Abstract:
A method of fluid processing a semiconductor workpiece, including disposing a workpiece holder with a housing capable of containing a fluid, the workpiece holder retaining the workpiece, providing an agitation system connected to the housing and comprising a member disposed within the housing adjacent the workpiece holder, and agitating the fluid by moving the member substantially parallel to a surface of the workpiece with a non-uniform oscillatory motion, the non-uniform oscillatory motion being a series of substantially continuous geometrically asymmetric oscillations wherein each consecutive oscillation of the series is geometrically asymmetric having at least two substantially continuous opposing strokes wherein reversal positions of each substantially continuous stroke of the substantially continuous asymmetric oscillation are disposed asymmetrically with respect to a center point of each immediately preceding substantially continuous stroke of the oscillation.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. Ser. No. 10/971,726 filed on Oct. 22, 2004 which claims the benefits of and priority to U.S. Provisional Patent Application Ser. No. 60/513,761 filed on Oct. 22, 2003, which is owned by the assignee of the instant application and the disclosures of which are incorporated herein by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to a method and apparatus for fluid processing a workpiece, and more particularly to a method and apparatus for controlling fluid flow and electric field distribution during the fluid processing of a workpiece. 
     BACKGROUND OF THE INVENTION 
     Electrodeposition, among other processes, is used as a manufacturing technique for the application of films e.g., metal films) to various structures and surfaces, such as semiconductor wafers and silicon workpieces. An important feature of systems used for such processes is their ability to produce films with uniform and repeatable characteristics such as film thickness, composition, and profile relative to the underlying workpiece profile. 
     A number of factors can prevent the formation of a uniform film. For example, the plating current can spread out when passing from the anode to the cathode of the system, which can result in thicker plated deposits near the outer edge of a workpiece. In addition, the fluid distribution in a process chamber, particularly at an anode or cathode surface, may not be uniform. Non-uniform fluid distribution at the cathode can cause a variation in the thickness of the diffusion boundary layer across the workpiece surface, which can lead to non-uniform film thickness. Moreover, inefficient fluid mixing near a surface where a film is being deposited can result in air or gas bubbles becoming entrapped at the surface. This can inhibit further deposition in the vicinity of the gas bubble, which can cause a non-uniform deposition. Finally, if a workpiece is not securely retained in a process chamber, the position of the workpiece can change during processing, and when fluid processing a workpiece, fluid can leak into unwanted areas if a secure, fluid-tight seal is not formed with the workpiece. 
     Prior art systems suffer from one or more of these limitations, and a need therefore exists for new and improved methods and apparatus for controlling fluid flow and electric field distribution during the fluid processing of a workpiece and for reliably retaining a workpiece during processing. 
     SUMMARY OF THE INVENTION 
     The invention, in various aspects, features a system application and removal of materials from one or more surfaces of the workpiece(s). The application and removal can be performed by fluid flow control and/or electric field control at a surface of a workpiece. A workpiece can be planar or substantially planar, and can be thin or ultra-thin. Suitable workpieces include, but not limited to, semiconductor wafers, silicon workpieces, interconnection substrates, and printed circuit boards. This field is sometimes referred to as fluid processing or wet processing, and includes electrodeposition, electroplating, electroless plating, chemical etching, resist coating, resist stripping, dielectric coating, and workpiece cleaning, among other processes. 
     In one embodiment, the invention, features a method and apparatus for fluid processing a workpiece. The system can include a process module and a system of one or more fluid processing elements to control the fluid flow and/or the electric field distribution during the fluid processing of the workpiece. In various embodiments, a member can be used to agitate the fluid during deposition of a film. The member can employ a non-uniform oscillatory motion to agitate the fluid. The member can be an agitation paddle (e.g., a SHEAR PLATE agitation paddle available from NEXX Systems, Inc. in Billerica, Mass.). In some embodiments, a plate is used to shape an electric field incident on a surface of a workpiece. 
     By controlling the fluid flow and the electric field distribution, improved deposition of the film on the workpiece surface can result. Furthermore, a vertical configuration and/or a workpiece holder that can retain a plurality of workpieces in a back-to-back configuration can be used to improve throughput and to reduce the footprint of the workpiece processing system. This can increase productivity and reduce cost. In addition, using a modular architecture for the processing system can allow a system layout to be optimized to the fluid process and to the throughput requirements. 
     In one aspect, the invention features an apparatus for fluid processing a workpiece. The apparatus includes a housing capable of containing a fluid and a workpiece holder disposed within the housing and adapted to retain the workpiece. The apparatus also includes a member disposed within the housing adjacent the workpiece holder and adapted to move substantially parallel to a surface of the workpiece with a non-uniform oscillatory motion to agitate the fluid. In one embodiment, the non-uniform oscillatory motion includes a reversal position that changes after each stoke of the non-uniform oscillatory motion. The non-uniform oscillatory motion can include a primary oscillation stroke and at least one secondary oscillation stroke. The length of the primary oscillation stroke can be substantially the same as the separation of spaced openings defined by the member, and a secondary oscillation stroke can change the reversal position of the non-uniform oscillatory motion of the member. 
     In one embodiment, the member defines a plurality of spaced openings. In one embodiment, the member includes a plurality of spaced blades. The profile of the plurality of spaced blades can include a cup shape or an angled profile. In some embodiments, the member includes two paddle plates joined by a spacer feature into a single assembly so that the workpiece holder is insertable into the member. In one embodiment, the apparatus also includes a linear motor assembly to move the member. 
     In one embodiment, the apparatus includes a plate disposed adjacent the member to shape the electric field incident on a surface of the workpiece. A body of the plate can define a plurality of holes, the diameters of which vary (e.g., with a substantially radial pattern) on a surface of the plate. In various embodiments, the member can form a non-periodic fluid boundary layer at the surface of the workpiece. In one embodiment, the member reduces a fluid boundary layer thickness at the surface of the workpiece, e.g., to less than about at 10 μm. The member can be positioned less than about 2 mm from the surface of the workpiece. 
       FIG. 17  shows a graphical representation of an exemplary non-uniform oscillation profile  288  for agitating a fluid during fluid processing of a workpiece. The exemplary workpiece  30  and center point  252  in  FIGS. 15 and 16  are referenced for illustrative purposes. The position of the center point  252  of the member  204   x  relative to the work-piece point  256  on the surface of the workpiece  30  is plotted versus time. In this embodiment of the member  204   x , the separation of the center points  252  is about 20 mm. The primary oscillation stroke is substantially the same as the separation between the center point  252  and an adjacent center point of the member  204   x . The secondary oscillation stroke is about 40 mm. Line  292  shows the relative travel of the center point as a result of the primary oscillation stroke. Line  296  shows the relative travel of the center point as a result of the secondary oscillation stroke. As can be seen in  FIG. 17 , the line  296  extends substantially through the center of each stroke, with a center of each stroke offset with respect to each previous and succeeding stroke, thereby demonstrating the continuous nature of the change of each oscillation (from oscillation to oscillation) and also the change within each oscillation (from one stroke of an oscillation to a next stroke or return stroke of an oscillation) as discussed further below. As may be realized from  FIG. 17 , the resultant non-uniform oscillation profile is formed by a series of oscillations with each consecutive oscillation in the series being asymmetric. In other words, as shown in  FIG. 17 , the strokes of one oscillation are offset from each other, and moreover, the strokes of an oscillation are offset from strokes of adjacent oscillations. More particularly, as shown in  FIG. 17 , an oscillation includes a first stroke  288   b  and an opposing second stroke or return stroke  288   d . Further, the first stroke  288   b  includes a starting point  288   a  and an ending point  288   c , and the opposing or return second stroke  288   d  includes a starting point  288   c  and an ending point  288   e . The ending point for the first stroke corresponds to the starting point of the second stroke (or return stroke) and thus also provides a reversing position  288   c  for the oscillation. As also shown in  FIG. 17 , the oscillation itself is asymmetrical in that the first stroke  288   b  is not symmetrical to the second or return stroke  288   d  about the reversing position  288   c  as is apparent from the fact that, within one oscillation, the starting point  288   a  for the first stroke is offset from the ending point for the second stroke  288   e . As can also be seen, each of the succeeding reversal points of successive oscillations is offset from that of respective adjacent oscillations. 
