Patent Publication Number: US-7905994-B2

Title: Substrate holder and electroplating system

Description:
BACKGROUND 
     Electroplating is a well-known process used in the microelectronics industry for depositing a metal film or forming other electrically conductive structures. For example, electroplating is commonly used for depositing a copper-based metallization layer from which interconnects in an integrated circuit (“IC”) can be formed. Other structures that can be formed using electroplating includes through-substrate interconnects, through-mask plated films, and electroplated bumps for flip-chip type electrical connections. 
     In many conventional electroplating processes, a substrate to be electroplated is held in a substrate holder and immersed in an electroplating aqueous solution. A consumable or inert anode is also immersed in the electroplating aqueous solution. The substrate holder can include a base and a cover having an opening formed therein that exposes a surface of the substrate when the base and cover are assembled together. The substrate holder can also include provisions for electrically contacting the substrate, such as electrical contact pins that contact a peripheral region of the substrate. The substrate functions as a cathode of an electrochemical cell in which the electroplating aqueous solution functions as an electrolyte. A voltage source may apply a voltage between the substrate and the anode to cause metal ions from the electroplating aqueous solution to deposit onto the exposed surface of the substrate and form a plated film. 
     It is desirable that the electrical contact pins reliably electrically contact the substrate within the substrate holder to ensure that the plated film is deposited on the exposed surface of the substrate under controlled electrochemical conditions. For example, moving the substrate holder carrying the substrate to immerse the substrate in the electroplating aqueous solution and aggressively moving the substrate holder carrying the substrate in the electroplating aqueous solution during the electroplating process can cause the electrical contact pins to lose or unreliably contact the substrate. If the electrical contact between the electrical contact pins and the substrate is not reliable, the quality and/or uniformity of the electroplated film may not be of acceptable quality for use in an IC. 
     In addition to the substrate holder providing a reliable electrical contact between the substrate and the voltage source, it is often desirable to seal the electrical contact pins and regions of the substrate that are not desired to be electroplated from the electroplating aqueous solution. When the electrical contact pins are not isolated from the electroplating aqueous solution, the electrical contact pins can also be electroplated and, consequently, cause variability in the electroplated film morphology and/or thickness. 
     Therefore, there is still a need for an improved substrate holder that is capable of isolating selected portions of a substrate from an electroplating aqueous solution and providing a reliable electrical contact to the substrate. 
     SUMMARY 
     One or more embodiments of the invention relate to a substrate holder configured for holding at least one substrate during electroplating, an electroplating system that may employ such a substrate holder, and methods of use. In one embodiment of the invention, a substrate holder includes a base, a cover, at least one seal assembly, an electrode, and at least one compliant member. The base is configured to support a substrate that includes a surface having a peripheral region. The cover includes at least one opening configured to expose only a portion of the surface of the substrate therethrough. The at least one seal assembly is configured to substantially seal a region between the base and cover to substantially isolate the electrode from an electroplating aqueous solution environment. The electrode includes at least one contact portion that is configured to be positioned within the region substantially sealed by the at lest one seal assembly and extend over at least a portion of the peripheral region of the substrate. The at least one compliant member, comprising a polymeric material, is configured to be positioned within the region between the at least one contact portion and either the peripheral region of the substrate or the cover. During use, the electrode is electrically coupled to the peripheral region of the substrate and the exposed surface of the substrate may be electroplated. 
     In another embodiment of the invention, an electroplating system includes a substrate-loading station operable to load one or more substrates onto a base. The electroplating system further includes a substrate-holder-transport unit that carries a cover of a substrate holder and operable to assemble the cover with the base to form a substrate holder. The electroplating system also includes a substrate-unloading station operable to remove the one or more substrates from the base. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate several embodiments of the invention, wherein like reference numerals refer to like components or features in different views or embodiments shown in the drawings. 
         FIG. 1  is an isometric view of a substrate holder configured to hold at least one substrate according to one embodiment of the invention. 
         FIG. 2A  is plan view of the cover shown in  FIG. 1 , with the seals inserted into corresponding seal seats and the electrode inserted into an electrode seat formed in the cover. 
         FIG. 2B  is an isometric view of the base shown in  FIG. 1 , with a substrate positioned in one of the recess and the other recess empty. 
