Patent Publication Number: US-RE46088-E

Title: Maintainable substrate carrier for electroplating

Description:
STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     The invention described herein was made with Governmental support under contract number DE-FC36-07GO17043 awarded by the United States Department of Energy. The Government may have certain rights in the invention. 
    
    
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is related to commonly-owned U.S. patent application Ser. No. 12/889,219, now U.S. Pat. No. 8,317,987, entitled “Non-Permeable Substrate Carrier for Electroplating,” filed on even date herewith Sep. 23, 2010 by Emmanuel Abas; Chen-An Chen; Diana Ma; and Kalyana Ganti. The present application is also related to commonly-owned U.S. patent application Ser. No. 12/889,228, now U.S. Pat. No. 8,221,600, entitled “Sealed Substrate Carrier for Electroplating,” filed on even date herewith Sep. 23, 2010 by Kalyana Ganti. 
     BACKGROUND 
     1. Field of Art 
     This disclosure relates generally to the field of electroplating. More particular, this disclosure relates to a carrier for use in electroplating substrates. 
     2. Description of the Related Art 
     Electroplating is a deposition technique that may be used to form a metal layer on a substrate. In some electroplating processes, the anode may be made out of the metal to be deposited, and the cathode may be the substrate to be plated. Both the anode and the cathode are immersed in an electrolyte solution, and a voltage is applied across the anode and cathode so that an electrical current flows between them. This causes oxidation of the metal at the anode so that ions of the metal are dissolved in the solution. This also causes reduction of the metal ions at the cathode so that a layer of the metal is deposited onto the substrate. In other electroplating processes, the solution may have ions of the metal to be plated, and the anode may be a non-consumable anode. In this case, the metal ions may be periodically replenished in the bath. 
     In order to efficiently electroplate a large number of substrates, a carrier may be used to hold multiple substrates and to apply electrical voltages to those substrates during the electroplating process. The carrier may be used to transfer the substrates between different chemical baths and also to safely handle them during rinsing and drying steps. 
     The present application discloses improved substrate carriers for electroplating. 
     SUMMARY 
     One embodiment relates to a substrate carrier for use in electroplating a plurality of substrates. The carrier includes a non-conductive carrier body on which the substrates are placed and conductive lines embedded within the carrier body. A plurality of conductive clip attachment parts are attached in a permanent manner to the conductive lines embedded within the carrier body. A plurality of contact clips are attached in a removable manner to the clip attachment parts. The contact clips hold the substrates in place and conductively connecting the substrates with the conductive lines. 
     Another embodiment relates to a method of electroplating substrates. The substrates are clipped to a substrate carrier. The substrate carrier comprises a non-conductive carrier body, conductive lines embedded within the carrier body, conductive clip attachment parts are attached in a permanent manner to the conductive lines, and contact clips attached in a removable manner to the clip attachment parts. The substrate carrier is mounted onto a mechanical arm, and a voltage is applied to the substrates via the contact clips. The substrate carrier with the substrates clipped thereon is dipped into an electroplating bath, and the substrates are unclipped from the substrate carrier when the electroplating is complete. 
     Another embodiment relates to a method of manufacturing a substrate carrier for use in electroplating a plurality of substrates. First and second non-conductive plates are formed, each plate having an inner face and an outer face. Metal lines are provided and clip attachment parts are conductively attached to the metal lines in a permanent manner. The inner faces of the plates are bonded with the metal lines and clip attachment parts embedded therein, and openings are formed from the outer faces to access the clip attachment parts. 
     Other embodiments, aspects and features are also disclosed in the present application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the subject matter may be derived by referring to the detailed description and claims when considered in conjunction with the following figures, wherein like reference numbers refer to similar elements throughout the figures. 
         FIG. 1  is a planar view of an inner face of a non-conductive plate for a non-permeable substrate carrier in accordance with an embodiment of the invention. 
         FIG. 2  is a planar view of an outer face of the non-conductive plate in accordance with an embodiment of the invention. 
         FIG. 3  is a perspective view of a substrate holding area the outer face of the non-conductive plate in accordance with an embodiment of the invention. 
         FIG. 4  is a planar view of a conductive assembly including an electrically-conductive bus bar and electrically-conductive lines in accordance with an embodiment of the invention. 
         FIG. 5A  is a first perspective view of a portion of the conductive assembly of  FIG. 4  in accordance with an embodiment of the invention. 
         FIG. 5B  is a second perspective view of a portion of the conductive assembly of  FIG. 4  in accordance with an embodiment of the invention. 
         FIG. 6  is a planar view showing a thermoplastic overmold (or overcoat) applied to a portion the conductive bus bar in accordance with an embodiment of the invention. 
         FIG. 7  is a cross-sectional view which depicts various layers in the bonding of two carrier plates and a conductive assembly in accordance with an embodiment of the invention. 
