Abstract:
A porous member cleaning method enables effective cleaning of the interior of a porous member even when it has a small pore size, a high density and a large volume. The porous member cleaning method includes: disposing a porous member in a hermetic space, and cleaning the interior of the porous member with a pressurized cleaning liquid passing through the interior of the porous member; and then disposing the porous member in said hermetic space or in a different hermetic space, and supplying pressurized pure water to the interior of the porous member so that the pure water passes through the interior of the porous member.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a cleaning method and a cleaning apparatus for porous members, and more particularly to a cleaning method and a cleaning apparatus which are useful for cleaning a porous member provided in an electroplating apparatus for forming interconnects by filling an interconnect material, such as copper, into fine interconnect patterns (recesses) formed in a surface of a substrate, such as a semiconductor wafer, or a porous member for use in a CMP apparatus or a cleaning apparatus, and to a plating apparatus provided with the cleaning apparatus.  
         [0003]     2. Description of the Related Art  
         [0004]     The applicant has proposed a plating apparatus (electrolytic processing apparatus) in which a porous member (high-resistance structure) is disposed between a substrate and an anode, and the porous member is impregnated with a plating solution so as to make the electrical resistivity of the porous member impregnated with the plating solution higher than the electrical resistivity of the plating solution, thereby making the influence of the surface sheet resistance of the substrate as small as negligible and making it possible to form a plated film having a more uniform thickness over an entire surface of the substrate (see, for example, Japanese Patent Laid-Open Publication No. 2002-235192).  
         [0005]     Cutting debris, an organic material, etc., produced by processing, adhere to a surface and the interior (interior surfaces of pores) of such a porous member. It is therefore necessary to pre-clean the porous member before incorporating and using it in a plating apparatus. Further, there are cases where pores of a porous member are clogged, e.g., with a black film which was formed on a soluble anode and fell from the anode into the pores of the porous member in a non-plating time, or with a secondary product with an additive contained in a plating solution. The porous member therefore needs to be cleaned periodically or according to necessity.  
         [0006]     Cleaning of such a porous member has conventionally been carried out by ultrasonic cleaning in substantially the same manner as cleaning for a common substrate, in particular, by a method which, as illustrated in  FIG. 15 , comprises disposing a porous member  302  in a cleaning vessel  300  and immersing the porous member  302  in a cleaning liquid  302 , which is introduced into the cleaning vessel  300  from its bottom and is allowed to overflow into an overflow tank  306 , while applying ultrasonic waves from an ultrasonic oscillator  308  to the cleaning liquid  304  in the cleaning vessel  300 , thereby cleaning the porous member  302 , and then introducing pure water as a rinsing liquid into the cleaning vessel  300  to rinse the cleaned porous member  302  with pure water.  
       SUMMARY OF THE INVENTION  
       [0007]     It has generally been difficult with ultrasonic cleaning of a porous member to fully clean the interior of the porous member. Thus, it takes a long time to fully clean the interior of a porous member especially when the porous member has a large volume and small-sized pores. There is recently a demand for the formation of a plated film having a more uniform thickness over an entire surface of a substrate. In order to meet the demand, it is necessary to supply a plating solution through a porous member more uniformly to a substrate. This requires stricter specifications for the porosity and the pore size of the porous member, making it more difficult to uniformly clean the interior of the porous member.  
         [0008]     The present invention has been made in view of the above situations. It is therefore an object of the present invention to provide a cleaning method and a cleaning apparatus for porous members, which enable effective cleaning of the interior of a porous member even when it has a small pore size, a high density and a large volume, and a plating apparatus provided with the cleaning apparatus.  
         [0009]     In order to achieve the above object, the present invention provides a porous member cleaning method comprising: disposing a porous member in a hermetic space, and cleaning the interior of the porous member with a pressurized cleaning liquid passing through the interior of the porous member; and then disposing the porous member in said hermetic space or in a different hermetic space, and supplying pressurized pure water to the interior of the porous member so that the pure water passes through the interior of the porous member.  
         [0010]     The interior of a porous member can be cleaned more effectively by thus directly cleaning the interior (interior surfaces of pores) of the porous member with a cleaning liquid passing through the interior, without using an external force as in ultrasonic cleaning. Further, by replacing the cleaning liquid, remaining in the interior of the porous member, with pure water, adverse effects of the cleaning liquid on processing, such as plating, can be prevented.  
         [0011]     Preferably, the cleaning liquid and/or pure water in the hermetic space is bubbled with a gas.  
         [0012]     By thus allowing a cleaning liquid and/or pure water, bubbled with a gas, to pass through the interior of a porous member, particles, etc. adhering to the interior of the porous member, i.e., the interior surfaces of pores, can be securely peeled off and removed from the interior pore surfaces. An inert gas, such as N 2 , may be used for the bubbling.  
         [0013]     The cleaning liquid is, for example, sulfuric acid, nitric acid, hydrofluoric acid, hydrochloric acid, a hydrogen peroxide solution, pure water, or a mixed solution thereof, an alkaline cleaning liquid or a neutral detergent, or a combination thereof.  
         [0014]     The porous member is composed of, for example, a porous ceramic comprising silicon carbide, alumina, aluminum nitride, zirconia or vanadium oxide, or a porous resin.  
         [0015]     In a preferred aspect of the present invention, the porous member has a porosity of not more than 40% and a pore size of not more than 100 μm.  
         [0016]     The temperature of the cleaning liquid and the temperature of the pure water are preferably each 20 to 120° C.  
         [0017]     The present invention provides a porous member cleaning apparatus comprising: a hermetic vessel for mounting a porous member and forming a hermetic space in the vessel; a pressurized fluid injection section, connected to the hermetic vessel, for selectively injecting one of a pressurized cleaning liquid and pressurized pure water into the hermetic vessel so that the cleaning liquid or pure water passes through the interior of the porous member; and a fluid discharge section for discharging the cleaning liquid or pure water which has passed through the interior of the porous member.  
