Patent Document

CROSS REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority to U.S. Application No. 60/316,461, filed on Aug. 31, 2001. 
    
    
     TECHNICAL FIELD 
     The present invention is directed to reactors for processing microelectronic workpieces in the fabrication of microelectronic devices. More particularly, the present invention is directed to reactors for applying an electrophoretic emulsion (“EPE”), such as an electrophoretic photoresist (“EPR”), onto a microelectronic workpiece in an automated single wafer processor. 
     BACKGROUND 
     In the fabrication of microelectronic devices and micromechanical devices several layers of material are deposited and worked on a single substrate to produce a large number of individual devices. After forming the devices in and/or on the substrate, the substrate is cut into a plurality of pieces to separate the individual devices from each other. In the process of forming these devices on the substrate, layers of photoresist are deposited and worked (i.e., patterned, developed, etched, and so forth) to form the features of the devices in and/or on the substrate. 
     One photoresist deposition technology used in the fabrication of microelectronic devices is a spin-on resist processes in which the resist is deposited onto a spinning substrate. The resist spreads across the substrate under the influence of centrifugal force. For the creation of some devices, however, spin-on resist processes are problematic. For example, one problem of spin-on techniques is that excess photoresist may be deposited on certain portions of the substrate and/or an insufficient amount of photoresist may be deposited on other portions. Another problem of spin-on techniques is that the layer of photoresist may not conform to the topography of the features on a workpiece. This problem can be a significant concern if the resist is to cover large step heights or small features. As the devices become more complicated, the constraints of forming uniform, conformal layers of photoresist may exceed the capabilities of spin-on processes. Further, some processes require the application of thick layers of resist, but spin-on processes may not be able to deposit the resist to the required thickness. Therefore, spin-on techniques may not provide adequate results for depositing resist onto microelectronic devices in many situations. 
     A different photoresist deposition technique used in the manufacture of printed circuit boards is EPR deposition. The electrolytic deposition of EPR in the printed circuit board industry is normally carried out through a “rack-and-tank” type system in which the workpiece is hung vertically and both sides of the workpiece are submerged in an electrolytic bath containing the emulsion.  FIG. 1  schematically illustrates a conventional rack-and-tank type system  1  for electrolytically depositing EPR onto printed circuit boards. The rack-and-tank type system  1  includes a plurality of tanks  2   a – 2   e  that include various solutions and/or emulsions  3   a – 3   e . For example, the system  1  can include a preclean tank  2   a  having a preclean solution  3   a , a rinse tank  2   b  having a rinse solution  3   b , an electrolytic tank  2   c  having an EPR emulsion  3   c , a permeate tank  2   d  having a permeate solution  3   d , and another rinse tank  2   e  having a rinse solution  3   e . The electrolytic tank  2   c  includes electrodes  4   a  and  4   b . The system  1  also includes a rack  5  having a plurality of hangers  6  that suspend individual workpieces  7  in a vertical orientation. The hangers  6  also electrically contact conductive layers on the workpieces  7  to which the EPR is plated. In operation, the rack  5  moves the workpieces  7  through the tanks  2   a – 2   e  to preclean, rinse, deposit EPR, dip in a permeate solution, and then rinse. When the workpieces  7  are submerged in the EPR tank  2   c , a voltage differential is applied to the electrodes  4   a–b  and the workpiece  7  causing the resist material to coat the workpiece. 
     Electrolytically depositing EPR has several benefits that may be useful in applications for microelectronic workpieces. First, electrolytic EPR can deposit a uniformly thick layer of resist across a workpiece. Second, electrolytic EPR deposition can form layers that conform to highly topographical surfaces. Third, electrolytic EPR deposition can form thick layers of resist with good uniformity. 
     The conventional rack-and-tank type systems used for printed circuit boards, however, are not suitable for integration with other automated microfabrication tools because station-to-station contamination may be problematic. For example, rack-and-tank deposition systems are relatively messy because they fully submerge both sides of the workpiece in the EPR bath. This completely coats the workpiece with emulsion, and thus there is no clean area on the workpiece for robotic transfer units to transfer the workpieces among processing stations. Furthermore, rack-and-tank type systems are prone to forming or entraining bubbles in the EPR bath during deposition. In the case of the electrophoretic deposition of a photoresist, bubbles can migrate to the workpiece and result in defects in the resist layer called “pinholes.” The pinhole defects are generally 10 μm–50 μm in diameter. Areas of the workpiece having pinhole defects may not be patterned with small microelectronic structures and are thus potentially wasted areas of the workpiece. For example, even if defects occur in only 10% of the chip sites at each mask step during photolithography, less than 50% of the chips will be functional after a seven mask process is completed. Conventional rack-and-tank type EPR equipment mitigates pinholes by holding the workpiece vertically and vibrating the workpiece in the EPR bath. The vibration energy used for printed circuit boards, however, typically exceeds the force that can be safely applied to semiconductor workpieces (i.e., semiconductor wafers) and other types of delicate microelectronic workpieces. 
     Electrolytic EPR deposition equipment for printed circuit boards has been proposed for use in coating microelectronic workpieces in the production of microelectronic devices, such as semiconductor devices and micromachines. However, it has been generally rejected by the microfabrication industry. As the present inventors have recognized, the printed circuit board EPR deposition equipment is not suited to the close tolerance work, cleanliness, and throughput requirements typically expected in the microfabrication industry. For example, full submersion of the workpiece during EPR deposition renders conventional EPR deposition methods impractical for integration into automated, multi-stage processing tools for microelectronic device processing because the EPR will foul and contaminate the single-wafer type robotic handling equipment. Additionally, the equipment for EPR deposition is prone to the formation of bubbles during the deposition process, and the conventional system of vibrating the workpiece may break several workpieces. Other problems of using EPR deposition systems designed for processing printed circuit boards in applications for fabricating micro-devices on semiconductor wafers or other types of workpieces include: (a) contamination of other processing stations; (b) additional steps for removing edge beads from workpieces; and (c) insufficient electrical contact with the workpieces. 
     SUMMARY 
     The present invention provides reactor for use in a system that enables the use of electrophoretic resists and other electrophoretic emulsions in the microfabrication industry for the production of microelectronic devices. Several embodiments reactors and methods of the invention can be used as a replacement for, or supplement to, current photoresist deposition technology. For example, many embodiments enable the application of electrophoretic resists in automated equipment that meets the standards for cleanliness and throughput desired by the microelectronic fabrication industry. The reactors and methods for providing electrophoretic resist (“EPR”) layers on microelectronic workpieces for the microfabrication of microelectronic devices may also be employed to deposit other electrophoretic emulsions (“EPE”), such as those suitable for use as dielectrics or color filter materials for flat panel computer screens. 
     In one embodiment, a reactor for depositing electrophoretic material onto a workpiece comprises a head having a workpiece holder and a reactor base. The workpiece holder of the head includes a support member and a plurality of electrical contacts projecting inwardly from the support member for providing an electrical current to the workpiece. The workpiece holder is configured to hold the workpiece at least substantially horizontal in a processing position. The reactor base includes an overflow cup, a processing cup in the overflow cup, a gas control system in the processing cup, and an electrode in the processing cup. 
     In other embodiments, the reactor base can further comprise a reservoir below the overflow cup, a thermal element in the reservoir, and a drainage passage between the overflow cup and the reservoir through which an EPE fluid can flow downward. In still another embodiment, the reactor base can further comprise an ultrafilter configured to separate an EPE into a permeate solution and a concentrated EPE. In still another embodiment, the reactor base can include an in-situ ancillary processing assembly above the overflow cup. The in-situ processing assembly can include a nozzle to direct a flow of an ancillary processing fluid different than the EPE fluid radially inward and a collector to catch spent ancillary processing fluid above the weir. 
     In several embodiments, the reactors include an EPE deposition station having a gas control system configured to inhibit bubbles from residing on the workpiece. For example, the gas control systems or methods of controlling bubbles can comprise: (a) rotating the workpiece during deposition; (b) agitating the electrolytic bath during deposition; (c) vibrating the workpiece during deposition; (d) creating an impinging flow of emulsion directed substantially transversely and/or parallel to the workpiece; (e) trapping bubbles in the electrolytic bath before they reach the workpiece; (f) removing bubbles from the electrolytic bath before they reach the workpiece; (g) applying a voltage to the electrode or the workpiece according to a predetermined delay; (h) providing a plurality of counter electrodes adapted to be positioned within the processing chamber and further adapted to receive a voltage potential; (i) using mechanical agitation of the bath and/or components to remove bubbles from the workpiece; (j) separating the counter electrode from the workpiece using a membrane or other member through which electrical current can flow; (k) providing a low velocity flow to allow bubbles to rise to the surface of a storage reservoir; and/or avoiding turbulence in the fluid flow. By inhibiting gases from residing on the processing side of the workpiece, the workpiece can be held substantially horizontally in the EPE so that the backside or another region of the workpiece is isolated from the EPE. This allows the workpiece to be handled for transport to and processing in other stations without fouling the equipment with EPE. Also, inhibiting gases from residing on the processing side of the workpiece produces a good quality layer on the workpiece. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of rack-and-tank type EPR deposition system used to deposit resist onto printed circuit boards in accordance with the prior art. 