         FIG. 8  is a perspective view depicting a semiconductor wafer clipped to a substrate carrier in accordance with an embodiment of the invention. 
         FIG. 9A  is a perspective view of a first clip assembly in accordance with an embodiment of the invention. 
         FIG. 9B  is an exploded view showing the parts of the first clip assembly as separated. 
         FIG. 10A  is a perspective view of a second clip assembly in accordance with an embodiment of the invention. 
         FIG. 10B  is an exploded view showing the parts of the second clip assembly as separated. 
         FIG. 10C  further illustrates the Z shape of the lever. 
         FIG. 11  is a top view showing a double-clip assembly in accordance with an embodiment of the invention. 
         FIG. 12  is a perspective view of an outer face on one side of a permeable substrate carrier in accordance with an embodiment of the invention. 
         FIG. 13  is a closer-up perspective view of a portion of the permeable substrate carrier of  FIG. 12  in accordance with an embodiment of the invention. 
         FIG. 14  is a flow chart of a method of manufacturing and maintaining a single-piece substrate carrier for electroplating in accordance with an embodiment of the invention. 
         FIG. 15  is a flow chart of a method of using the carrier to electroplate a plurality of substrates in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely illustrative in nature and is not intended to limit the embodiments of the subject matter or the application and uses of such embodiments. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Any implementation described herein as exemplary is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
     Conventional substrate carriers for electroplating have problems that are difficult to diagnose and solve. One problem with conventional substrate carriers is that they sometimes break the substrates during loading of the substrates onto the carrier. Applicants have analyzed the breakages and have discovered that the breakages frequently occur in the vicinity of the metal clips used to hold the substrates to the carrier. Applicants have further analyzed these breakages and have determined that they are often due to a portion of the clip impacting the edge of the substrate when the clip is not fully in a “closed” position. 
     Another problem with conventional substrate carriers is that the plating of some of the substrates is frequently incomplete in that there is non-uniform coverage of the substrate. The positions of the incompletely-plated substrates in the carrier are not always the same and appear to be somewhat random. Applicants have analyzed the incompletely plated substrates and have discovered that the incompletely-plated “stain” is often at a bottom portion of the substrate. Applicants have determined that these “stains” are due to plating solution residue that becomes trapped at the bottom of the carrier pockets and is not rinsed out. 
     Other problems relate to a lack of durability of the carriers. In other words, mechanical breakages limit the useful lifespan of the conventional substrate carriers before repair or replacement is necessary. The contact clips frequently fail due to being broken or damaged, or having too low tension, or not contacting the substrate in the proper location. In addition, the pads on the carrier often break or crack. Moreover, the carrier body itself often cracks or breaks, and the copper conductors within the carrier often fail due to etching by the chemical baths. Applicants have determined that that contributing factors for breakage of the carrier body include overstacking of carriers during staging and mishandling of the carriers. 
     The present application discloses improved substrate carriers that provide solutions to one or more of the above-discussed problems. 
     In accordance with one embodiment of the invention, a substrate carrier is provided that does not have openings allowing solution to go from one side of the carrier to the other side. In other words, the substrate carrier is effectively continuous and non-permeable to the electrolyte solution. A conventional view is that such openings are advantageous in reducing the weight of the carrier and allowing the electrolyte solution to flow through from side to side. However, applicants have surprisingly found that a “flat” carrier body which is effectively continuous and non-permeable (without openings going through the body) has various advantages. First, applicants believe that the flat carrier body provides a sheeting action which assists in the complete removal of the electrolyte solution during rinsing. In addition, although the flat carrier body is conventionally thought to be substantially heavier (due to the lack of open space), applicants have designed a flat carrier body with internal cavities so as to substantially reduce its weight. 
     In accordance with another embodiment of the invention, a robust substrate carrier is provided which has improved adhesion between thermoplastic and metal layers. The improved adhesion results in a superior hermetic seal which prevents chemical solutions from prematurely corroding metal within the carrier. As disclosed herein, the adhesion problems may be solved or reduced by replacing a previous weak metal-to-thermoplastic surface bond interface with two strong bond interfaces. The two strong bond interfaces are an improved metal-to-thermoplastic surface bond interface (using a bonding technique which provides superior adhesion, such as injection molding, for example) and a thermoplastic-to-thermoplastic surface bond interface. 
     In accordance with another embodiment of the invention, a substrate carrier is provided which has reduced downtime due to component failures. The component failures may comprise, for example, failures of the clips which hold the substrates to be plated to the carrier. As disclosed herein, a substrate carrier may be configured such that clips and other components may be removably attached. This advantageously enables the carrier to be kept in service without the substantial downtime needed to repair more permanently attached components. 