         [0018]     The porous member cleaning apparatus preferably further comprises a gas supply section for supplying a gas for bubbling to the cleaning liquid and/or pure water which has been injected into the hermetic vessel.  
         [0019]     The present invention provides a plating apparatus comprising: a substrate holder for holding a substrate; a cathode section including a sealing member for contact with a peripheral portion of a surface of the substrate held by the substrate holder to water-tightly seal the peripheral portion, and a cathode contact for contact with the substrate to feed electricity to the substrate; and an anode section movable between a processing position above the substrate holder and a porous member cleaning position lateral to the processing position, including an anode which, when the anode section is located in the processing position, is disposed opposite the substrate held by the substrate holder, and a porous member disposed between the anode and the substrate, wherein a porous member cleaning section for sequentially introducing a cleaning liquid and pure water into the interior of the porous member of the anode section to clean the interior of the porous member with the cleaning liquid and to replace the cleaning liquid in the interior of the porous member with pure water, is provided in the porous member cleaning position.  
         [0020]     By thus incorporating the porous member cleaning section for cleaning a porous member integrally into the plating apparatus having the porous member, the porous member can be cleaned periodically or according to necessity without each taking the porous member out of the plating apparatus.  
         [0021]     In a preferred aspect of the present invention, the porous member cleaning section is provided in association with a plating solution tray, disposed lateral to the substrate holder, for storing a plating solution for use in idling.  
         [0022]     By thus providing the porous member cleaning section in association with the plating solution tray for storing a plating solution for use in idling, a significant increase in the size of the plating apparatus can be avoided.  
         [0023]     The present invention provides a method for cleaning a porous member in a plating apparatus, comprising: moving an anode section to a porous member cleaning position lateral to a substrate holder, said anode section including an anode which, when the anode section is located in a processing position, is disposed opposite a substrate held by the substrate holder, and a porous member disposed between the anode and the substrate; and then introducing a cleaning liquid and pure water into the interior of the porous member of the anode section, located in the porous member cleaning position, to clean the interior of the porous member with the cleaning liquid and to replace the cleaning liquid in the interior of the porous member with pure water.  
         [0024]     According to the present invention, the interior of a porous member can be cleaned more effectively by directly cleaning the interior (interior surfaces of pores) of the porous member with a cleaning liquid passing through the interior. The present invention thus enables effective cleaning of the interior of a porous member even when it has a high density and a large volume.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is an overall plan view of a substrate processing apparatus provided with a plating apparatus according to an embodiment of the present invention;  
         [0026]      FIG. 2  is a plan view of the plating apparatus shown in  FIG. 1 ;  
         [0027]      FIG. 3  is an enlarged cross-sectional view of a substrate holder and a cathode section of the plating apparatus shown in  FIG. 1 ;  
         [0028]      FIG. 4  is a front view of a pre-coating/recovery arm of the plating apparatus shown in  FIG. 1 ;  
         [0029]      FIG. 5  is a plan view of the substrate holder of the plating apparatus shown in  FIG. 1 ;  
         [0030]      FIG. 6  is a cross-sectional view taken along line B-B of  FIG. 5 ;  
         [0031]      FIG. 7  is a cross-sectional view taken along line C-C of  FIG. 5 ;  
         [0032]      FIG. 8  is a plan view of the cathode section of the plating apparatus shown in  FIG. 1 ;  
         [0033]      FIG. 9  is a cross-sectional view taken along line D-D of  FIG. 8 ;  
         [0034]      FIG. 10  is a plan view of an electrode arm section of the plating apparatus shown in  FIG. 1 ;  
         [0035]      FIG. 11  is a schematic cross-sectional diagram showing the main portion of the plating apparatus shown in  FIG. 1  when plating is performed;  
         [0036]      FIG. 12  is a schematic cross-sectional diagram showing the main portion of the plating apparatus shown in  FIG. 1  when a porous member is cleaned;  
         [0037]      FIG. 13  is a schematic diagram showing a porous member cleaning apparatus according to an embodiment of the present invention;  
         [0038]      FIG. 14  is a schematic diagram showing a porous member cleaning apparatus according to another embodiment of the present invention; and  
         [0039]      FIG. 15  is a schematic diagram showing a conventional porous member cleaning apparatus. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0040]     Preferred embodiments of the present invention will now be described in detail with reference to the drawings.  
         [0041]      FIG. 1  is an overall plan view showing a substrate processing apparatus provided with a plating apparatus according to an embodiment of the present invention. As shown in  FIG. 1 , this substrate processing apparatus is provided with a rectangular facility which houses therein two loading/unloading units  10  for housing a plurality of substrates W therein, two plating apparatuses  12  for performing plating process, a transfer robot  14  for transferring substrates W between the loading/unloading units  10  and the plating apparatuses  12 , and plating solution supply equipment  18  having a plating solution tank  16 .  
         [0042]     The plating apparatus  12 , as shown in  FIG. 2 , is provided with a substrate processing section  20  for performing plating process and processing incidental thereto, and a plating solution tray  22  for storing a plating solution for use in idling is disposed adjacent to the substrate processing section  20 . There is also provided an electrode arm section  30  having an anode section  28  which is held at the front end of an arm  26  swingable about a rotating shaft  24  and which moves between the substrate processing section  20  and the plating solution tray  22 . Furthermore, a pre-coating/recovering arm  32 , and fixed nozzles  34  for ejecting pure water or a chemical liquid such as ion water, and further a gas or the like toward a substrate are disposed laterally of the substrate processing section  20 . In this embodiment, three of the fixed nozzles  34  are disposed, and one of them is used for supplying pure water.  