         FIG. 2  is a cross-sectional view of one embodiment of a processing reactor that may be used to implement an EPE deposition process. 
         FIG. 3  is a view of a gas control system including a bubble trap and weir configuration for use in the reactor shown in  FIG. 2 . 
         FIG. 4  is an exploded isometric view of the reactor depicted in  FIG. 2 . 
         FIG. 5  is an isometric cut-away view of an in-situ rinse assembly for use in the reactor depicted in  FIG. 2 . 
         FIG. 6  is a cut-away isometric view of another embodiment of a processing base for use in a reactor to perform an EPE deposition process. 
         FIG. 7  is a cut-away isometric view of still another embodiment of a processing base for use in a reactor to perform an EPE deposition process. 
         FIG. 8  is another on the embodiment of a reactor base related to the reactor base shown in  FIG. 7 . 
         FIG. 9  is a cross-section of a reactor illustrating a still further embodiment of a reactor base. 
         FIG. 10  is an isometric view of selected components of the embodiment shown in  FIG. 9 . 
         FIGS. 11 and 12  illustrate one embodiment of an electrical contact assembly that may be used in an embodiment of the reactor. 
         FIG. 13  illustrates one embodiment of a fluid flow control system that may be used in the processing tool of  FIG. 2 . 
         FIG. 14  is an isometric view of one embodiment of an automated microelectronic workpiece processing tool in accordance with the present invention. 
         FIGS. 15–17  are top plan schematic views illustrating additional embodiments of integrated tools in accordance with other embodiments of the invention. 
         FIG. 18  is a process flow diagram illustrating one sequence of procedures in which the controller may be programmed to execute an electrophoretic deposition process. 
         FIG. 19  is a flow diagram of another control sequence for electrophoretic deposition and photoresist processing in accordance with additional embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, the terms “microelectronic workpiece” or “workpiece” refer to substrates onto or in which microelectronic devices are formed, such as microelectronic circuits or components, thin-film recording heads, micromachines or micromechanical elements, data storage elements, and similar devices. Micromachines or micromechanical elements are included within this definition because the manufacturing processes that are used to make them are typically the same as or similar to the manufacturing processes used in the fabrication of integrated circuits. The substrates can be semiconductive pieces (e.g., doped silicon wafers), non-conductive pieces (e.g., various ceramic substrates), or conductive pieces. Typical workpieces are relatively thin and disk-shaped, although not necessarily circular, as ordinarily understood in the microfabrication industry. 
     Several embodiments of the apparatus and methods are described in the context of depositing an electrophoretic photoresist (EPR) onto a workpiece, but the present invention is by no means limited to deposition of EPR. As noted earlier, many of the following embodiments can be used to deposit suitable electrophoretic emulsions (EPEs) other than EPR emulsions. For example, other materials that can be contained in an emulsion and deposited by electrophoresis include phosphor materials for use in high resolution flat panel display devices and various selectively depositable dielectric materials. In EPE applications, the charged particles in suspension are typically “micelles” (i.e., stable organic particles suspended in the aqueous phase of the bath). 
     Deposition by electrophoresis in accordance with the following apparatus and methods has advantages over other methods of deposition. For example, electrophoresis is especially useful to deposit a material on three dimensional structures because it can cover even highly topographical surfaces with a conformal layer of material. Additionally, several embodiments of the following apparatus and methods can eliminate edge beading that results in spin-on or rack-and-tank deposition techniques. Furthermore, electrophoretic deposition techniques can accurately deposit much thicker layers of resist compared to spin-on techniques. Another benefit of several embodiments of the present invention is automated deposition of an electrophoretic material that enables EPR-based photolithography to be integrated with other automated semiconductor processes. Still another benefit of several embodiments of the apparatus and methods described below is that they mitigate problems caused by bubbles in the system. 
     EMBODIMENTS OF EPE DEPOSITION REACTORS  
     EPE deposition reactors electrochemically deposit EPRs or other EPEs onto microelectronic workpieces. As used herein, the term “electrochemically” includes (a) electrical processes that establish an electrical field in a bath using the workpiece as an anode or a cathode and (b) electroless processes that rely on the electrochemical interaction between the workpiece and the bath without inducing an electrical field in the bath. In general, the EPE deposition reactors are suitable for microfabrication techniques used in manufacturing semiconductor devices or other micro-devices that have small features (e.g., feature sizes less than 10 microns or even less than 1 micron). Several embodiments of reactors for use in processing tools are single-wafer units that hold a workpiece at least substantially horizontally so that the EPE bath contacts only one side of the workpiece. This allows the other side of the workpiece to remain “clean” so that single-wafer handling equipment is not fouled by the EPE. Several embodiments of reactors also hold the workpiece in a manner that prevents an edge bead from forming around the perimeter of the workpiece. As explained in more detail below, the reactors are also configured to control bubbles to mitigate pinholes, and the reactors can also optionally include in-situ rinse capabilities to rinse either the microelectronic workpieces or components of the reactor to mitigate cross contamination of fluids and consumption of resist micelles. 
       FIG. 2  illustrates one embodiment of a reactor assembly  100  that defines the deposition station  11  for use in a processing tool for depositing EPEs on workpieces. Generally stated, the reactor assembly  100  comprises a reactor head  105  and a reactor base  110 . The reactor head  105  includes a stator  70 , a rotor  120  carried by the stator  70 , and a workpiece holder  125  carried by the rotor  120 . The reactor base  110  includes a processing area or vessel suitable for EPR deposition or deposition of other EPEs. The general design of the reactor depicted in  FIG. 2  can also be used to implement other processing operations and, as such, can be modified for use at other processing stations within a processing tool. For example, the reactor assembly  100  can be modified to execute rinse/dry processes, etching processes, and electrochemical processes (e.g., electropolishing, anodization, electroless plating, electroplating, seed layer enhancement, etc.). For such other processes, the reactor base  110  may be modified to contain different chemistry and/or different chemical delivery mechanisms. 
     1. Reactor Bases 
     Reactors in accordance with several embodiments of the invention provide gas control systems to control bubbles in the EPE fluids in a manner that mitigates the formation of pinholes on the workpiece. As explained in more detail below, several embodiments of gas control systems can entrap existing bubbles before they reach the workpiece, sweep bubbles away from the workpiece, and/or prevent the formation of bubbles. In general, several different methods and devices can be used either individually or together to control bubbles in the reactor. 
     a. Embodiments of Reactor Base Configurations 
       FIG. 2  illustrates one embodiment of the reactor base  110  for depositing an EPE on the workpiece  16 . In this embodiment, the workpiece  16  is positioned with respect to the reactor base  110  so that the side of the workpiece which is to be processed faces downward in a generally horizontal plane. The particular reactor base  110  shown in  FIG. 2  can be functionally divided into four principal, vertically separate regions or subassemblies. A first region  135  provides an environmentally controlled reservoir of processing fluid. A second region  140  defines a fluid input/output region including channels and passageways through which processing fluids flow to and from the reactor base  110 . A third region  145  defines a deposition region in which the photoresist or other electrophoretic solution/emulsion is deposited onto the workpiece  16 . The third region  145  may include one or more components that reduce and/or eliminate bubbles that can cause pin-hole formations in the deposited layer. A fourth region  150  can be an in-situ secondary processing region in which the workpiece may be rinsed in-situ, the contact assembly  125  may be cleaned in-situ, or other pre- or post-deposition procedures can take place. 
     As illustrated, the first region  135  includes an emulsion tank  155  and a temperature control apparatus  160  disposed in the tank  155 . The temperature control apparatus  160  can be an element that heats and/or cools the EPE chemistry in the tank  155 . The EPE chemistry is contained and maintained at a desired temperature within the tank  155  for delivery to a processing area  215  area in the deposition region  145 . The temperature control apparatus  160  may be constructed from a relatively inert material, such as stainless steel. One such temperature control apparatus suitable for use in the illustrated embodiment is available from Thermo Haake, Inc. (Paramus, N.J.). 
     The fluid input/output region  140  includes a chamber base  165  having several channels including a first primary chemical delivery conduit  170   a , a second primary chemical delivery conduit  170   b , and an emulsion return conduit  175 . The chemical delivery conduits  170   a  and  170   b  are connected for fluid communication with corresponding flow channels within chamber base  165 . The location and arrangement of the flow channels within chamber base  165  can be altered depending on the position of the chamber base within the reactor and the position of the reactor in the automated processing tool  10 . In an alternate embodiment, the first and second conduits  170   a  and  170   b  can be at the same elevation in the chamber base  165 , but extend along different radial positions. The fluid input/output region  140  also includes one or more drainage passages  180  (only one such passage shown). The drainage passage  180  may be an annular channel that is generally concentric with the center of and formed integrally with the chamber base  165 . 
     The deposition region  145  includes an overflow cup  185  stacked vertically above the emulsion tank  155  and a concentrically disposed processing cup  190  mounted within the overflow cup  185 . The overflow cup  185  can be a generally cylindrical member that peripherally surrounds the processing cup  190 . Both the overflow cup  185  and the processing cup  190  may be mounted on the chamber base member  165 . In the illustrated embodiment, the processing cup  190  has an annular upper structure and a tapered, frusto-conical lower portion  210  that slopes downwardly and radially inwardly. As shown, drainage passage  180  extends between the overflow cup  185  and the emulsion tank  155  so that processing fluid flowing over the rim of the upper portion of processing cup  190  flows downwardly through the overflow cup  185  and the drainage passage  180  to the emulsion tank  155 . The dimensions of the overflow cup  185  may be similar to other types of reaction vessels used in wet processing tools (e.g., electroless plating reactors, etching reactors, rinse/dry capsules, etc.). As such, the reactor  100  is readily interchangeable with other reactors in designing a tool so that a single processing tool frame may be used as a basis for a wide range of different types of processing tools. 