       FIG. 1  is a planar view of an inner face  102  of a non-conductive (electrically-insulating) plate for a non-permeable substrate carrier in accordance with an embodiment of the invention. The non-conductive plate itself is electrically insulating. Also shown positioned on the inner face is a conductive assembly including an electrically-conductive bus bar  120  at a top of the carrier and conductive lines  128  going from the bus bar  120  towards the bottom of the carrier. 
     In this exemplary embodiment, the inner face  102  includes fifteen “X” shaped ribbing patterns  106 , each X-shaped ribbing pattern  106  separating four pocket indentations  104 . These pocket indentations  104  substantially reduce the weight of the plate. 
     In addition, shown at the center of the X-shaped ribbing pattern  106  is a center location  111  which corresponds to a center pad location  211  on the outer face  202  (see  FIG. 2 , which is described below). Also shown at a perimeter around each X-shaped ribbing pattern  106  are first perimeter locations  112  which correspond to perimeter pad locations  212  on the outer face  202  (see  FIG. 2 ). Shown at slightly farther out perimeter around each X-shaped ribbing pattern  106  are second perimeter locations  114  which correspond to alignment peg locations  214  on the outer face  202  (see  FIG. 2 ). 
     Further shown in  FIG. 1  is a conductive assembly including a metal bus bar  120  coupled to metal lines  128 . For example, the metal bus bar  120  may be machined stainless steel and the metal lines  128  may be copper lines. The metal bus bar  120  may be coupled to the metal lines  128  in an electrically-conductive manner by welding of a metal cover plate  129  (which may also be stainless steel, for example). Metal bushings may be welded in the bushing holes  127  to securely interconnect the plate  129  and a top portion  402  (see  FIG. 4 ) of the metal lines  128 . In addition, metal clipping pins  130  are attached to the metal lines  128  at either side of the X-shaped ribbing patterns  106 . These metal clipping pins may be configured to allow removable clips to be attached onto the outer surface  202  of the carrier. Some of the metal clipping pins  130  are attached to metal lines  128  at an edge of the plate and others are attached to metal lines  128  in an interior of the plate. 
     The metal bus bar  120  is machined to have a plurality of openings. Two “keyhole” shaped openings  122  may be included to mount the carrier onto a mechanical work arm. The “keyhole” shape includes an alignment feature  123  which enables a more consistent alignment between the work arm and the carrier. On either side of each keyhole-shaped opening  122  may be a side opening  124 . The side openings  124  advantageously reduce a weight of the metal bus bar  120 . A handle opening  126  is provided at a top center location to facilitate manual holding of the carrier. The bus bar  120  may also include a series of bonding holes  132  to facilitate the secure attachment of a thermoplastic overcoat  602  (see  FIG. 6 , which is described below). 
     Also shown in  FIG. 1  are dowel pin holes  140  at the corners of the carrier. These dowel pin holes  140  go through both the non-conductive plate and the metal bus bar  120  and may be used for the alignment of the carrier when it is loaded onto a table or loader. 
       FIG. 2  is a planar view of an outer face  202  of the non-conductive plate in accordance with an embodiment of the invention. A portion of the conductive bus bar  120  is also shown. In this exemplary embodiment, the outer face  202  is designed to be substantially “flat” to reduce a tendency for electrolyte solution to remain trapped in corners and crevices of the carrier. 
     The outer face  202  includes fifteen center pad attachment points  211 . Shown on a first perimeter around each center pad attachment point  211  are perimeter pad attachment points  212 . These pad attachment points ( 211  and  212 ) may comprise, for example, mounting holes for removably attaching plastic pads. 
     Shown on a second perimeter around each center pad attachment point  211  are alignment peg attachment points  214 . Points on the second perimeter are slightly farther out from the center point than points on the first perimeter. The peg attachment points  214  may comprise, for example, mounting holes for removably attaching plastic pegs. 
     Fifteen areas  213  for holding a substrate (such as a silicon wafer, for example) are present on the outer face  202  in this exemplary embodiment. Each substrate holding area  213  is surrounded by the alignment peg attachment points  214 . The pad attachment points ( 211  and  212 ) are located within the substrate holding area  213  such that pads attached at those points provide spacing between the substrate and the surface of the outer face  202 . 
     Further shown in  FIG. 2  are clip attachment features  210 . In accordance with an embodiment of the invention, each clip attachment feature may comprise a threaded outer surface  502  of a metal clipping pin (see  FIG. 5B , described below). The clip attachment features are located on opposite sides of each substrate holding area  213 . In the exemplary embodiment shown, the clip attachment features may be aligned in vertical columns, including clip attachment features  210  along each side of the plate and clip attachment features  210  between neighboring substrate holding areas  213  in an interior region of the plate. 