         [0043]     The substrate processing section  20 , as shown in  FIG. 3 , has a substrate holder  36  for holding a substrate W with its surface (surface to be plated) facing upwardly, and a cathode section  38  located above the substrate holder  36  so as to surround a peripheral portion of the substrate holder  36 . Further, a substantially cylindrical bottomed cup  40  surrounding the periphery of the substrate holder  36  for preventing scatter of various chemical liquids used during processing is provided so as to be vertically movable by an air cylinder (not shown).  
         [0044]     The substrate holder  36  is adapted to be raised and lowered by the air cylinder  44  between a lower substrate transfer position A, an upper plating position B, and a pretreatment/cleaning position C intermediate between these positions. The substrate holder  36  is also adapted to rotate at an arbitrary acceleration and an arbitrary velocity integrally with the cathode section  38  by a rotating motor and a belt (not shown). Substrate carry-in and carry-out openings (not shown) are provided in confrontation with the substrate transfer position A in a side panel of the plating apparatus  12  facing the transfer robot  14 . When the substrate holder  36  is raised to the plating position B, a sealing member  90  and cathode contacts  88  (to be described below) of the cathode section  38  are brought into contact with the peripheral portion of the substrate W held by the substrate holder  36 . On the other hand, the cup  40  has an upper end located below the substrate carry-in and carry-out openings, and when the cup  40  ascends, the upper end of the cup  40  reaches a position above the cathode section  38  closing the substrate carry-in and carry-out openings, as shown by imaginary lines in  FIG. 3 .  
         [0045]     The plating solution tray  22  serves to store a plating solution for performing idling (replacement of plating solution and deforming) while wetting a porous member  110  and an anode  98  (to be described later on) of the electrode arm section  30  with the plating solution, when plating has not been performed. The plating solution tray  22  is set at a size in which the porous member  110  can be accommodated, and the plating solution tray  22  has a plating solution supply port and a plating solution drainage port (not shown). A photo-sensor is attached to the plating solution tray  22 , and can detect brimming with the plating solution in the plating solution tray  22 , i.e., overflow, and drainage.  
         [0046]     The electrode arm section  30  is vertically movable by a vertical movement motor, which is a servomotor, and a ball screw, and swingable between an idling position above the plating solution tray  22  and a processing position above the substrate processing section  20  by a swing motor, as described bellow. A compressed actuator may be used.  
         [0047]     As shown in  FIG. 4 , the pre-coating/recovering arm  32  is coupled to an upper end of a vertical support shaft  58 . The pre-coating/recovering arm  32  is swingable by a rotary actuator  60  and is also vertically moveable by an air cylinder (not shown). The pre-coating/recovering arm  32  supports a pre-coating nozzle  64  for discharging a pre-coating liquid, on its free end side, and a plating solution recovering nozzle  66  for recovering the plating solution, on a portion closer to its proximal end. The pre-coating nozzle  64  is connected to a syringe that is actuatable by an air cylinder, for example, for intermittently discharging a pre-coating liquid from the pre-coating nozzle  64 . The plating solution recovering nozzle  66  is connected to a cylinder pump or an aspirator, for example, to draw the plating solution on the substrate from the plating solution recovering nozzle  66 .  
         [0048]     As shown in  FIGS. 5 through 7 , the substrate holder  36  has a disk-shaped substrate stage  68  and six vertical support arms  70  disposed at spaced intervals on the circumferential edge of the substrate stage  68  for holding a substrate W in a horizontal plane on respective upper surfaces of the support arms  70 . A positioning plate  72  is mounted on an upper end of one of the support arms  70  for positioning the substrate by contacting the end face of the substrate. A pressing finger  74  is rotatably mounted on an upper end of the support arm  70 , which is positioned opposite to the support arm  70  having the positioning plate  72 , for abutting against an end face of the substrate W and pressing the substrate W to the positioning plate  72  when rotated. Chucking fingers  76  are rotatably mounted on upper ends of the remaining four support arms  70  for pressing the substrate W downwardly and gripping the circumferential edge of the substrate W.  
         [0049]     The pressing finger  74  and the chucking fingers  76  have respective lower ends coupled to upper ends of pressing pins  80  that are normally urged to move downwardly by coil springs  78 . When the pressing pins  80  are moved downwardly, the pressing finger  74  and the chucking fingers  76  are rotated radially inwardly into a closed position. A support plate  82  is disposed below the substrate stage  68  for engaging lower ends of the opening pins  80  and pushing them upwardly.  
         [0050]     When the substrate holder  36  is located in the substrate transfer position A shown in  FIG. 3 , the pressing pins  80  are engaged and pushed upwardly by the support plate  82 , so that the pressing finger  74  and the chucking fingers  76  rotate outwardly and open. When the substrate stage  68  is elevated, the opening pins  80  are lowered under the resiliency of the coil springs  78 , so that the pressing finger  74  and the chucking fingers  76  rotate inwardly and close.  
         [0051]     As shown in  FIGS. 8 and 9 , the cathode section  38  comprises an annular frame  86  fixed to upper ends of vertical support columns  84  mounted on the peripheral portion of the support plate  82  (see  FIG. 7 ), a plurality of, six in this embodiment, cathode contacts  88  attached to a lower surface of the annular frame  86  and projecting inwardly, and an annular sealing member  90  mounted on an upper surface of the annular frame  86  in covering relation to upper surfaces of the cathode contacts  88 . The sealing member  90  is adapted to have an inner peripheral edge portion inclined inwardly downwardly and progressively thin-walled, and to have an inner peripheral end suspending downwardly.  