     The reactor assembly  100  also includes a counter electrode  195 . As shown, the counter electrode  195  is an annular ring in which the height of the material from which it is formed is greater than the width of the material. The counter electrode  195  sits upon a shelf  200  at the interior of the processing cup  190 . The counter electrode  195  is coupled to one or more electrical connecting members  205  that conduct electrical power from a power supply to the counter electrode  195 . The counter electrode  195  can alternatively comprise a plurality of linear or curved segments positioned around the shelf  200  of the processing cup  190 . 
     The deposition region  145  includes a processing area  215  in which the workpiece  16  contacts the processing fluid to effect the desired photoresist deposition process. In the illustrated embodiment, the photoresist emulsion and associated solvents enter the processing area  215  through a diffuser  220  in the processing cup  190 . The first delivery conduit  170   a  and/or the second delivery conduit  170   b  can provide the fluid flow to the diffuser  220 . 
       FIG. 2  also illustrates one manner of supplying and recycling the emulsion or other type of solution in the reactor  100 . As shown, a pump  310  is provided to generate the flow of the emulsion through the system. A manifold  330  is disposed in line with the pump  310  to control the flow of the emulsion. Fluid within the emulsion tank  155  flows through the inlet  335  of the manifold  330 . A filter  311  can be disposed in the flow to remove particles and/or bubbles from the flow. The manifold  330  allows the emulsion to flow to one or more of the inlet conduits  170   a  and/or  170   b  that, in turn, direct the flow of the emulsion to the diffuser  220  in the cup  190 . Optionally, the diffuser  220  may include a dual port system whereby emulsion from the first inlet conduit  170   a  provides a flow of the emulsion to holes in the peripheral portion of the diffuser  220  and emulsion from the second inlet conduit  170   b  provides a flow of the emulsion to holes in the central portion of the diffuser  220 . The distribution of the flow between the first and second inlet conduits  170   a  and  170   b  may be tailored using one or two pumps to independently control the flows between the conduits  170   a  and  170   b . Other manners of implementing a dual port system are also feasible. 
     In some circumstances, there should not be a flow of the emulsion through the diffuser  220  or otherwise through the deposition region  145 . To this end, an auxiliary flow path may be provided to maintain circulation of the emulsion when the primary flow path to the deposition region  145  is closed. In the illustrated embodiment, this feature is implemented using a recirculation pump  345  that generates an auxiliary flow of emulsion through inlet  335  to the return conduit  175 . This prevents the emulsion within the emulsion tank  155  from remaining stagnant when it is not being supplied to the deposition region  145  to increase the longevity of the emulsion. 
     b. Embodiments of Gas Control Systems 
     As explained above in the Background section, one problem of photoresist deposition is the accumulation of bubbles proximate the process side of the workpiece. When a workpiece is horizontally oriented in the bath in the manner shown in  FIG. 2 , it traps such gases on its underside because gas bubbles in the electrolytic bath tend to float the surface toward the workpiece. The bubbles entrapped on the workpiece result in pinhole-sized voids in the surface of the photoresist that significantly decrease the quality of the deposited material and thus the overall component yield. It is for this reason that conventional electrophoretic photoresist deposition processes have used systems that hold the workpiece vertically in the deposition tank. The present inventors, however, recognized several advantages of holding the workpiece horizontally. For example, one advantage of holding the workpiece horizontally is that the EPE contacts only one side of the workpiece. As such, the other side of the workpiece can be isolated from the EPE solution to remain clean for handling by the automated robotics. To obtain this advantage, the inventors developed several gas control systems that reduce and/or eliminate bubbles at the surface of the workpiece. The gas control systems are generally integrated with the reactor base  110  and/or the reactor head  105  of the reactor  100 . 
     In several embodiments, the deposition station may include a gas control system configured to inhibit bubbles from migrating to and/or residing on the workpiece. As explained in more detail below, the gas control systems can include: (a) rotating the workpiece during deposition; (b) agitating the electrolytic bath during deposition; (c) vibrating the workpiece during deposition; (d) creating an impinging flow of emulsion directed substantially transversely and/or parallel to the workpiece; (e) trapping bubbles in the electrolytic bath before they reach the workpiece; (f) removing bubbles from the electrolytic bath before they reach the workpiece; (g) applying a voltage to the electrode or the workpiece according to a predetermined delay; (h) providing a plurality of counter electrodes adapted to be positioned within the processing chamber and further adapted to receive a voltage potential; (i) using mechanical agitation of the bath and/or components to remove bubbles from the workpiece; (j) separating the counter electrode from the workpiece using a membrane or other member through which electrical current can flow; (k) providing a low velocity flow to allow bubbles to rise to the surface of the reservoir  155 ; and/or avoiding turbulence in the fluid flow over the weir  265  into the reservoir by keeping the fluid level in the overflow cup  185  near the level of the weir  265  (see, e.g.,  FIG. 3 ). 
     In accordance with one embodiment of a gas control system, the reactor base  110  includes a chemical delivery system that provides a flow of EPE which sweeps bubbles away from the surface of the workpiece. For example, the diffuser  220  in the cup  190  can direct fluid flows from the conduits  170   a  and/or  170   b  to desired zones of the processing area  215 . The diffuser  220 , for example, can be configured to direct a portion of the flow to the counter electrode  195  and another portion toward the center of the workpiece  16 . In the illustrated embodiment, the diffuser  220  is dome-shaped and includes a hole pattern that directs one portion of the flow to the workpiece surface and another portion toward the counter electrode  195 . The portion directed toward the counter electrode  195  should flow toward the upper portion of the electrode  195  so that bubbles generated at the electrode  195  can be trapped before reaching the workpiece as explained in more detail below. The portion of the flow directed to the central portion of the workpiece sweeps bubbles proximate to the workpiece surface toward the outer periphery of the workpiece where they can escape. 
     In accordance with another embodiment of a gas control system, the rotor  120  may rotate the workpiece during a plating cycle to drive bubbles from the area proximate the workpiece surface. The workpiece is preferably rotated throughout a majority of the deposition cycle. The flow of photoresist chemistry impinging the workpiece surface and the rotation of the workpiece  16  combine to generate a fluid flow within the processing area  215  that moves radially outward from the center of workpiece  16 . Such an outward flow physically sweeps bubbles toward the workpiece periphery where they can escape from the processing fluid. This aspect of controlling bubbles can be combined with the flow aspects of the diffuser  220 . 
     The gas control system of the embodiment illustrated in  FIG. 2  can also include structures that trap the bubbles present in the photoresist emulsion before they reach the surface of the workpiece  16 . This embodiment differs from the foregoing embodiments in that it does not necessarily physically remove bubbles from the surface of the workpiece or a zone adjacent to the workpiece. Rather, this embodiment reduces the presence of bubbles in the photoresist emulsion in the area below the workpiece surface to prevent bubbles from reaching the workpiece. This effect may be achieved, in part, by directing the flow of the photoresist chemistry through the reactor base so that bubbles are trapped at a trapping area. For example, as explained above, the diffuser  220  can direct a portion of the fluid flow toward a bubble trapping region that is vertically above the counter electrode  195 . Once the bubbles are trapped, they may be directed to an area remote of the workpiece. For example, they may be directed outside of the reactor base through a bubble exhaust vent, and from there to a reactor base exhaust vent. 
       FIG. 2  illustrates one embodiment of a bubble trap  225  for use in the reactor  100 , and  FIG. 3  illustrates the bubble trap  225  in greater detail. As shown in  FIG. 2 , the bubble trap  225  can be an annular component located at the top of the counter electrode  195 . Referring to  FIG. 3 , the bubble trap  225  may include a sloped ledge  229  having an upper surface  230  and a lower surface  235 . The upper surface  230  defines a flow area  240  through which the photoresist emulsion passes before reaching the processing area  215 . The sloped lower surface  235  extends radially inward so that it overlies the counter electrode  195 . The lower surface  235 , which is radially exterior to flow area  240 , can slope downwardly toward the center of the cup  190  to define a bubble trap region  245  that entraps bubbles generated at the counter electrode  195  or otherwise entrained in the fluid flow. 
     The bubble trap  225  operates in coordination with the diffuser  220  and the shape of the counter electrode  195 . During deposition, the diffuser  220  directs a portion of the photoresist emulsion radially outward over the surfaces of the counter electrode  195 , which then flows upward toward the bubble trap region  245  of bubble trap  225 . Without being limited to theory, it is believed that many of the bubbles present in the photoresist emulsion are generated by chemical reactions that occur at the counter electrode during EPR deposition. By directing a portion of the flow over the surfaces of the counter electrode, bubbles formed on the counter electrode are swept upward and then radially outward through the bubble trap region  245  of the bubble trap  225 . The vertical sides of the counter electrode facilitate in entraining the bubbles at the electrode  195  in the upward flow of emulsion flowing toward the top  225 . The bubbles swept into the bubble trap  225  can then be directed through a bubble vent  250  to remove the bubbles from the process flow in the cup  190 . In the illustrated embodiment, the bubble vent  250  may be an annular channel through which the bubbles may escape. However, as shown in  FIG. 4 , the bubble vent  250  can be a plurality of distributed holes. 
