Abstract:
An apparatus for use in processing a workpiece to fabricate a microelectronic component is set forth. The apparatus comprises a process container having a process fluid therein for processing the workpiece and a workpiece holder configured to hold the workpiece. A position sensor is employed to provide position information indicative of the spacing between a surface of the workpiece and a surface of the process fluid. A drive system provides relative movement between the surface of the workpiece and the surface of the process fluid in response to the position information. Preferably, the relative movement provided by the drive system comprises a first motion that causes the surface of the workpiece to contact the surface of the process fluid, and a second motion opposite the direction all of and following the first to generate and maintain a column of process fluid between the surface of the process fluid and the surface of the workpiece. In this manner, the drive system causes the surface of the workpiece to contact the surface of the process fluid to the exclusion of other surfaces of the workpiece thereby limiting processing of the workpiece to only the desired surface. In accordance with one embodiment, the apparatus is configured to electroplate a material onto the surface of the workpiece.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of International PCT Patent Application No. PCT/US98/20743, designating the US, filed Sep. 30, 1998, entitled APPARATUS AND METHOD FOR CONTROLLING WORKPIECE SURFACE EXPOSURE TO PROCESSING LIQUIDS DURING THE FABRICATION OF MICROELECTRONIC COMPONENTS, which claims priority from U.S. patent application Ser. No. 08/940,517, filed Sep. 30, 1997, and U.S. patent application Ser. No. 08/940,523, filed Sep. 30, 1997, now U.S. Pat. No. 6,015,462. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     The fabrication of microelectronic components from a wotkpiece, such as a semiconductor wafer substrate, polymer substrate, etc., involves a substantial number of processes. Generally stated, there are four categories of processing operations performed on the workpiece to fabricate the microelectronic component(s). Such operations include material deposition, patterning, doping and heat treatment. 
     Material deposition processing involves depositing thin layers of electronic material to the surface of the workpiece (hereinafter described as, but not limited to, a semiconductor wafer). Patterning provides removal of selected portions of these added layers. Doping of the semiconductor wafer is the process of adding impurities known as “dopants” to the selected portions of the wafer to alter the electrical characteristics of the substrate material. Heat treatment of the semiconductor wafer involves heating and/or cooling the wafer to achieve specific process results. 
     Numerous processing devices, known as processing “tools”, have been developed to implement the foregoing processing operations. These tools take on different configurations depending on the type of workpiece used in the fabrication process and the process or processes executed by the tool. One tool configuration, known as the Equinox(R) wet processing tool and available from Semitool, Inc., of Kalispell, Mont., includes one or more semiconductor workpiece processing stations that utilize a semiconductor workpiece holder and a process bowl or container for implementing wet processing operations. Such wet processing operations include electroplating, etching, etc. 
     In accordance with one configuration of the foregoing Equinox(R) tool, the workpiece holder and the process bowl are disposed proximate one another and function to bring the semiconductor wafer held by the workpiece holder into contact with a processing fluid disposed in the process bowl. Restricting the processing fluid to the appropriate portions of the semiconductor wafer, however, is often problematic. 
     Conventional semiconductor workpiece processors have utilized various techniques to facilitate complete exposure of these appropriate portions to the processing fluid while concurrently shielding the remaining portions of the semiconductor wafer that are not to be contacted. For example, such conventional systems may require application of tape to the back side of the semiconductor wafer to prevent process fluid from contacting the portions of the wafer beneath the tape. Other configurations use a suction cup arrangement for contacting and holding to the back side of the semiconductor wafer to thereby prevent the processing fluid from contacting the back side. 
     Although such conventional techniques often adequately fulfill the purpose of preventing process fluid from coming in contact with the back surface of the semiconductor wafer, such techniques present their own set of problems. For example, additional processing steps are required to apply the tape. Further, additional parts are required when a physical cover is used to prevent processing fluid contact with the back side of the workpiece. Still further, semiconductor workpieces are fragile and care must be taken not to damage the wafer during covering of the wafer surface. The increased wafer handling inherent in the conventional techniques increases the risk of wafer damage. 