         [0052]     When the substrate holder  36  has ascended to the plating position B, as shown  FIG. 3 , the cathode contacts  88  are pressed against the peripheral portion of the substrate W held by the substrate holder  36  for thereby allowing electric current to pass through the substrate W. At the same time, an inner peripheral end portion of the sealing member  90  is brought into contact with an upper surface of the periphery of the substrate W under pressure to seal its contact portion in a watertight manner. As a result, the plating solution supplied onto the upper surface (surface to be plated) of the substrate W is prevented from seeping from the end portion of the substrate W, and the plating solution is prevented from contaminating the cathode contacts  88 .  
         [0053]     In this embodiment, the cathode section  38  is vertically immovable, but rotatable in a body with the substrate holder  36 . However, the cathode section  38  may be arranged such that it is vertically movable and the sealing member  90  is pressed against the surface, to be plated, of the substrate W when the cathode section  38  is lowered.  
         [0054]     As shown in  FIGS. 10 and 11 , the anode section  28  of the electrode arm section  30  includes a housing  94  which is coupled via a ball bearing to the free end of the pivot arm  26 , and a porous member  110  which is disposed such that it closes the bottom opening of the housing  94 . The housing  94  has at its lower end an inwardly-projecting portion  94   a , while the porous member  110  has at its top a flange portion  110   a . The porous member  110  is secured to the housing  94  in such a state that a seal ring (not shown) is interposed between the inwardly-projecting portion  94   a  and the flange portion  110   a . Thus, a hollow plating solution chamber  100  is defined between the porous member  110  sealed its periphery with the seal ring and the inner surface of the housing  94 .  
         [0055]     The porous member  110  is composed of porous ceramics such as silicon carbide, alumina, SiC, mullite, zirconia, titania, cordierite, aluminum nitride or vanadium oxide or a porous resin such as a sintered compact of polypropylene or polyethylene, or a sponge. A porosity of the porous member  110  is preferably not more than 40%, and an average pore diameter is preferably not more than 100 μm. A thickness of the porous member  110  is generally 1 to 20 mm, preferably 5 to 20 mm, more preferably 8 to 15 mm. The porous member  110 , in this embodiment, is constituted of porous ceramics of alumina having a porosity of not more than 30%, and an average pore diameter of not more than 100 μm. The porous ceramic plate per se is an insulator, but the porous member  110  is constituted so as to have a smaller conductivity than the plating solution by causing the plating solution to enter its interior complicatedly and follow a considerably long path in the thickness direction.  
         [0056]     The porous member  110  is disposed in the plating solution chamber  100  such that the porous member  110  has a high resistance. Hence, the influence of the surface sheet resistance of the substrate becomes a negligible degree. Consequently, the difference in current density over the surface of the substrate due to electrical resistance on the surface of the substrate W becomes small, and the uniformity of the plated film over the surface of the substrate improves.  
         [0057]     In the plating solution chamber  100 , an anode  98  is disposed above the porous member  110 , and a plating solution introduction pipe  104  is disposed above the anode  98 . The plating solution introduction pipe  104  has a plating solution introduction port  104   a  connected to a plating solution supply pipe  102  which extends from the plating solution supply unit  18  (see  FIG. 1 ). A plating solution discharge port  94   b  provided in an upper plate of the housing  94  is connected to a plating solution discharge pipe  106 .  
         [0058]     A manifold structure is employed for the plating solution introduction pipe  104  so that the plating solution can be supplied uniformly onto the surface to be plated of the substrate. In particular, a large number of narrow tubes  112 , communicating with the plating solution introduction pipe  104 , are connected to the pipe  104  at predetermined positions along the long direction of the pipe  104 . Further, small holes are provided in the anode  98  and the porous member  110  at positions corresponding to the narrow tubes  112 . The narrow tubes  112  extend downwardly in the small holes and reach the lower surface or its vicinity of the porous member  110 .  
         [0059]     Thus, the plating solution, introduced from the plating solution supply pipe  102  into the plating solution introduction pipe  104 , passes through the narrow tubes  112  and reaches the bottom of the porous member  110 , and pass through the porous member  110  and fills the plating solution chamber  100 , whereby the anode  98  is immersed in the plating solution. The plating solution is discharged from the plating solution discharge pipe  106  by application of suction to the plating solution discharge pipe  106 .  
         [0060]     In order to suppress slime formation, the anode  98  is made of copper (phosphorus-containing copper) containing 0.03 to 0.05% of phosphorus. It is also possible to use an insoluble material for the anode  98 .  
         [0061]     The cathode contacts  88  are electrically connected to the negative pole of a plating power source, and the anode  98  is electrically connected to the positive pole of the plating power source.  
         [0062]     When carrying out electroplating, the substrate holder  36  is positioned at the plating position B (see  FIG. 3 ). The anode section  28  is lowered until the processing position where the distance between the substrate W held by the substrate holder  36  and the porous member  110  becomes, e.g., about 0.1 to 3 mm. A plating solution is supplied from the plating solution supply pipe  102  to the upper surface (surface to be plated) of the substrate W while impregnating the porous member  110  with the plating solution and filling the plating solution chamber  100  with the plating solution. Then, the cathode contacts  88  are electrically connected to the negative pole of a plating power source and the anode  98  is electrically connected to the positive pole of the plating power source so as to carry out plating of the surface to be plated of the substrate W.  
         [0063]     As shown in  FIG. 12 , a porous member cleaning section  120  for cleaning the porous member  110  of the anode section  28  is provided in association with the plating solution tray  22 . In this embodiment, a hermetic space is formed in the plating solution tray  22  by covering the opening of the plating solution tray  22  with the anode section  28 , and the porous member  110 , defining the hermetic space, is cleaned with a cleaning liquid supplied from the porous member cleaning section  120  into the plating solution tray  22  and, in addition, the cleaning liquid remaining in the porous member  110  is replaced with pure water (rinsing liquid) supplied from the porous member cleaning section  120  into the plating solution tray  22 .  