       FIG. 3  is a perspective view of a substrate holding area  213  on the outer face  202  of the non-conductive plate in accordance with an embodiment of the invention. As shown, at a center of the substrate holding area  213  is a center pad  311  (attached to the center attachment point  211  shown in  FIG. 2 ). Shown on a first perimeter around the center pad  311  are perimeter pads  312  that are removably attached to the perimeter attachment points  212 . For example, the center and perimeter attachment points ( 211  and  212 ) may comprise insertion holes, and the pads ( 311  and  312 ) may be attached by inserting stubs on the underside of the pads into the insertion holes. The pads ( 310  and  311 ) may be are provided so as to advantageously create a rinsing space between the surface of the outer face  202  and the substrate to be plated. The pads ( 310  and  311 ) may be made of plastic and may be configured to be removable for ease of replacement when they become worn or damaged. In one implementation, the pads may have a flat surface that is in a “tear drop” shape. 
     Shown on a second perimeter around the center pad  311  are alignment pegs  314  that are removably attached to the alignment peg attachment points  214 . (Points on the second perimeter are slightly farther out from the center pad  311  than points on the first perimeter.) For example, the peg attachment points  214  may comprise insertion holes, and the pegs  314  may be attached by inserting a stub at the bottom of each peg into an insertion hole. The pegs  314  have the dual functionalities of holding the substrate to be plated within the substrate holding space and protecting the clips from damage that may be caused by the substrate. The pegs  314  may be made out of plastic and may be configured to be removable for ease of replacement when they become worn or damaged. In one implementation, the pegs  314  may be tapered. 
     As further shown, on one side of the substrate holding area  213  is a first set of three clip attachment features  210 , and on the other aide is a second set of three clip attachment features  210 . The clip attachment features  210  may be configured such that electrically-conductive clips may be removably attached for ease of replacement when they become worn or damaged. The clip attachment features  210  form an electrically-conductive path between the conductive assembly (such as depicted in  FIG. 4 ) and the electrically-conductive clips. 
     In addition,  FIG. 3  depicts relief cuts  316  surrounding the clip attachment features  1210 . These relief cuts  316  are recessed areas that facilitate proper positioning of a base of a clip assembly (for example, see base  1012  of clip assembly  1000  shown in  FIGS. 10A and 10B ). 
       FIG. 4  is a planar view of a conductive assembly (weldment) including an electrically-conductive bus bar  120  and metal lines  128  in accordance with an embodiment of the invention. As shown, metal clipping pins  130  are attached to the metal lines  128 . As further shown, the metal lines  128  are attached to a connecting plate  402  which is used to connect the conductive bus bar  120  to the metal lines  128 . In one embodiment, the bus bar  120  may be formed from stainless steel, and the metal lines  128  may comprise copper lines. 
       FIGS. 5A and 5B  are two perspective views showing portions of the conductive assembly of  FIG. 4  in accordance with an embodiment of the invention. As shown in  FIG. 5A , the connecting plate  402  is sandwiched between two metal cover plates  129 . Bushings may then be welded in the bushing holes  127  so as to electrically and mechanically connect the conductive bus bar  120  to the metal lines  120 . The metal clipping pins  130  are attached in a permanent manner (for example, welded) to the metal lines  120 . As shown in  FIG. 5B , the metal clipping pins  130  may include a threaded outer surface  502 . Furthermore, a thermoplastic layer (or overcoat)  504  may be deposited, for example, by injection molding, around the metal clipping pins  130  on the metal lines  128 . In addition, a further thermoplastic layer (or overcoat)  506  may be deposited, for example, by dip coating or spray coating, over the metal lines  128 . For ease of illustration, only a small segment of the metal lines  128  is shown with the thermoplastic layer  506  in  FIG. 5B . However, the thermoplastic layer  506  may be coated over either a portion of, or an entirety of, the metal lines  128  in accordance with embodiments of the invention. 
       FIG. 6  is a planar view showing a thermoplastic overmold (or overcoat)  602  applied to a portion the conductive bus bar  120  in accordance with an embodiment of the invention. As shown, the thermoplastic overmold  602  preferably spans a horizontal length of the conductive bus bar  120 . In this exemplary configuration, the thermoplastic overmold  602  fills the bonding holes  132  the so as to bond securely to the conductive bus bar  120 . The thermoplastic overmold  602  over select portions of the conductive bus bar  120  may be applied, for example, by injection molding. 
       FIG. 7  is a cross-sectional view which depicts various layers in the bonding of two carrier plates and a conductive assembly in accordance with an embodiment of the invention. Note that  FIG. 7  is not to scale and depicts the various layers for purposes of explanation. 
     As shown, a lower portion of the conductive bus bar  120  is sandwiched between the inner faces  102  of the two non-conductive carrier plates  700 . As shown, the thermoplastic overmold  602  covers both sides of the conductive bus bar  120 . A solvent cement layer  732  may be used to form a plastic-to-plastic bond between the inner surfaces  102  of the non-conductive carrier plates  700  and the thermoplastic overcoat  602  on the conductive bus bar  120 . 