     In yet another aspect, the invention features an apparatus for varying an electric field at a surface of a workpiece. The apparatus includes a housing capable of containing a fluid, a workpiece holder disposed within the housing and adapted to retain the workpiece, and a plate disposed within the housing and spaced from the workpiece. The plate defines a plurality of holes having a distribution of hole sizes to vary a property of the electric field passing through the plate to the surface of the workpiece. In one embodiment, the distribution of hole sizes includes a continuous gradient of hole size (e.g., a substantially radial pattern). In one embodiment, the electric field proximate to the surface of the workpiece is uniform. The property of the electric field can include amplitude. In one embodiment, the plate includes a non-conductive material that serves to block a portion of the electric field as it passes through the plate to the surface of the workpiece. 
       FIG. 18  shows a graphical representation of another exemplary non-uniform oscillation profile  300  for agitating a fluid during fluid processing of a workpiece. In this embodiment of the member  204   x , the separation of the center points  252  is about 20 mm. The primary oscillation stroke is substantially the same as the separation between the center point  252  and an adjacent center point of the member  204   x . The first secondary oscillation stroke is about 30 mm. The second secondary oscillation stroke is about 40 mm. The oscillatory motion can include additional secondary oscillation strokes. Line  304  shows the relative travel of the center point as a result of the primary oscillation stroke. Line  308  shows the relative travel of the center point as a result of the first secondary oscillation stroke. Line  312  shows the relative travel of the center point as a result of the second secondary oscillation stroke. As is apparent from  FIG. 18 , with this profile, not only are there successive changes in reversal positions and starting/end point positions of the oscillations, but also, a plurality of oscillations form successive cycles of oscillations, with each successive cycle having a maximum  300   a ,  300   b ,  300   c ,  300   d ,  300   e . As can be seen in  FIG. 18 , for each maximum, immediately preceding and succeeding reversal positions are lower than the maximum, thereby demarcating the maximum of a given cycle. As also shown in  FIG. 18 , the maximum reversal positions for each cycle are also offset with respect to each other, with the maximum reversal position  300   a  offset from the maximum reversal position  300   b  of an adjacent cycle of plural oscillations. The maximum  300   b  is, in turn, offset from the maximum reversal position  300   c  of the next cycle of plural oscillations, with successive cycles having respective maximum reversal positions  300   d ,  300   e  which are offset from the maximum reversal position of an adjacent cycle. Thus, the arrangement of  FIG. 18  provides a further modification in that, in addition to having strokes of an oscillation and adjacent oscillations being offset (as in  FIG. 17 ), a plurality of oscillations form a cycle, with one cycle of oscillations differing from an adjacent cycle of oscillations as is apparent from their maximum reversal positions being offset from one another. 
     In still another aspect, the invention features a method for varying an electric field at a surface of a workpiece. The method includes disposing a workpiece holder within a housing capable of containing a fluid and positioning a plate within the housing spaced from the workpiece holder. The workpiece holder retains workpiece, and the plate defines a plurality of holes having a distribution of hole sizes. The method also includes passing the electric field through uric plate to vary a property of the electric field incident on the surface of the workpiece. 
     In various embodiments, the method can include minimizing electric field imaging and/or fluid flow imaging of the member on the surface of the workpiece via a non-uniform oscillatory motion. In one embodiment, the method includes removing gas bubbles entrapped in the fluid from the surface of the workpiece. In various embodiments, the method an include depositing or dissoluting a metal or a plastic on a surface of the workpiece. In one embodiment, the method includes forming a non-periodic fluid boundary layer at the surface of the workpiece via the non-uniform oscillatory motion of the member. In one embodiment, the method includes decreasing a fluid boundary layer thickness at the surface of the workpiece via the non-uniform oscillatory motion of the member. 
     In another aspect, the invention provides an apparatus for fluid processing a workpiece. The apparatus includes a housing capable of containing a fluid, a workpiece holder disposed within the housing and adapted to retain the workpiece, and a member defining a plurality of spaced openings. The member can be disposed within the housing adjacent the workpiece holder and can be adapted to move substantially parallel to a surface of the workpiece so that the plurality of spaced openings can agitate the fluid. In one embodiment, a non-uniform oscillatory motion of the plurality of spaced openings agitates the fluid. The non-uniform oscillatory motion, can include a reversal position that changes after each stoke of the non-uniform oscillatory motion. In one embodiment, the non-uniform oscillatory motion includes a primary oscillation stroke and at least one secondary oscillation stroke. The length of the primary oscillation stroke can be substantially the same as the separation of spaced openings defined by the member, and a secondary oscillation stroke can change the reversal position of the non-uniform oscillatory motion of the member. In one embodiment, a linear motor assembly moves the member. 
     In one embodiment, the apparatus also includes plate disposed adjacent the member to shape the electric field incident on a surface of the workpiece. A body of the plate can define a plurality of holes, diameters of which varying on a surface of the plate. The plurality of holes can vary in a substantially radial pattern. The member can form a non-periodic fluid boundary layer at the surface of the workpiece. In one embodiment, the member reduces a fluid boundary layer thickness at the surface of the workpiece, e.g., to less than about at 10 μm. In one embodiment, the member is positioned less than about 2 mm from the surface of the workpiece. 
     In still another aspect, the invention features a method of fluid processing a workpiece. The method includes disposing a workpiece holder within a housing capable of containing a fluid and positioning a member within the housing adjacent the workpiece holder. The workpiece holder retains the workpiece, and the member defines a plurality of spaced openings. The method also includes agitating the fluid with the plurality of spaced openings by moving the member substantially parallel a surface of the workpiece. 
     In various embodiments, the method can include minimizing electric field imaging and/or fluid flow imaging of the member on the surface of the workpiece via a non-uniform oscillatory motion. In one embodiment, the method includes removing gas bubbles entrapped in the fluid from the surface of the workpiece. In various embodiments, the method can include depositing or dissoluting a metal or a plastic on a surface of the workpiece. 
     In another aspect, the invention features an apparatus for fluid processing a workpiece. The apparatus includes a mean for retaining the workpiece in a housing capable of containing a fluid, and a means for agitating the fluid with a non-uniform oscillatory motion substantially parallel, to a surface of the workpiece. 
     In yet another aspect, the invention provides an apparatus for varying an electric field at a surface of a workpiece. The apparatus includes a mean for retaining the workpiece in a housing capable of containing a fluid, and a means defining a plurality of holes having distribution of hole sizes for varying the electric field incident on the surface of the workpiece. 
     In still another aspect, the invention features an apparatus for fluid processing a workpiece. The apparatus includes a mean for retaining the workpiece in a housing capable of containing a fluid, and a means defining a plurality of spaced openings for agitating the fluid with a motion substantially parallel to a surface of the workpiece. 
     Other aspects and advantages of the invention will become apparent from the following drawings, detailed description, and claims, all of which illustrate principles of the invention, by way of example only. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages of the invention described above, together with further advantages, may be better understood by referring to the following description taken in conjunction with the accompanying drawings. In drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. 
         FIG. 1  depicts a block diagram of an exemplary production system for a workpiece. 
         FIG. 2  shows a perspective view of an illustrative embodiment of a workpiece holder according to the invention. 
         FIG. 3  shows a cross-section of an exemplary workpiece holder for retaining a plurality of workpieces according to the invention. 
         FIG. 4  shows a cross-section of exemplary workpiece holder according to the invention. 
         FIG. 5  depicts an exploded view of another exemplary workpiece holder according to the invention. 