         [0064]     In particular, a flange portion  94   c  is provided at the top of the housing  94  of the anode section  28 , while a seal ring  122  is provided in the upper surface of the plating solution tray  22  at a position to be in contact with the flange portion  94   c . When the anode section  28  is lowered, the flange portion  94   c  comes into pressure contact with the seal ring  122  in the upper surface of the plating solution tray  22 , whereby the plating solution tray  22  is sealed by the seal ring  122 , forming a hermetic space.  
         [0065]     The porous member cleaning section  120  includes a cleaning liquid tank  126  for storing a cleaning liquid  124  which is, for example, sulfuric acid, nitric acid, hydrofluoric acid, hydrochloric acid, a hydrogen peroxide solution, pure water, or a mixed solution thereof, an alkaline cleaning liquid or a neutral detergent, or a combination thereof, a cleaning liquid supply pipe  128  for supplying the cleaning liquid  124  in the cleaning liquid tank  126  to the plating liquid tray  22 , and a cleaning liquid discharge pipe  130 , which is to be connected selectively to the plating solution introduction inlet  104   a  or to the plating solution discharge outlet  94   b , for discharging the cleaning liquid or the like in the housing  94 . The cleaning liquid supply pipe  128  is provided with a squeeze pump  132  and a filter  134 , and the cleaning liquid discharge pipe  130  is provided with a liquid feeding pump  136 .  
         [0066]     An overflow tank  22   b , defined by an overflow weir  22   a , is provided in the plating solution tray  22 . The cleaning liquid, which has flowed into the overflow tank  22   b , is either returned, via a three-way valve  138   a  and a return pipe  140 , to the cleaning liquid tank  126  or discharged out via the three-way valve  138   a  and a waste liquid pipe  142 . Similarly, the cleaning liquid flowing in the cleaning liquid discharge pipe  130  is either returned, via a three-way valve  138   b  and a return pipe  144 , to the cleaning liquid tank  126  or discharged out via the three-way valve  138   b  and a waste liquid pipe  146 . The cleaning liquid supply pipe  128  is selectively connected, via a three-way valve  138   c  upstream of the squeeze pump  132 , to a pure water pipe  148  for supplying pure water as a rinsing liquid, and is selectively connected, via a three-way valve  138   d  downstream of the filter  134 , to a waste liquid pipe  150 . When pure water is used as a cleaning liquid for the porous member, the cleaning operation can be carried out solely with the pure water pipe  148  without the above switching of pipes.  
         [0067]     The operation of the porous member cleaning section  120  upon cleaning of the porous member  110  of the anode section  28  will now be described.  
         [0068]     First, the anode section  28  is positioned at the idling position above the plating solution tray  22 . The anode section  28  is then lowered to bring the flange portion  94   c  of the anode section  28  into pressure contact with the seal ring  122  in the upper surface of the plating solution tray  22 , thereby sealing the peripheral portion of the plating solution tray  22  with the seal ring  122 . The plating solution tray  22  has previously been emptied of the plating solution, and the plating solution introduction inlet  104   a  and the plating solution discharge outlet  94   b  have been connected to the cleaning liquid discharge pipe  130 .  
         [0069]     Next, the squeeze pump  132  is driven to pressurize the cleaning liquid  124  and supply the cleaning liquid  124  from the cleaning liquid tank  126  to the plating solution tray  22 , and the liquid feeding pump  136  is driven, for example, at a time point when the plating solution tray  22  has become filled with the cleaning liquid, to discharge the cleaning liquid, initially containing a plating solution, from the housing  94 . Thus, the pressurized cleaning liquid  124 , which has flowed into the plating solution tray  22 , is allowed to pass through the interior of the porous member  110  and flow into the housing  94 , thereby cleaning the interior (interior surfaces of pores) of the porous member  110  with the cleaning liquid  124 . By thus directly cleaning the interior (interior surfaces of pores) of the porous member  110  with the cleaning liquid  124  passing through the interior, the interior of the porous member  110  can be cleaned with good efficiency even when the porous member  110  has a high density and a large volume. According to the present invention, it is also possible to apply ultrasonic waves to at least one of the porous member  110 , the cleaning liquid  124  and the porous member cleaning section  120 , during cleaning of the porous member  110  with the pressurized cleaning liquid  124 , so as to increase the cleaning efficiency.  
         [0070]     When the cleaning liquid, discharged through the cleaning liquid discharge pipe  130 , contains a plating solution, the cleaning liquid is discharged out via the three-way valve  138   b  and the waste liquid pipe  146  and, when the cleaning liquid has come to contain no plating solution, the cleaning liquid is returned, via the three-way valve  138   b  and the return pipe  144 , to the cleaning liquid tank  126  and is allowed to circulate. The flow rate of the cleaning liquid during the cleaning is, for example, 10 to 20 L/min.  
         [0071]     After cleaning the porous member  110  with the cleaning liquid  124  for a predetermined time, the supply of the cleaning liquid  124  to the plating solution tray  22  is stopped. The cleaning time is, for example, about 3 hours when sulfuric acid is used as the cleaning liquid. Thereafter, the cleaning liquid remaining in the plating solution tray  22  is withdrawn from the tray  22  through the cleaning liquid supply pipe  128  and the waste liquid pipe  150 , while the cleaning liquid in the overflow tank  22   b  is returned through the return pipe  140  to the cleaning tank  126 .  
