Patent Publication Number: US-7897024-B2

Title: Conducting belt for use with anode holder and anode holder

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a conducting belt for use with an anode holder and an anode holder, and more particularly to a conducting belt for supplying an electric current to an anode for plating a surface of a substrate such as a semiconductor wafer, and an anode holder for holding such an anode. The present invention is also concerned with a plating apparatus for plating a substrate using the conducting belt. The plating apparatus may be a bump plating apparatus for forming bumps on a surface of a semiconductor substrate or a plating apparatus for plating via holes having high aspect ratios and large depths, e.g., a diameter of 10 μm to 20 μm and a depth of 70 μm to 150 μm. 
     2. Description of the Related Art 
     In recent years, there has been used a method of forming metal films and organic films on substrates such as semiconductor wafers by a plating process in forming semiconductor circuit interconnections and bumps. For example, it has widely been practiced to form bumps (protruding connecting electrode) or interconnections of gold, silver, copper, solder, nickel or a multilayer of these metals at predetermined portions on a surface of a semiconductor wafer having semiconductor circuits and fine interconnections for connecting semiconductor circuits, thereby electrically connecting the semiconductor circuits via the bumps to electrodes of a package substrate or tape automated bonding (TAB) electrodes. The interconnections and the bumps may be formed by any of various methods including an electroplating method, an electroless plating method, a vapor deposition method, and a printing method. Of these methods, the electroplating process has been used most widely because it can produce finer patterns at a higher film deposition rate to produce semiconductor chips with more I/O terminals and smaller pitches. For details, reference should be made to Japanese laid-open patent publication No. 2000-96292. Metal films formed by the electroplating process that are most widely used have characteristics of high purity, high deposition rate, and easy film-thickness control. 
       FIG. 15  of the accompanying drawings schematically shows a vertical-immersion plating apparatus in which a substrate and an anode are vertically placed in a plating tank. As shown in  FIG. 15 , the plating apparatus includes a plating tank  101  containing a plating solution Q therein. An anode  103  held by an anode holder  102  and a substrate W held by a substrate holder  104  are vertically immersed in the plating solution Q in such a manner that the anode  103  and the substrate W are spaced in confronting relation from each other and lie parallel to each other. When an electric current is supplied between the anode  103  and the substrate W by a plating power supply  105 , a surface W 1  of the substrate W which is exposed from the substrate holder  104  is electroplated. The plating tank  101  is combined with a plating solution circulator  106  for circulating the plating solution Q by supplying the plating solution Q from an inlet port  111  into the plating tank  101  and discharging the plating solution Q from the plating tank  101  through an outlet port  112 . 
     As shown in  FIG. 15 , the vertical-immersion plating apparatus performs plating of the substrate W by placing the substrate W so as to face the anode  103  that is held by the anode holder  102 . Although a plate-like anode is shown as an anode, an anode ball housed in a cage may be used as an anode. However, the plate-like anode held by the anode holder offers the following advantages: 
     1) A shield plate may be mounted on the anode holder, and such shield plate may make it possible to adjust the opening diameter of the anode, thereby easily controlling in-plane uniformity (see, for example, Japanese laid-open patent publication No. 2005-29863). 
     2) Because the anode is in the form of a plate, the anode can easily be held parallel to the substrate to improve in-plane uniformity. 
     As described above, using the anode holder to hold the anode while the substrate is being plated by the vertical-immersion plating apparatus is advantageous. However, the plating apparatus is required to have the following functions in order to meet growing demands for finer interconnections and increased throughputs: 
     1) Finer interconnections to be formed on substrates require certainty of supply of an electric current to the anode. 
     2) As the substrate to be processed is larger in size, the anode is also larger in size. Since the larger anode cannot easily be replaced manually with another anode due to their weight, a new jig is needed for anode replacement. 
     3) The replacement of the anode needs to be performed efficiently in a short period of time. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a conducting belt and an anode holder which can reliably supply an electric current to an anode, can allow easy replacement of the anode with a new anode, and can improve the efficiency in replacement work of an anode to shorten operation time. 
     According to a first aspect of the present invention, there is provided a conducting belt for use with an anode holder for supplying an electric current to an anode, the anode and a substrate being vertically disposed so as to face each other in a plating tank of a plating apparatus, the conducting belt comprising: a belt capable of contacting an outer circumferential edge of the anode and holding the anode. 