     Referring to  FIGS. 2 and 3 , the exterior and uppermost portion of the upper surface  230  of the bubble trap  225  may define a weir  265 . The photoresist chemistry in the processing area  215  flows over the weir  265  and into the overflow cup  185 . The weir  265  accordingly creates an upper surface of the bath. The volume of fluid purged over processing weir  265  can equal the volume of fluid flowing through the bubble vent  250  so that the proportion of emulsion and solvent directed over counter electrode  195  substantially equals the proportion of emulsion directed toward the center of workpiece  16 . A balanced flow of this kind depends on the rate at which the photoresist emulsion is introduced into the processing area  215  and the relative size and shape of the bubble vent  250 . It is well within the scope of the present invention to alter the relative size of processing weir  265  and the bubble vent  250  to achieve a balanced flow so that the volume of processing fluid flowing over processing weir  265  is substantially equal to the amount of processing fluid flowing through the bubble vent  250 . 
     In an optional embodiment shown in broken lines in  FIG. 3 , the bubble trap  225  can further include a bubble weir  270  extending annularly around the exterior sidewall of the processing cup  190 . As shown, the bubble weir  270  includes an annulus  275  and a lower shelf  280  that extends in a radially inward direction from the annulus  275 . The upper portion of annulus  275  terminates at a vertical elevation that is just slightly below the top of weir  265 . The lower shelf  280  engages and seals with the exterior surface of the processing cup  190  in an area just below the bubble vent  250 . 
     As the fluid flows through the reactor  100 , the difference in elevation between the upper portion of annulus  275  and the weir  265  results in a radially outward flow of the photoresist emulsion in the interstitial region between these structures. Bubbles exiting through the bubble vent  250 , therefore, travel up to the surface of the photoresist emulsion where this radially outward flow sweeps the bubbles further away from the workpiece  16 . This action may assist in further reducing and/or eliminating bubbles that have already made their way to the surface of the workpiece thereby giving rise to higher product yields. 
     c. Embodiments of In-situ Secondary Processing 
     With reference to both  FIGS. 2 and 5 , the in-situ secondary processing region  150  of the reactor base  110  may include components for performing other processes on the workpiece and/or the contact assembly  125  at the same reactor site. Typically, such secondary processes are ancillary to the deposition process that takes place in the deposition region  145 . For example, the secondary processing region  150  of the reactor base  110  may include an in-situ rinse assembly  285 .  FIG. 5  illustrates one embodiment of an in-situ rinse assembly  285  suitable for use in the secondary processing region  150 . The in-situ rinse assembly  285  shown in  FIG. 5  is described in more detail in International Application PCT/US00/28210, filed Oct. 12, 2000 and published Apr. 19, 2001 as WO 01/27357, the disclosure of which is hereby incorporated by reference. 
     In the illustrated embodiment, a permeate solution comprised of the continuous aqueous phase of the electrophoretic emulsion may be used to rinse the workpiece and/or the contact assembly after a deposition cycle. The in-situ rinse assembly  285  can include one or more nozzles  290  that spray the rinsing solution at the underside of the workpiece  16 . The nozzles  290  can also spray the permeate solution at the electrical contact assembly  125 . By rinsing the workpiece and the contact assembly with the permeate solution, residual EPE is removed from the contact assembly so that a more consistent and reliable engagement may be achieved between the electrical contact assembly and the workpiece. This further enables automated EPE deposition because single-wafer assemblies need not be manually cleaned after only a few deposition cycles. 
     It is sometimes desirable, although not necessary, to at least partially inhibit mixing of the processing chemicals used in different processing steps. The reactor base  110  therefore includes a separate collection system for collecting spent permeate (e.g., permeate that has contacted one or more surfaces of the workpiece  16 ). The collection system can include one or more fluid channels  300  that are disposed around the inner periphery of the in-situ rinse assembly  285 . As shown, the fluid channels  300  are annular lips that project radially inwardly and upwardly in the secondary processing region  150  proximate to the position of the workpiece  16  as it undergoes processing in the secondary processing portion  150 . 
     To operate the in-situ processing system, the control system  46  causes the reactor head  105  ( FIG. 2 ) to move the workpiece  16  to an intermediate position above the main processing area  215  but below the lower boundary of the collection channels  300 . While at this position, the workpiece  16  is spun at a high rotation rate to fling off a bulk portion of any excess EPE used in the cup  190 . This reduces “drag out” of EPE and waste of the photoresist. After the bulk portion of the excess EPE has been removed from the workpiece, the control system  46  causes the reactor head  105  to move the workpiece  16  to a second processing position at the elevation of the collection channels  300 . In this position, a stream of permeate or other secondary processing solution is sprayed from the nozzles  290  to contact the lower surface of the workpiece  16 . This spray impinges a deposited film on the workpiece  16 . As the liquid stream is directed toward the workpiece surface, the rotor assembly  120  rotates at a high rotation rate so that the liquid impinging on the workpiece surface is flung radially outward under the influence of centrifugal forces. The liquid sprayed from the nozzles  290  is thus collected by the collection channels  300  where it may be reintroduced into the reservoir or removed from the reactor for recycling, disposal, etc. 
     The one or more nozzles  290  may direct the stream of permeate or other secondary solution at a fixed angle with respect to the horizontal plane. In such instances, the control system  46  may direct the reactor head  105  to gradually raise the workpiece as the permeate is provided through the nozzles. This creates a “chasing” effect whereby the point of contact between the permeate stream and the workpiece surface varies with the height of the reactor head  105 . 
     The secondary processing region  150  can also include an exhaust shroud  340  above the in-situ rinse assembly  285 . Referring to  FIG. 4 , the exhaust shroud  340  may include an annulus  345  having an opening  350  through which the arm that carries the processing head  105  ( FIG. 2 ) may move vertically as the processing head  105  is lowered into the processing position or raised to the load/unload position. The annulus  345  opens to an exhaust vent  355  that may be connected to a pump (not shown). The exhaust shroud  340  is particularly useful for use with EPEs, such as some EPRs that contain volatile components or harmful vapors. The vapor phase of the EPE can thereby be confined to the processing base  110  to prevent contamination of the exterior environment and/or the tool region  13  of the tool. 
     d. Additional Embodiments of Gas Control Systems 
       FIG. 6  is a cutaway isometric view of a further embodiment of a reactor base  110   a  suitable for use in the reactor  100 . Similar components are labeled with the same reference numerals in  FIGS. 2–6 . The reactor base  110   a  includes a bubble trap  225   a  that is similar to the bubble trap  225  shown in  FIGS. 2 and 3 , except that the bubble trap  225   a  includes a ledge having a downwardly extending lip  360 . The lip  360  may provide more protection against defects caused by bubbles. The inventors, however, have discovered that the radial width of the ledge and the extent that the ledge has a downwardly depending lip affects the quality of the deposited layer of resist. The size and configuration of the ledge and/or lip is a function of several factors, such as the percentage of solids in the EPE (e.g., micelle concentration), strength of the electrical field, configuration of the counter electrode, and distance between the bubble trap and the workpiece. It will be appreciated that the radial width of the ledge, the distance between the ledge and the workpiece, the extent that the lip depends downwardly, and other factors can be varied according to the specific application to provide the desired surface quality without undue experimentation. 
       FIG. 7  illustrates another embodiment of a reactor base  110   b  suitable for use in the reactor  100 . Similar components are labeled with the same reference numerals in  FIGS. 2–7 . In this embodiment, the reactor base  110   b  includes a dual chemical delivery system that provides an agitated fluid flow to the surface of the workpiece that assists in driving bubbles at the workpiece surface radially outward away from the workpiece. In addition to the primary chemical delivery conduits  170   a  and/or  170   b  that direct a primary flow of the photoresist through the diffuser  220   b , the reactor base  110   b  can further include a secondary conduit  365  and a sprayer bar  370  coupled to the conduit  365 . An additional flow of photoresist chemistry is delivered to the processing area  215   b  through the spray bar  370 , which may be disposed immediately adjacent the process side of the workpiece  16 . The spray bar  370  may be configured as a cross-like structure having several linearly disposed holes on the side facing workpiece  16  for the diffusion of photoresist emulsion toward the workpiece surface. Together, the diffuser head  220   b  and the spray bar  370  direct an agitated flow of photoresist emulsion toward the workpiece  16  during deposition. This agitated flow, which in the illustrated embodiment is primarily directed to the central portions of the workpiece, assists in driving bubbles proximate to the workpiece surface toward the outer periphery of the workpiece where the bubbles can escape the fluid flow. 
     As above, the workpiece may be rotated to further assist in driving bubbles from the area proximate the workpiece surface. To this end, as the flow generated by the diffuser head  220   b  and the spray bar  370  impinges on the surface of the workpiece, the rotor assembly  120  ( FIG. 2 ) rotates the workpiece. The impinging flow of emulsion toward the workpiece surface and the rotational motion of the workpiece  16  combine to generate a flow moving radially outward from the center of workpiece  16  to physically move bubbles toward the workpiece periphery. 
       FIG. 7  illustrates another bubble trap  225   b . In this embodiment, the bubble trap  225   b  may have an annular cross-section in the horizontal plane and a funnel-shaped cross-section in the vertical plane. As shown, this particular shape substantially surrounds the counter electrode  195  in such a manner that nearly all of the bubbles forming on the electrode are captured by the bubble trap  225   b . The particular configuration of the bubble trap  225   b  will depend upon the parameters explained above to ensure adequate surface quality. 