         [0072]     Next, the pure water pipe  148  is connected via the three-way valve  138   c  to the cleaning liquid supply pipe  128 . The squeeze pump  132  is driven to supply pressurized pure water as a rinsing liquid into the plating solution tray  22 , and the liquid feeding pump  136  is driven, for example, at a time point when the plating solution tray  22  has become filled with pure water, to discharge pure water, initially containing the cleaning liquid, from the housing  94 . At the same time, pure water, which has been supplied into the plating solution tray  22  and passed through the interior of the porous member  110 , and pure water, which has flowed into the overflow tank  22   b , are discharged as waste through the waste liquid pipes  142 ,  146 .  
         [0073]     Thus, the pressurized pure water, which has flowed into the plating solution tray  22 , is allowed to pass through the interior of the porous member  110  and flow into the housing  94 , thereby replacing the cleaning liquid, remaining in the interior of the porous member  110 , with pure water. By thus replacing the cleaning liquid, remaining in the interior of the porous member  110 , with pure water, adverse effects of the cleaning liquid on plating can be prevented.  
         [0074]     During the pure water rinsing (pure water replacement), the electric conductivity of pure water that has passed through the interior of the porous member  110  is monitored and, when the electric conductivity has reached a predetermined value, the supply of pure water to the plating solution tray is stopped, thereby terminating the replacement operation. Thereafter, pure water, remaining in the plating solution tray  22 , is withdrawn from the tray  22  through the cleaning liquid supply pipe  128  and the waste liquid pipe  150 . It is also possible to terminate the replacement operation after elapse of a predetermined time period determined, e.g., by experiment.  
         [0075]     Next, ordinary idling is carried out. In particular, while introducing a plating solution into the plating solution tray  22  and keeping the porous member  110  immersed in the plating solution in the plating solution tray  22 , the plating solution in the housing  94  is withdrawn and circulated, thereby carrying out replacement of the plating solution in the housing  94  and defoaming of the plating solution.  
         [0076]     By incorporating the porous member cleaning section  120  for cleaning the porous member  110  integrally into the plating apparatus  12  having the porous member  110 , according to this embodiment, the porous member  110  can be cleaned periodically or according to necessity without taking the porous member  110  out of the plating apparatus  12 . Further, by carrying out cleaning of the porous member  110  at the idling position with the cleaning liquid supplied to the plating solution tray  22  for storing a plating solution for use in idling, a significant increase in the size of the plating apparatus can be avoided.  
         [0077]     It is also possible to separately provide a cleaning liquid tray, e.g., beside the plating solution tray, to move the anode section to above the cleaning liquid tray and then lower the anode section so as to cover the opening of the cleaning liquid tray with the anode section, thereby forming a hermetic space in the cleaning liquid tray, and to carry out cleaning of the porous member of the anode section, in substantially the same manner as described above, by sequentially supplying a pressurized cleaning liquid and pressurized pure water (rinsing liquid) to the cleaning liquid tray. A pure water rinsing tray may also be provided separately from the cleaning liquid tray for cleaning in order to save time taken for replacing a chemical solution with pure water in the cleaning liquid tray and save the amount of liquid supplied, or to facilitate reuse of the cleaning liquid.  
         [0078]     The operation of the above-described substrate processing apparatus will now be described.  
         [0079]     First, a substrate W to be plated is taken out from one of the loading/unloading units  10  by the transfer robot  14 , and transferred, with a surface to be plated facing upwardly, through the substrate carry-in and carry-out opening defined in the side panel, into one of the plating apparatuses  12 . At this time, the substrate holder  36  is in the lower substrate transfer position A. After the hand of the transfer robot  14  has reached a position directly above the substrate stage  68 , the hand of the transfer robot  14  is lowered to place the substrate W on the support arms  70 . The hand of the transfer robot  14  is then retracted through the substrate carry-in and carry-out opening.  
         [0080]     After the hand of the transfer robot  14  is retracted, the cup  40  is elevated. Then, the substrate holder  36  is lifted from the substrate transfer position A to the pretreatment/cleaning position C. As the substrate holder  36  ascends, the substrate W placed on the support arms  70  is positioned by the positioning plate  72  and the pressing finger  74 , and then reliably gripped by the chucking fingers  76 .  
         [0081]     On the other hand, the anode section  28  of the electrode arm section  30  is in the idling position over the plating solution tray  22  now, and the porous member  110  and the anode  98  is positioned in the plating solution tray  22 . At the same time that the cup  40  ascends, the plating solution starts being supplied to the plating solution tray  22  and the anode section  28 . Until the step of plating the substrate W is initiated, the new plating solution is supplied, and the plating solution discharge pipe  106  is evacuated to replace the plating solution in the porous member  110  and remove air bubbles (idling) from the plating solution in the porous member  110 . When the ascending movement of the cup  40  is completed, the substrate carry-in and carry-out openings in the side panel are closed by the cup  40 , isolating the atmosphere in the side panel and the atmosphere outside of the side panel from each other.  
         [0082]     When the cup  40  is elevated, the pre-coating step is initiated. Specifically, the substrate holder  36  that has received the substrate W is rotated, and the pre-coating/recovering arm  32  is moved from the retracted position to a position confronting the substrate W. When the rotational speed of the substrate holder  36  reaches a preset value, the pre-coating nozzle  64 , mounted on the tip end of the pre-coating/recovering arm  32 , intermittently discharges a pre-coating liquid which comprises a surface active agent, for example, toward the surface to be plated of the substrate W. At this time, since the substrate holder  36  is rotating, the pre-coating liquid spreads all over the surface to be plated of the substrate W. Then, the pre-coating/recovering arm  32  is returned to the retracted position, and the rotational speed of the substrate holder  36  is increased to spin the pre-coating liquid off and dry the surface to be plated of the substrate W.  