       FIG. 8  is a perspective view depicting a semiconductor wafer  804  clipped to a substrate carrier in accordance with an embodiment of the invention. As shown, the wafer  804  may be placed in a space defined by alignment pegs  314  along its perimeter. Underneath the wafer  804  may be spaced from the outer face  202  of the carrier by a plurality of pads (for example, a center pad  311  and perimeter pads  312 ) (not shown). In this exemplary embodiment, electrically-conductive clips  802  are attached to the clip attachment features  210  on opposite sides of the wafer  804 . When holding the wafer  804  to the carrier, each electrically-conductive clip  802  may be positioned so that its contact point rests on a metallic contact pad  806  on the surface of the wafer  804 . In an exemplary embodiment, the wafer  804  is configured such that each contact pad  806  is located directly above one of the perimeter pads  312  so that the clip may press the wafer directly against the pad (see neighboring space for another wafer on the right). 
       FIG. 9A  is a perspective view of a first clip assembly  900  in accordance with an embodiment of the invention. As shown, the first clip assembly  900  may include a clip  901 , a screw  912  and an O-ring  914 . In this exemplary embodiment, the clip  901  may be formed from a single stainless steel piece (SS 301 which is fully hardened, for example). In addition, the screw  912  may be threaded on the inside so that it may be screwed onto the outer thread  502  of the clip attachment pin  130 . 
       FIG. 9B  is an exploded view showing the parts of the first clip assembly  900  as separated. In addition, various features of the clip  901  are labeled. As seen, the clip  901  includes a base  902  with a hole  904 . The clip attachment pin  130  fits through the O-ring  914  and the hole  904 , and then the screw  912  may be screwed onto outer thread  502  of the clip attachment pin  130 . The base  904  of the clip  901  may also include one or more alignment features  903  so as to provide for the correct angular orientation of the clip once it is attached. 
     As further shown, a spring  905  may extend upward from the base  902 . In this case, the spring comprises folds of the metal which forms the clip. A clip arm  906  may start at the top of the spring  905  and extend away from the base  902 . As seen, the arm  906  may be tapered in an exemplary embodiment to improve its lifetime. A tip portion  908  may extend downward from the end of the arm  906  which is furthest from the base  902 . A contact feature  910  may be formed at the lowest point of the tip portion  908 . The contact feature  910  is the part of the clip  901  which makes physical contact with the substrate to be plated (for example, at the contact pads  806  on a surface of a semiconductor wafer). In one implementation, the contact feature  910  is approximately 1 mm wide. 
       FIG. 10A  is a perspective view of a second clip assembly  1000  in accordance with an embodiment of the invention. In this exemplary embodiment, the second clip assembly  1000  may include both metal and plastic parts.  FIG. 10B  is an exploded view showing parts of the second clip assembly  1000  as separated. As shown, the second clip assembly may a plastic base  1012 , a metal spring-attachment plate  1014 , a metal screw  1016 , a metal double-torsion spring-loaded clip  1018 , a plastic lever  1020 , and a rubber O-ring  1022 . 
     The screw  1016  includes a shaft which fits through an opening of the spring attachment plate  1014 , the O-ring  1022 , and through an opening in the base  1012 . In an exemplary implementation, the shaft  1042  may be threaded internally so as to be screwed onto an outer thread  502  of a metal clipping pin  130 . The lever  1020  is also attached to the base  1020  using features  1030 . 
     Wire ends  1038  at a base of the spring-loaded clip  1018  fit into ferrule features  1040  on the spring attachment plate  1014 . The arm  1036  of the spring-loaded clip  1018  fits through an opening  1034  in the lever  1020 . When the arm  1042  of the lever  102  is pressed down, the arm  1036  of the clip  1018  is raised. When the arm  1042  of the lever  102  is released, the arm  1036  of the clip  1018  is lowered. 
     The shaft of the screw  1016  may pass through the O-ring  1022 , a hole in the spring-attachment plate  1014 , and a hole in the base  1012 . The shaft of the screw  1016  may have an inner thread which screws onto the outer thread of the clip attachment pin  130  so as to attach the base  1012  to the outside face  202  of the non-conductive carrier plate. The O-ring  1022  may fit into a recessed ring surrounding the hole in the base  1012  so as to prevent the electrolytic solution of the plating bath from reaching to the clip attachment pin  130 . 
     The spring-loaded clip  1018  may be made of stainless steel (SS 301, for example) and may include wire ends  1038  that fit into ferrules  1040  of the spring-attachment plate  1014 . The spring-loaded clip  1018  may further include an arm  1036  that may be squeezed so as to fit in and through a spring hole  1034  in the lever  1020 . The spring opening  1034  may provide dual functionalities of protecting the spring coils  1037  and limiting the right-to-left and left-to-right movements of the arm  1036 . The lever  1020  may include male rotatable attachment features  1030  that fit into corresponding female rotatable attachment features  1028  of the base  1012 . The male rotatable attachment features  1030  thus form a pivot shaft for pivotally mounting the lever  1020 . 