         FIG. 6  shows another exploded view the workpiece holder of  FIG. 5 . 
         FIG. 7  snows a plan view of a portion of an exemplary member having a plurality of flex features according to the invention. 
         FIGS. 8A-8C  depict diagrammatic representations of the movement and action of the member and the flex feature(s) of an apparatus for retaining a workpiece according to the invention. 
         FIG. 9  depicts a perspective view of another exemplary workpiece holder including a hole bored through for processing a plurality of surfaces of a workpiece according to the invention. 
         FIG. 10  shows an exploded view of an exemplary apparatus for processing a workpiece according to the invention. 
         FIG. 11  depicts a sectional view of another exemplary embodiment of an apparatus for processing a workpiece according to the invention. 
         FIG. 12  depicts a perspective view of an exemplary embodiment of a member for agitating a fluid during fluid processing of a workpiece according to the invention. 
         FIG. 13  shows a section view of another exemplary embodiment of a member for agitating a fluid during fluid processing of a workplace according to the invention. 
         FIG. 14  shows a section view of another exemplary embodiment of a member for agitating a fluid during fluid processing of a workpiece according to the invention. 
         FIG. 15  depicts a diagrammatic representation of the position of a portion of a member for agitating a fluid adjacent a workpiece surface during a oscillatory motion according to the invention. 
         FIG. 16  shows a diagrammatic representation of oscillatory motion of a portion of a member adjacent a workpiece surface for agitating a fluid according to the invention. 
         FIG. 17  shows a graphical view of an exemplary non-uniform oscillation profile for agitating a fluid during fluid processing of a workpiece according to the invention. 
         FIG. 18  depicts a graphical view of another exemplary non-uniform oscillation profile for agitating a fluid during fluid processing of a workpiece according to the invention. 
         FIG. 19  shows a graphical view of boundary layer thickness versus fluid agitation speed according to the invention. 
         FIG. 20  depicts a plan view of an exemplary embodiment of a plate for varying an electric field during processing of a workpiece according to the invention. 
         FIG. 21A  shows a plan view of an exemplary loading station for workpieces according to the invention. 
         FIG. 21B  shows a side view of the loading station depicted in  FIG. 21A . 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates an exemplary production system  10  for a workpiece. The production system  10  can utilize various features of the invention. The production system  10  can include a loading station  14  for delivering a workpiece to a workpiece holder  18 . The production system  10  can also include one or more modules  22 , e.g., process modules, for processing a workplace. The loading station  14  and the one or more modules  22  can be mounted in a single framework, or in adjacent frameworks. The framework can include a transport system  26  for moving a workpiece holder  18  from the loading station  14  to a first module and between modules. An exemplary production system is a Stratus System available from NEXX Systems, Inc. in Billerica, Mass. 
     The workpiece (examples of which are shown in subsequent figures) can be planar, substantially planar, and/or thin or ultra-thin. In various embodiments, the workpiece has a circular shape or a substantially circular shape. In other embodiments, the workpiece is non-circular. For example, the workpiece can be rectangular, square, oval, or triangular, or have another suitable geometric configuration. In various embodiments, the workpiece can be, for example, a semiconductor wafer, silicon workpiece, interconnection substrate, printed circuit board, or other workpiece suitable for processing. The loading station  14  can be an automated loading station, such as an automated wafer handling front end available from Newport Automation in Irvine, Calif. or Brooks Automation in Chelmsford, Mass. 
     The workpiece holder  18 , according to the invention, can be used to retain a single workpiece, or a plurality of workpieces. The workpiece holder  18  can utilize a back-to-back configuration for two or more workpieces. Furthermore, the workpiece holder  18  can have a hole bored through its center for processing a plurality of surfaces of a single workpiece. These embodiments are described in more detail below. 
     Each of the one or more modules  22 , according to the invention, can be used for cleaning, rinsing, drying, pretreating, plating, buffering/holding, etching, electrodepositing, electroplating, electroetching, electrodissolution, electroless depositing, electroless dissolution, photoresist depositing, photoresist stripping, chemical etch processing, seed layer etching, and similar processes requiring fluid flow and/or electric field control and use. In various embodiments, the workpiece is retained by the workpiece holder  18  while processing is performed. Each of the one or more modules  22  and/or the workpiece holder  18  can be used to apply a variety of films to a surface of a workpiece, including, but not limited to, metal, plastic, and polymer films. Suitable metals include, but are not limited to, copper, gold, lead, tin, nickel, and iron. In addition, alloys, compounds, and solders of these metals (e.g., lead/tin and nickel/iron) can be applied to a workpiece surface. 
     In various embodiments, the film deposited can have a thickness between about 1 μm and about 150 μm. Using the features of the invention, the film can be high purity, and the thickness can be uniform across the surface of the workpiece. The film can have uniform electrical properties on (i) a flat, continuous uniform surface, (ii) on a flat continuous surface micro-scale topography, and/or (iii) on a flat surface with topography and/or photo-resist patterning. 
     In various embodiments, the production system  10  can include between one and thirty modules, although additional modules can be used depending on the application. Various novel features of the one or more modules  22  are described in more detail below. Each of the one or more modules  22  can include a robust and modular construction so that it can be removed from the production system  10 . As such, the production system  10  can be customizable for specific applications. For example, a module and a workpiece holder can be configurable for processing different sized workpieces, e.g., 150, 200, 250 or 300 mm wafers, with minimal lost production time during customization. 
     In addition, the layout of a processing system, e.g., the position or sequence of one or more process modules, can be optimized for a specific fluid process or for a series of processes, which can lead to increased throughput. For example, a vertical line architecture, e.g., as utilized by the Stratus system, can be combined with a dual wafer processing system. Deposition modules can be about 20 cm wide, and the number of modules can be adjusted to match the rate of the loading station. An exemplary rate is about 40 workpieces per hour. 
     Furthermore, the layout of a processing system can orient a workpiece in a vertical configuration. For a process or series of processes having a long deposition time, a vertical configuration can enable a significant number of workpieces to be processed simultaneously. For example, for a process time longer than about 10 minutes, over 20 workpieces can be processed simultaneously. In addition, in a process that generates substantial volumes of gas or air at the workpiece surface, electrophoretic deposition of photoresist, a vertical configuration can facilitate the removal of air or gas bubbles from the surface of a workpiece. 
     The production system  10  itself can be manual or automated. The production system  10  can include a computer that controls the operation of the loading station  14  and/or the transport system  26 , as well the one or more modules  22 . In one exemplary embodiment of an automated system, a freshly loaded workpiece is transported from the loading station  14  to the most distant module, and then subsequent processing returns the finished workpiece to the loading station  14 . 
       FIG. 2  shows an illustrative embodiment of workpiece holder  13  for retaining a workpiece  30 . In this illustrative embodiment, the workpiece holder  18  includes a handle  34  that can be used to lift and/or transport the workpiece holder  18 . The handle can be engageable with the transport mechanism  26  shown in  FIG. 1 . The workpiece holder  16  also includes a body  38  and a ring  42  for contacting the workpiece  30 . In various embodiments, the body  38  of the workpiece holder  18  is formed from a plastic, such as high density polyethylene (HDPE) or polyvinylidene fluoride (PVDF). The body  38  can also include a guide strip (shown in  FIGS. 5 and 6 ) formed in at least one edge  44 . The guide strip(s) can be used to align the workpiece holder  13  in one of the modules  22 . 
     The ring  42  can press, hold, and/or retain the workpiece  30  against, the body  38  of the workpiece holder. Contact between the workpiece  30  and the ring  42  occurs at the outer perimeter of the workpiece  30 , e.g., by contacting less than 2 mm of the outer perimeter of the workpiece  30 . In various embodiments, the ring  42  includes a flexible member encased in an elastomer. Portion(s) of the elastomer can be used to contact the workpiece  30 , and, in some embodiments, can create a seal with the workpiece  30 . 