     According to the present invention, the conductive belt can hold a disk-shaped anode by tightening the outer circumferential edge of the anode by a circular belt. Since the belt tightens the outer circumferential edge of the anode, an electric current is reliably supplied through the conducting belt to the anode. Thus, there is no need to perform positional alignment between the anode and the conducting belt, and the time required to replace the anode can be shortened. As the conducting belt usually has a width of 1 cm to 2 cm, the area of contact between the conducting belt and the anode is large, and any contact resistance between the conducting belt and the anode can be reduced. 
     In the preferred aspect of the present invention, the belt is capable of contacting the outer circumferential edge of the anode substantially in its entirety. 
     In a preferred aspect of the present invention, the belt has opposite ends fastened to each other by a fastener to hold the anode. 
     In a preferred aspect of the present invention, the fastener comprises a bolt and a nut. 
     In a preferred aspect of the present invention, there is provided a conducting belt further comprising an electrically conductive bracket fixed to an end of the belt, the electrically conductive bracket having a contact for supplying the electric current. 
     According to a second aspect of the present invention, there is provided an anode holder for vertically holding an anode, the anode and a substrate being vertically disposed so as to face each other in a plating tank of a plating apparatus, the anode holder comprising: an anode holder base having a hole defined therein for housing a conducting belt for supplying an electric current to the anode; and an anode mask mounted on the anode holder base for covering a portion of a front surface of the anode. The conducting belt comprises a belt capable of contacting an outer circumferential edge of the anode and holding the anode. 
     According to the present invention, the exposed area of the anode can be adjusted by the anode mask. Further, the conducting belt is masked by the anode holder and is not exposed to a plating solution during a plating process. 
     In a preferred aspect of the invention, an anode holder further comprises: a rear cover mounted on a rear surface of the anode holder base for covering a rear surface of the anode. 
     In a preferred aspect of the present invention, the anode mask has a circular opening, and the circular opening has a diameter smaller than the diameter of the anode. 
     In a preferred aspect of the present invention, the anode holder base includes a hand for transferring the anode holder. 
     In a preferred aspect of the present invention, the anode holder base includes a solution discharge hole for allowing a solution to be discharged therethrough. 
     According to a third aspect of the present invention, there is provided a plating apparatus comprising: a plating tank for vertically placing therein an anode holder holding an anode and a substrate holder holding a substrate thereon in confronting relation to each other; a temporary storing unit for exchanging the anode holder; and a transfer robot for transferring the anode holder between the plating tank and the temporary storing unit. The anode holder comprises an anode holder base having a hole defined therein for housing a conducting belt for supplying an electric current to the anode; and an anode mask mounted on the anode holder base for covering a portion of a front surface of the anode. The conducting belt comprises a belt capable of contacting an outer circumferential edge of the anode and holding the anode. 
     According to the present invention, the anode holder, which has such a structure as to cope with the transfer robot, can be conveyed by the transfer robot. 
     In a preferred aspect of the present invention, a plating apparatus further comprises: a cleaning tank for cleaning the anode holder. 
     In a preferred aspect of the present invention, a plating apparatus further comprises: a blowing tank for removing water droplets from the anode holder. 
     According to the present invention, the anode holder can be transferred by the transfer robot through a removal section to the outside of the apparatus after the anode holder is cleaned by cleaning water, and water droplets are removed from the anode holder. 
     According to a fourth aspect of the present invention, there is provided an anode held by a conducting belt for use with an anode holder for supplying an electric current to an anode. The anode and a substrate are vertically disposed so as to face each other in a plating tank of a plating apparatus. The conducting belt comprises a belt capable of contacting an outer circumferential edge of the anode and holding the anode. 
     In a preferred aspect of the present invention, the anode is disk-shaped. 
     The conducting belt according to the present invention offers the following advantages: 
     1) Since the conducting belt is brought into contact with the entire or substantially entire outer circumferential edge of the anode, the conducting belt can supply an electric current to the anode from the entire or substantially entire outer circumferential edge of the anode. Therefore, a contact failure is prevented from occurring between the conducting belt and the anode. 
     2) As the area of contact between the conducting belt and the anode is large, any contact resistance between the conducting belt and the anode is reduced. 