     Therefore, the present inventors have recognized a need to improve on the techniques currently used to control the contact between the processing fluid and the appropriate portions of the semiconductor workpiece. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention are described below with reference to the following accompanying drawings. 
     FIG. 1 is a schematic representation of a process module of a semiconductor workpiece processor. 
     FIG. 2 is a side view of a first embodiment of a process head of the process module holding a semiconductor workpiece. 
     FIG. 3 is a side view, similar to FIG. 2, of a second embodiment of a process head of the process module. 
     FIG. 4 is a side view of the process head of FIG. 2 positioning a semiconductor workpiece in contact with a process fluid within a process container of the process module. 
     FIG. 5 is a side view illustrating the formation of a column of process fluid intermediate the semiconductor workpiece and the process fluid bath. 
     FIG. 6 is a functional block diagram illustrating various components according to one embodiment of the semiconductor workpiece processor. 
     FIG. 7 is a functional block diagram of an embodiment of a control system of the semiconductor workpiece processor. 
     FIG. 8 is a functional block diagram of an embodiment of position sensor circuitry of the semiconductor workpiece processor. 
     FIG. 9 is a schematic diagram of the position sensor circuitry shown in FIG.  8 . 
     FIG. 10 is a flow chart illustrating a method of monitoring and controlling the position of a semiconductor workpiece. 
    
    
     SUMMARY OF THE INVENTION 
     An apparatus for use in processing a workpiece to fabricate a microelectronic component is set forth. The apparatus comprises a process container having a process fluid therein for processing the workpiece and a workpiece holder configured to hold the workpiece. A position sensor is employed to provide position information indicative of the spacing between a surface of the workpiece and a surface of the process fluid. A drive system provides relative movement between the surface of the workpiece and the surface of the process fluid in response to the position information. Preferably, the relative movement provided by the drive system comprises a first motion that causes the surface of the workpiece to contact the surface of the process fluid, and a second motion opposite the direction all of and following the first to generate and maintain a column of process fluid between the surface of the process fluid and the surface of the workpiece. In this manner, the drive system causes the surface of the workpiece to contact the surface of the process fluid to the exclusion of other surfaces of the workpiece thereby limiting processing of the workpiece to only the desired surface. In accordance with one embodiment, the apparatus is configured to electroplate a material onto the surface of the workpiece. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates one embodiment of a semiconductor workpiece processor  10 . In this embodiment, the processor  10  includes a semiconductor processing head  12  and a process container or bowl  14 . The processing head  12  includes one or more components that are adapted to support a semiconductor workpiece W, such as a semiconductor wafer. The semiconductor wafer W has a first or lower surface S 1  and a second or upper surface S 2 . 
     In the illustrated embodiment, the processing head  12  includes a workpiece holder  16 . The workpiece holder  16  of the illustrated embodiment includes fingers or supports  18  coupled with a lower surface  20  thereof. Fingers  18  of holder  16  are configured to support a semiconductor workpiece W adjacent a lower surface  20  of head  12 . In the disclosed embodiment, workpiece holder  16  is configured to support semiconductor workpiece W so that the lower surface S 1  thereof is presented for contact with a processing fluid or bath disposed in the process cup. Process head  12  may include a rotor motor or the like that is configured to rotate or spin the holder  16  and the semiconductor workpiece W held thereby. Such rotation of workpiece W may occur during processing of the workpiece when it is in contact with the processing fluid, or when the workpiece W is removed from such contact. 
     Workpiece holder  16  is configured for vertical movement with respect to process bowl  14 . More specifically, a vertical drive motor  22  is provided to implement vertical movement of process head  12 , workpiece holder  16  being in fixed vertical relationship with the process head  12  and resulting in concurrent movement thereof. In the configuration shown in FIG. 1, vertical drive motor  22  is coupled with a vertically oriented shaft  24  that, in turn, is coupled with a horizontal supporting member  26 . Support member  26  is joined at a first end thereof with vertical shaft  24 . A second end of support member  26  engages and supports process head  12 . 
