Abstract:
A plating system comprises: a plating unit which plates a water; a plating solution storage tank which stores a plating solution; and a plating solution supply system which supplies the plating solution in the plating solution storage tank to the plating unit. A dissolved oxygen removing unit which removes dissolved oxygen from the plating solution flowing in the plating solution supply system is provided in the middle of the plating solution supply system.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a solution treatment system provided with a solution treatment unit which gives a solution treatment to a substrate such as a semiconductor wafer and to a solution treatment method.  
           [0003]    2. Description of the Related Art  
           [0004]    In recent years, wiring which constitutes a semiconductor device has been made more microscopic owing to the improvement in the degree of integration of the semiconductor device. With this, the forming technique of the microscopic wiring and securing of its reliability have become important objects. As one of means for attaining these objects, an embedded wiring method which forms wiring by embedding a metal in trenches or connection holes formed in a semiconductor wafer (hereinafter, simply referred to as a “wafer”) has come to the force.  
           [0005]    As a unit which can carry out such an embedded wiring method, a plating unit which embeds a metal by electrolytic plating in trenches or connection holes formed in a wafer is known. In this plating unit, the metal is embedded in the trenches or the connections holes of the wafer by applying a voltage between a pair of electrodes while the wafer is in contact with a plating solution.  
           [0006]    In the plating unit as described above, when the metal is embedded in the trenches or the connection holes of the wafer, an additive contained in the plating solution is consumed with the elapse of time to lower an embedding speed. This reduction in the embedding speed causes decrease in throughput. Therefore, the plating solution, after used for a certain period, is replaced by a new plating solution to suppress the decrease in throughput.  
           [0007]    There exists, however, such a problem that the plating solution has to be replaced frequently since the embedding speed starts to lower in a short time.  
         SUMMARY  
         [0008]    It is an object of the present invention to provide a solution treatment system and a solution treatment method which can decrease the frequency of replacing a treatment solution by suppressing reduction in solution treatment speed.  
           [0009]    A solution treatment system of the present invention comprises: a solution treatment unit which includes a treatment solution tank to store a treatment solution and a pair of electrodes and which gives a solution treatment to a substrate; a treatment solution storage tank which stores the treatment solution; a treatment solution supply system which supplies the treatment solution stored in the treatment solution storage tank to the solution treatment unit; and a dissolved oxygen removing unit which is disposed in the middle of the treatment solution supply system and which removes dissolved oxygen from the treatment solution flowing in the treatment solution supply system. Since the solution treatment system of the present invention is provided with the dissolved oxygen removing unit, the reduction in solution treatment speed can be suppressed to decrease the frequency of replacing the treatment solution.  
           [0010]    It is preferable that the solution treatment system described above further comprises: a treatment solution stirring system which stirs the treatment solution stored in the treatment solution storage tank; and a dissolved oxygen removing unit which in disposed in the middle of the treatment solution stirring system and which removes the dissolved oxygen from the treatment solution flowing in the treatment solution stirring system. By providing the treatment solution stirring system and the dissolved oxygen removing unit, the reduction in the solution treatment speed can be further suppressed.  
           [0011]    Another solution treatment system of the present invention comprises; a solution treatment unit which includes a treatment solution tank to store a treatment solution and a pair of electrodes and which gives a solution treatment to a substrate; a treatment solution storage tank which stores the treatment solution; a treatment solution supply system which supplies the solution treatment unit with the treatment solution stored in the treatment solution storage tank; a treatment solution stirring system which stirs the treatment solution stored in the treatment solution storage tank; and a dissolved oxygen removing unit which is disposed in the middle of the treatment solution stirring unit and which removes dissolved oxygen from the treatment solution flowing in the treatment solution supply system. Since the solution treatment system of the present invention is provided with the dissolved oxygen removing unit, the reduction in the solution treatment speed can be suppressed to decrease the frequency of replacing the treatment solution.  
           [0012]    It is preferable that the solution treatment system described above further comprises a housing accommodating the treatment solution storage tank and an inert gas supply system which supplies an inert gas into an inner part of the housing. The inert gas of the present invention means a nonoxide gas. Specifically, for example, a rare gas such as helium, neon, argon, xenon, and krypton or nitrogen can be named. By providing the housing and the inert gas supply system, oxygen is not easily taken into the treatment solution.  