         [0083]     After the completion of the pre-coating step, the plating step is initiated. First, the substrate holder  36  is stopped against rotation, or the rotational speed thereof is reduced to a preset rotational speed for plating. In this state, the substrate holder  36  is lifted to the plating position B. When the peripheral portion of the substrate W is brought into contact with the cathode contacts  88 , it is possible to pass an electric current, and at the same time, the sealing member  90  is pressed against the upper surface of the peripheral portion of the substrate W, thus sealing the peripheral portion of the substrate W in a watertight manner.  
         [0084]     Based on a signal indicating that the pre-coating step for the loaded substrate W is completed, the electrode arm section  30  is swung in a horizontal direction to displace the anode section  28  from a position over the plating solution tray  22  to a position over the plating processing position. After the anode section  28  reaches this position, the anode section  28  is lowered toward the cathode section  38 . At this time, the porous member  110  does not contact with the surface to be plated of the substrate W, but is held closely to the surface to be plated of the substrate W at a distance ranging from 0.1 mm to 3 mm. When the descent of the anode section  28  is completed, the cathode contacts  88  are connected to the negative pole of the plating power source and the anode  98  is connected to the positive pole of the plating power source so as to initiate the plating process. The substrate holder  36  may be rotated at low speed during plating, if necessary.  
         [0085]     When the plating process is completed, the electrode arm section  30  is raised and then swung to return the anode section  28  to the position above the plating solution tray  22  and to lower to the idling position. Then, the pre-coating/recovering arm  32  is moved from the retreat position to the position confronting to the substrate W, and lowered to recover the remainder of the plating solution on the substrate W by a plating solution recovering nozzle  66 . After recovering of the remainder of the plating solution is completed, the pre-coating/recovering arm  32  is returned to the retreat position, and pure water is supplied from the fixed nozzle  34  for supplying pure water toward the central portion of the substrate W for rinsing the plated surface of the substrate. At the same time, the substrate holder  36  is rotated at an increased speed to replace the plating solution on the surface of the substrate W with pure water. Rinsing the substrate W in this manner prevents the splashing plating solution from contaminating the cathode contacts  88  of the cathode section  38  during descent of the substrate holder  36  from the plating position B.  
         [0086]     After completion of the rinsing, the washing with water step is initiated. That is, the substrate holder  36  is lowered from the plating position B to the pretreatment/cleaning position C. Then, while pure water is supplied from the fixed nozzle  34  for supplying pure water, the substrate holder  36  and the cathode section  38  are rotated to perform washing with water. At this time, the sealing member  90  and the cathode contacts  88  can also be cleaned, simultaneously with the substrate W, by pure water directly supplied to the cathode section  38 , or pure water scattered from the surface of the substrate W.  
         [0087]     After washing with water is completed, the drying step is initiated. That is, supply of pure water from the fixed nozzle  34  is stopped, and the rotational speed of the substrate holder  36  and the cathode section  38  is further increased to remove pure water on the surface of the substrate W by centrifugal force and to dry the surface of the substrate W. The sealing member  90  and the cathode contacts  88  are also dried at the same time. Upon completion of the drying, the rotation of the substrate holder  36  and the cathode section  38  is stopped, and the substrate holder  36  is lowered to the substrate transfer position A. Thus, the gripping of the substrate W by the chucking fingers  76  is released, and the substrate W is just placed on the upper surfaces of the support arms  70 . At the same time, the cup  40  is also lowered.  
         [0088]     All the steps including the plating step, the pretreatment step accompanying to the plating step, the cleaning step, and the drying step are now finished. The transfer robot  14  inserts its hand through the substrate carry-in and carry-out opening into the position beneath the substrate W, and raises the hand to receive the plated substrate W from the substrate holder  36 . Then, the transfer robot  14  returns the plated substrate W received from the substrate holder  36  to one of the loading/unloading units  10 .  
         [0089]     The porous member  110  of the anode section  28  is cleaned by using the porous member cleaning section  120  either periodically or after processing a predetermined number of substrates, for example. In particular, after the completion of the plating process, the electrode arm section  30  is raised and pivoted to return the anode section  28  to above the plating solution tray  22 . The anode section  28  is then lowered to below the idling position so as to seal the peripheral portion of the anode section  28  with the seal ring  122 . The plating solution has previously been withdrawn from the plating solution tray  22 . A high-pressure cleaning liquid and high-pressure pure water are sequentially introduced into the plating solution tray  22  form the porous member cleaning section  120  in the above-described manner, thereby cleaning the interior of the porous member  110  of the anode section  28  and replacing the cleaning liquid remaining in the interior of the porous member  110  with pure water (rinsing liquid). After completion of the cleaning of the porous member  110 , the next plating processing will be started.  
         [0090]      FIG. 13  schematically shows a porous member cleaning apparatus according to an embodiment of the present invention, which can be used to clean, e.g., the porous member  110  provided in the plating apparatus  12  after taking the porous member  110  out of the plating apparatus  12 . The porous member cleaning apparatus includes an upwardly-open hermetically-sealable hermetic vessel  200 , a ring-shaped holder member  202  attached to an upper portion of the hermetic vessel  200 , and a lid  204  which is detachable or openable/closable and water-tightly covers the top of the hermetic vessel  200 .  
         [0091]     The holder member  202  is to hold the porous member  110  by dropping it into the opening of the holder member  202  and to close an opening of the hermetic vessel  200  with the porous member  110 . A seal ring  206  is mounted to the upper surface of the holder member  202  at a position where the seal ring  206  surrounds the porous member  110 . The cleaning apparatus also includes a ring-shaped retainer plate  208  having such a width as to cover the seal ring  206  and a peripheral region of the porous member  110  held by the holder member  202 . After dropping the porous member  110  into the opening of the holder member  202 , the retainer plate  208  is brought into pressure contact with the peripheral region of the upper surface of the porous member  110  while squashing the seal ring  206  by the retainer plate  208 , and the retainer plate  208  is fixed to the holder member  202  by a fixture  210 , such as a bolt. A hermetic space peripherally sealed with the seal ring  206 , with the opening closed with the porous member  110 , is thus formed in the hermetic vessel  200 .  