     3) Since the entire or substantially entire outer circumferential edge of the anode is secured by the conducting belt, there is no need to perform positional alignment between the anode and the conducting belt. Further, the anode can easily be machined because the anode is in the form of a circular disk. 
     4) The anode can easily be replaced with a new one simply by loosening the conducting belt, placing the new anode in position, and retightening the conducting belt. 
     5) Since the anode is in the form of a circular disk and is held by the conducting belt, the anode is free of wasteful areas. 
     The anode holder according to the present invention offers the following advantages: 
     1) The anode can easily be replaced with a new one simply by removing the rear cover, loosening the fastener, placing the new anode in position, retightening the fastener, and attaching the rear cover again. 
     2) The anode mask has its inside diameter smaller than the diameter of the anode. Therefore, even if the anode held by the conducting belt is overused beyond its replacement period, the anode is prevented from falling out of the anode holder or suffering from a conductive fault. 
     3) The solution discharge hole defined in the lower end of the anode holder allows the plating solution to be discharged quickly and reliably from the anode holder through the solution discharge hole. 
     The plating apparatus according to the present invention offers the following advantages: 
     1) Since the anode holder is removed by the transfer robot which is fully automatized, the anode holder can easily be replaced. 
     2) For removing the anode holder from the plating apparatus, the anode holder is taken out of the plating tank by the transfer robot, and cleaned in the cleaning tank to remove the plating solution from the anode holder. Then, water droplets are removed from the anode holder in the blowing tank, and the anode holder is removed from the plating apparatus through the temporary storing unit. Thus, the operator is not required to touch the plating solution for the removal of the anode holder, and hence the safety of the operator can be ensured. 
     3) Since the anode holder can easily be removed, the anode mask can easily be replaced. 
     4) The transfer robot has a high level of positioning accuracy, and can perform fine adjustment of position. Consequently, the anode holder can be placed in a desired position with high reproducibility, and the interelectrode distance between the substrate and the anode can easily be changed. 
     The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front elevational view showing a conducting belt which holds an anode, the conducting belt being for use with an anode holder; 
         FIG. 2  is a side elevational view showing the conducting belt; 
         FIG. 3  is an enlarged view showing an encircled area A in  FIG. 1 , and showing a fastening assembly in detail; 
         FIG. 4  is a perspective view showing the conducting belt; 
         FIG. 5  is a front elevational view, partly in cross section, showing an anode holder; 
         FIG. 6  is a cross-sectional view taken along line VI-VI of  FIG. 5 ; 
         FIG. 7  is an exploded perspective view showing the anode holder; 
         FIG. 8  is a view showing the anode holder which is immersed in a plating solution; 
         FIG. 9  is a schematic plan view showing a plating apparatus incorporating the conducting belt shown in  FIGS. 1 through 4  and the anode holder shown in  FIGS. 5 through 7 ; 
         FIG. 10  is a plan view showing a linear motor unit of a transfer apparatus in the plating apparatus; 
         FIG. 11  is a front elevational view showing the linear motor unit shown in  FIG. 10 ; 
         FIG. 12  is a front elevational view showing a transporter in the plating apparatus; 
         FIG. 13  is a plan view showing a gripping mechanism mounted on an arm of the transporter; 
         FIG. 14  is a vertical cross-sectional view showing the gripping mechanism shown in  FIG. 13 ; and 
         FIG. 15  is a vertical cross-sectional view showing a conventional vertical-immersion plating apparatus in which a substrate and an anode are vertically placed in a plating tank. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A conducting belt for use with an anode holder and an anode holder according to an embodiment of the present invention will be described with reference to  FIGS. 1 through 8 . The conducting belt and the anode holder are typically employed in the vertical-immersion plating apparatus as shown in  FIG. 15 . Structural details of the plating apparatus having a plating tank will not be described below in the following embodiments. 
       FIGS. 1 through 4  show a conducting belt for use with an anode holder according to the embodiment of the present invention.  FIG. 1  is a front elevational view of a conducting belt which holds an anode, and  FIG. 2  is a side elevational view of the conducting belt. 