           [0013]    It is preferable that the solution treatment system described above further comprises a dissolved oxygen measuring unit which measures the concentration of the dissolved oxygen contained in the treatment solution. By providing the dissolved oxygen measuring unit, the concentration of the dissolved oxygen can be accurately controlled.  
           [0014]    It is preferable that the treatment solution used in the above-described solution treatment system contains an additive. As the additive contained in the treatment solution, for example, a sulfur compound can be named. As the sulfur compound, for example, an organic bivalent sulfur compound can be named. By including the additive in the treatment solution, the solution treatment speed can be made higher. Furthermore, even when the additive is contained in the treatment solution, the consumption of the additive can be suppressed.  
           [0015]    The treatment solution used in the above-described solution treatment system may be a plating solution. The use of the plating solution as the treatment solution makes it possible to plate the substrate.  
           [0016]    A solution treatment method of the present invention comprises: a dissolved oxygen removing step of removing dissolved oxygen from a treatment solution in a treatment solution storage tank; a treatment solution supply step of supplying a treatment solution tank with the treatment solution from which the dissolved oxygen is removed; and a solution treatment step of bringing a substrate into contact with the treatment solution supplied to the treatment solution tank and passing an electric current through the substrate to give a solution treatment to the substrate. Since the solution treatment method of the present invention comprises the dissolved oxygen removing step, the reduction in solution treatment speed can be suppressed to decrease the frequency of replacing the treatment solution.  
           [0017]    The dissolved oxygen removing step described above may be carried out when the treatment solution is supplied to the treatment solution tank. Carrying out the dissolved oxygen removing step when the treatment solution is supplied to the treatment solution tank makes it possible to surely suppress the reduction in the solution treatment speed.  
           [0018]    The dissolved oxygen removing step described above may be carried out when the treatment solution in the treatment solution storage tank is stirred. Carrying out the dissolved oxygen removing step when the treatment solution in the treatment solution storage tank is stirred makes it possible to further suppress the reduction in the solution treatment speed.  
           [0019]    It is preferable that the solution treatment method described above further comprises an inert gas supply step of supplying an inert gas into an inner part of a housing accommodating the treatment solution storage tank. When the inert gas supply step is included, oxygen is not easily taken into the treatment solution. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 in a view schematically showing the structure of a plating system according to an embodiment.  
         [0021]    [0021]FIG. 2 is a schematic vertical sectional view of a plating unit according to the embodiment.  
         [0022]    [0022]FIG. 3 is a schematic plan view of the inside of the plating unit according to the embodiment.  
         [0023]    [0023]FIG. 4 is a view schematically showing the structure of a dissolved oxygen removing unit according to the embodiment.  
         [0024]    [0024]FIG. 5 is a view schematically showing the inside of the dissolved oxygen removing unit while a plating solution according to the embodiment is supplied.  
         [0025]    [0025]FIG. 6 is a flow chart showing the flow of processes carried out in the plating unit according to the embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0026]    A plating system according to the present invention will be explained below. FIG. 1 is a view schematically showing the structure of a plating system according to an embodiment, FIG. 2 is a schematic vertical sectional view of a plating unit according to the embodiment, and FIG. 3 is a schematic plan view of the inside of the plating unit according to the embodiment.  
         [0027]    As shown in FIG. 1 to FIG. 3, a plating system  1  includes a plating unit  2  to plate a wafer W and a plating solution storage tank  6  which stores a plating solution used in the plating unit  2 .  
         [0028]    Hereinafter, the plating unit  2  will be explained. The plating unit  2  is covered with a housing  21  made of a synthetic resin. Inside the housing  21 , a driver  22  which holds a wafer W and a plating solution tank  23  which stores the plating solution are mainly provided. In this embodiment, the driver  22  is disposed directly above the plating solution tank  23 .  
         [0029]    In the housing  21  near an upper part of the plating solution tank  23 , a separator  26  having therein an exhaust port  24  which sucks an evaporated plating solution or a scattered plating solution and a cleaning nozzle  5  which cleans the plating applied onto the wafer W is disposed. A through hole is provided in the center of this separator  26  so as to enable the driver  22  to move between a transfer position (I) and a plating position (IV) which will be explained later. Furthermore, a gate valve  27  which allows the wafer W to be carried into/out of the plating unit  1  is provided near the later-explained transfer position (I) in the housing  21 .  