     Movement of vertical shaft  24  in either an upward or downward direction provides corresponding movement of head  12 , and the workpiece holder  16  fixed thereto, upward or downward with respect to process bowl  14 . In particular, vertical drive motor  22  is configured to lower head  12  to a position in which semiconductor workpiece W is in contact with process solution or fluid  38  within process bowl  14 . Typically, the process fluid  38  is a liquid bath, such as an electroplating bath. 
     Contact between the semiconductor workpiece W and the process fluid  38  results in the processing of preselected portions, such as the lower surface S 1 , of the exposed surface of semiconductor workpiece W. The processing may include electroless plating, electroplating or etching processes. In the illustrated embodiment, processing head  12  is preferably configured to rotate about a horizontal axis to facilitate engagement and extraction of the semiconductor workpieces W to and from the workpiece holder  16 . For example, head  12  may be configured to rotate about an axis defined by support member  26 . Semiconductor workpieces W may be engaged with holder  16  or removed therefrom when head  12  is rotated to a position in which holder  16  is face-up (not shown). 
     Various details of one embodiment of process bowl  14  are illustrated in the cross-sectional views of FIGS. 1,  4  and  5 . As illustrated, process bowl  14  of processor  10  includes sidewalls  28  and a lower wall  30  that together defined defining a process compartment  32 . Sidewalls  28  are annular in the described embodiment to define a substantially circular process compartment  32  within bowl  14 . 
     A ring  34  is provided within process compartment  32 . Ring  34  is spaced apart from sidewalls  28  and defines an annularly-shaped compartment  36  therebetween. Ring  34  is operable to receive and contain the process fluid  38 , such as a plating bath, within fluid compartment  36 . Further, the upper portion of ring  34  forms a weir that maintains the level of process fluid  38  at a substantially constant level. In one embodiment, a flow of process fluid  38  is provided to the processing bowl  14  to generate an upwardly directed flow that spills over ring  34  to insure that process fluid  38  that ultimately contacts the wafer is fresh (e.g., in the case of electroplating, it insures that the requisite concentration of the metal that is to be plated is present at the surface to be plated). 
     The illustrated process bowl  14 , processing head  12 , and workpiece holder  16  of processor  10  are exemplary configurations only. Other configurations of process module  10  are considered and within the scope of the present invention. 
     In the illustrated embodiment, the processor  10  is configured for electroplating. To this end, an anode  37  is provided within the fluid compartment  36  of process container  14  while the semiconductor workpiece W constitutes the cathode. As described in further detail below, the fingers  18  may be constructed as electrodes that conduct the requisite electroplating power to the surface S 1  of semiconductor workpiece W for the plating operation. Both the anode  37  and cathode of processor  10  are coupled with a plating power supply  15  (shown in FIG.  8 ). 
     As previously mentioned, some semiconductor workpiece processing methods, such as the electroplating operations described herein, require processing of only selected portions (e.g., a single side) of a given semiconductor workpiece W. In such situations, the other portions (e.g., upper side S 2 ) must be shielded to prevent contact with the process fluid. 
     Processor  10  is designed to provide such selective contact between the semiconductor workpiece W and the process fluid  38 , such as an electroplating bath. More particularly, in the preferred embodiment disclosed herein, processor  10  is adapted to allow processing of the lower surface S 1  of semiconductor workpiece W while inhibiting processing of the upper surface S 2 . During this mode of operation, the upper surface S 2  and, in some instances, even the edges of the semiconductor workpiece W are prevented from contacting the process fluid  38 . 
     To this end, as will be explained in further detail below, processor  10  is operated to provide controlled relative vertical movement between the processing head  12  and the surface of the processing fluid  38  until surface S 1  of semiconductor workpiece W first contacts the fluid. In the illustrated embodiment, it is the processing head  12  that is moved vertically to provide such contact while the process bowl  14  remains fixed. After contact between the surface S 1  and the surface of the fluid  38  is established, the surface S 1  is pulled vertically in a direction away from fluid  38  by a small, predetermined distance. The surface tension of the fluid  38  results in a meniscus whereby the processing fluid  38  is prevented from contact with the upper surface S 2  and, in most instances, the peripheral edges of the workpiece W. 