     As shown in  FIGS. 1 and 2 , the conducting belt, generally denoted by  1 , comprises a belt-like thin plate in the form of a ring composed of an electrically conductive material such as titanium. The conducting belt holds a disk-shaped anode  5  fitted therein. The conducting belt  1  has opposite ends  1   a ,  1   b  (holding portions) fastened to each other by a bolt  6  and nuts  7  (i.e., first fastener) to secure the anode  5  therein. The conducting belt  1  has a thickness of 1 mm to 3 mm and a width of 1 cm to 2 cm. Since a substrate W to be plated is in the form of a circular disk, the anode  5  is also in the form of a circular disk. The anode  5  has an outside diameter of 150 mm to 300 mm and a thickness of 10 mm to 20 mm. 
       FIG. 3  is an enlarged view showing an encircled area A in  FIG. 1 , and showing a fastening assembly in detail. As shown in  FIG. 3 , the bolt  6  is inserted into the opposite ends  1   a ,  1   b  of the conducting belt  1  and the double nuts  7  are screwed onto the bolt  6  to fasten the anode  5  by the conducting belt  1 . The circular anode  5  has its outer circumferential edge which is entirely or substantially entirely in close contact with the inner circumferential surface of the conducting belt  1 . 
     As shown in  FIGS. 1 and 3 , an electrically conductive bracket  2  is fixed to an extended fixing portion of the end  1   a  of the conducting belt  1  by a bolt  8  and double nuts  9  (i.e., second fastener). The electrically conductive bracket  2  has a contact  3  on its distal end. The contact  3  is brought into contact with a contact (not shown) provided in the plating tank, so that the contact  3  can be supplied with an electric current from a plating power supply. 
       FIG. 4  is a perspective view of the conducting belt  1 . 
     As shown in  FIG. 4 , the ends  1   a ,  1   b  of the conducting belt  1  are bent radially outwardly from the circular thin plate at an angle of substantially 90°. The ends  1   a ,  1   b  have bolt insertion holes  1   c  defined therein for the insertion of the bolt  6  therethrough. The end  1   a  is longer than the end  1   b  and has a notch  1   d  defined therein for the insertion of the bolt  8  therethrough. 
     The conducting belt  1  which is constructed as shown in  FIGS. 1 through 4  offers the following advantages: 
     1) Since the conducting belt  1  is brought into contact with the entire or substantially entire outer circumferential edge of the anode  5 , the conducting belt  1  can supply an electric current to the anode  5  from the entire or substantially entire outer circumferential edge of the anode  5 . Therefore, a contact failure is prevented from occurring between the conducting belt  1  and the anode  5 . 
     2) As the area of contact between the conducting belt  1  and the anode  5  is large, any contact resistance between the conducting belt  1  and the anode  5  is reduced. 
     3) Since the entire outer circumferential edge of the anode  5  is secured by the conducting belt  1 , there is no need to perform positional alignment between the anode  5  and the conducting belt  1 . Further, the anode  5  can easily be machined because the anode  5  is in the form of a circular disk. 
     4) The anode  5  can easily be replaced with a new one simply by loosening the conducting belt  1 , placing the new anode in position, and retightening the conducting belt  1 . 
     5) Since the anode  5  is in the form of a circular disk and is held by the conducting belt  1 , the anode  5  is free of wasteful areas. 
     The anode  5  and the conducting belt  1  shown in  FIGS. 1 through 4  are held by an anode holder  10  shown in  FIGS. 5 through 7 . The anode holder  10  will be described below with reference to  FIGS. 5 through 7 . 
       FIG. 5  is a front elevational view, partly in cross section, of the anode holder  10 ,  FIG. 6  is a cross-sectional view taken along line VI-VI of  FIG. 5 , and  FIG. 7  is an exploded perspective view of the anode holder  10 . As shown in  FIGS. 5 and 6 , the anode holder  10  comprises an anode holder base  11  for mounting thereon the anode  5  held by the conducting belt  1 , a rear cover  12  mounted on the reverse surface of the anode holder base  11  for holding the reverse surface of the anode  5 , and an anode mask  13  mounted on the front surface of the anode holder base  11  for covering a portion of the front surface of the anode  5 . 