         [0030]    The plating solution tank  23  is, for example, a dual tank consisting of an inner tank  23 A to be filled with the plating solution and an outer tank  23 B to which the plating solution overflowing from the inner tank  23 A flows. The inner tank  23 A is formed in a substantially cylindrical shape with its upper surface open and its bottom surface closed. A blowout pipe  28  which blows out the plating solution protrudes from a bottom part of the inner tank  23 A.  
         [0031]    On the circumference of the blowout pipe  28 , an anode electrode  29  in a substantially disc shape is disposed coaxially with the inner tank  23 A. The anode electrode  29  is electrically connected to a not-shown external power supply which is provided outside the housing  21 . Note that a voltage is applied between the anode electrode  29  and a later-described cathode electrode  45  in order to plate a surface to be plated of the wafer W.  
         [0032]    A diaphragm  30  dividing the inner tank  23 A into an upper region and a lower region is provided between an end portion of the blowout pipe  28  and the inner tank  23 A above the anode electrode  29 . The diaphragm  30  is structured to pass ions therethrough but not to pass therethrough impurities which are produced at the time the anode electrode  29  is dissolved and bubbles, for example, oxygen and hydrogen which are produced during the plating. Here, the upper region of the inner tank  23 A and the lower region of the inner tank  23 A which are separated by the diaphragm  30  will be hereinafter referred to as a cathode region and an anode region respectively.  
         [0033]    Openings  31 ,  32  are formed in the bottom part of the inner tank  23 A and later described pipes  111 A,  121 A are connected to the openings  31 ,  32  respectively.  
         [0034]    The outer tank  23 B is formed in a substantially cylindrical shape with its upper surface open and its bottom surface closed, similarly to the inner tank  23 A. An opening  33  through which the plating solution overflowing from the inner tank  23 A flows into a later-described cathode-side storage region is formed in the bottom part of the outer tank  23 B.  
         [0035]    The driver  22  has a holder  34  which holds the wafer W and a motor  35  which rotates the wafer W together with the holder  34  on a substantially horizontal level.  
         [0036]    A holder raising/lowering mechanism  36  which raises/lowers the holder  34  relative to the plating solution tank  23  is attached to the motor  35 . Incidentally, the holder raising/lowering mechanism  36  in this embodiment raises/lowers the entire driver  22 .  
         [0037]    The holder raising/lowering mechanism  36  is composed of, for example, a support beam  37  which is attached to the motor  35  and which supports the driver  22 , a guide rail  38  attached to an inner wall of the housing  21 , and a vertically expansible/contractible cylinder  36  which raises/lowers the support beam  37  along the guide rail  38 . By driving the cylinder  39 , the driver  22  supported by the support beam  37  is raised/lowered along the guide rail  38 .  
         [0038]    Concretely, the holder  34  ascends/descends to move to the transfer position (I) where the wafer W is to be carried in/out, a cleaning position (II) where the plating applied onto the wafer W is to be cleaned, a spin-dry position (III) where spin dry to remove excessive plating solution and moisture from the plated wafer W is to be performed, and a plating position (IV) where the surface to be plated of the wafer W is to be plated. The wafer W held by the holder  34  located in the transfer position (I) and the cleaning position (II) is above the level of the plating solution when the inner tank  23 A is filled with the plating solution. The wafer W held by the holder  34  located in the spin-dry position (III) and the plating position (IV) is under the level of the plating solution.  
         [0039]    The holder  34  has a cylindrical holder container  40 . One wafer W is accommodated in an inner space of the holder container  40  in a substantially horizontal state. An opening  41  through which the wafer W is to be carried into/out of the holder container  40  is formed in a sidewall of the holder container  40 . A shutter  42  which opens/closes freely is provided near the opening  41 . The shutter  42  is closed after the wafer W is carried in so that the opening  41  is covered, thereby preventing the plating solution from entering the inner space of the holder container  40 .  