     Preferably, this controlled vertical motion is responsive, at least in part, to one or more signals indicative of the real-time position of the surface S 1  with respect to the surface of the fluid  38 . In the illustrated embodiment, one or more conductors are disposed in fixed relation with the head  12 . These conductors may be disposed to contact the fluid  38  at different vertical positions along the vertical movement path of the head  12  toward and away from the surface of fluid  38 . As such, contact between a particular conductor or electrode and the surface of fluid  38  corresponds to a given distance between the semiconductor workpiece W and fluid  38 . Multiple relative distances may be sensed by employing multiple conductors disposed to contact fluid  38  at different vertical positions along the vertical movement path. 
     Various electronic techniques may be used to sense contact between a particular conductor and fluid  38 . Where, as here, the processor  10  is configured for electroplating, it is possible to take advantage of the conductivity of the electroplating solution, designated as fluid  38 , so as to minimize the number of additional components required to implement the position sensing. To this end, a reference voltage is generated between the conductor and anode  37 . When a given conductor contacts the electroplating solution, electrical continuity is established in an electrical circuit that comprises the conductor, anode, and process fluid  38 . This continuity condition can be detected and used as an indicator of contact between a given conductor and the surface of the electroplating solution. 
     In the illustrated embodiment, fingers  18  perform dual functions. First, fingers  18  are constructed to provide plating power to the surface S 1  of semiconductor workpiece W. Second, fingers  18  are used as conductors/sensors that assist in providing an indication of the position of semiconductor workpiece W relative to process fluid  38 . 
     Each finger  18  shown in FIG. 2 comprises a centrally disposed conductive material that is used to receive and conduct an electric signal in the manner described above, and a dielectric coating  40  disposed about selected portions of the conductive material. As illustrated, the dielectric coating  40  only covers a portion of the centrally disposed conductive material thereby providing exposed conductors  42 . 
     As workpiece holder  16  is lowered toward process bowl  14 , the exposed conductors  42  of the fingers  18  contact process fluid  38 . Contact between the exposed conductors  42  and fluid  38  (e.g., a conductive electroplating solution) completes an electrical circuit. With reference to FIG. 2, this continuity condition first occurs when the surface S 1  is a distance d 1  from the surface of fluid  38 . As such, it becomes possible to determine when the surface S 1  and the surface of fluid  38  are a predetermined distance d 1  apart, in effect monitoring the vertical position of the surface S 1  with respect to the surface of fluid  38 . 
     Sensing of the relative position depends upon the positioning of the exposed portions of conductors  42  within fingers  18  relative to the surface S 1 . As shown in FIG. 2, conductors  42  are brought into contact with process fluid  38  corresponding to a distance d 1  intermediate lower surface S 1  of workpiece W and a surface or meniscus  39  of process fluid  38 . With reference to FIG. 3, however, the dielectric  40  of the fingers  18  exposes exposed conductors  42  so that a measurable current flow (or other reference signal) is first generated wine the surface S 1  and meniscus  39  are spaced from one another by a distance d 2 . Exposing different portions of conductors  42  enables sensing of the position of semiconductor workpiece W with respect to process fluid  38  at various positions along the vertical movement path. 
     Referring to FIG. 4, the embodiment of workpiece holder  16  shown in FIG. 2 has been lowered a sufficient extent to submerge the lower portions of fingers  18  within process fluid  38  and place the surface S 1  into contact with the meniscus  39 . Preferably, for example, workpiece holder  16  has been lowered a distance d 1  from the position shown in FIG. 2 after the reference signal indicative of spacing d 1  is first detected. The lower surface S 1  of workpiece W is thus wetted with process solution  38  in the position shown in FIG.  4 . Semiconductor workpiece W may be held at the position shown in FIG. 4 to provide processing of the lower surface S 1  thereof while preventing contact of the fluid  38  with the upper surface S 2 . 
     In some instances, it may be desirable to further limit the extent of contact between the processing fluid  38  and semiconductor workpiece W. This may be accomplished in the manner illustrated in FIG. 5, which shows that process head  16  has been raised a predetermined distance (possibly, a programmable distance) following contacting of lower surface S 1  of semiconductor workpiece W with surface  39  of process fluid  38 . By raising the process head  16  in this manner, a column  35  of process fluid  39  is provided between the lower surface S 1  of semiconductor workpiece W and the remaining process fluid  38  within fluid compartment  36 . The column  35  of process fluid  39  may be a few millimeters in height. For example, column  35  may have a height within a range of approximately zero millimeters to five millimeters, and typically within a range of one to three millimeters. 