       FIG. 8  shows another variation of the reactor base  110   b  of  FIG. 7  that is adapted to process a smaller diameter wafer using the same basic reactor base components. The reactor  110   b  shown in  FIG. 8  includes a bubble trap  225   e  and a spray bar  370   e . The bubble trap  225   e  has a maximum outer diameter D 1  that is the same as the maximum outer diameter of the bubble trap member  225   b  of the reactor base shown in  FIG. 7 . As a result, the bubble trap member  225   e  of  FIG. 8  and the bubble trap member  225   b  of  FIG. 7  are effectively interchangeable inserts that can be used in the same reactor base. However, the bubble trap member  225   e  terminates at a process weir  265   e  that defines an opening having a smaller diameter D 2  than the corresponding diameter of the reactor base shown in  FIG. 7 . This results in a virtual electrode at the opening that is smaller than the virtual electrode of the reactor base of  FIG. 7 . Whereas the larger virtual electrode of the reactor base of  FIG. 7  may be suitable for processing of 300 mm diameter wafers, the reactor base of  FIG. 8  may be tailored for processing of a smaller diameter wafer, such as a 200 mm or 150 mm wafer. Similarly, the length of the spray bar  370   e  in  FIG. 8  is reduced in comparison to the spray bar  370  of the embodiment shown in  FIG. 7  so that it can fit within the diameter D 2  of the opening. 
     The exterior walls of the bubble trap member  225   e  present a sloped surface over which the electrophoretic emulsion flows as though reactor base is initially filled with fluid. In this manner, gas entrapment and bubble formation that might otherwise occur with the agitation that would result from an abrupt vertical transition over the process weir  265  may be reduced and/or completely avoided . 
       FIGS. 9 and 10  illustrate another embodiment of a reactor base suitable for use in reactor  100 . This embodiment includes a reactor base  110   c  that is substantially similar to those previously described, with the exception that it includes a plurality of counter electrodes  375 . In certain applications, a plurality of counter electrodes can be helpful in controlling the rate of deposition and the thickness of the resist. For example, one problem of depositing thick layers of resist is that bubbles are more likely to form. By using a plurality of counter electrodes, it may be possible to provide greater control over the rate of deposition. Such control of the deposition rate can ensure that bubbles do not get caught up in the resist layer during deposition. 
     In the specific embodiment shown in  FIG. 9 , the reactor base  110   c  includes counter electrodes  375   a–c  and corresponding bubble trapping members  380   a–c  immediately above the counter electrodes. The bubble trapping members  380  may be comprised of inverted U-shaped rings having an internal dimension that is just slightly larger than the width of each counter electrode  375 . With particular reference to  FIG. 10 , the counter electrodes  375  may be interconnected with one another by a conductive or non-conductive web of material  382  to form a single counter electrode unit  390 . Similarly, the bubble trap members  380  may be interconnected by webbing  384  to form a single bubble trap structure  385 . In general, the principles described in relation to the reactor bases above also apply to reactor base  110   c , with the exception that the flow of the emulsion from the diffuser  220  is directed up and over electrodes  375  in a manner that causes any bubbles to be trapped within trapping members  380 . The bubbles can remain in the trapping members  380  or flow to a corresponding vent in the periphery of the bubble trap structure  385 . The remaining parts of reactor base  110   c  generally operate substantially the same as described above. 
     Various other structures can be incorporated into the reactor to reduce and/or eliminate bubbles proximate to the surface of the workpiece  16 . For example, the workpiece can be vibrated during deposition through the use of a common vibration device that is attached to the rotor assembly  120  ( FIG. 2 ). Alternatively, the vibration device may be attached to the stator  70  ( FIG. 2 ). In each instance, such vibration assists in preventing the bubbles from adhering to the surface of the workpiece. A suitable vibration device that may be used is a series MVS1 &amp; MSP (3000 rpm) from Vibratechniques, Ltd. (New England House, Brighton, U.K.). 
     The generation of an agitated flow of photoresist emulsion at the surface of the workpiece can also be accomplished through the use of a moveable paddle. Such a paddle can be placed just below the surface of the workpiece  16  where it can oscillate to drive bubbles that are present at the surface of the workpiece toward the peripheral portions thereof. The paddle may have a triangular cross-section and may be mounted just below the surface of the workpiece in a right-side up or upside down orientation. An oscillating drive may then be attached to the paddle to effect the back-and-forth, horizontal oscillation of the paddle during the EPR deposition process. The paddle may also have holes through which the EPE can flow. Suitable paddles are similar to the plating systems disclosed in articles by Rice et al., “Copper Electrodeposition Studies With A Reciprocating Paddle,”  J. Electrochem. Soc. , vol. 135, No. 11, November 1988, Mehdizadeh et al., “The Influence of Lithographic Patterning on Current Distribution in Electrodeposition: Experimental Study and Mass. Transfer Effects,”  J. Electrochem. Soc. , vol. 140, No. 12, December 1993 and Schwartz et al., “Mass-Transfer Studies in a Plating Cell With A Reciprocating Paddle,”  J. Electrochem. Soc.,  vol. 134, No. 7, July 1987. 
     Still another embodiment for controlling bubbles is a process for operating the reaction vessel. The present inventors have found that the use of pulsed plating current during deposition may also reduce the overall bubble content of the bath. Without being limited to the following theory, it is believed that a continuous current generates more bubbles at the counter electrodes or the workpiece surface because gas is not given time to diffuse into solution. When the electrical current is interrupted for even a brief period of time, many bubbles will simply break up and dissolve into solution. Bubbles that would otherwise inherently evolve at the workpiece surface or the counter electrode during the deposition, such as O 2  or H 2  bubbles, may not form at the electrode or the workpiece. Still further, an ultrafiltration system can be used to remove some gas bubbles and prevent the same from entering the electrolytic bath with introduction of the photoresist emulsion. For example, filters  311  ( FIG. 2 ) can remove bubbles, or other filters in the system for filtering permeate solution can be used to remove bubbles. 
     Although not required, it is useful to employ one or more of the gas control systems described herein in a combined manner to achieve the desired result. For example, in view of the teachings herein, it is possible to combine ultrafiltration, rotation of the workpiece, agitation of the bath, vibration of the workpiece, impinging flow, short distance from the overflow weir  265  to the fluid level in the overflow cup  185 , and bubble traps in the same reactor to produce relatively void-free photoresist films. 
     2. Reactor Heads 
     Reactor heads for use in EPE reactors in accordance with several embodiments of the invention mitigate pinholes formed by bubbles in the EPE bath and enable the integration of electrochemical deposition of EPRs and other EPEs in microfabrication processes. One feature of the reactor heads that mitigates pinholes is that the reactor heads are configured to rotate the workpiece during the electrochemical processing. Additionally, as explained in more detail below, several embodiments of reactor heads enable the integration of electrochemical EPE deposition with other microfabrication processes because the reactor heads are configured to limit the contact between the workpiece and the EPE bath to only selected processing regions of the workpiece so that other regions of the workpiece are isolated from the EPE bath. As such, single-wafer handling equipment used in other microfabrication techniques can be used to handle workpieces processed by the EPE reactors. A reactor head that is suitable for use in the illustrated reactor is described in International Patent Application Nos. PCT/US99/15847 and PCT/US99/15850, the disclosures of which are hereby incorporated by reference. 
     Referring back to  FIG. 2 , the illustrated embodiment of the reactor head  105  for the reactor assembly  100  includes a stator assembly  70  and a rotor assembly  120 . The reactor head  105  receives and carries an associated microelectronic workpiece  16 , positions the microelectronic workpiece  16  in a process side down orientation within the processing area  215  of the base  110  and rotates or spins the workpiece  16 . The reactor head  105  also includes the contact assembly  125  with contacts that engage the electrically conductive surface of the workpiece  16  to electrically couple the workpiece to a voltage potential. The contact assembly  125  also includes structures that effectively isolate the non-processed side (“backside”) or other regions of the workpiece from fluids used during the deposition process. This is in contrast to the rack-and-tank EPR processes used in printed circuit board manufacturing that immerse the entire workpiece vertically in the electrolyte causing both sides of the workpiece to be covered with the photoresist. 
     The reactor head  105  may be mounted on a “lift and rotate” apparatus  130  configured to rotate the reactor head  105  from an upwardly facing disposition in which it receives the microelectronic workpiece  16  (not shown) to a downwardly facing disposition in which the surface of the microelectronic workpiece  16  may be brought into contact with the photoresist chemistry contained in the EPR base  110  (shown in  FIG. 2 ). A robot unit can load the microelectronic workpiece  16  on the rotor assembly  120  for processing and remove the microelectronic workpiece  16  from the rotor assembly  120  after processing. A reactor head that is suitable for use in the illustrated reactor is described in International Patent Application Nos. PCT/US99/15847 and PCT/US99/15850, the disclosures of which are hereby incorporated by reference. 
     One embodiment of the contact assembly  125  is shown in more detail in  FIGS. 11 and 12 . The contact assembly  125  is removably attached to the rotor assembly  120  and provides electrical contact between the microelectronic workpiece  16  and a source of electrical power. In the illustrated embodiment, electrical contact between the workpiece  16  and the contact assembly  125  occurs at a large plurality of discrete flexure contacts  425  ( FIG. 12 ) that are effectively separated from the EPE when the workpiece  16  is loaded in the contact assembly. 
     Referring to  FIG. 11 , the contact assembly  125  can have a central open region  430  within which the workpiece is exposed. As shown in  FIGS. 11 and 12 , the contact assembly  125  includes a primary support member  445 , an outer body member  435  carried by the support member  445 , a plurality of flexure contacts  425  projecting radially inwardly from the support member  445 , and an interior wafer guide  450  on the interior of the support member  445 . Referring to  FIG. 12  alone, the contact assembly  125  can further include an annular wedge  440  that secures the flexural members  425  to the support member  445 . The annular wedge  440 , the flexure contacts  425 , and the support member  445  are preferably formed from platinized titanium; the wafer guide  450  and the outer body member  435  are preferably formed from a dielectric material that is compatible with the processing environment. 
