     In a case in which the control device  40  executes the second control, the control device  40  opens the opening/closing valve Va and fully opens the needle valve MNV. Then, the liquid passes through both the bypass line BPL and the cooling liquid supply line CSL. The needle valve MNV has a relatively large fluid resistance. Therefore, the liquid supply unit  30  can increase the flow amount of liquid to be supplied to the heat exchanging member  11  by opening the opening/closing valve Va and causing the liquid to pass not only through the cooling liquid supply line CSL but also through the bypass line BPL. The control device  40  causes the pump unit  60  to operate to control the flow amount of the liquid to be supplied to the heat exchanging member  11  in the large flow amount region. 
     In this manner, the control device  40  has a configuration of switching the first control and the second control. Therefore, the control device  40  can precisely control the flow amount of liquid in the small flow amount region and the flow amount of liquid in the large flow amount region. 
       FIG. 9  is a diagram illustrating yet another embodiment of a liquid supply unit. Since configurations and operations of this embodiment that will not be described in particular are the same as those in the aforementioned embodiments, repeated description thereof will be omitted. In  FIG. 9 , illustration of elements other than main components is omitted. 
     As illustrated in  FIG. 9 , the liquid supply unit  30  includes a heating liquid branching line HBL that is branched from the heating liquid supply line HSL and a cooling liquid branching line CBL that is branched from the cooling liquid supply line CSL. 
     One end of the heating liquid branching line HBL is connected to the heating liquid supply line HSL, and the other end thereof is connected to the heating liquid supply tank  31 . The heating liquid branching line HBL includes an orifice  70  that restricts the flow amount of heating liquid passing through the heating liquid branching line HBL. If the pump device  32  is driven, then the large flow amount of heating liquid is supplied to the heat exchanging member  11  through the heating liquid supply line HSL, and the small flow amount of heating liquid is returned to the heating liquid supply tank  31  through the heating liquid branching line HBL. 
     In the embodiment illustrated in  FIG. 9 , a circulation flow of the heating liquid (large circulation flow) that circulates between the heating liquid supply tank  31  and the heat exchanging member  11  is formed by the heating liquid supply line HSL and the heating liquid returning line HRL. A circulation flow of the heating liquid (small circulation flow) is formed by a part of the heating liquid supply line HSL and the heating liquid branching line HBL. The flow amount of heating liquid to be supplied to the heat exchanging member  11  is controlled by the pump device  32 . The heating liquid in the heating liquid supply tank  31  is circulated by forming the small circulation flow of the heating liquid, and as a result, the temperature of the heating liquid is constantly maintained. 
     As illustrated in  FIG. 9 , the liquid supply unit  30  may further include an auxiliary liquid supply line  71  connected to the heating liquid supply tank  31 . The heating liquid in the heating liquid supply tank  31  is gradually evaporated with elapse of time. Therefore, the auxiliary liquid supply line  71  may be provided in order to constantly maintain the amount of heating liquid stored in the heating liquid supply tank  31 . In the embodiment illustrated in  FIG. 9 , the auxiliary liquid supplied to the heating liquid supply tank  31  is pure water. 
     In the aforementioned embodiments, the cooling liquid supply line CSL is connected to the cooling liquid supply source provided in the plant where the polishing apparatus PA is placed. In the embodiment illustrated in  FIG. 9 , the cooling liquid supply line CSL and the cooling liquid returning line CRL are connected to a cooling liquid supply tank  81 . 
     One end of the cooling liquid branching line CBL is connected to the cooling liquid supply line CSL, and the other end thereof is connected to the cooling liquid supply tank  81 . The cooling liquid branching line CBL includes an orifice  80  that restricts the flow amount of cooling liquid passing through the cooling liquid branching line CBL. 
     In the embodiment illustrated in  FIG. 9 , the needle valve MNV is not provided, and instead, the pump unit  60  is provided. If the pump unit  60  is driven, then the large flow amount of cooling liquid is supplied to the heat exchanging member  11  through the cooling liquid supply line CSL, and the small flow amount of cooling liquid is returned to the cooling liquid supply tank  81  through the cooling liquid branching line CBL. 
     A circulation flow of the cooling liquid (large circulation flow) that circulates between the cooling liquid supply tank  81  and the heat exchanging member  11  is formed by the cooling liquid supply line CSL and the cooling liquid returning line CRL. A circulation flow of the cooling liquid (small circulation flow) is formed by a part of the cooling liquid supply line CSL and the cooling liquid branching line CBL. The flow amount of cooling liquid to be supplied to the heat exchanging member  11  is controlled by the pump unit  60 . The cooling liquid in the cooling liquid supply tank  81  is circulated by forming the small circulation flow of the cooling liquid, and as a result, the temperature of the cooling liquid is constantly maintained. 
     The plurality of aforementioned embodiments may be combined as long as the combination are possible. For example, the embodiment illustrated in  FIG. 3  and the embodiment illustrated in  FIG. 6  may be combined. In this case, the liquid supply unit  30  according to the embodiment illustrated in  FIG. 6  includes the pump device  32  including the plurality of pumps  33 A and  33 B. 
     In one embodiment, the embodiment illustrated in  FIG. 6  and the embodiment illustrated in  FIG. 9  may be combined. The control device  40  may control operations of the pump unit  60  on the basis of the pressure difference between the pressure measured by the supply-side pressure sensor CPMa (see  FIG. 6 ) and the pressure measured by the returning-side pressure sensor CPMb. 
     The aforementioned embodiments have been described for the purpose of allowing those who have ordinary skills in the art to which the present invention belongs to be able to perform the present invention. Various modifications of the aforementioned embodiments can be achieved by those skilled in the art as a matter of course, and technical ideas of the present invention can be applied to other embodiment as well. Therefore, the present invention is not limited to the described embodiments and is to be interpreted in the widest range in accordance with the technical ideas defined by the claims. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure covers modifications and variations provided so that they fall within the scope of the following claims and their equivalents.