         FIG. 3  is a cross-sectional view of the substrate holder shown in  FIG. 1  taken along line  3 - 3 . 
         FIG. 4  is an enlarged cross-sectional view of the substrate holder shown in  FIG. 3  that illustrates how an annular compliant member establishes electrical contact between an electrode and a peripheral region of the substrate. 
         FIG. 5  is an enlarged cross-sectional view of a substrate holder including an electrode having a serrated contact surface for establishing electrical contact with a peripheral region of a substrate according to another embodiment of the invention. 
         FIG. 6  is an enlarged cross-sectional view of a substrate holder including an electrode having a substantially planar contact surface for establishing electrical contact with a peripheral region of a substrate according to yet another embodiment of the invention. 
         FIG. 7  is an isometric view of a substrate holder configured to hold two or more substrates according to another embodiment of the invention. 
         FIG. 8  is plan view of the cover shown in  FIG. 7 , with the seals inserted into corresponding seal seats and the electrode inserted into an electrode seat formed in the cover. 
         FIG. 9  is an enlarged, partial cross-sectional view of the substrate holder shown in  FIG. 7  taken along line  9 - 9 . 
         FIG. 10  is schematic diagram of an electroplating system that may utilize any of the disclosed substrate holder embodiments according to another embodiment of the invention. 
         FIG. 11  is a schematic diagram illustrating how the substrate-holder-transport unit is operable to rotate a substrate holder prior to immersion into a container. 
     
    
    
     DETAILED DESCRIPTION 
     One or more embodiments of the invention relate to a substrate holder configured for holding at least one substrate during electroplating and an electroplating system that may employ such a substrate holder. The substrate holder may be employed in an electroplating system for electroplating a selected surface of the at least one substrate and may further be robust enough to be moved at a selected rate (e.g., in an oscillatory manner and/or rotated) when immersed in the electroplating aqueous solution during electroplating. For example, a compliant polymeric material may help establish and maintain electrical contact between the at least one substrate and an electrode even when the substrate holder is being moved, and/or may help reduce mechanical play between components of the substrate holder. 
       FIGS. 1 ,  2 A- 2 B,  3 , and  4  show a substrate holder  100  configured to hold at least one substrate according to one embodiment of the invention. Referring to the isometric shown in  FIG. 1 , the substrate holder  100  includes a base  102  and a cover  104 , and substrates  106   a  and  106   b  may be secured therebetween. For example, a plurality of fasteners  107  may be used to secure the base  102  and cover  104  together to capture the substrates  106   a  and  106   b  therebetween. The base  102  and cover  104  may be formed from a material, such as ultra-high molecular weight polypropylene or another suitable material. In some embodiments of the invention, a vacuum mechanism may be used to attract the base  102  and cover  104  together by way of a vacuum port formed through the base  102  or the cover  104  instead of the fasteners  107  shown in the illustrated embodiment. As used herein, the term “substrate” refers to any workpiece capable of being electroplated. For example, suitable substrates include, but are not limited to, semiconductor substrates (e.g., single-crystal silicon wafers in full or partial form, single-crystal gallium arsenide wafer in full or partial form, etc.) with or without active and/or passive devices (e.g., transistors, diodes, capacitors, resistors, etc.) formed therein and with or without a seed layer formed thereon to promote electroplating, printed circuit boards, flexible polymeric substrates with a conductive film thereon, and many other types of substrates. 
     Still referring to  FIG. 1 , the cover  104  includes openings  108   a  and  108   b  formed therein through which surfaces  110   a  and  110   b  of corresponding substrates  106   a  and  106   b  are exposed. A bus member  112  of an electrode  206  (See  FIG. 2A ) projects out of the assembly of the base  102  and cover  104  to provide an externally accessible feature for electrically connecting the electrode  206  to a voltage source. For example, the electrode  206  may be made from number of different electrically conductive metals or alloys. Application of a voltage between the bus member  112  and a reference electrode when the substrate holder  100  is immersed in an electroplating aqueous solution causes the surfaces  108   a  and  108   b  to be electroplated with, for example, copper or another selected metal or alloy that is capable of being electroplated from an electroplating aqueous solution. 