     Such raising of semiconductor workpiece W minimizes the likelihood that process fluid  38  will splash onto the upper surface S 2  thereof. Further, such raising assists in preventing the process fluid  38  from contacting peripheral edge portions of the semiconductor workpiece W. The positioning of semiconductor workpiece W with respect to process fluid  38  may vary and is dependent upon the specific type of plating coverage or other processing desired. 
     In the illustrated embodiment, the reference signal (here, present only when an electrical circuit is established comprising the exposed conductor  42 , the process fluid  38 , and anode  37 ) is applied to position sensor circuitry  60  (FIG.  6 ). Position sensor  60  is configured to generate a position indication signal responsive to the reference signal. The position indication signal may be applied to a control system  80  of the semiconductor workpiece processor  10 . Control system  80  is responsive to the position indication signal to control the vertical drive motor  22  thereby providing controlled movement of process head  16  and semiconductor workpiece W relative to process fluid  38 . 
     Referring to FIG. 6, one configuration of a semiconductor workpiece processor  8  is shown in a block diagram. The illustrated workpiece processor  8  includes a control system  80 , process module  10  and position sensor  60 . Control system  80  is electrically coupled with position sensor circuitry  60  and process module  10 . 
     One embodiment of the control system  80  is shown in FIG.  7 . As illustrated, control system  80  comprises at least a central processing unit  82  (CPU) and a memory device  84 . Central processing unit  82  is operable to interface with memory device  84 . Memory  84  may implemented as either RAM or ROM or both and is configured to store operational code described below with respect to the flow chart of FIG.  10 . The central processing unit  82  of control system  80  is configured via the operational code to receive position information from position sensor  60  and control vertical drive motor  22  and the positioning of semiconductor workpiece W responsive thereto. 
     Referring to FIG. 8, one embodiment of position sensor  60  is shown. The illustrated position sensor  60  includes a voltage reference  62 , relay  64 , comparator  68 , sensitivity control circuitry  70 , and signal logic circuitry  72 . The relay  64  is coupled with the anode  37  of process bowl  14  and the fingers  18  of workpiece holder  12  of process module  10 , as well as plating power supply  15 . The signal logic  72  and relay  64  of position sensor  60  are coupled with the control system  80  of the semiconductor workpiece processor  8 . 
     In general, position sensor  60  generates and outputs a signal indicative of the vertical distance between surface S 1  and meniscus  39 . In the illustrated embodiment, a binary signal is generated to the control system  80 . This signal transitions from a logical “false” to a logical “true” when a predetermined distance between surface S 1  and meniscus  39  is first reached. 
     The position sensor  60  includes a voltage reference  62  that operates as a reference signal generator. The reference signal generated by voltage reference  62  is preferably a low voltage, low current electric signal. In the described embodiment, the reference signal is one volt and approximately two milliamps. 
     The reference signal is selectively applied to processor  10  responsive to control signals from control system  80 . Upon start-up and prior to processing of a semiconductor workpiece W, control system  80  applies an appropriate control signal to relay circuit  64 . Relay circuit  64  is energized responsive to receiving the control signal and applies the reference signal to the anode in process bowl  14  and to the fingers  18  via electrical connection lines  11  and  13 , respectively. 
     When the surface S 1  of semiconductor workpiece W reaches a predetermined distance, such as d 1  of FIG. 2, from meniscus  39  of process fluid  38 , the reference signal applied via line  11  is electrically connected through fingers  18  and the fluid  38  to anode  37 . This signal is provided from the relay circuitry  64  to an input of comparator  68 . The comparator circuit  68  compares the magnitude of the signal to a predetermined threshold value that is provided at the output of sensitivity control  70 . If the magnitude of the detected signal exceeds the threshold value, comparator  68  generates a signal to the input of signal logic  72  which, in turn, provides a logical “true” signal to control system  80 . (It will be recognized that signal logic circuit  72  may be unnecessary when the output signal from compared are  68  transitions between binary states that may be recognized by the control system.) Adjusting sensitivity control  70  adjusts the threshold value and, in turn, the trip point for comparator  68 . Sensitivity control  70  comprises a potentiometer in accordance with one embodiment of the invention. 