         [0040]    A circular opening  43  which enables the surface to be plated of the wafer W to be in contact with the plating solution is formed in a bottom surface of the holder container  40 . Here, the wafer W according to this embodiment is held by the holder  34  by a so-called facedown method, with its surface to be plated facing downward. The wafer W has on its surface to be plated a thin film made of the same substance as the plating, namely, a so-called seed layer, which is formed by a film forming unit disposed in a different system, for example, a PVD unit. By forming the seed layer on the wafer W, a voltage applied to the later-described cathode electrode  45  is also applied to the surface to be plated of the wafer W. Furthermore, trenches to form wiring therein and connection holes to serve for interlayer connection are formed on the surface to be plated of the wafer W.  
         [0041]    A ring-shaped seal member  44  which is elastically deformed is provided on an inner bottom surface of the holder container  40 . A later-described pressing member  50  presses the wafer W against the seal member  44  so that the seal member  44  is elastically deformed, thereby preventing the plating solution from entering the holder container  40 .  
         [0042]    The cathode electrode  45  to supply electricity to the surface to be plated of the wafer W is provided on the seal member  44 . The cathode electrode  45  is electrically connected to a not-shown external power supply. On the cathode electrode  45 , formed are hemisphere-shaped contacts  46  at positions of, for example, 128 equal parts into which the circumference is divided, being in contact with an outer circumferential part of the surface to be plated of the wafer W. The contacts  46  are formed in the hemisphere shape so that each of the contacts  46  is in contact with the wafer W at a substantially constant area.  
         [0043]    A wafer raising/lowering mechanism  47  which holds the wafer W and raises/lowers the wafer W relative to the holder  34  extends from the inner space of the holder container  40  to a position above the motor  35 . The wafer raising/lowering mechanism  47  is composed of, for example, an expansible/contractible chuck member  48  and a vacuum pump  49  which sucks an inner part of the chuck member  48 .  
         [0044]    Not-shown sucking grooves are formed, for example, in three places of the chuck member  48 , and the vacuum pump  49  sucks the air inside the sucking grooves to attach the wafer W to the chuck member  48  by suction so that the wafer W is held by the chuck member  48 . Incidentally, the chuck member  48  is structured to rotate with the holder  34  when the motor  35  is driven.  
         [0045]    The wafer raising/lowering mechanism  47  raises/lowers the wafer W between a transfer position (i) where the wafer W is to be carried in/out and a holder holding position (ii) where the wafer W is to be held by the holder  34 .  
         [0046]    The pressing member  50  which presses the wafer W against the seal member  44  is provided in the inner space of the holder container  40 . The pressing member  50  is formed in a ring shape and is structured to ascend/descend relative to the holder  34  when a not-shown pressing member raising/lowering mechanism is driven. The pressing member  50  is lowered to press the wafer W against the seal member  44  so that the seal member  44  is elastically deformed to seal a gap between the wafer W and the seal member  44 .  
         [0047]    Next, the plating solution storage tank  6  and an area around the plating solution storage tank  6  will be explained.  
         [0048]    The inside of the plating solution storage tank  6  is divided into two parts by a partitioning plate  61 . Concretely, it is divided into an anode-side storage region which stores the plating solution to be supplied to the anode-side region in the plating unit  2  and a cathode-side storage region which stores the plating solution to be supplied to the cathode-side region of the plating unit  2 .  
         [0049]    Here, the plating solution stored in the plating solution storage tank  6  will be explained. The plating solution stored in the plating solution storage tank  6  contains additives such as a retardant which suppresses the embedding of the plating, an accelerator which accelerates the embedding of the plating, and so on. The retardant is mainly composed of a high molecular compound and the accelerator is mainly composed of a sulfur compound.  
         [0050]    The plating solution storage tank  6  is covered with a housing  7  which is made of a synthetic resin and which can maintain a substantially airtight condition. Openings  71 ,  72  are formed in two places of the housing  7  respectively. An inert gas supply system  8  which supplies an inert gas into the housing  7  is connected to the opening  71 .  
         [0051]    The inert gas supply system  8  is provided with an inert gas storage cylinder  81  which stores the inert gas such as nitrogen. A pipe  82  through which the inert gas in the inert gas storage cylinder  81  is supplied into the housing  7  is connected to the inert gas storage cylinder  81  and the housing  7 . In the middle of the pipe  82 , a valve  83  to adjust the flow rate of the inert gas is provided.  