       FIG. 2A  is plan view of the cover  104  shown in  FIG. 1  that shows many of the internal components of the substrate holder  100  in more detail. The substrate holder  100  includes seal assemblies  200   a  and  200   b , each of which extends about a corresponding opening  108   a  and  108   b  of the cover  104 . Each seal assembly  200   a  and  200   b  comprises an annular, inner seal  202  and an annular, outer seal  204  that extends circumferentially about the inner seal  202 . The inner seal  202  and outer seal  204  of each seal assembly  200   a  and  200   b  may reside in corresponding seal seats  402  and  404  (See  FIG. 4 ) formed in the cover  104 . According to various embodiments of the invention, the inner seal  202  and outer seal  204  may be an O-ring, a gasket, or another suitable seal. 
     The electrode  206  of the substrate holder  100  is disposed within an electrode seat  406  (See  FIG. 4 ) and under the outer seal  204 . The electrode  206  includes contact rings  208   a  and  208   b  (i.e., contact portions), each of which may be generally equally spaced from the bus member  112  and electrically interconnected thereto via interconnects  210   a  and  210   b . A more uniform current distribution over the surfaces  110   a  and  110   b  of corresponding substrates  106   a  and  106   b  may be obtained during an electroplating process by generally equally spacing the contact rings  208   a  and  208   b  from the bus member  112 . The electrode  206  is configured so that the contact ring  208   a  may be positioned between the inner seal  202  and outer seal  204  of the seal assembly  200   a  and the contact ring  208   b  may be positioned between the inner seal  202  and outer seal  204  of the seal assembly  200   b . Each interconnect  210   a  and  210   b  may include a slot (not shown) formed therein that receives a portion of a corresponding outer seal  204 . When the substrate holder  100  is fully assembled, the seal assemblies  200   a  and  200   b  function to substantially seal the contact rings  208   a  and  208   b  from an electroplating aqueous solution that the substrate holder  100  is immersed in. As will be discussed in more detail with respect to  FIGS. 3 and 4 , the contact rings  208   a  and  208   b , ultimately, establish electrical contact with corresponding peripheral regions of the substrates  106   a  and  106   b  when assembled between the base  102  and the cover  104 . In certain embodiments of the invention, the contact rings  208   a  and  208   b  may be replaced with partial rings. 
     Still referring to  FIG. 2A , a peripheral seal  211  (e.g., an O-ring, a gasket, or the like) may also be provided in a seal seat  408  (See  FIG. 4 ) that extends peripherally about the seal assemblies  200   a  and  200   b  to substantially seal portions of the interconnects  210   a  and  210   b  and the bus member  112  from the electroplating aqueous solution that the substrate holder  100  is immersed in. A plurality of through holes  205  may be formed in the cover  104  in which one of the fasteners  107  (See  FIG. 1 ) may be inserted therethrough. 
       FIG. 2B  more clearly illustrates the configuration of the base  102 . The base  102  includes recesses  212   a  (not shown) and  212   b  in which corresponding substrates  106   a  and  106   b  (not shown) may be received. In  FIG. 2B , the recess  212   a  is not shown because the substrate  106   a  is positioned therein. The base  102  may further include a plurality of partial or through holes  214  in which one of the fasteners  107  (See  FIG. 1 ) may be inserted therein. 
       FIGS. 3 and 4  best show how the components of the substrate holder  100  assemble together. Although the seal assembly  200   b  and contact ring  208   b  are not shown in  FIGS. 3 and 4 , it should be understood that they function the same as the seal assembly  200   a  and contact ring  208   a  shown in  FIGS. 3 and 4 .  FIG. 3  is a cross-sectional view of the substrate holder  100  shown in  FIG. 1  taken along line  3 - 3  and shows the overall assembly of the base  102 , cover  104 , substrate  106   a , and relative positions of the seal assembly  200   a , peripheral seal  211 , and contact ring  208   a.    
       FIG. 4  is an enlarged cross-sectional view of the substrate holder  100  shown in  FIG. 3  that best shows how the contact ring  208   a  establishes electrical contact with the substrate  106   a . The inner seal  202  and outer seal  204  of the seal assembly  200   a  each resides in corresponding seal seats  402  and  404 , and the contact ring  208   a  resides in the electrode seat  406 . When engaged between the base  102  and cover  104  by fastening the base  102  and cover  104  together with the fasteners  107  or by vacuum attraction, the seal assembly  200   a  comprised of the inner seal  202  and outer seal  204  forms an annular, substantially sealed region  407  adjacent to a peripheral region  410  of the surface  108   a  of the substrate  106   a . The inner seal  202  seals with the peripheral region  410  and the cover  104 , and the outer seal  204  may seal against the base  102  and the cover  104 . 