       FIG. 12  shows one embodiment of a flexure contact  425  in greater detail. The flexure contact  425  can include an upstanding portion  470 , a transverse portion  475 , a vertical transition portion  480 , and a wafer contact portion  485 . Similarly, the wedge  440  includes an upstanding portion  490  and a transverse portion  495 . The upstanding portion  490  of the wedge  440  and the upstanding portion  470  of the flexure contact  425  are secured within a first annular groove  455  of the support member  445 . In operation, a workpiece is centered to rest on the wafer contacts  425 . The contact portions  485  contact a perimeter portion of the workpiece around a first diameter. 
     The outer body member  435  includes an upstanding portion  520 , a transverse portion  525 , a vertical transition portion  530 , and a further transverse portion  535  that terminates in a lip  540 . The upstanding portion  520  includes an annular extension  545  that extends radially inward to engage a corresponding annular notch  550  disposed in an exterior wall of the support member  445 . The transverse portion  535  extends radially inward beyond the contact portions  485  of the flexure contacts  425 . The transverse portion  535  and contacts  425  resiliently deform as a wafer is driven downwardly through the central opening. With the workpiece  16  in proper engagement with the contact portions  485 , the lip  540  engages workpiece  16  and provides a barrier between the processing solution and the outer peripheral edge of the workpiece, the backside of workpiece, and the flexure contacts  425 . A seal, such as a polymeric material, can extend around the lip  540  to prevent EPE from leaking into the region of the contacts  425  or around the backside of the workpiece. The outer number  435  accordingly isolates the backside and peripheral portion of the processing side of the workpiece  16  from the EPE. As such, the backside remains clean and the edge is not covered by an edge bead of resist. 
     Although the flexure contacts  425  shown in  FIGS. 11 and 12  are discrete components, they may be joined with one another as an integral assembly in other embodiments. For example, the upstanding portions  470  of the flexure contacts  425  may be joined to one another by a web of material, such as platinized titanium, that is either formed as a separate piece or is otherwise formed with the flexures from a single piece of material. The web of material may be formed between all of the flexure contacts or between select groups of flexure contacts. For example, a first web of material may be used to join half of the flexure contacts (e.g., 18 of the flexure contacts in the illustrated embodiment) while a second web of material is used to join a second half of the flexure contacts (e.g., the remaining 18 flexure contacts in the illustrated embodiment). Different groupings are also possible. 
     EMBODIMENTS OF FLUID FLOW CONTROL SYSTEMS 
       FIG. 13  illustrates one embodiment of a fluid flow control system, shown generally at  800 , that may be used in connection with the reactor of  FIG. 2 . Although not mandatory, it is beneficial to place the fluid flow control system  800  under the control of the control system  46  ( FIG. 2 ) so that the control system may coordinate the flow of fluid with the various other operations executed within the processing tool  10 . 
     In the illustrated system, fluid flow begins generally in emulsion tank  155 . The photoresist emulsion contained therein is maintained at a predetermined temperature by the thermal unit  160 , as explained above. During normal operation, a suction is created through activation of pump  805  to draw emulsion from emulsion tank  155  through line  810  to valves  815  and  820 . Valves  815  and  820  are normally open and generally lead to lines  825  and  830  which feed, for example the diffuser  220  shown in  FIG. 2 . Optional filters  831  can be placed in lines  825  and  830 . The lines  825  and  830  generally correspond to the primary chemical delivery conduits  170   a–b  ( FIG. 2 ) that provide the EPR emulsion to the processing area  215  of the reactor base  110 . The fluid flow in lines  825  and  830  may be monitored by flow meters that may be in communication with the control system  46 . Information regarding the rate of fluid flow can be obtained from the meters and used by the control system  46  to control the overall EPR deposition process. 
     Turning now to the fluid flow generated through activation of a pump  855 , it can be seen that fluid is drawn from the emulsion tank  155  through a line  865  and through an open valve  835  into a particle filter  860 . The particle filter  860  is chosen to remove particles within the range of 5–10 microns and separate such large particles from the flow of the photoresist chemistry. The flow of emulsion continues through the particle filter  860  and into an ultrafilter unit  870 . Suitable ultrafilter units are available from Koch International Ltd. (part #P4-HFM-183-LPP). The ultrafilter unit  870  separates the flow of photoresist chemistry into a permeate solution that is drawn into a permeate tank  875  through line  867  and a concentrated emulsion that is provided through line  846 . A valve  880  controls the flow through line  867 , and a value  847  controls the flow through line  846 . The ultrafiltration unit  870  has a semipermeable membrane filter which retains large molecules or colloidal particles while permitting the passage of water, solvents and other small molecules. In other words, it separates the photoresist emulsion into a concentrate and a permeate. The permeate solution is a conservation-type solution that is used for rinsing the contacts and workpiece. In this manner, the processing chemistry does not have to be replaced after each cleaning because the permeate can flow back into emulsion tank  155  and mix with the concentrated emulsion to be used again for deposition. 
     The permeate is comprised of mostly water, solvents, and other small molecules. After the permeate is separated, a concentrated emulsion is drawn through line  846  through valve  847  and through flow meter  848  to flow into the emulsion tank  155 . The emulsion separated using ultrafilter  870  is of a slightly higher concentration than the emulsion in the emulsion tank because the permeate solution containing mostly water is pulled from the total bath chemistry. After ultrafiltration, the permeate solution is stored for use during a conservation in-situ rinse at a desired temperature maintained by another thermal unit  856  within the permeate tank  875 . The thermal unit  856  may be of the same type and configuration as the thermal unit  160 . 
     During in-situ rinsing and/or contact cleaning operations, fluid is drawn from the permeate tank  875  through line  858  by way of pump  890 . Fluid flow from the permeate tank  875  proceeds through pump  890 , valve  862 , and a particle filter  864 . The particle filter  864  can suitably be a 0.1 micron filter. The fluid flow continues through line  885  to valves  895  and  900 . During an in-situ rinse procedure, valve  895  is closed and valve  900  is open to administer the permeate rinse through line  905  and into the in-situ rinse assembly  285 . When the in-situ rinse procedure is not in operation, valve  900  is closed and valve  895  is open so that any overflow from permeate tank  875  can return to the deposition chamber through line  910 . This permeate return is continued given that ultrafiltration continues through ultrafilter  870  during normal operation of the reactor  100 . The permeate level in tank  875  is constantly being fed through a circuit including line  858 , pump  890 , valve  872 , and line  866 . If the recirculation flow just described exceeds capacity, excess or overflow permeate may be returned to the deposition chamber via valve  895  and line  910 . 
     PHOTORESIST DEPOSITION PROCESS 
     The photoresist used in the foregoing system and reactors may be any electrodepositible resist material such as, for example, those available under the trade designation PEPR™ 2170 available from Shipley Company, Inc. (Newton, Massachusetts). It will be apparent to one skilled in the art that the process parameters used to electrodeposit the photoresist will vary depending upon the photoresist used. The following description of the deposition process includes parameters that may be used in connection with the PEPR™ 2170 photoresist, but they are believed to be generally applicable to the deposition of most electrophoretic photoresists or other patternable materials. 
     The deposition of PEPR™ 2170 is an anodic process, where the workpiece functions as the anode. The resist described here is mostly self-limiting and deposits between 5 and 12 microns of photoresist, although thicker resist films may be achieved by manipulation of the solids content and solvent content of the bath. The thickness of the resist film is controlled by varying the concentration of the plasticizer (PEPR 2170® TC, a solvent comprised mainly of octonone). The plasticizer is added by either manual or automatic dosing and has proven to be a simple, reliable means of controlling resist thickness. 
     EXAMPLE 1 
     An electrolytic bath containing 10 to 13 percent solids (PEPR™ 2170 Photoresist) and 10 percent solvents (primarily octonone or the “thickness controller” provided by The Shipley Company). The bath can contain 5–15% solids in other applications. No pre-cleaning steps were used and the bath was held at 30° C. A workpiece was inserted into the EPR reactor and the head was closed. The total EPR deposition process for a 200 mm workpiece in this particular example took slightly under 95 seconds (see Table 1). A first dwell step was conducted with the workpiece rotating at 75 rpm for 5 seconds, and a second dwell step was conducted with a reduction in rotation of the workpiece down to 10 rpm up to the 1 minute mark. At the 1 minute mark rotation was increased to 150 rpm and a voltage of 150 volts was applied to the electrolytic bath for the next 30 seconds. At the 90 second mark, the head was lifted to approximately 700 cts out of level and rotation of the workpiece was slowed to 75 rpm. A spin-off step was then conducted at 200 rpm for 3 seconds. (See Table 1). 
     EXAMPLE 2 
     An electrolytic bath containing 10% solids (PEPR™ 2170 photoresist) and 10% solvents (primarily octonone or the “thickness controller” provided by The Shipley Company). No precleaning steps were used and the bath was held at 30° C. A workpiece was inserted into the EPR processing chamber when the head of the chamber was held in a cracked position at an angle of 700 cts out of level. The total EPR deposition process for a 200 mm workpiece in this particular example took slightly under 95 seconds (see Table 2). A spin up step was initiated for 5 seconds while the workpiece was spinning at an rpm of 60 with the head in a cracked position. Next, a dwell step was performed with the head closed for a period of 1 minute with a rotation of 60 rpm wherein vibration was applied to the head for the final 10 seconds of the dwell step. Voltage was applied at the 80 second mark with a potential of 150 volts and the workpiece was spun at 150 rpm while vibration was applied to the reactor head (see Table 2). At the 85 second mark, the reactor head was again cracked at approximately 700 cts and the voltage was turned off while the workpiece rotated at 60 rpm for 5 seconds. The final 3 seconds of the procedure included a spin off step, where the head was cracked and the substrate was spun at 200 rpm. 
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                   
                   