         [0052]    An inert gas exhaust system  9  which exhausts the inert gas out of the housing  7  is connected to the opening  72 . The inert gas exhaust system  9  is mainly composed of a vacuum pump  91  and a pipe  92  connected to the vacuum pump  91  and the housing  7 . The operation of the vacuum pump  91  causes the air or nitrogen inside the housing  7  to be exhausted from the housing  7 .  
         [0053]    A dissolved oxygen measuring unit  10  which measures the concentration of dissolved oxygen contained in the plating solution is provided on the periphery of the plating solution storage tank  6 . The concentration of the dissolved oxygen contained in the plating solution is measured by the dissolved oxygen measuring unit  10  so that the concentration of the dissolved oxygen is accurately controlled.  
         [0054]    The dissolved oxygen measuring unit  10  measures the concentration of the dissolved oxygen contained in the plating solution, utilizing a diaphragm polarographic method. Concretely, the dissolved oxygen measuring unit  10  is provided with not-shown anode electrode and cathode electrode. An oxidation reaction occurs in the anode electrode so that electrons are discharged. In the cathode electrode, a reduction reaction occurs so that the dissolved oxygen is reduced to ion hydroxide. These reactions cause an electric current to pass between the anode electrode and the cathode electrode. Since the amount of this electric current is proportional to the concentration of the dissolved oxygen, the concentration of the dissolved oxygen contained in the plating solution is measured by measuring this electric current.  
         [0055]    A plating solution supply system  11  which supplies the plating solution in the plating solution storage tank  6  to the plating unit  2  is connected to the plating unit  2  and the plating solution storage tank  6 . The plating solution supply system  11  is composed of an anode-side supply system  111  which supplies the plating solution in the anode-side storage region to the anode-side region and a cathode-side supply system  112  which supplies the plating solution in the cathode-side storage region to the cathode-side region.  
         [0056]    The anode-side supply system  111  includes a pipe  111 A whose one end is disposed in the anode-side storage region and other end is connected to the opening  31 . A pump  111 B which pumps out the plating solution in the anode-side storage region to send it to the anode-side region and a filter  111 C which removes impurities from the plating solution pumped out by the pump  111 B are provided in the middle of the pipe  111 A.  
         [0057]    Furthermore, a flowmeter  111 D which measures the flow rate of the plating solution sent to the anode-side region and a flow rate control unit  111 E electrically connected to the pump  111 B and the flowmeter  111 D are provided in the middle of the pipe  111 A. The flowmeter  111 D and the flow rate control unit  111 E are provided in the middle of the pipe  111 A so that the operation of the pump  111 B is adjusted based on the flow rate measured by the flowmeter  111 D to adjust the flow rate of the plating solution pumped out by the pump  111 B.  
         [0058]    The cathode-side supply system  112  includes a pipe  112 A whose one end is disposed in the cathode-side storage region and other end is connected to the blowout pipe  28 . A pump  112 B which pumps out the plating solution in the cathode-side storage region to send it to the cathode-side region, a filter  112 C, a flowmeter  112 D, and a flow rate control unit  112 E are provided in the middle of the pipe  112 A.  
         [0059]    A plating solution drainage system  12  which drains out the plating solution used in the plating unit  2  and has the plating solution flow into the plating solution storage tank  6  is connected to the plating unit  2  and the plating solution storage tank  6 . The plating solution drainage system  12  is composed of an anode-side drainage system  121  which drains out the plating solution from the anode-side region and has the plating solution flow into the anode-side storage region and a cathode-side drainage system  122  which drains out the plating solution from the cathode-side region and has the plating solution flow into the cathode-side storage region.  
         [0060]    The anode-side drainage system  121  is mainly composed of a pipe  121 A, with one end thereof connected to the opening  32  and the other end thereof disposed in the anode-side storage region. The cathode-side drainage system  122  is mainly composed of a pipe  122 A, with one end thereof connected to the opening  33  and the other end thereof disposed in the cathode-side storage region, and a filter  122 B.  
         [0061]    A plating solution stirring system  13  which stirs the plating solution is connected to the plating solution storage tank  6 . The plating solution stirring system  13  is composed of an inter-anode/cathode stirring system  131  which stirs the plating solution between the cathode-side storage region and the anode-side storage region, an anode-side stirring system  132  which stirs the plating solution in the anode-side storage region, and a cathode-side stirring system  133  which stirs the plating solution in the cathode-side storage region.  