     Still referring to  FIG. 4 , in the illustrated embodiment, an annular first compliant member  412 , made from an electrically conductive polymer, is disposed between the contact ring  208   a  and peripheral region  410 , and an annular second compliant member  414  made from a polymeric material is disposed between the contact ring  208   a  and the cover  104 . Of course, it is understood, that another first compliant member  412  is disposed between the contact ring  208   b  and peripheral region  410 . The first compliant member  412  may contact substantially all of the surface area of the peripheral region  410  so that an electrical potential applied to the substrate  106   a  is distributed generally uniformly over the surface  110   a  thereof. 
     Suitable electrically conductive polymers for the first compliant member  412  include, but are not limited to, organic electrically conductive polymers, such as polyacetylene, polypyrrole, polythiophene, polyaniline, polyfluorene, poly(3-alkylthiophene), polytetrathiafulvalene, polynaphthalene, poly(p-phenylene sulfide), and poly(para-phenylene vinylene). For example, in one specific embodiment of the invention, the first compliant member  412  may be made from polyacetylene oxidized with iodine, which exhibits an electrical conductivity similar to that of silver. In another specific embodiment of the invention, the first compliant member  412  may be made from iodine-doped polyacetylene. In another specific embodiment of the invention, the first compliant member  412  may be made from poly(3-dodecylthiophene) doped with iodine. Poly(3-dodecylthiophene) doped with iodine may exhibit an electrical conductivity of about 1000 S/cm. Other organic electrically conductive polymers that the first compliant member  412  may be made from include conductive nylon 8715, polyester urethane 4931, and polyether urethane 4901, each of which is commercially available from HiTech Polymers of Hebron, Ky. In yet another embodiment of the invention, electrically conductive particles (e.g., graphite or metallic particles) may be embedded in a polymeric matrix. In yet another embodiment of the invention, the first compliant  412  may comprise an O-ring (e.g., an O-ring made from Teflon®), polyvinyl fluoride, or polyethylene) partially or completely coated with an electrically conductive film made from a metal or alloy (e.g., gold, copper, or alloys thereof). The second compliant  414  may be made from the same or similar materials as the first compliant member  412  and does need to be electrically conductive. 
     Still referring to  FIG. 4 , the first compliant member  412  establishes electrical contact between the peripheral region  410  of the substrate  106   a  and the contact ring  208   a . Because the first compliant member  412  is made from a compliant material (e.g., an electrically conductive polymer), it provides a reliable electrical contact to the peripheral region  410  of the substrate  106   a  even when the substrate holder  100  is being moved (e.g., during electroplating). The second compliant member  414  may help reduce any mechanical play present between the contact ring  208   a  and the cover  104  to further help maintain electrical contact between the peripheral region  410  and the first compliant member  412 . Additionally, the stiffness of the first compliant member  412  may be less than that of the inner seal  202  and outer seal  204  of the seal assembly  200   b  and the peripheral seal  211  so that the sealing force applied to the substrate  106   a  is greater than that of the force applied to the contact ring  208   a.    
       FIG. 5  is an enlarged cross-sectional view of a substrate holder  500  according to another embodiment of the invention. The substrate holder  500  is structurally similar to the substrate holder  100  shown in  FIGS. 1 ,  2 A- 2 B,  3 , and  4 . Therefore, in the interest of brevity, components in both substrate holders  100  and  500  that are identical to each other have been provided with the same reference numerals, and an explanation of their structure and function will not be repeated unless the components function differently in the substrate holders  100  and  500 . 
     Still referring to  FIG. 5 , the substrate holder  500  differs mainly from the substrate holder  100  shown in  FIGS. 1 ,  2 A- 2 B,  3 , and  4  in that the substrate holder  500  has a contact ring  208   a ′ with a non-planar contact surface. The contact ring  208   a ′ includes a serrated contact surface  502  that establishes electrical contact with the peripheral region  410  of the surface  110   a  of the substrate  106   a . The serrated contact surface  502  may help break through any surface oxides or debris present on the surface  110   a  of the substrate  106   a.    