                 Head 
               
               
                 Step 
                 Name 
                 Time 
                 Potential 
                 RPM 
                 Vibration 
                 Position 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1. 
                 Spin Up 
                 0:05 
                   
                 75 
                 No 
                 Closed 
               
               
                 2. 
                 Dwell 
                 1:00 
                   
                 10 
                 No 
                 Closed 
               
               
                 3. 
                 Deposit 
                 0:15 
                 150 volts 
                 150 
                 No 
                 Closed 
               
               
                 4. 
                 Lift 
                 0:05 
                   
                 75 
                 No 
                 Cracked 
               
               
                 5. 
                 Spin Off 
                 0:03 
                   
                 200 
                 No 
                 Cracked 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                   
                   
                   
                 Head 
               
               
                 Step 
                 Name 
                 Time 
                 Potential 
                 RPM 
                 Vibration 
                 Position 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1. 
                 Spin Up 
                 0:05 
                   
                 60 
                 No 
                 Cracked 
               
               
                 2. 
                 Dwell 
                 1:00 
                   
                 60 
                 Yes (for the 
                 Closed 
               
               
                   
                   
                   
                   
                   
                 last 10 seconds 
               
               
                 3. 
                 Deposit 
                 0:15 
                 150 volts 
                 150 
                 Yes 
                 Closed 
               
               
                 4. 
                 Lift 
                 0:05 
                   
                 60 
                 No 
                 Cracked 
               
               
                 5. 
                 Spin Off 
                 0:03 
                   
                 200 
                 No 
                 Cracked 
               
               
                   
               
             
          
         
       
     