     The lever (actuating arm)  1020  may be formed in a “Z” shape. The Z shape is illustrated in  FIG. 10C . The Z shape of the lever  1020  advantageously allows for a wide window for opening the clips, particularly when they are arranged into a double-clip assembly  1100  as described below in relation to  FIG. 11 . 
     When the clip assembly  1000  is attached to the clip attachment pin  130 , a handle  1042  of the lever  1020  may be pressed down to open (disengage) the clip by lifting up the arm of the spring-loaded clip  1018  and so raise the contact feature  1044  at its tip. Releasing the handle  1042  of the lever  1020  causes the clip to close (engage) by lowering the arm of the spring-loaded clip  1018  so that the contact feature  1044  exerts a downward force to hold in place the substrate to be plated. 
     In accordance with an embodiment of the invention, the clip assembly  1000  forms an electrically-conductive path from the metal clipping pins  130  to the substrate to be electroplated. In one implementation, the screw  1016 , the spring-attachment plate  1014  and the clip  1018  are each metallic so as to form the electrically-conductive path from the metal clipping pins  130  to the substrate to be electroplated. 
       FIG. 11  is a top view showing a double-clip assembly  1100  in accordance with an embodiment of the invention. Such a double-clip assembly  1100  is preferably attached to the clip attachment features  210  which are located between two substrate holding areas  213 . As shown, in this embodiment, the base  1012  is configured with two sets of female rotatable attachment features  1028  (one set to the left of the screw  1016  and one set to the right of the screw  1016 ) such that two levers  1020  may be pivotally mounted to the base  1012 . Two spring arms  1018  are attached by inserting their wire ends  1038  into two sets of ferrules  1040  on the spring-attachment plate  1014  and by squeezing them into the spring holes  1034  of the levers  1020 . One spring arm  1018  is oriented with its tip portion is over a first substrate holding area  213  towards the top of the diagram, and the other spring arm  1018  is oriented with its tip is over a second substrate holding area  213  towards the bottom of the diagram. 
     In accordance with an embodiment of the invention, a robotic machine may be configured to open all the clips surrounding each substrate holding area  213  and a wafer (or other substrate to be processed) may be placed therein. The opening of the clips may be accomplished by simultaneously pressing down on the handles  1042  to raise the arms of the corresponding spring-loaded clips  1018 . The clips surrounding each substrate holding area  213  may then be closed by the robotic machine releasing the handles  1042  to lower the arms of the corresponding spring-loaded clips  1018  such that the contact features  1044  press against the metallic contact pads  806  to hold the wafer (or other substrate or other substrate to be plated) firmly in place. Once all the wafers (or other substrates) to be processed have been thus loaded onto the carrier, then the plating and other processing may be performed. After the processing, a robotic machine may be configured to re-open all the clips surrounding each substrate holding area  213  so that the processed wafers (or other substrates) may be removed and replaced with wafers to be subsequently processed. 
       FIG. 12  is a perspective view of an outer face  1202  on one side of a permeable substrate carrier in accordance with an embodiment of the invention. In this alternate embodiment, the two plates forming each substrate carrier each include at least one opening for each substrate holding area. The embodiment illustrated has one large opening  1204  at the center of each substrate holding area. As shown, the openings  1204  may be circular, for example. The openings  1204  reduce the weight of the carrier body and allows rinsing solution to flow through (permeate) the carrier body. Applicants believe that the openings  1204  reduce a drag force when the carrier is removed from a bath. 
     The conductive assembly (weldment) including the electrically-conductive bus bar  120  at the top of the carrier and conductive lines  128  going from the bus bar  120  towards the bottom of the carrier may be the same as, or similar to, the conductive assembly described above in relation to  FIGS. 4, 5A, 5B, 6 and 7 . 
     Further shown in  FIG. 12  are clip attachment features  1210  on left and right sides of each opening  1204 . Electrically-conductive clips are preferably attached to the clip attachment features  1210 . The electrically-conductive clips may be the same as, or similar to, the clip assembly  900  described above in relation to  FIGS. 9A and 9B , or the clip assemblies ( 1000  and  1100 ) described above in relation to  FIGS. 10A, 10B, 10C and 11 . 
     In addition,  FIG. 12  shows support ribs  1220  on the left, bottom, and right sides of the carrier body. These support ribs  1220  provide structural strength to the carrier body. In accordance with an embodiment of the invention, the support ribs  1220  have a tapered profile to advantageously facilitate non-retention of electrolyte solution. 