     In various embodiments, the ring  42  can have a circular shape, a substantially circular shape, or be non-circular (e.g., rectangular, square, oval, or triangular, or have another suitable geometric configuration). In one embodiment, the ring  42  has a low profile relative to the workpiece  30 . For example, in one detailed embodiment, the ring  42  extends less than about 1 mm beyond the plane of the exposed surface of the workpiece  30 . In various embodiments, the ring  42  can be a contact ring or a sealing ring. In one embodiment, the ring  42  is the sealing ring assembly described in U.S. Pat. No. 6,540,899 to Keigler, the entire disclosure of which is herein incorporated by reference. 
       FIG. 3  depicts a cross-section of an illustrative embodiment of a workpiece holder  18  that can be used to retain a plurality of workpieces  30 . The body  38  of the workpiece holder  18 ′ includes a first surface  43  in a first plane and a second surface  45  in a second plane (e.g., a front surface and a back surface). Each surface has associated with it a ring  42  for retaining a respective workpiece  30 , e.g., for retaining the respective workpiece  30  against the respective surface  43  or  45  of the workpiece holder  18 ′. For example, a first ring can retain a first workpiece on the first surface of the workpiece holder in the first plane, and a second ring can retain a second workpiece on the second surface of the workpiece holder in a second plane. 
     According to the embodiment illustrated in  FIG. 3 , the first and second planes are parallel to each other and spaced apart. In various embodiments, the first and second planes form an angle. In one embodiment, the first and second planes are orthogonal. In other embodiments, the first and second planes form either an acute angle or an obtuse angle. It is understood that the invention is not limited to a workpiece holder with only two planes. Embodiments using a single plane or more than two planes can be used. Two planes axe used here to illustrate, an exemplary embodiment of an apparatus retaining a plurality of workpieces. 
     In one embodiment, the workpieces are held in a back-to-back configuration, and, in a detailed embodiment, the workpieces are centered on each other in the back-to-back configuration. In some embodiments, the workpieces are held on distinct, surfaces of the workpiece holder and are offset from one another. In another embodiment, a plurality of workpieces can be held on a single surface of a workpiece holder, e.g., in a side-by-side configuration. In some embodiments, a plurality of workpieces can be held on one surface of a workpiece holder, while at least one additional workpiece is held on a second surface of a workpiece holder. 
       FIG. 4  illustrates a cross-section of another embodiment of a workpiece holder  18 , which an exemplary system for retaining the workpiece  30  against the workpiece holder  18 . A ring  42  holds the workpiece  30  against a body  38 ′ of the workpiece holder  18 ″. The workpiece  30  contacts the body  38  at a contact point  46 . The body  38  can define a recess  50  so that the workpiece  30  only contacts a portion of the body  38 ′. 
     According to the illustrated embodiment, the body of the workpiece holder  18 ″ defines a groove  54  for holding at least a member  58 , a backing member  62 , and a bladder  66 . The member  58  is flexible, and can also be referred to as a flexure plate. The member  58  can have a circular shape, a substantially circular shape, or be non-circular (e.g., rectangular, square, oval, or triangular, or have another suitable geometric configuration). In some embodiments, the member  58  can be a ring or a plate, and in one detailed embodiment, can have a substantially planar ring-shape. In various embodiments, the member  58  can be formed from a spring-like material, such as stainless steel or titanium. The member  58  can include at least one retaining feature (e.g., as shown in  FIGS. 5 and 6 ) that can engage at least one engagement feature of the ring, for example, engagement feature  70  of the ring  42 . In various embodiments, the ring  42  and the member  58  are removably attached to the workpiece holder  18 ″. 
     The backing member  62  can be a plate or a push plate, and can include at least one push pin  74 . In various embodiments, the backing member  62  can have a circular shape, a substantially circular shape, or be non-circular. In various embodiments, the backing member  62  can be a ring or a plate. The backing member  62  can be formed from a metal, a plastic, or a polymer material. The bladder  66 , which can be a pneumatic bladder, defines a cavity  78  that can be filled with a fluid, such as air, to inflate the bladder  66 . When inflated, the bladder  66  pushes against the backing member  62  causing the at least one push in  74  to contact the member  58 , which causes the member to flex. The bladder  66  can have a circular shape, a substantially circular shape, or be non-circular, and, in various embodiments, can be a ring or a plate. In various embodiments, the bladder  66  can be formed from a fluoroelastomer, urethane, or mylar material. 
       FIGS. 5 and 6  show exploded views of another exemplary workpiece holder  18 ′″ for retaining the workpiece  30 .  FIG. 5  shows the view from a first perspective, and  FIG. 6  shows the view from a second perspective. This embodiment of the workpiece holder  18 ″ includes the ring  42 ′, the groove  54 , the backing member  62 , and the bladder  66 . The workplace holder  18  can also include a handle  34  and a member  58 ′. 
     The workpiece holder  18 ′″ shown in  FIGS. 5 and 6  also includes a body  38 ″, which can include a guide strip  82 . In one embodiment, the recess  50  defined in the body  38 ″ includes multiple contact points  46  for providing support to the workpiece  30 . In the illustrated embodiment, the body  38 ″ includes at least one port  86  for providing a fluid to the bladder  66  and/or vacuum to the underside of the ring  42 ′ via ducts (not shown) in the body  38 ″. In various embodiments, the body  38 ″ can also include at least one electrical contact  90  to communicate electrical current to the workpiece  30 . The backing member  62  can be connected to a stud  92  that is engageable with the body  38 ″. The stud  92  provides a force to contact the backing member  62  to the member  58 ′. 
     The ring  42 ′ illustrated in  FIG. 6  includes at least one engagement feature  70 , which, in one embodiment, is formed as one or more studs. A sealing groove  94  can circumscribe the outer perimeter of the ring  42 ′. The sealing groove  94 , which can be an elastomer region of the ring  42 ′, can mate with a sealing boss  98  that can circumscribe a perimeter of the workpiece holder  18 ′″. In one embodiment, this mating forms a barrier to fluid entry, e.g., a fluid-tight seal, between the workpiece holder  18 ′″ and the ring  42 ′. 
     In various embodiments, the ring  42 ′ also includes an inner sealing surface  102  that can form a barrier to fluid entry with the workpiece  30 . The inner sealing surface  102  can form an electrical connection with the workpiece  30  as well. For example, the inner sealing surface  102  can include flexure fingers that contact the workpiece  30 . The flexure fingers can include exposed terminal tips for making electrical contact. The electrical current path can carrying up to 75 amps of electrical current to the workpiece surface and can allow for independent electrical current control to a plurality of workpieces. 
     In various embodiments, the inner sealing surface  102  can include an elastomer region that is deflected under sufficient force to form a barrier to fluid entry. 
     In some embodiments, the member  58  defines at least one retaining feature  110  and at least one flex feature  114 . The member  58  can include at least one tab section  118 . The features of the member  58  can be cut, e.g., laser cut, into the member  58 ′. The at least one retaining feature  110  can be engageable with the at least one engagement feature  70  of the ring  42 ′. In various embodiments, the at least one retaining feature  110  can be a keyhole slot or a capture slot out into the member  58 ′. In one embodiment, the at least one flex feature  114  has a ram&#39;s head shape. 
     In one embodiment, the member  58 ′ defines a plurality of flex features  114 . In combination, the plurality of the flex features  114  can provide an effective long path around the main body  122  of the member  58 ′ to allow for substantial flexing of the member  58 ′. In one embodiment, the plurality of flex features  114  can provide a force at least substantially uniformly around the perimeter of an object, e.g., a workpiece  30 , when the member is flexed. The force can be provided substantially normal to the plane of the member  58 ′. When the force is applied, the ring  42 ′ can retain the object. The flex feature(s)  114 , in this embodiment or in other embodiments, can be formed about a perimeter of the member  58 ′, e.g., an inner perimeter, an outer perimeter, or on both the inner and outer perimeters. 