     AUTOMATED EPE PROCESSING TOOLS 
     The following description of automated processing tools provides several examples of methods and systems for performing automated EPE deposition. The automated processing tools can be integrated with additional microfabrication processing tools to form a complete microfabrication processing system in which the system includes an automated EPE processing tool. For example, it is well within the scope of the present invention to have different configurations of automated processing tools that include other types of processing stations, such as an exposure station, a chemical etching station, or metal depositing station. Such other processing stations could be contained within an enclosed or a partially enclosed housing including EPE processing stations, or they could be located in automated processing tools separate from the EPE processing stations. As explained in more detail below, the microelectronic workpieces can be transferred between the automated processing tools manually or by automatic robotic handling equipment. 
       FIG. 14  is an isometric view of an automated microelectronic processing tool  10  having an EPE deposition station  11  for deposition of EPR or other electrophoretic materials. The processing tool  10  may include a cabinet  12  having an interior region  13  that is at least partially isolated from an exterior region  14 , such as a clean room. The cabinet  12  may be an enclosed structure including a plurality of apertures  15  (only one shown in  FIG. 14 ) through which microelectronic workpieces  16  contained in cassettes  17  can be moved to and from a load/unload station  18 . In other embodiments, the cabinet can be open, such as the layouts and tool platforms shown in U.S. application Ser. Nos. 10/080,914 and 10/080,915, which are herein incorporated by reference. 
     The load/unload station  18  may have one or more container supports  20  each housed in a corresponding protective shroud  22 . The container supports  20  are configured to position the workpiece cassettes  17  proximate to the apertures  15  in the cabinet  12 . In this position, the microelectronic workpieces  16  can be accessed by one or more robotic transfer mechanisms inside or along the cabinet  12 . The workpiece cassettes  17  can be configured to house the microelectronic workpieces  16  in a “mini” clean environment in which groups of microelectronic workpieces may be transferred, automatically or manually, between processing tools. The particular embodiment shown in  FIG. 14  illustrates a load/unload station suited for handling FOUP wafer holders that are typically used in connection with 300 mm semiconductor workpieces. The cassettes  17 , however, can be open cassettes that do not provide “mini” clean environments. As such, other load/unload station configurations may be used depending on the characteristics of the particular type of workpiece that is to be processed in the tool  10 . 
     The embodiments of the tool  10  shown in  FIG. 14  include one or more EPE deposition stations  11 , one or more fluid processing stations  24 , a workpiece handling system  26 , and a photoresist baking station  25 . One or more of the EPE deposition stations  11  may also incorporate structures that are adapted for executing an in-situ rinse or other secondary in-situ process. Following EPE deposition, the in-situ rinse may be used to rinse the workpiece at the EPE station  11  before it is transferred to another station. In this way, cross-contamination with other reactors is reduced and the footprint of the processing tool is more efficient. Further, the in-situ rinse may be used to clean the electrodes and/or any seals that contact the workpiece during deposition. Any buildup of material on the electrodes and/or seals may thereby be removed to ensure consistent wafer-to-wafer contact. This in-situ cleaning process may be accomplished by subjecting only the electrodes to the rinse cycle without a workpiece loaded in the EPE station  11 . The fluid processing stations  24  may execute one or several process sequences, such as pre-cleaning and/or pre-wetting the workpiece before EPR deposition, cleaning the workpiece after EPR deposition, developing the EPR coating following patterning, depositing a metallization layer on the workpiece, enhancing the seed layer prior to either EPR deposition or metallization deposition, and so forth. 
     The particular embodiment of the processing tool shown in  FIG. 14  is a “linear” tool in which the processing stations are aligned in a generally linear fashion on opposite sides of the workpiece handling system  26 . In this type of system, the workpiece handling system  26  includes a linear track  28  and one or more robotic transfer mechanisms  30  that travel along the linear track  28 . In the particular embodiment shown in  FIG. 14 , a first set of processing stations is arranged in a generally linear manner along a first row R 1 -R 1  and a second set of processing stations is arranged in a generally linear manner along a second row R 2 -R 2 . The linear track  28  extends between the first and second rows of the processing stations so that the robot unit  30  can access one or more of the processing stations along the track  28  to load and/or unload workpieces. 
     The robotic transfer mechanisms  26 , as well as the actuatable components of the processing stations  11  and  24 , are in communication with a control unit  46 . The control unit  46  can implement software programming or other computer operable instructions in response to user input parameters. The control unit  46  may include at least one graphical user interface  48  including, for example, a user-friendly display through which the user input parameters are entered into the control unit  46 . Optionally, the user interface may be located on an area of the tool or at a remote location. In the case of the latter implementation, the control unit  46  may also include a communicating link for communicating with the remote user interface. It will be recognized, that a number of control units  46  may be connected to a common control system (not illustrated) that is used to control and oversee the operations performed in the microfabrication facility or sections thereof. Among its many functions, the control unit  46  is programmed to control the transfer of microelectronic workpieces between the various processing stations and between the input/output section and the processing stations. Further, the control unit  46  is programmed to control the operation of the components at the individual processing stations to implement specific processing sequences in response to the user input parameters. 
     ADDITIONAOL EMBODIMENTS OF PROCESSING STATION LAYOUTS 
       FIGS. 15–17  illustrate alternate layouts for processing stations in EPE deposition tools in accordance with additional embodiments of the invention to implement an automated EPE deposition process. With specific reference to  FIG. 15 , tool  10   a  comprises EPE deposition stations  11 , the load/unload station  18 , one or more fluid processing stations  32 , and a thermal processing station  34 . The fluid processing stations  32  may execute one or several process sequences, such as pre-wetting the workpiece prior to EPR deposition, cleaning the workpiece subsequent to EPR deposition, developing the EPR coating following patterning, depositing a metallization layer on the workpiece, enhancing the seed layer prior to either EPR deposition or metallization deposition, and so forth. 
     The workpieces are transferred between the processing stations  11 ,  34  and  32  using one or more robotic transfer mechanisms  36 ,  38  that are disposed for linear movement along a central track  28 . All of the processing stations, as well as the robotic transfer mechanism, are disposed in a cabinet, such as the one shown in  FIG. 14 . The cabinet can be provided with filtered air at a positive pressure to thereby limit airborne contaminants that may reduce the effectiveness of the workpiece processing. To further enhance the resistance of the overall process to cross-contamination between processing stations, the robotic transfer mechanisms  36  and  38  may be dedicated to specific processing stations. 
       FIG. 16  illustrates another embodiment of a processing tool  10   b  in which a processing station  40  is located in a separate portion of the integrated tool set. Unlike the embodiment of  FIG. 15 , in this embodiment, at least one processing station, such as a thermal processing station, is serviced by a dedicated robotic mechanism  42 . The dedicated robotic mechanism  42  accepts workpieces that are transferred to it by the robotic transfer mechanisms  36  and/or  38 . Transfer may take place through an intermediate staging door/area  44 . As such, it becomes possible to separate one portion of the workpiece processing tool, such as the thermal processing portion  45 , from other portions of the tool. Additionally, using such a construction, the illustrated further processing station may be implemented as a separate module that is attached to upgrade an existing tool set. For example, processing portion  45  may be added to an existing electrochemical metallization deposition tool so that the metallization deposition and the EPR deposition take place in the same processing tool. It will be recognized that other types of processing stations may be located in portion  45  in addition to or instead of the thermal processing station  40 . 
     Other types of processing tool layouts may also be used. For example, in certain tools sold under the brand name Equinox(TM) available from Semitool, of Kalispell, Mont., the processing stations are disposed radially about a centrally located robotic transfer mechanism and a load/unload station. This platform is illustrated in  FIG. 17 . As illustrated in  FIG. 17 , a rotary tool  10   c  may include the same basic processing stations and similar robotic transfer apparatus to the linear tool. Accordingly, the same reference numerals are utilized here. Additional configurations are possible, such as those used in the processing tools available from Applied Materials of Santa Clara, Calif., and Novellus, Inc., of Portland, Oreg. 
     The robotic transfer mechanisms  36 ,  38  and  42  as well as the actuatable components of the processing stations  11 ,  34 ,  32  and  40  are in communication with the control unit  46  that implements software programming in response to user input parameters. It will be recognized, that a number of control units  46  may be connected to a common control system (not illustrated) that is used to control and oversee the operations performed in the microfabrication facility or sections thereof. Among its many functions, the control system  46  is programmed to control the transfer of microelectronic workpieces between the various processing stations and between the input/output section and the processing stations. Further, the control unit  46  is programmed to control the operation of the components at the individual processing stations to implement specific processing sequences in response to the user input parameters. 
     PROCESS CONTROL SEQUENCES 
     The control unit  46  can operate the processing tool  10  to deposit an electrophoretic material onto a workpiece in accordance with several different control sequences. The control sequences generally provide automated deposition of resists or other materials onto semiconductor wafers or other types of microelectronic workpieces in a manner that can be integrated with the other types of single-wafer processing equipment used in patterning microfeatures. Several embodiments of such control sequences provide automated sequences by maintaining clean surfaces on the workpiece. As such, the control sequence can use single-wafer handling equipment compatible with stepper machines and other microfabrication equipment. Several embodiments of control sequences also limit cross-contamination between the EPEs and other fluids which can reduce throughput and increase maintenance. 
       FIG. 18  illustrates one processing sequence  50  of a number of possible sequences. The particular sequences and parameters used in the EPE deposition processes depend on the particular manufacturing processes that are to be implemented. In the illustrated embodiment of the processing sequence  50 , the processing tool  10  ( FIG. 14 ) receives a microelectronic workpiece from a cassette  17  ( FIG. 14 ) and transfers it to one of the processing stations. The processing sequence  50 , for example, can include a first fluid process  52 , such as a pre-clean/pre-wetting process, in a fluid processing station  24  ( FIG. 14 ). In an alternate embodiment, the processing sequence  50  can include a seed layer repair/enhancement procedure before the first fluid process  52  because it may be useful to enhance or otherwise deposit additional conductive material onto the microelectronic workpiece before it is subject to the pre-clean/pre-wetting process. Such enhancement or repair of the seed layer may provide better photoresist film characteristics. Methods and apparatus for processing a conductive seed layer are shown and described in U.S. Pat. No. 6,197,181, which is hereby incorporated by reference in its entirety. 
     After the pre-clean/pre-wetting process or other type of first fluid process  52 , the control system  46  causes the robotic transfer mechanism  30  to remove the workpiece from the pre-clean/pre-wetting station and transfer it to the electrophoretic deposition station  11 . At the electrophoretic deposition station  11 , the sequence  50  further includes a deposition process  54  in which a microelectronic workpiece is subject to an EPE deposition process, such as depositing EPR. The specific parameters used in the deposition process  54  are input either directly or indirectly into the control system  46  by the user. It will be recognized that the particular parameters depend on the EPE type, the size of the workpiece, the type of underlying conductive layer, the thickness of the photoresist layer desired, and several other parameters. 
     After completing the deposition process  54 , the sequence  50  includes subjecting the microelectronic workpiece to an in-situ rinse process  56  carried out in the deposition station  11 . This process reduces contamination of other components because residual EPE is rinsed from the workpiece before it is loaded onto the robot  30  ( FIG. 14 ). Further, the control system  46  may direct the execution of an in-situ contact cleaning operation at any time. This latter process assists in ensuring that there is consistent contact between the contacts used to provide electroplating power and the conductive surface on a workpiece. 
     After the in-situ rinse process  56 , the sequence  50  further includes a second fluid process such as a rinsing process  58 . For example, the control system  46  may direct the robotic transfer mechanism  30  to remove the microelectronic workpiece from the deposition station  11  and transfer it to a deionized water rinse station for executing the rinsing process  58 . After the rinsing process  58 , the workpiece can be removed from the tool  10  for subsequent processing. In an alternate embodiment, the sequence can optionally include a thermal process  59 . For example, the control system  46  may also be programmed to direct the workpiece to a station at which the thermal process  59  is executed after completing the rinsing process  58 . The thermal process  59  may include both heating and subsequent cooling of the workpiece to effectively cure the photoresist. When the thermal process  59  occurs in the tool  10 , the workpiece can be removed from the tool  10  after baking and cooling the resist. As explained in more detail below, the workpiece is typically processed in additional tools for further processing the resist or other electrophoretic material deposited on the workpiece. 
     Additional Embodiments of Control Sequences 
       FIG. 19  is a flow diagram illustrating a control sequence  50   a  in accordance with another embodiment of the invention. In addition to the control sequence  50  described above in  FIG. 18 , subsequent processes of the control sequence  50   a  that may be executed on the microelectronic workpiece include an exposure procedure  60  followed by a photoresist development procedure  62 . Although the exposure procedure  60  and the development procedure  62  may be implemented in the processing tool  10  ( FIG. 14 ), it is more frequently executed in a separate tool. After the exposure procedure  60  and the development procedure  62  have been executed, the microelectronic workpieces may be transferred back to the processing tool  10  for execution of a chemical etching and/or metallization plating operations  64 . As shown at stage  66 , the overall process may be repeated as necessary until the desired structures are formed on or in the substrate. 
     It should be understood that the present invention may be practiced in many different ways and that the description above is merely exemplary. The description is not intended to limit the invention in any way to the illustrated embodiments. Rather, it is the intention of the inventors to both literally and through equivalents encompass all changes and improvements that validly fall within the bound of the claims below.

Technology Category: 3