     Also shown in  FIG. 12  are horizontal support bars  1222 . The horizontal support bars  1222  may be configured between rows of the openings  1204  to provide additional structural strength to the carrier body. In accordance with an embodiment of the invention, the raised horizontal support bars  1222  have a tapered profile to advantageously facilitate non-retention of electrolyte solution. 
     In addition,  FIG. 12  shows a plurality of stacking features  1224  on the carrier body. In one implementation, the stacking features  1224  may be arranged periodically along the horizontal support bars  1222 . The stacking features  1224  are configured so as to maintain alignment and separation between carrier bodies when they are stacked. 
       FIG. 13  is a closer-up perspective view of a portion of the permeable substrate carrier of  FIG. 12  in accordance with an embodiment of the invention. As shown, each side surrounding an opening  1204  includes substrate alignment features  1314 . The substrate alignment features  1314  are positioned around the opening  1204  and are configured such that the wafer (or other substrate) to be plated fits within a region having these substrate alignment features  1314  at its perimeter. 
     As further shown, there are several spacing features  1312  positioned around the opening  1204 . The spacing features  1312  are positioned to lie underneath the wafer or other substrate to be plated when it is clipped to the substrate carrier. The spacing features  1312  provides a space or gap between the substrate and the carrier. 
     In addition,  FIG. 13  depicts relief cuts  1316  surrounding the clip attachment features  1210 . These relief cuts  1316  are recessed areas that facilitate proper positioning of a base of a clip assembly (for example, see base  1012  of clip assembly  1000  shown in  FIGS. 10A and 10B ). 
       FIG. 14  is a flow chart of a method  1400  of manufacturing and maintaining a single-piece substrate carrier for electroplating in accordance with an embodiment of the invention. The single-piece substrate carrier is substantially more robust when compared against a prior multiple-piece substrate carrier. 
     Blocks  1402  through  1408  pertain to the manufacture of a conductive assembly. The conductive assembly may be, for example, configured as the conductive assembly (weldment) described above in relation to  FIG. 4 . 
     In block  1402 , an electrically-conductive bus bar is fabricated. In one example, the bus bar may be fabricated by machining a 6 millimeter thick stainless steel (SS 316, for example) bar to a shape with openings such as described above in relation to the bus bar  120  shown in  FIG. 1 . After machining, the bus bar may be deburred and cleaned. 
     In block  1404 , a portion of the bus bar spanning its horizontal length is overmolded or overcoated with a thermoplastic. The overmolding or overcoating may be performed, for example, by injection molding chlorinated polyvinyl chloride (CPVC) over a lower portion of the bus bar. In one example, the thermoplastic overcoat may be formed over an area of the bus bar such as the area  602  shown in  FIG. 6 . 
     In block  1405 , the bus bar and metal lines may be pre-treated prior to being conductively attached together. The pre-treatment may comprise degreasing with sand blasting and/or using a grit cloth to remove surface deposits and may also comprise cleaning with multiple washes and air drying. The pre-treatment may also include pre-treating with chemicals to promote adhesion between the bus bar (stainless steel, for example) and the metal lines (copper, for example). 
     In block  1406 , metal lines are conductively attached to the bus bar. This may be accomplished, for example, by welding the metal lines (for example, copper) to the bus bar (for example, stainless steel). In one example, the metal lines may be configured similarly to the configuration of metal lines  128  shown in  FIG. 4 . 
     In block  1408 , clip-attachment parts are conductively attached to the metal lines, and thermoplastic layers may be deposited. The thermoplastic layers may include, for example, a thermoplastic layer (see  504  in  FIG. 5B ) surrounding each clip-attachment parts and a thermoplastic layer (see  506  in  FIG. 5B ) over the metal lines. 
     Blocks  1410  and  1412  pertain to the manufacture of the non-conductive plates for the carrier body. In one embodiment, the non-conductive plates may be formed from CPVC material. Other embodiments may use different thermoplastic materials. 
     In block  1410 , two non-conductive plates are formed with various features for the carrier body. In a first embodiment, the carrier body is designed to be non-permeable to electrolytic solution and may comprise non-conductive plates with an inner face  102  as shown in  FIG. 1  and an outer face  202  as shown in  FIG. 2 . In this embodiment, although holes are formed through the plates for the clip attachment parts, the thermoplastic layer around the clip attachment parts are bonded to the inner face of the non-conductive plate to maintain the non-permeable aspect of the carrier body. In a second embodiment, the carrier body is designed to be permeable to electrolytic solution and may be configured with large circular openings  1204  as shown in  FIG. 12 . 
     In block  1412 , the surfaces of the plates are prepared prior to bonding. For example, the surfaces may be sand blasted and then cleaned with multiple washes and air drying. 
     Blocks  1414  through  1416  pertain to the integration of the conductive assembly and the carrier plates to form a single-piece substrate carrier. In block  1414 , a solvent cement is applied to areas of the inner faces of the two plates. In the plates are made of CPVC, then an exemplary solvent cement may be a CPVC solvent cement, such as, for instance, Weld-On® 724™ solvent cement. 