     In some embodiments, the groove  54 , e.g., a ring shaped cavity defined in the body  38 ″, can include at least one tooth feature  126  that can engage at least one tab section  118  of the member  58 ′. When a plurality of tab sections  118  are flexed away from the main body  122 , a force arises between the tab sections  118  perpendicular to the plane of the workpiece  30 . 
     Referring to  FIGS. 5 and 6 , the ring  42 ′ and the member  58 ′ can be removably attached to the workpiece holder  18 ′″. In one embodiment, one or more engagement features  70  of the ring  42 ′ can be engaged by (e.g., inserted or attached) one or more retaining features  110  of the member  58 ′. In an embodiment using keyhole slots, for example, the ring  42 ′ can be rotated by several degrees until the engagement feature(s)  70  stop against narrower end of the retaining feature(s)  110 . This causes the shoulder of the engagement feature(s)  70  to lie behind the member  58 ′. The bladder  66  can then be partially or entirely deflated. Flexure force formed by the flex features  114  causes the member  58 ′ to deflect and pull against the one or more engagement features  70 . In this embodiment, this pulls the ring  42 ′ toward the workpiece holder  18 ′″. 
     In one embodiment, flexing a member provides a force to at least one engagement feature to cause a ring to form a barrier to fluid entry with a workpiece. For example, the force can cause the member  58 ′ to pull the at least one engagement feature  70  of the ring  42 ′ to cause it to push against the workpiece  30  to form the barrier to fluid entry. The at least one flex feature  114  can be adapted to provide the force substantially normal to the plane of the member  58 ′ to form the barrier. The flex feature  114  can be positioned about a perimeter of the member  58 ′ to provide the force at least substantially uniformly from the perimeter (e.g., an inner perimeter, an outer perimeter, or as shown in  FIGS. 5 and 6 , both the inner and outer perimeters.) The force deforming the member  58 ′ can be about one kilogram per linear centimeter of the ring&#39;s  42 ′ perimeter. 
     To remove a first workpiece from the workpiece holder or to exchange a first and second workpiece, the force between the member  58 ′ and the ring  42 ′ can be removed by inflating the bladder  66  so that the backing member  62  contacts the member  58 ′ (with or without push pins  74 ) to deform it. The force engaging the engagement feature(s)  70  is relaxed so that they can be disengaged from the retaining feature(s)  110 . In one embodiment, the force engaging the engagement feature(s)  70  is relaxed so that the ring  42 ′ can be rotated and moved away from the workpiece holder  18 ′″. The first workpiece can be removed from the ring  42 ′, and if desired, a fresh workpiece can be disposed on the ring  42 ′. 
     In one embodiment, the fluid seal can hold the workpiece with sufficient force to prohibit fluid intrusion even when all power to the processing system is lost due to an unforeseen event. In one embodiment, the barrier to fluid entry can tested after a workpiece loading procedure and/or prior to processing a workpiece to ensure a workpiece has been properly loaded. For example, a small vacuum, e.g., about minus 0.05 atm, is applied to the cavity of the workpiece holder  18 ′″. The vacuum can be applied, for example, to the recess  50 . The path to the vacuum can then be closed off, and the leak-up rate of the vacuum can be measured. If the vacuum in the workpiece holder  18 ′″ does not change by more than a prescribed amount over a defined time period, then the integrity of the barrier is considered to be verified (e.g., about 10 percent in less than about 5 seconds). If the vacuum changes at a faster rate, the ring  42 ′ may not be mounted properly, and the workpiece can be unloaded and reloaded. 
       FIG. 7  shows a detailed, view of a portion  128  of the member  58 ′, including retaining features  110 , flex features  114 , and tab sections  118 . As illustrated, the member  58 ′ defines lines  130  and  134  extending about the inner and outer perimeters of the member  58 ′, respectively. The lines  130  and  134  are cut at least substantially through the main body  122 . In one detailed embodiment, the lines  130  and  134  are cut through the main body  122 . The lines do not extend continuously about the perimeters. Instead, the lines  130  and  134  are series of distinct lines. For example, line  130   a  extends from a first retaining features  114   a  to an adjacent flex features  114   b . The line  130   a  terminates in the two tear-drop shaped regions  138   a  and  138   b  defined in the flex features  114   a  and  114   b , respectively. According to the illustrated embodiment, the flex feature  114 ,  114   a  or  114   b  also includes an Ω-shaped line  142 . In one embodiment, two proximate tear-drop shaped regions and an Ω-shaped line combine to form an individual flex feature. The flex feature can have a ram&#39;s head shape. 
     In one embodiment, using a series of distinct lines can provide a substantially long path around a perimeter of the member along which the member can be flexed. Furthermore, using a series of distinct lines can promote an at least substantially uniform force from the perimeter. 
     In various embodiments, the tab sections  118  include a notch  146 . In one embodiment, the notch  146  interfaces with a corresponding catch in a groove  54  of the workpiece holder. The notch  146  can prevent the member  58  from rotating. The member  58 ′ can include outer tab sections  148 , which can be used to retain the member  58 ′ in the workpiece holder. 
     The movement of the member  58  or  58 ′ and the action of the flex feature(s)  114  can be shown diagrammatically. For illustrative purposes and without being bound to theory,  FIGS. 8A-8C  show diagrammatic representations. 
       FIG. 8A  shows the member  58  or in a relaxed state. Plate  150  and springs  154  represent the member  58  or  58 ′. The flex feature(s)  114  can act like springs  154  to apply force. Anchor points  138  represent restraining features of a workpiece holder. For example, the anchor points  138  can be the tooth feature(s)  126  formed in the groove  54  of the workpiece holder. The anchor points  138  can restrain the tabs sections  118  of the member  53  or  58 ′. 
       FIG. 8B  shows a portion of the ring  42  or  42 ′, including the engagement feature  70  (shown as a stud in  FIGS. 8B and 8C ). A force  162  is applied to the plate  150  (i.e., the member  58  or  58 ′) to flex the member  58  or  58 ′ into an overextended state. When overextended, engagement between the ring  42  or  42  and the member  58  or  58 ′ can be made (e.g., in one embodiment, the retaining feature captures the engagement feature). In a detailed embodiment, engagement occurs between the engagement feature  70  and the retaining feature  110 . In one embodiment, the force  162  is applied by the backing member  62 . The springs  154  the flex features  114 ) exert a force  166  in substantially the opposite direction as the force  162 . 
       FIG. 8C  depicts the apparatus in a state where the member  58  or  58 ′ is applying the force  166  to the engagement feature  70  via its retaining feature  110 . The springs  154  exert the force  166  substantially normal to the plane of the member  58  or  58 ′. In one embodiment, the force  166  causes the member  58  or  58 ′ to pull the engagement feature  70 , which causes the ring  42  or  42 ′ to contact the workpiece  30 . This contact can form a barrier to fluid entry between the workpiece  30  and the ring  42  or  42 ′. 
       FIG. 9  depicts another exemplary embodiment of a workpiece holder  170 . This embodiment can be used to process a plurality of surfaces of the workpiece  30 . The workpiece holder  170  includes a ring  42  for retaining the workplace. The body  174  of the workpiece holder  170  defines a hole  178  bored through from a first surface  182  to a second surface  186 . The diameter of the hole  178  is smaller than the diameter of the ring  42 . In various embodiments, the workpiece holder  18 ′″ includes the features described above including, but not limited to, the member  58  or  58 ′, the backing member  62 , and the bladder  66 . The underside of the workpiece  30  and the edge of the hole  178  can form a seal to isolate these components from the fluid used in the fluid processing. 