     As shown in  FIG. 7 , the anode holder base  11  is in the form of a substantially rectangular thin plate, and has a circular housing hole  11   a  defined centrally therein for housing the anode  5  that is held by the conducting belt  1 . The anode holder base  11  has a pair of substantially T-shaped hands  11   b ,  11   b  on its upper end which can be gripped by a robot when the robot transfers the anode holder  10  for replacing the exhausted anode. As shown in  FIG. 5 , the contact  3  on the distal end of the electrically conductive bracket  2  connected to the conducting belt  1  is held on a lower surface of one of the hands  11   b . As shown in  FIG. 6 , the anode holder base  11  has a solution discharge hole  11   h  defined in a lower end thereof for allowing the plating solution to be discharged quickly and reliably therethrough from the anode holder  10  when the anode holder  10  is lifted out of the plating tank for anode replacement. 
     As shown in  FIG. 7 , the rear cover  12  is in the form of a substantially rectangular thin plate, and has a circular pressing portion  12   a  disposed centrally thereon. As shown in  FIG. 6 , the circular pressing portion  12   a  is slightly thicker than the outer circumferential region of the rear cover  12 . Thus, the circular pressing portion  12   a  is fitted into the circular housing hole  11   a  of the anode holder base  11  when the rear cover  12  is mounted on the anode holder base  11 . Consequently, the circular pressing portion  12   a  presses the rear surface of the anode  5  that is housed in the circular housing hole  11   a.    
     The anode mask  13  is in the form of an annular plate having a central opening  13   a  defined therein. The opening  13   a  of the anode mask  13  has a diameter smaller than the diameter of the anode  5 , so that the anode mask  13  mounted on the anode holder base  11  covers or masks an outer peripheral portion of the anode  5  that is housed in the housing hole  11   a . The diameter of the opening  13   a  can be selected to control the electric field on the front surface of the anode  5 . The anode mask  13  is made of vinyl chloride, PEEK (polyether ether ketone), PVDF (polyvinylidene difluoride), or the like. 
     In  FIGS. 5 through 7 , the anode  5  mounted on the anode holder base  11  has its rear surface pressed by the rear cover  12 . However, the anode  5  may have its front surface pressed by a front cover. In such a modification, the anode mask may be mounted on the front cover, or the front cover may double as the anode mask. 
     The anode holder  10  shown in  FIGS. 5 through 7  offers the following advantages: 
     1) The anode  5  can easily be replaced with a new one simply by removing the rear cover  12 , loosening the double nuts  7 , placing the new anode  5  in position, retightening the double nuts  7 , and attaching the rear cover  12  again. 
     2) The anode mask  13  has its inside diameter smaller than the diameter of the anode  5 . Therefore, even if the anode  5  held by the conducting belt  1  is overused beyond its replacement period, the anode  5  is prevented from falling out of the anode holder  10  or suffering from a conductive fault. 
     3) The solution discharge hole  11   h  defined in the lower end of the anode holder  10  allows the plating solution to be discharged quickly and reliably from the anode holder  10  when the anode holder  10  is lifted out of the plating tank. 
       FIG. 8  shows the anode holder  10  which is immersed in the plating solution. As shown in  FIG. 8 , the anode holder  10  is disposed in the plating solution in such a manner that the hands  11   b ,  11   b  are positioned above a plating solution level L. The contact  3  held on one of the hands  11   b ,  11   b  is brought into contact with a contact plate  16  fixed to a holder  15  provided in the plating tank. The contact plate  16  is connected to the plating power supply (not shown in  FIG. 8 ) through an electric supply line  17 . Therefore, the anode  5  held by the anode holder  10  that is connected to the contact  3  is supplied with an electric current from the plating power supply through the electric supply line  17  and the contact plate  16 . 
       FIG. 9  is a schematic plan view of the plating apparatus incorporating the conducting belt  1  shown in  FIGS. 1 through 4  and the anode holder  10  shown in  FIGS. 5 through 7 . 
     As shown in  FIG. 9 , the plating apparatus comprises a loading/unloading unit U 1  for loading and unloading the substrate W, and a plating processing unit U 2  for performing various processing including plating of the substrate W, cleaning of the substrate W, and the like. The loading/unloading unit U 1  comprises three cassette tables  22  for placing thereon cassettes  20  which house substrates W such as semiconductor wafers, an aligner  24  for aligning an orientation flat or a notch of a substrate W with a predetermined direction, and a spin drier  26  for drying the plated substrate W by spinning the plated substrate at a high speed. The loading/unloading unit U 1  also has a substrate mounting/dismounting unit  30  for placing a substrate holder  18  thereon, and mounting the substrate W on the substrate holder  18  and dismounting the substrate W from the substrate holder  18 . The cassette tables  22 , the aligner  24 , the spin drier  26 , and the substrate mounting/dismounting unit  30  are disposed around a transfer robot  32  for transferring substrates W between the cassette tables  22 , the aligner  24 , the spin drier  26 , and the substrate mounting/dismounting unit  30 . 