         [0092]     To the bottom of the hermetic vessel  200  is connected a cleaning liquid supply pipe  216  as a pressurized fluid injection section, extending from a cleaning liquid tank  214  for storing therein a cleaning liquid  212 . The cleaning liquid supply pipe (pressurized fluid injection section)  216  is provided with a squeeze pump  218  and a filter  220 . The cleaning liquid supply pipe  216  is capable of being selectively connected to a pure water pipe  224  via a three-way valve  222   a  upstream of the squeeze pump  218 . To the bottom of the hermetic vessel  200  is also connected a gas supply pipe  226  for supplying an inert gas, such as N 2 , to a liquid (cleaning liquid and/or pure water) in the hermetic vessel  200  for bubbling of the liquid.  
         [0093]     A cleaning liquid discharge pipe  228  as a fluid discharge section is connected to the lid  204 . The cleaning liquid discharge pipe (fluid discharge section)  228  is to be selectively connected via a three-way valve  222   b  to one of a waste liquid pipe  232  and a return pipe  230  connected to the cleaning liquid tank  214 .  
         [0094]     The operation of the porous member cleaning apparatus upon cleaning of the porous member  110  will now be described.  
         [0095]     First, with the lid  204  detached or open, the porous member  110  is dropped into the opening of the holder member  202  and the retainer plate  208  is fixed to the holder member  202  by the fixture  210 , thereby forming a hermetic space peripherally sealed with the seal ring  206 , with the opening closed with the porous member  110 , in the hermetic vessel  200 . The lid  204  is then attached or closed.  
         [0096]     Thereafter, the squeeze pump  218  is driven to pressurize the cleaning liquid  212  and feed the liquid sequentially from the cleaning liquid tank  214  into the hermetic vessel  200 . As with the above-described embodiment, the flow rate of the cleaning liquid is, for example, 10 to 20 L/min. At the same time, an inert gas, such as N 2 , is supplied from the gas supply pipe  226  into the cleaning liquid, which has been fed into the hermetic vessel  200 , to bubble the liquid. The pressurized cleaning liquid is thus allowed to pass through the interior of the porous member  110  and reach to above the porous member  110 , thereby cleaning the interior of the porous member  110  with the cleaning liquid. Specially, by allowing the cleaning liquid, which is bubbled with the gas, to pass through the interior of the porous member  110 , according to this embodiment, particles, etc. adhering to the interior of the porous member  110 , i.e., the interior surfaces of pores, can be securely peeled off and removed from the interior pore surfaces.  
         [0097]     During the cleaning, the cleaning liquid, which has reached to above the porous member  110  and has accumulated inside the lid  204 , is discharged through the cleaning liquid discharge pipe  228 . When the cleaning liquid, discharged through the cleaning liquid discharge pipe  228 , contains a plating solution, the cleaning liquid is discharged out via the three-way valve  222   b  and the waste liquid pipe  232  and, when the cleaning liquid has come to contain no plating solution, the cleaning liquid is returned, via the three-way valve  222   b  and the return pipe  230 , to the cleaning liquid tank  214  and is allowed to circulate. After cleaning the porous member  110  with the cleaning liquid  212  for a predetermined time, the supply of the cleaning liquid  212  to the hermetic vessel  200  is stopped.  
         [0098]     Next, the pure water pipe  224  is connected via the three-way valve  222   a  to the cleaning liquid supply pipe  216 , and pressurized pure water as a rinsing liquid is supplied into the hermetic vessel  200  at a flow rate of 10 to 20 L/min, so that the pressurized pure water is allowed to pass through the interior of the porous member  110  and reach to above the porous member  110 , thereby replacing the cleaning liquid remaining in the interior of the porous member  110  with pure water. As with the cleaning liquid, the pure water, which has been supplied into the hermetic vessel  200 , may be bubbled with an inert gas, such as N 2 , supplied from the gas supply pipe  226 . The liquid discharged out of the lid  204  during the pure water replacement is discharged to the outside from the waste liquid pipe  146 .  
         [0099]     After completion of the pure water replacement operation, the driving of the squeeze pump  218  is stopped, and the liquid remaining inside the lid  204  is removed. The lid  204  is then either detached or opened. Thereafter, the retainer plate  208  is detached, and the porous member  110  after cleaning is taken out of the holder member  202  to reuse the porous member  110  in, e.g., a plating apparatus.  
         [0100]      FIG. 14  shows a porous member cleaning apparatus according to another embodiment of the present invention. This embodiment differs from the embodiment shown in  FIG. 13  in that the cleaning liquid supply pipe (pressurized fluid supply section)  216  is connected to the lid  204  and the cleaning liquid discharge pipe (fluid discharge section)  228  is connected to the hermetic vessel  200 , so that a pressurized cleaning liquid and pressurized pure water are sequentially supplied into the region (hermetic space) surrounded by the porous member  110 , the holder member  202  and the lid  204  and are passed through the interior of the porous member  110 , and the cleaning liquid or pure water, which has passed through the interior of the porous member  110  and accumulated inside the lid  200 , is either discharged as waste or reused. The other construction of this embodiment is substantially the same as the embodiment shown in  FIG. 13 , hence a description thereof is omitted.  
         [0101]     While the present invention has been described with reference to the preferred embodiments thereof, it is understood that the present invention is not limited to the particular embodiments, but various modifications may be made therein within the technical concept of the invention.