       FIG. 10  shows an exemplary apparatus for processing (e.g., fluid processing) a workpiece. The apparatus can include a module  22 , which itself can include a housing  200 . In one embodiment, the module  22  contains a fluid, e.g., the housing  200  defines a cavity in which the fluid can be disposed. As illustrated in  FIG. 10 , the apparatus also includes an embodiment of the workpiece holder  18 , a member  204 , a plate  208 , and an anode  21  in some embodiments, one or more of these elements are not used or are not present. Variations are described in more detail below. In various embodiments, the member  204 , the plate  208  and/or the anode  212  are disposed within the module  20  and/or the housing  200 . Because of the modular design, these elements can be removably or fixably disposed within the housing  200 . 
     In  FIG. 10 , the workpiece holder  18  is shown removed from the housing  200 . The workpiece holder  18  need not be integrated with the module  22  or the housing  200 . In one detailed embodiment, the workpiece holder  18  is removable from the housing  200 . The workpiece holder  18  can be transportable between two or more modules  22 . The housing  200  can include, grooves defined in the inner surface of two opposing sides. The edges  44  of the workpiece holder  18  or the guide strips  82  of the workpiece holder  18 ″ can be inserted into the grooves. 
     An exemplary housing  200  can be less than about 180 mm in length for electrodeposition or electroetch applications. For applications that do not require a plate  208  or an anode  212 , the length can be about 75 mm. The width of the housing  200  can be between about 300 mm and about 500 mm. In an exemplary embodiment for a 200 mm workpiece, the module dimensions can be about 180 mm by 400 mm, although the dimensions can vary depending on the application and/or workpiece size. 
     In various embodiments, the member  204  is a paddle assembly or a fluid agitation paddle. In one detailed embodiment, the member  204  is a SHEAR PLATE agitation paddle. The member  204  can be moved substantially parallel to a surface of a workpiece being retained by the workpiece holder  18 . The member  204  can be moved with a non-uniform oscillatory motion to agitate the fluid in various embodiments, the oscillation frequency of the member  204  can be between about 0 Hz and about 20 Hz, although the frequency can be higher depending on the application. In one embodiment, the oscillation frequency of the member  204  is between about 4 Hz and about 10 Hz. In one detailed embodiment, the oscillation frequency is about 6 Hz. 
     In some embodiments, the member  204  is moved by one or more motors  216 . The member  204  can be connected to the motor(s)  216  using connection rods  220 . In one detailed embodiment, the motor(s)  216  are linear drive motors or a linear motor assembly. Suitable linear motors include linear drive motors available from the LinMot Corporation in Delavan, Wis. In various embodiments, the motors  216  can be fixably or removably attached to the housing  200 . The motors  216  can be positioned on the center plane of the housing  200 . In one detailed embodiment, the weight of the member  204  and the inertial forces incurred during reciprocating motion of the member  204  is supported by the linear motors via the magnetic field forces between the motor slider and the motor windings rather than by mechanical bearings. The one or more motors  216  can be computer controlled. 
     In various embodiments, the plate  208  can be a shield plate or shield assembly. The plate  208  can be used to shape the electric field incident on a surface of a workpiece being retained by the member  204 . The plate  208 ′ can be formed from a non-conducting materials. Suitable materials include, but are not limited to, HDPE and PVDF. In various embodiments, the plate  208  can have a circular shape, a substantially circular shape, or be non-circular (e.g., rectangular, square, oval, or triangular, or have another suitable geometric configuration). A feature of the plate  208  is that it can be removed and replaced with little effort. This allows a single module to be configurable for processing different sized workpieces with minimal lost production time. 
     In one embodiment, the anode  212  forms the outer wall of the housing  200 . In one embodiment, the anode  212  can be a component of an anode assembly, which forms the outer wall of the housing  200 . In various embodiments, the housing  200  has an outer wall and either the anode  212  or the anode assembly are removably attached the wall or spaced from the wall. 
     In various embodiments, the anode  212  can be a copper disk. In one embodiment, the exposed surface area of the anode  212  is about 300 cm 2 . In one embodiment, the anode  212  is consumed during electrodeposition or another fluid process such as copper or solder deposition. One feature of the anode  212  is that it can be removed and replaced with little effort, minimizing lost production time. 
     In embodiments using an anode  212 , the workpiece surface serves as the cathode. It is noted that in some embodiments, it is preferred that the polarity of the system is reversed. That is, the workpiece surface is controlled to be anodic relative to a cathode placed in the module  22 . In such an embodiment, the anode  212  would be replaced by a cathode. 
       FIG. 11  shows cross-section of another exemplary embodiment of an apparatus for processing a workpiece. This embodiment can be used, for example, to process two workpieces simultaneously. A housing  200 ′ includes a side wall  224  and end walls  226 , and the relative positioning of members  202 , members  204   a  and  204   b , plates  203  and anodes  212  is shown. These elements or the distances are not shown to scale. Although the members  204   a  and  204   b  are shown as two separate structures, they can form a single assembly. 
     In an embodiment of the housing  200 ′ for fluid processing, fluid enters the housing  200 ′ through at least one port  228  in a bottom wall of the housing  200 ′. The port  223  can, in some embodiments, be located in a center portion, of the bottom wall  230  of the housing  200 ′. In one embodiment, the port  228  can be positioned in a bottom portion of a side wall  224 . The fluid flows up along the surfaces of the one or more workpieces. The fluid can flow between the workpiece holder  18  and the respective member  204 ,  204   a , or  204   b  or between the workpiece holder  18  and the plate  208 . In various embodiments, the fluid exits the housing  200  through the top of the housing, through a top portion of a side wall  224 , or through a top portion of an end wall  226 . Arrows show the general direction of flow. 
     In various embodiments, the flow rate can be between about 20 liters per minute and about 40 liters per minute. In one detailed embodiment, the flow rate is about 28 liters per minute. In one embodiments, the fluid is an electrolyte. The electrolyte can be circulated through the housing  200 ′ from a reservoir during the process. The turnover rate can be about 0.8 minutes at a flow rate of about 27.6 liters per minute. An exemplary solution can include copper sulfate, water, sulfuric acid, and hydrochloric acid. 
     The distance between a workpiece  30  and the respective member  204 ,  204   a , or  204   b  can be about 1 mm and about 5 mm, although the distance can vary depending on the application. In one embodiment, the member  204 ,  204   a , or  204   b  is positioned less than about 2 mm from the surface of the workpiece  30 . The shorter the distance between the elements, the better is the fluid mixing at the surface. In a detailed embodiment where the ring  42  extends about 1 mm from the outer surface of the workplace, the member  204 ,  204   a , or  204   b  can move in a plane about 1.5 mm from the surface of the workpiece  30 . The plate  208  can be positioned between about 2 and about 20 mm from the surface of the workpiece  30 , although the distance can vary depending on the application in one detailed embodiment, the plate  208  is positioned about 5 mm from the workpiece surface. 
       FIG. 12  depicts a perspective view of an exemplary embodiment of a member  204 ′ for agitating a fluid during fluid processing of a workpiece. The member  204 ′ includes a first plate  232  and a second plate  234 . Each plate  232  and  234  defines a series of spaced openings  236 . The shape of the spaced openings  236  can be, for example, oval or rectangular. Each plate  232  and  234  can also include a series of spaced blades  240  for agitating the fluid. The profile of the spaced blades  240  can be straight, angled, cup-shaped, or square. The center points of the series of spaced openings  236  or the series of spaced blades  240  can be positioned in a substantially equidistant periodic array. For example, the centers can be positioned with about 10 to about 30 mm between them. In one detailed embodiment, the centers are position about 20 mm apart. 
     In one embodiment, the series of spaced openings  236  agitates the fluid when the member  204 ′ is moved. In one embodiment, the series of spaced blades  240  agitates the fluid when the member  204 ′ is moved. In one embodiment, both the openings  236  and the blades  240  agitate the fluid. In one detailed embodiment, an edge surface of a spaced blade  240  agitates the fluid. 