     The plating unit U 2  comprises, successively in order from the substrate mounting/dismounting unit  30 , a stocker  34  for storing and temporarily placing substrate holders  18 , a pre-wetting tank  36  for immersing a substrate W in pure water to wet the substrate W for making the surface of the substrate W highly hydrophilic, a pre-soaking tank  38  for etching away an oxide film having large electric resistance from a surface of a seed layer formed on the substrate W with a chemical solution such as sulfuric acid or hydrochloric acid, a water cleaning tank  40  for cleaning the surface of the substrate W and the anode holder  10  with pure water, a plating tank  44  for plating the substrate W, another water cleaning tank  40 , another plating tank  44 , still another water cleaning tank  40 , and a blowing tank  42  for removing water from the cleaned substrate W and the cleaned anode holder  10 . Each of the plating tanks  44  serves to perform copper plating of the substrate W. Alternatively, each of the plating tanks  44  may perform nickel plating, solder plating, or gold plating of the substrate W. 
     A transfer apparatus  50  is disposed alongside of the stocker  34  and the tanks  36 ,  38 ,  40 ,  42 ,  44  for transferring the substrate holders  18  together with the substrates W between these stocker and tanks. The transfer apparatus  50  includes a transporter  52  for transporting the substrates W between the substrate mounting/dismounting unit  30  and the stocker  34 , and transporting the substrates W between the stocker  34 , the pre-wetting tank  36 , the pre-soaking tank  38 , the water cleaning tanks  40 , the plating tanks  44 , and the blowing tank  42 . The transporter  52  also serves to transport the anode holders  10  between a temporary storing unit  70  (described later), the pre-wetting tank  36 , the pre-soaking tank  38 , the water cleaning tanks  40 , the blowing tank  42 , and the plating tanks  44 . 
     The substrate mounting/dismounting unit  30  comprises a flat support plate  46  angularly movable about a rotational shaft  45  at an angle of 90° between a vertical position and a horizontal position. Two substrate holders  18  are placed parallel to each other on the support plate  46  when the flat support plate  46  is in the horizontal position. After the substrate W is transferred between one of the substrate holders  18  and the transfer robot  32 , the support plate  46  is angularly moved from the horizontal position to the vertical position, and transfers the substrate holder  18  to or from the transporter  52 . 
     The temporary storing unit  70  for replacing an anode holder  10  and temporarily placing an anode holder  10  is disposed between the water cleaning tank  40  and the plating tank  44 . Alternatively, the temporary storing unit  70  may be disposed in any position between any adjacent equipment located between the stocker  34  and the blowing tank  42 . Further, the temporary storing unit  70  may be disposed between the blowing tank  42  and a housing  47  as indicated by the imaginary lines in  FIG. 9 . 
     The substantially T-shaped hands  11   b ,  11   b  provided on the upper end of the anode holder  10  serve as supports for transferring the anode holder  10  or suspending the anode holder  10  (see  FIGS. 5 and 8 ). In the temporary storing unit  70 , the anode holder  10  is vertically suspended by the hands  11   b  hanging on an upper surface of a circumferential wall of the temporary storing unit  70 . Further, the anode holder  10  is transferred by the transporter  52  with the hands  11   b  of the suspended anode holder  10  gripped by the transporter  52 . In each of the pre-wetting tank  36 , the pre-soaking tank  38 , the water cleaning tanks  40 , the blowing tank  42 , and the plating tanks  44 , the anode holder  10  is suspended by the hands  11   b  hanging on an upper surface of a circumferential wall of the tank. 