         [0062]    The inter-anode/cathode stirring system  131  includes a pipe  131 A with one end thereof disposed in the anode-side storage region and the other end thereof disposed in the cathode-side storage region. A pump  131 B which pumps out the plating solution in the anode-side storage region to sent it to the cathode-side storage region, a filter  131 C, a flowmeter  131 D, and a flow rate control unit  131 E are provided in the middle of the pipe  131 A.  
         [0063]    Here, when the cathode-side storage region is filled with the plating solution, the plating solution overflows from the cathode-side storage region to flow into the anode-side storage region. The plating solution thus flows in/out between the anode-side storage region and the cathode-side storage region so that the plating solution is stirred between the cathode-side storage region and the anode-side storage region.  
         [0064]    The anode-side stirring system  132  includes a pipe  132 A which is so connected to the plating solution storage tank  6  that both ends thereof are positioned in the anode-side storage region. A pump  132 B which pumps out the plating solution in the anode-side storage region to send it to the anode-side storage region, a filter  132 C, a flowmeter  132 D, and a flow rate control unit  132 E are provided in the middle of the pipe  132 A.  
         [0065]    The cathode-side stirring system  133  includes a pipe  133 A which is so connected to the plating solution storage tank  6  that both ends thereof are positioned in the cathode-side storage region. A pump  133 B which pumps out the plating solution in the cathode-side storage region to send it to the cathode-side storage region, a filter  133 C, a flowmeter  133 D, and a flow rate control unit  133 E are provided in the middle of the pipe  133 A.  
         [0066]    In the middle of each of the pipes  111 A,  112 A,  131 A,  132 A,  133 A, a dissolved oxygen removing unit  14  which removes the dissolved oxygen contained in the plating solution is provided.  
         [0067]    [0067]FIG. 4 is a view schematically showing the structure of the dissolved oxygen removing unit  14  according to this embodiment. Note that FIG. 4 shows the dissolved oxygen removing unit  14  provided in the middle of the pipe  111 A. As shown in FIG. 4, the dissolved oxygen removing unit  14  has a cylindrical container  141  whose upper surface and bottom surface are open. An opening  142  allowing the plating solution from which the dissolved oxygen is removed to flow out therethrough to an external region is formed in a side surface of the cylindrical container  141 . The pipe  111 A is connected to a peripheral portion of the opening  142 .  
         [0068]    Covers  143 ,  144  which cover an upper part and a bottom part of the cylindrical container  141  are provided on an outer side of the upper part and an outer side of the bottom part of the cylindrical container  141  respectively. A not-shown vacuum pump is connected to the covers  143 ,  144 . The operation of this vacuum pump causes the pressure inside the covers  143 ,  144  to be lower.  
         [0069]    Seal members  145 ,  146  which seal an inner space of the cylindrical container  141  are provided on an inner side of the upper part and the inner side of the bottom part of the cylindrical container  141  respectively. Furthermore, a plating solution supply pipe  147  which supplies the plating solution into the cylindrical container  141  is inserted into the cylindrical container  141 . One end of the plating solution supply pipe  147  is connected to the pipe  111 A and the other end thereof is buried in the seal member  146 . A plurality of openings  148  which allows the plating solution to flow out therethrough are formed in a portion, which is positioned inside the cylindrical container  141 , of the plating solution supply pipe  147 .  
         [0070]    A plurality of hollow fiber membranes  149  having a hydrophobic property and gas permeability are provided in a vertical direction inside the cylindrical container  141 . Concretely, the hollow fiber membranes  149  are arranged in a circle to surround the plating solution supply pipe  147 . Incidentally, the hollow fiber membranes  149  form a plurality of circles and they surround the plating solution supply pipe  147  in multiple circles. The hollow fiber membranes  149  pass through the seal members  145 ,  146  so that both of end portions of the hollow fiber membranes  149  are exposed in the covers  143 ,  144 . Since both of the end portions of the hollow fiber membranes  149  are exposed in the covers  143 ,  144 , the pressure inside the hollow fiber membranes  149  is reduced when the aforesaid vacuum pump is operated.  