     The plates  232  and  234  can be formed from a suitable metal, plastic, or polymer. Suitable metals include titanium, stainless steel, or aluminum. Suitable plastics include polyvinyl chloride (PVC), chlorinated PVC (CPVC), HDPE, and PVDF. In various embodiments, either of the plates  232  and  234  can be positioned between about 2 mm and about 10 mm from the surface of the workpiece, although smaller or larger distances can be used depending on the application. In a detailed embodiment, the thickness of at least one of the plates  232  and  234  is between about 3 mm and about 6 mm, although smaller or larger distances can be used depending on the application and/or the construction of the material. Relatively thin pieces can be used so that the plate  208  can be positioned as close to the workpiece as possible. This improves the uniformity of deposition. 
     The first and second plates  232  and  234  can be joined by one or more spacer features  244  and to form the member  204 ′. In  FIG. 12 , the first and second plates  232  and  234  are shown attached to the spacer features  244  by screws  248 , although other means may be used, including, but not limited to, rivets, glues, epoxies, adhesives, or outer suitable attachment means. The plates  232  and  234  and the spacer features  244  can define a cavity in which an embodiment of the workpiece holder  18  can be inserted during processing. The spacer features  244  can facilitate alignment of the member  204 ′ to the workpiece holder  18 . 
     In various embodiments, the member  204  or  204 ′ can be aligned to the workpiece holder  18  by the housing  200  in a manner that offers high precision without requiring mechanical support of the member  204  or  204 ′. As described above, the motors  216  can support the member  204  or  204 ′. Precise and consistent separation between the member  204  or  204 ′ and the workpiece holder  18  can be achieved using guide wheels (not shown) mounted on the housing  200 . The guide wheels can turn freely on an axle that is securely mounted on a side wall, of the housing  200 . Alignment wheels can also be mounted the housing  200  for positioning the workpiece holder  18 . The relationship between the guide wheels and the alignment wheels can be such that the member  204  or  204 ′ to the workpiece surface is consistent to within less than about ¼ mm. This promotes substantially uniform fluid boundary layer to occur at the workpiece surface when the member  204  or  204 ′ is moved substantially parallel to the workpiece surface. 
     The axles for guide wheels can serve as journal bearing shafts. The member  204  or  204 ′ can be moved with virtually zero frictional or bearing forces, which can significantly reduce repair and maintenance costs that are associated with systems that use load bearing frictional surfaces or bearings. 
       FIG. 13  shows a cross-section of another exemplary embodiment of a member  204 ″ for agitating a fluid during fluid processing of a workpiece. The spaced blades  240 ′ have a cup shape. In  FIG. 13 , the spaced bladed  240 ′ are shown adjacent the workpiece  30  being retained on the workpiece holder  18  using the ring  42 . In various embodiments, the series of spaced openings  236  and/or the series of spaced blades  240 ′ agitate the fluid when the member  204 ″ is moved. In one embodiment, an edge surface of a spaced blade  240 ′ agitates the fluid. In this embodiment, the edge surface can be a side surface, a pointed surface, or a rounded surface. 
       FIG. 14  shows a cross-section of another exemplary embodiment of a member  204 ′″. The spaced blades  240 ″ have an angled profile, and are shown adjacent the workpiece  30  being retained on the workpiece holder  18  using the ring  42 . In various embodiments, the series of spaced openings  236  and/or the series of spaced blades  240 ″ agitate the fluid when the member  204 ″ is moved. 
     As described above, the member  204 ,  204 ′,  204 ″ or  204 ′″ (referred to herein collectively as  204   x ) can be used to agitate the fluid. In some embodiments, the member  204   x  can be moved using a non-uniform oscillation profile. In one exemplary embodiment, the non-uniform oscillatory motion includes a reversal position that changes after each stoke of the non-uniform oscillatory motion. 
     For example, referring to  FIG. 15 , a blade  240 ,  240 ′, or  240 ″ or a center point of a spaced opening  236  (referred to herein collectively as a center point  252 ) adjacent a particular workpiece point  256  on a surface of the workpiece  30  need not return to the same workplace point  256  after one complete oscillation stroke. The center point  252  can travel along the surface of the workpiece  30  as the member  204   x  oscillates, and after one complete oscillation stroke, the center point  252 ′ can be at a nearby workpiece point  260 . 
     In one embodiment, the non-uniform oscillatory motion includes a primary oscillation stroke and at least one secondary oscillation stroke. The length of the primary oscillation stroke can be substantially the same as the separation of the spaced openings  236  defined by the member  204   x . In one detailed embodiment, the length of the primary oscillation stroke can be substantially the same as the separation of adjacent spaced openings  236 . 
     Referring to  FIG. 16 , an exemplary primary oscillation stroke  264  can change a reversal position of an oscillation stroke of the member  204   x . In one detailed embodiment, the primary oscillation stroke  264  changes a reversal position  268  of the center point  252  of the member  204   x . An exemplary first secondary oscillation stroke  272  can change a reversal position of an oscillatory motion of the member  204   x . In one detailed embodiment, the first secondary oscillation stroke  272  changes a reversal position  276  of the center point  252 . In various embodiments, this can also be understood as changing a reversal, position of the primary oscillation stroke  264 . An exemplary second secondary stroke  280  can change a reversal position of an oscillatory motion of the member  204   x . In one detailed embodiment, the second secondary stroke  230  changes a reversal position  284  of the center point  252 . In various embodiments, this can also be understood as changing a reversal position of the first secondary oscillation stroke  272 . 
     As illustrated, a center point  252  is used to show the relative motion of the member  204   x . Any point X along the surface of the member  204   x , though, can be used to show the change in reversal position of that point X as the member  204   x  moves. In some embodiments, the member can be formed from a plurality of pieces. Each piece includes one or more spaced openings or one or more spaced blades. In one embodiment, each piece can be connected to a separate motor so that its motion is independent of a proximate piece. In one embodiment, each piece can be connected to the same motor so that the pieces move in concert. In some embodiments, the plurality of pieces is positioned on the same side of a workpiece so that the motion of two or more pieces of the member  204   x  agitates the fluid. 
       FIG. 17  shows a graphical representation of an exemplary non-uniform oscillation profile  288  for agitating a fluid during fluid processing of a workplace. The exemplary workpiece  30  and center point  252  in  FIGS. 15 and 16  are referenced for illustrative purposes. The position of the center point  252  of the member  204   x  relative to the work-piece point  256  on the surface of the workpiece  30  is plotted versus time. In this embodiment of the member  204   x , the separation of the center points  252  is about 20 mm. The primary oscillation stroke is substantially the same as the separation between the center point  252  and an adjacent center point of the member  204   x . The secondary oscillation, stroke is about 40 mm. Line  292  shows the relative travel of the center point as a result of the primary oscillation stroke. Line  2965  shows the relative travel of the center point as a result of the secondary oscillation stroke. As may be realized from  FIG. 17 , the resultant non-uniform oscillation profile is formed by a series of oscillations with each consecutive oscillation in the series being asymmetric. 
     By using a combination of primary and secondary strokes, the reversal position of the oscillation pattern in front of the workpiece  30  can change sufficiently relative to the process time. This can preclude a non-uniform time averaged electric field or fluid flow field on the surface of the workpiece. This can minimize an electric field image or a fluid flow image of the member on the surface of the workpiece, which improves the uniformity of a deposition. 
       FIG. 18  shows a graphical representation of another exemplary non-uniform oscillation profile  300  for agitating a fluid during fluid processing of a workpiece. In this embodiment of the member  204   x , the separation of the center points  252  is about 20 mm. The primary oscillation stroke is substantially the same as the separation between the center point  252  and an adjacent center point of the member  204   x . The first secondary oscillation stroke is about 30 mm. The second secondary oscillation stroke is about 40 mm. The oscillatory motion can include additional secondary oscillation strokes. Line  304  shows the relative travel of the center point as a result of the primary oscillation stroke. Line  308  shows the relative travel, of the center point as a result of the first secondary oscillation stroke. Line  312  shows the relative travel of the center point as a result of the second secondary oscillation stroke. 