       FIG. 6  is an enlarged cross-sectional view of a substrate holder  600  according to another embodiment of the invention. The substrate holder  600  is structurally similar to the substrate holder  100  shown in  FIGS. 1 ,  2 A- 2 B,  3 , and  4 . Therefore, in the interest of brevity, components in both substrate holders  100  and  600  that are identical to each other have been provided with the same reference numerals, and an explanation of their structure and function will not be repeated unless the components function differently in the substrate holders  100  and  600 . The substrate holder  600  differs mainly from the substrate holder  100  shown in  FIGS. 1 ,  2 A- 2 B,  3 , and  4  in that the substrate holder  600  includes a contact ring  208   a ″ with a substantially planar contact surface  602  that establishes electrical contact with the peripheral region  410  of the surface  110   a  of the substrate  110   a.    
     It is noted that in the substrate holders  100 ,  500 , and  600  shown in  FIGS. 3 ,  5 , and  6 , the second compliant member  414  may be omitted. However, the thickness of the contact rings  208   a / 208   b ,  208   a ′, and  208   a ″ should be suitably increased to help prevent any mechanical play with the cover  104 . 
       FIG. 7  is an isometric view of a substrate holder  700  configured to hold two or more substrates according to another embodiment of the invention. The substrate holder  700  enables electroplating a greater number of substrates at one time than the substrate holders  100 ,  500 , and  600  shown in  FIGS. 1 ,  5 , and  6 . Accordingly, the substrate holder  700  provides a greater process throughput in electroplating processes than the substrate holders  100 ,  500 , and  600 . 
     Still referring to  FIG. 7 , the substrate holder  700  includes a base  702  and a cover  704 . The cover  704  includes a plurality of openings  706  formed therein that expose corresponding surfaces  708  of substrates  710  therethrough captured between the cover  704  and the base  102 . A main bus member  802  of an electrode  800  (See  FIG. 8 ) projects out of the assembly of the base  102  and cover  104  to provide an externally accessible feature for electrically connecting the electrode  800  to a voltage source during electroplating operations. 
       FIG. 8  is plan view of the cover  704  shown in  FIG. 7  that shows many of the internal components of the substrate holder  700  in more detail. It is noted that the substrate holder  700  differs mainly from the substrate holder  100  in that the structure of the electrode  800  is different. As shown in  FIG. 8 , the substrate holder  700  includes a plurality of seal assemblies  804 , each of which includes an inner seal  806  (e.g., an O-ring, a gasket, or the like) and an outer seal  808  (e.g., an O-ring, a gasket, or the like) extending thereabout. Each inner seal  806  and outer seal  808  is disposed in a corresponding seal seat  906  and  908  (See  FIG. 9 ) and extends about a corresponding opening  706 . A peripheral seal  810  (e.g., an O-ring, a gasket, or the like) similar in structure and functionality to the peripheral seal  211  shown in  FIG. 2A  of the substrate holder  100  may be disposed in a seal seat  910  (See  FIG. 9 ) formed in the cover  704 . 
     Still referring to  FIG. 8 , the electrode  800  is disposed within an electrode seat  909  (See  FIG. 9 ) formed in the cover  704  and under the outer seals  808 . The electrode  800  includes bus bars  814  and  816  connected to the main bus member  802 . The electrode  800  further includes a plurality of contact rings  818  arranged in rows  820 - 822 . Each contact ring  818  of the row  820  is connected to the bus bar  814  via an interconnect  824 , each contact ring  818  of the row  822  is connected to the bus bar  816  via an interconnect  826 , and each contact ring  818  of the row  821  is connected to both the bus bar  814  and  816  via interconnects  828 . Each contact ring  818  may be spaced from the bus bar  814 ,  816 , or both a substantially equal distance. 