       FIGS. 10 and 11  show a linear motor unit  85  as a driving unit of the transfer apparatus  50 . Specifically,  FIG. 10  is a plan view of the linear motor unit  58  of the transfer apparatus  50 , and  FIG. 11  is a front elevational view of the linear motor unit  58  shown in  FIG. 10 . As shown in  FIGS. 10 and 11 , the linear motor unit  85  basically comprises an elongate base  86  and a slider  87  movable along the base  86 . The transporter  52  is mounted on an upper surface of the slider  87 . A cable conveyer bracket  89  and a cable conveyer receiver  90  are disposed alongside of the base  86 , and a cable conveyer  92  extends along the cable conveyer bracket  89  and the cable conveyer receiver  90 . 
     As shown in  FIGS. 10 and 11 , since the transporter  52  is driven by the linear motor unit  85 , the transporter  52  can be moved over a long distance and can be reduced in length to reduce the overall length of the transfer apparatus  50 . The transfer apparatus  50  can be free of components such as a long ball screw which require dimensional accuracy and maintenance. 
       FIGS. 12 through 14  show the transporter  52  in detail. Specifically,  FIG. 12  is a front elevational view of transporter  52 ,  FIG. 13  is a plan view of a gripping mechanism mounted on an arm of the transporter  52 , and  FIG. 14  is a vertical cross-sectional view of the gripping mechanism. The transporter  52  comprises a transfer robot for transferring the substrate holder  18  and also transferring the anode holder  10 . Hereinafter, the case where the transporter  52  transfers or transports the anode holder  10  will be described. As shown in  FIGS. 12 and 13 , the transporter  52  basically comprises a transporter body  53 , an arm  54  extending laterally from the transporter body  53 , an arm lifting/lowering mechanism  55  for lifting and lowering the arm  54 , and gripping mechanisms  57  disposed in the arm  54  for detachably gripping the hands  11   b  of the anode holder  10 . The arm lifting/lowering mechanism  55  comprises a rotatable ball screw  58  extending vertically, and a nut  59  screwed onto the ball screw  58 . An LM base  60  is coupled to the nut  59 . A timing belt  64  is trained around a drive pulley  62  fixed to a drive shaft of a lifting/lowering motor  61  and a driven pulley  63  fixed to the upper end of the ball screw  58 . The drive shaft of the lifting/lowering motor  61  is fixed to the transporter body  53 . When the lifting/lowering motor  61  is energized, the ball screw  58  is rotated about its own axis by the timing belt  64 , and the LM base  60  coupled to the nut  59  which is screwed onto the ball screw  58  is vertically moved along an LM guide. 
     As shown in  FIGS. 13 and 14 , the arm  54  has a pair of spaced side plates  74  with the gripping mechanisms  57  disposed therebetween. Although the two gripping mechanisms  57  are shown in the illustrated embodiment, one of them will be described below as they are identical in structure to each other. 
     The gripping mechanism  57  comprises a fixed holder  75  having an end transversely movably disposed between the side plates  74 , guide shafts  76  extending through the fixed holder  75 , and a movable holder  77  coupled to ends (lower ends in  FIG. 14 ) of the guide shafts  76 . The fixed holder  75  is coupled by a cylinder joint  79  to a transversely moving cylinder  78  mounted on one of the side plates  74 . A shaft holder  82  is connected to other ends (upper ends in  FIG. 14 ) of the guide shafts  76 . The shaft holder  82  is coupled to a vertically moving cylinder  80  by a cylinder connector  81 . 
     When the transversely moving cylinder  78  is actuated, the fixed holder  75  is transversely moved between the side plates  74  together with the movable holder  77 . When the vertically moving cylinder  80  is actuated, the movable holder  77  is vertically moved while being guided by the guide shafts  76 . 
     For gripping the hands  11   b  of an anode holder  10  which is suspended in the temporary storing unit  70  or the like with the gripping mechanism  57 , the movable holder  77  is lowered to a position lower than the hands  11   b  while the movable holder  77  is prevented from interferring with the hands  11   b . Thereafter, the transversely moving cylinder  78  is actuated to position the fixed holder  75  above the hands  11   b  and to position the movable holder  77  beneath the hands  11   b . Then, the vertically moving cylinder  80  is actuated to lift the movable holder  77  until the fixed holder  75  and the movable holder  77  grip the hands  11   b  therebetween. The hands  11   b  can be released when the vertically moving cylinder  80  is actuated to lower the movable holder  77 . 