     The period of the first secondary oscillation stroke is about 2 seconds, and the period of the second secondary oscillation stroke is about 10 seconds. This can move the position at which the oscillation reversal occurs, which can spread the reversal point of each spaced blade or the center point of each spaced opening by about 0.1 mm. This can reduce or substantially eliminate any imaging of the reversal position onto the workpiece surface. 
     Oscillation of the member  204   x  can also form a non-periodic fluid boundary layer at the surface of the workpiece  30 . In one embodiment, the member  204   x  reduces fluid boundary layer thickness at the surface of the workpiece  30 . In one detailed embodiment, the fluid boundary layer thickness is reduced to less than about 10 μm. Furthermore, motion of the member can reduce or substantially eliminate entrapment of air or gas bubbles in the fluid from the surface of the workpiece  30 . In one detailed embodiment, fluid flow carries the air or gas bubbles near a growing film surface in a housing  200  for plating or depositing. 
       FIG. 19  illustrates a graphical representation of boundary layer thickness at a surface of a workpiece versus fluid agitation rate. The fluid agitation rate can be the oscillation rate of the member  204   x . As illustrated, the fluid boundary layer thickness is reduced from about 55 μm to less than about 10 μm as the rate is increased. The boundary layer can be derived from limiting current measurements, which can be determined by comparison to known behavior of a reference electrode, by linear sweep voltammetry, or by chronoamperometry. Fluid mixing is inversely proportional to the boundary layer thickness. Therefore, decreasing the boundary layer in a fluid process can improve fluid mixing at a workpiece surface. This can improve throughput and uniformity, and can also decrease materials consumption. 
       FIG. 20  depicts an exemplary embodiment of a plate  208 ′ for varying an electric field during processing of a workpiece  30 . Varying the electric field at the workpiece surface can promote uniform deposition of a film, although the electric potential drop through the workpiece surface varies from the workpiece perimeter to the workpiece center. In one embodiment, the plate  208 ′ is fabricated from a non-conducting material that can block the electric field as it passes from the plane of the anode  212  to the plane of surface of the workpiece  30 . The plate  208 ′ has a substantially circular shape. The plate  208 ′ can include fastening holes  314  for connecting the plate  208 ′ to the housing  200  or  200 ′, or to a support feature (not shown) that suspends the plate  208 ′ in the housing  200  or  200 ′. 
     In one embodiment, the plate  208  (shown in  FIGS. 10 and 11 ) or  208 ′ (shown in  FIG. 20 ) shapes the electric field incident on a surface of the workpiece  30 . A body  316  of the plate  208  or  208 ′ can define a plurality of holes  320 . The holes  320  can have a distribution of hole sizes, e.g., the diameter of the holes can vary on a surface of the plate. By varying the distribution of hole sizes, the average open area of a surface of the plate  208  or  208 ′ can be varied, and a property of the electric field passing through the plate  208  or  208 ′ to the surface of the workpiece  30  can be varied. The property of the electric field that is varied can be amplitude or potential. In various embodiments, the electric field proximate to the surface of the workpiece can be uniform. 
     In one embodiment, the distribution of hole sizes comprises a continuous gradient of hoe size. In one detailed embodiment, the holes vary in a substantially radial pattern. For example, as illustrated in  FIG. 20 , larger holes can be formed near the center of the plate  208 ′ while smaller holes are formed closer to the outer perimeter of the plate  208 ′. In various embodiments, the plate can have between about 500 and about 10,000 holes, although more or fewer holes can be used depending on the application and/or the workpiece size. In one embodiment, the plate can have between about 1,000 and about 5,000 holes. In one detailed embodiment, the plate  208  or  208 ′ can have about 3000 holes and be suitable for a 200 mm workpiece. In various embodiments, the diameter of the holes is between about 0.1 mm and about 20 mm, although larger and smaller diameter holes can be used depending on the application. In one embodiment, the largest diameter holes can be about 5 mm in diameter. The smallest diameter holes can have a diameter of about 1 mm. 
       FIGS. 21A and 21B  show an illustrative embodiment of a loading station  14 ′, which can be used to load one or more workpieces  30  on an embodiment of the workpiece holder  18 .  FIGS. 21A and 21B  include a holder  324  for the workpiece holder  13 , a base member  328  for moving a workpiece  30 , and an arm  332  connecting the holder  324  and the base member  328 .  FIG. 21B  shows workpieces  30  loaded onto the base member  328 . The arm  332  and the holder  324  can include a hinged connection  336  so that the arm  332  can move the base member  328  between a substantially horizontal position and a substantially vertical position, or to an intermediate position. The base member  328  and the arm  332  can be components of the same piece. 
     The holder  324  can retain the workpiece holder  18  while workpieces  30  are being loaded onto or removed from the workpiece holder  18 . In some embodiments, the holder  324  can retain the workpiece holder  18  while workpieces  30  are being loaded onto or removed from the base member  328 . The holder  324  can be a suitable metal, plastic, or polymer material. A second end effector (not shown) can be used to load a workpiece  30  onto the base  328 . The loading station  14 ′ can be coupled to a hydraulic mechanism and/or a computer to control the position of the arm  332 . 
     In various embodiments, the base member  328  can include an end effector  340  positioned in the central portion of the base member  328  and a chuck  344  positioned around the outer perimeter of the base member  323 . The end effector  340  can be a Bernoulli end effector, an electrostatic chuck, or a vacuum end effector. The end effector  340  can retain a workpiece  30  without contacting it. In some embodiments, the chuck  344  is a vacuum chuck or a suction chuck. The chuck  344  can retain the ring  42  on the base member  328 . In one embodiment, the end effector  340  can retain the workpiece  30  against the ring  42  while the workpiece  30  is loaded onto or removed from the workpiece holder  18 . In one embodiment, the end effector  340  can retain the workpiece  30  against the ring  42  without contacting the workpiece  30 . 
     In one embodiment, to load a workpiece  30  onto the workpiece holder  18 , the ring  42  is engaged by the chuck  344 . The workpiece  30  can be placed on the ring  42 . The end effector  340  can be activated to hold the workpiece  30  against the ring  42 . The arm  332  can be moved to a substantially vertical position ice workpiece holder  18  can engage the ring  42 . The end effector  340  can be disengaged from the workpiece  30 , and the chuck  344  can be disengaged from the ring  42 . The arm  332  can be moved from the plane of the workpiece holder  13  so that there is clearance. The workpiece holder  18  can be removed from the holder  324  and directed to a module for processing. The steps need not be completed in this order to load the workpiece  30 . 
     In one embodiment, to remove a workpiece  30  from the workpiece holder  18 , the arm  332  can be moved to a substantially vertical position. The end effector  340  can engage the workpiece  30 , and the chuck  344  can engage the ring  42 . The ring  42  is disengaged from the workpiece holder  18 . The arm  332  can be moved to a substantially horizontal position. The steps need not be completed in this order to remove the workpiece  30 . 
     The loading station  14 ′ can load a single workpiece  30  to a workpiece holder  18 , or can load a plurality of workpieces  30  to a workpiece holder  18 . In one embodiment, two workpieces are loaded onto the workpiece holder  18  substantially concurrently. In one embodiment, two workpieces are removed from the workpiece holder  18  substantially concurrently. In some embodiments, a first workpiece is loaded onto or removed from the workpiece holder  18  before a second workpiece is loaded or removed. 
     While the invention has been particularly shown and described with reference to specific illustrative embodiments, it should be understood that various changes in form and detail may be made without departing from the spirit and scope of the invention as defined by the appended claims. For example, although specific actions, movements, and processes may be described with reference to specific embodiments, these actions, movements, and processes may be performed by any embodiment employing like or similar features. Likewise, although the invention, in some embodiments, is described as a system employing individual features, some of the features can be utilized independent of the system.