       FIG. 9  is an enlarged, partial cross-sectional view of the substrate holder  700  shown in  FIG. 7  taken along line  9 - 9 . As with the electrode  206  of the substrate holder  100  shown in  FIGS. 1 ,  2 A- 2 B,  3 , and  4 , each contact ring  818  is disposed between the inner seal  806  and outer seal  808  of a corresponding seal assembly  804 . When the base  702  and cover  704  are urged together, the seal assemblies  804  substantially seal the contact rings  818  from an electroplating aqueous solution that the substrate holder  800  is immersed in. For example, vacuum plug  910  communicates with the space between the inner seal  806  and outer seal  808  through a vacuum port (not shown) formed in the base  702  so that a vacuum source may be used to attract the base  702  and cover  704  together and engage the seal assemblies  804  and the peripheral seal  810 . However, in other embodiments of the invention, the vacuum port may be formed in the base  702  instead of the cover  704 . In another embodiment of the invention, a plurality of fasteners may be used to urge the base  702  and cover  704  together to engage the seal assemblies  804  and the peripheral seal  810  in a manner similar to the substrate holder  100  shown in  FIG. 1 . 
     Still referring to  FIG. 9 , in a manner similar to the substrate holder  100 , each seal assembly  804  forms an annular substantially sealed region  912  adjacent to a peripheral region  914  of the surface  708  of the substrate  710 . Each contact ring  818  may be disposed within a corresponding sealed region  912 . Additionally, an annular first compliant member  412  may be disposed between a corresponding contact ring  818  and the peripheral region  914  to established electrical contact with a corresponding substrate  710  and an annular second compliant member  414  may be disposed between the corresponding contact ring  818  and the cover  704 . 
     In other embodiments of the invention, each contact ring  818  of the electrode  800  may have a non-planar contact surface, such as a serrated contact surface similar to the contact ring  208   a ′ shown in  FIG. 5  and the first compliant members  414  may be omitted. In yet another embodiment each contact ring  818  may have a substantially planar contact surface similar to the contact ring  208 ″ shown in  FIG. 6  and the first compliant members  414  may be omitted. In further embodiments of the invention, the second compliant members  416  used to reduce mechanical play between the electrode  800  and the cover  704  may be omitted. 
       FIG. 10  is a schematic diagram of an electroplating system  1000  that may employ any of the above-described embodiments of substrate holders according to another embodiment of the invention. The electroplating system  1000  includes a substrate-loading station  1002  that may include a substrate-presentation unit  1004  operable to pick-up a substrate  1006  (a cartridge of substrates  1006  is depicted in  FIG. 10 ) and present the substrate  1006  to a substrate-loading unit  1008 . For example, the substrate-presentation unit  1004  may be a robot with an extensible arm  1010  movable about three axes and having a retention mechanism, such as a vacuum mechanism or forks (as illustrated) that may support the substrate  1006 . The substrate-loading unit  1008  may include an extensible arm  1012  that is also movable about three axes and may have a similarly configured retention mechanism operable to pick-up and carry one of the substrates  1006 . The arm  1012  has a range of motion so that it can transport the substrates  1006  to controllably place them onto a base  1014  (depicted configured similar to the base  702  of the substrate holder  700 ). During use, the substrate-loading unit  1008  may place one of the substrates  1006  in each recess  1016  of the base  1014 . 
     The electroplating system  1000  further includes a plurality of isolated containers, each of which holds a specific fluid. In the illustrated embodiment, containers  1018 - 1022  are shown. For example, the container  1018  may hold a cleaning solution  1023 , container  1019  may hold a rinsing solution  1024  (e.g., water), container  1020  may hold an electroplating aqueous solution  1025  (e.g., as a sulfuric-acid-based solution), container  1021  may hold a post-plating cleaning solution  1026 , and container  1022  may hold a solution (e.g., isopropyl alcohol) to promote drying of a plated substrate after cleaning in the post-plating cleaning solution  1026 . In some embodiments of the invention, the containers  1018 - 1022  may be supported on a conveyor  1028  operable to move the containers  1018 - 1022  in conveying directions D 1  and D 2 . 
     The electroplating system  1000  further includes a substrate-holder transport unit  1030  having an extensible arm  1032  that is movable about three axes. The arm  1032  may carry a cover  1029  (depicted configured similar to the cover  704  of the substrate holder  700 ) including an electrode (not shown), compliant members (not shown), and various seals (not shown). For example, the cover  1029  may carry the internal components previously discussed (e.g., the seal assembly, peripheral seal, electrode, compliant members, etc.) with respect to the substrate holders  100 ,  500 , and  600 . The substrate-holder transport unit  1030  may further include provisions for electrically connecting the electrode (not shown) embedded in the cover  1029  to a voltage source  1060 , such as a wire  1034  that extends along the length of the arm  1032 , and a vacuum line  1036  for communicating a vacuum force through one or vacuum ports formed in the cover  1029 . 