     As shown in  FIG. 5 , one of the hands  11   b  of the anode holder  10  has a recess  11   e  defined in a lower edge thereof. As shown in  FIG. 14 , the movable holder  77  has a projection  77   a  on an upper surface thereof which can be fitted into the recess  11   e  of the anode holder  10 . When the hands  11   b  are gripped between the fixed holder  75  and the movable holder  77 , the projection  77   a  is fitted into the recess  11   e  to position and orient the hands  11   b  properly. 
     A processing operation of the plating apparatus constructed as shown in  FIGS. 9 through 14  will be described below. Hereinafter, the replacement work of the anode will be mainly described. First, a process of plating the substrate W will briefly be described below. After the substrate W is mounted on the substrate holder  18  in the loading/unloading unit U 1 , the transporter  52  of the transfer apparatus  50  grips the substrate holder  18  and suspends (temporarily places) the substrate holder  18  in the stocker  34 . Then, the transporter  52  removes the substrate holder  18  from the stocker  34 , and conveys the substrate holder  18  successively through the pre-wetting tank  36 , the pre-soaking tank  38 , the plating tanks  44 , and the water cleaning tanks  40  for successively pre-wetting, pre-soaking, plating, and cleaning the substrate W. 
     When the above plating process is repeated, the anode  5  is exhausted and needs to be replaced with a new one. A process of replacing the anode  5  will be described below. 
     The anode holder  10  which is immersed in the plating tank  44  and holds the exhausted anode  5  is lifted by the transporter  52 . At this time, the gripping mechanism  57  of the transporter  52  grips the anode holder  10 , and the arm  54  is lifted by the arm lifting/lowering mechanism  55 . Thereafter, the anode holder  10  is conveyed to the adjacent water cleaning tank  40 . Then, the arm  54  is lowered by the arm lifting/lowering mechanism  55  to bring the anode holder  10  into the water cleaning tank  40  in which the anode holder  10  is cleaned with water. The cleaned anode holder  10  is transferred by the transporter  52  to the blowing tank  42  in which water droplets are removed from the anode holder  10 . 
     Thereafter, the anode holder  10  is conveyed to the temporary storing unit  70  by the transporter  52 . Then, the anode holder  10  is taken out of the plating apparatus through the temporary storing unit  70  onto a working table (not shown). At this time, the anode holder  10  is removed from the lateral side of the plating apparatus. If the temporary storing unit  70  is positioned between the blowing tank  42  and the housing  47  as indicated by the imaginary lines in  FIG. 9 , then the anode holder  10  can be removed from the rear end of the plating apparatus. On the working table, the rear cover  12  is detached from the anode holder  10 , the conducting belt  1  is loosened, the exhausted anode  5  is replaced with a new anode  5 , and the conducting belt  1  is retightened. The conducting belt  1  can be loosened simply by loosening the nuts  7 , and can be retightened simply by retightening the nuts  7 . 
     Then, the rear cover  12  is attached to the anode holder base  11 , thereby completing the process of mounting the new anode  5  on the anode holder  10 . The anode holder  10  with the new anode  5  mounted therein is returned to the temporary storing unit  70  in the plating apparatus, and is then put back into the plating tank  44  by the transporter  52 . 
     The plating apparatus constructed as shown in  FIGS. 9 through 14  offers the following advantages: 
     1) Since the anode holder  10  is removed by the transporter (transfer robot)  52  which is fully automatized, the anode holder  10  can easily be replaced. 
     2) For removing the anode holder  10  from the plating apparatus, the anode holder  10  is taken out of the plating tank  44  by the transporter (transfer robot)  52 , cleaned in the water cleaning tank  40 , which is also used to clean the substrate W, to remove the plating solution from the anode holder  10 , dried in the blowing tank  42 , which is also used to dry the substrate W, and removed from the plating apparatus through the temporary storing unit  70 . The temporary storing unit  70  serves as an anode holder exchange area. Since the operator is not required to touch the plating solution for the removal of the anode holder  10 , the safety of the operator can be ensured. 
     3) Since the anode holder  10  can easily be removed, the anode mask  13  can easily be replaced. 
     4) The transporter (transfer robot)  52  has a high level of positioning accuracy, and can perform fine adjustment of position. Consequently, the anode holder  10  can be placed in a desired position with high reproducibility, and the interelectrode distance between the substrate W and the anode  5  can easily be changed. 
     Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.