         [0071]    In order to remove the dissolved oxygen contained in the plating solution by the dissolved oxygen removing unit  14 , the aforesaid vacuum pump is operated to reduce the pressure in the hollow fiber membranes  149 . This causes the dissolved oxygen contained in the plating solution flowing from the openings  148  to be sucked into the hollow fiber membranes  149  so that the dissolved oxygen contained in the plating solution is removed. Incidentally, the plating solution usually contains the dissolved oxygen of about 10 mg/L, which can be reduced to about 2 mg/L or lower by the dissolved oxygen removing unit  14 .  
         [0072]    Processes carried out in the plating system  1  will be explained below. FIG. 5 is a view schematically showing the inside of the dissolved oxygen removing unit  14  while the plating solution according to this embodiment is supplied, and FIG. 6 is a flow chart showing the flow of processes carried out in the plating unit  2  according to this embodiment.  
         [0073]    First, the valve  83  is opened so that the inert gas is supplied into the housing  7  from the inert gas storage cylinder  81 . Consequently, the inside of the housing  7  is filled with the inert gas.  
         [0074]    Next, the pumps  111 B,  121 B,  131 B,  132 B,  133 B are operated so that the plating solution is supplied to each of the anode-side region and the cathode-side region and at the same time it is stirred. Furthermore, the aforesaid vacuum pump is operated so that the dissolved oxygen contained in the plating solution flowing out of the openings  148  is removed as shown in FIG. 5. Incidentally, the dissolved oxygen sucked into the hollow fiber membranes  149  is discharged out of the dissolved oxygen removing unit  14  via the covers  143 ,  144 .  
         [0075]    Thereafter, while this state is maintained, the wafer W is plated according to the flow shown in FIG. 6 (STEP  1  to STEP  16 ).  
         [0076]    In this embodiment, the dissolved oxygen is removed from the plating solution so that the reduction in embedding speed is suppressed to decrease the frequency of replacing the plating solution. In other words, consumption of the additives contained in the plating solution is considered to be one of the causes for lowering the embedding speed as is previously stated. To be concrete, it is considered to be one of the causes that the accelerator contained in the plating solution is oxidized due to the dissolved oxygen contained in the plating solution and it loses the function as the accelerator. In this embodiment, the dissolved oxygen contained in the plating solution is removed so that the oxidization of the accelerator contained in the plating solution is suppressed. Therefore, the reduction in the embedding speed is suppressed to lengthen the life of the plating solution. This decreases the frequency of replacing the plating solution.  
         [0077]    Furthermore, the removal of the dissolved oxygen contained in the plating solution is especially effective in the case where the plating solution is caused to overflow from the inner tank  23 A as in this embodiment. The reason is that, in the case where the plating solution is caused to overflow from the inner tank  23 A, the amount of the dissolved oxygen contained in the plating solution is increased since the area of the plating solution in contact with the air becomes large at the time the plating solution overflows from the inner tank  23 A.  
         [0078]    In this embodiment, the inside of the housing  7  is filled with the inert gas so that the amount of the dissolved oxygen contained in the plating solution is decreased compared with a case when the plating solution in the plating solution storage tank  6  is in contact with the air. Specifically, by filling the inside of the housing  7  with the inert gas, the amount of the air in contact with the plating solution is reduced. This reduces the amount of oxygen taken into the plating solution in the plating solution storage tank  6 . Consequently, the amount of the dissolved oxygen contained in the plating solution is decreased.  
         [0079]    It is to be understood that the present invention is not limited to the described content of the above embodiment, and the structure, material, disposition of each of the members, and so on are allowed be changed appropriately without departing from the spirit of the present invention. In the above-described embodiment, the dissolved oxygen removing unit  14  is provided both in the plating solution supply system  11  and the plating solution stirring system  13  but it may be provided in either one of them.  
         [0080]    In the above-described embodiment, the dissolved oxygen removing unit  14  is provided both in the anode-side supply system  111  and the cathode-side supply system  112 , but it may be provided in either one of them. Moreover, the dissolved oxygen removing unit  14  is provided in all of the pipes  131 A,  132 A,  133 A of the inter-anode/cathode stirring system  131 , the anode-side stirring system  132 , and the cathode-side stirring system  133 , but it does not need to be provided in all of the pipes  131 A,  132 A,  133 A.  
         [0081]    In the above-described embodiment, the wafer W is used, but an LCD glass substrate is usable.