     During use, the substrate-holder-transport unit  1030  may controllably position the cover  1029  on the base  1014  loaded with substrates  1006  at the substrate-loading station  1002  and communicate a vacuum force through the vacuum line  1036  to urge the base  1014  and cover  1029  together to form an assembled substrate holder  1038  (depicted configured similar to the substrate holder  700 ). 
     As shown in  FIG. 11 , if desired, the substrate-holder-transport unit  1030  may rotate the substrate holder  1038  from a generally horizontal orientation to a generally vertical orientation so that the substrate holder  1038  may be more easily immersed in each container  1018 - 1022 . For example, the cover  1029  of the substrate holder  1038  may be pivotally connected to the arm  1032  via hinge  1031 . Then, the substrate holder  1038  may be sequentially immersed in each container  1018 - 1022 . In certain embodiments of the invention, the substrate holder  1038  is moved in the directions D 1  and/or D 2  by extending or retracting the arm  1032 , as desired. In other embodiments of the invention, the containers  1018 - 1022  may be translated in the direction D 1  and/or D 2  using the conveyor  1028 , as necessary or desired. When the substrate holder  1038  is immersed in the electroplating aqueous solution  1025  of the container  1020 , a selected voltage or voltage waveform may be applied between the electrode (not shown) embedded in the substrate holder  1038  and an anode  1040  immersed in the electroplating aqueous solution  1025  to cause metals ions from the electroplating aqueous solution to deposit on an exposed surface of the substrates  1006 . Additionally, the substrate-holder-transport unit  1030  may move the substrate holder  1038  (e.g., in a linearly oscillatory manner parallel to the anode  1040  in directions T 1  and T 2 ) to help improve electroplating characteristics. 
     In another embodiment of the invention, the substrate-holder-transport unit  1030  may be an overhead conveyor system that the cover  1029  is mounted on. 
     The electroplating system  1000  may also include a substrate-unloading station  1042  having a substrate-unloading unit  1044  that is configured the same or similarly to the substrate-loading unit  1008 . The substrate-unloading station  1042  may also include a substrate-stacking unit  1046  that is configured the same or similarly to the substrate-loading unit  1008  for carrying substrates  1006  presented to it by the substrate-unloading unit  1044  and stacking the substrates  1006  in a cartridge  1048 . 
     After electroplating the substrates  1006  and rinsing the electroplating substrates  1006 , the substrate-transport unit  1030  may move the substrate holder  1038  including electroplated substrates  1006  carried therein to the substrate-unloading station  1042  and de-activate the vacuum mechanism holding the base  1014  and cover  1029  together to thereby release and leave the base  1014  at the substrate-unloading station  1042 . Then, the substrate-unloading unit  1044  may individually pick-up and present each substrate  1006  to the substrate-stacking unit  1046  for stacking in the cartridge  1048 . 
     The electroplating system  1000  also comprises a control system  1050  that may include a computer  1052  with a processor  1054 , a memory  1056 , an operator interface  1058  (e.g., a monitor, keyboard, mouse, etc.), and may further include many other familiar computer components. The control system  1050  may further include a voltage source  1060  operable to apply a selected voltage between the electrode (not shown) embedded in the substrate holder  1038  and the anode  1040  to effect electroplating of the substrates  1006 , and a pump  1062  operable to generate a vacuum force communicated through the vacuum line  1036  that urges the base  1014  and cover  1029  together. The control system  1050  may be programmed, with computer readable instructions stored on the memory  1056 , to control the operation of the individual components of the electroplating system  1000  (e.g., the substrate-presentation unit  1004 , substrate-loading unit  1008 , substrate-holder-conveyor unit  1030 , substrate-unloading unit  1044 , and substrate-stacking unit  1046 ), as described above. 
     From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. For example, the recesses formed in the base of the substrate holders described above that receive substrates may be omitted. Additionally, although the seal and electrode seats are shown and described in the illustrated embodiments as being formed in the cover of the substrate holders, the seal and electrode seats may, instead, be formed in the base.