     In block  1416 , the inner sides of the two plates are bonded with the overmolded portion of the bus bar and the metal lines encased therebetween. The positioning of the bus bar and the metal lines against an inner face of one of the plates is depicted in  FIG. 1 , for example. The bonding process may involve, for example: application of a primer to the inner faces of the plates; application of a gum material on the areas of the inner faces where the metal lines are to be embedded; embedding the metal lines within the gum material; bonding the inner faces of the two plates; and curing the bonded plates (for example, for 72 hours). 
     Blocks  1417  and  1420  pertain to adding the clips, pads and pegs onto the outer faces of the carrier plates. 
     In block  1417 , post-bond drilling for the clip-attachment parts and tapping or threading of the clip-attachment parts are performed. Thereafter, in block  1418 , clips to hold the substrates to the carrier may be attached in a removable manner to the clip attachment features at the outer faces of the carrier. Because the clips are removably attached, they may be readily replaced when worn or damaged. In one embodiment, the clips may comprise clip assemblies  900  such as those depicted in  FIGS. 9A and 9B . In another embodiment, the clips may comprise single clips on the edges of the carrier and double clips on the interior of the carrier (where the double clips are between two substrate holding areas). The single clips may comprise, for example, the clip assembly  1000  depicted in  FIGS. 10A, 10B . The double clips may comprise, for example, the clip assembly  1100  depicted in  FIG. 11 . 
     In block  1420 , spacing pads and substrate-alignment pegs may be removably attached onto the outer faces of the carrier plates. Because the pads and pegs are removably attached, they may be readily replaced when worn or damaged. The spacing pads may be removably attached to the pad attachment points ( 211  and  212 ) at the outer faces  202  of the carrier. In one embodiment, the spacing pads may comprise the pads ( 311  and  312 ) depicted in  FIG. 3 . The substrate-alignment pegs may be removably attached to the alignment peg attachment points  214  at the outer faces  202  of the carrier. 
     Blocks  1422  and  1426  pertain to maintaining the substrate carrier. In block  1422 , the carrier is used to electroplate substrates. Use of the carrier typically involves dipping the carrier with the substrates clipped thereon into one or more electroplating baths while a voltage is applied to the substrates by way of the clips. See the method  1500  described below in relation to  FIG. 15 , for example. 
     Upon occasion, the clips may become worn or damaged. In accordance with an embodiment of the invention, the worn or damaged clips may be readily replaced per block  1424 . In one implementation, the replacement of the clips may be performed on a periodic schedule. This advantageously allows the carrier to be kept in service without the substantial downtime needed to repair more permanently attached clips. 
     Similarly, upon occasion, the spacing pads and/or alignment pegs may become worn or damaged. In accordance with an embodiment of the invention, the worn or damaged pads and/or pegs may be readily replaced per block  1426 . In one implementation, the replacement of the pads and/or pegs may be performed on a periodic schedule. This advantageously allows the carrier to be kept in service without the substantial downtime needed to repair more permanently attached pads and/or pegs. 
       FIG. 15  is a flow chart of a method  1500  of using a substrate carrier to electroplate a plurality of substrates in accordance with an embodiment of the invention. In block  1502 , a robotic loader may be used to clip a plurality of substrates to the substrate holding areas of the carrier. In block  1504 , the substrate carrier may be mounted on a work arm of an electroplating machine. 
     In block  1506 , the electroplating machine may mechanically dip the carrier into an electroplating bath. Per block  1508 , a voltage may be applied to the substrates by way of the electrically-conductive path traveling through the bus bar, the metal lines, and the clips. In one example, the substrates may comprise silicon wafers. The clips may make contact, for example, with a base (seed) layer of copper (or other metal) in gridlines on the surface of the wafers. A metal layer may then be deposited from the electroplating bath on top of the base layer. 
     Per block  1512 , if more metal layers are to be electroplated onto the substrates, then the method  1500  may loop back to block  1506  and the carrier may be mechanically dipped into a different electroplating bath to deposit a different metal layer so as to form a multi-layer stack for a metal contact, for example. When no more metal layers are to be electroplated onto the substrates, then per block  1514  the substrates may be removed from the carrier by a robotic machine, for example. Thereafter, the method  1500  may loop back to block  1502  and other (unplated) substrates to be processed may be robotically clipped onto the substrate carrier. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a number of variations exist. It should also be appreciated that the exemplary embodiment or embodiments described herein are not intended to unnecessarily limit the scope, applicability, or configuration of the claimed subject matter. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the described embodiment or embodiments. It should be understood that various changes can be made in the design and arrangement of elements without departing from the scope defined by the claims, which includes known equivalents and foreseeable equivalents at the time of filing this patent application.