     Signal logic  72  is preferably configured to store the logical binary value corresponding to the signal from the output of compared are  68 . Further, the signal logic  72  may generate a signal to the relay  64  that de-energizes the relay  64  when the stored signal is a logical “true”. Such de-energization of relay  64  insulates position sensor circuitry  60  from electrical connection lines  11 ,  13  and effectively replaces the reference signal with electroplating power provided at the output of plating power supply  15 . In this de-energized state, plating power supply  15  is operable to apply a high voltage and/or current across electrical connection lines  11 ,  13  and the anode and cathode of process module  10  responsive to control from central processing unit  82 . De-energizing relay  64  also protects position sensor circuitry  60  from the high voltages and/or currents generated by the power supply  15 . Once relay  64  has been de-energized, central processing unit  82  preferably generates one or more signals that are used to turn on plating power supply  15  to conduct electroplating of the semiconductor workpiece W. 
     Referring to FIG. 9, a detailed schematic of position sensor circuitry  60  described above is shown. The illustrated position sensor  60  includes voltage reference  62 , comparator  68 , sensitivity control  70 , and latches  73 ,  74 . In the illustrated embodiment, signal logic  72  comprises latches  73 ,  74 . Relay  64  is coupled with workpiece holder  12  via electrical connection line  13  and the anode  37  in process bowl  14  via electrical connection line  11 . Control system  80  receives the signal output from latch  73  and is operable to apply a reset signal to latch  73  and a start signal to latch  74  at the appropriate times. 
     Responsive to the assertion of a start signal via control system  80 , latch  74  is set. Setting latch  74  energizes relay  64  thereby coupling voltage reference  62  with the anode  37  of process bowl  14  via electrical connection  11 . In addition, energizing relay  64  electrically couples the fingers  18  of workpiece holder  12  with comparator  68  via electrical connection  13 . 
     The reference signal (minus small voltage drop across the fluid  38 ) is applied to comparator  68  upon contact between the process fluid  38  and exposed portions  42  of fingers  18  of process head  16 . This results in a change in the state of the output signal of comparator  68 . The state change sets latch  73  that, in turn, provides an output signal that resets latch  74 . 
     Latch  73  and logic gate  79  operate to provide a signal indicative of the fact that the predetermined distance, such as d 1  of FIG. 2, has been reached and applies this signal to control system  80 . Latch  73  effectively stores this signal state thereby enabling the central processing unit  82  of control system  80  to poll the signal according to timing of control system  80 . 
     Once the central processing unit  82  of control system  80  detects a transition to a logical “true” the state from the position sensor  60 , the central processing unit  82  provides a reset signal to clear latch  73 . Thereafter, the central processing unit of the control system  80  reasserts the start signal to set latch  74  once a subsequent semiconductor workpiece W is properly positioned within process head  16  and prior to the lowering of the head  16  and semiconductor workpiece W toward process fluid  38  within process container  14 . 
     As stated above, control system  80  is configured to monitor and detect the presence of the position indication signal from signal logic  72 . The presence of a logical “true” state of the position indication signal provides position information of the semiconductor workpiece W with respect to process fluid  38 . Responsive to receiving the position indication signal, control system  80  is configured to operate vertical drive motor  22  and adjust the vertical position of semiconductor workpiece W with respect to the process fluid  38 . More specifically, control system  80  can be operated to instruct vertical drive motor  22  to move process head  16  and the semiconductor workpiece W held thereby the predetermined distance, such as d 1  of FIG. 2, to contact the process fluid  38 . The particular distance moved is typically preselected and corresponds to the distance intermediate semiconductor workpiece W and the process fluid  38 . The semiconductor workpiece W may be lowered following the reception of the indication signal to account for the distance between the lower surface S 1  of the semiconductor workpiece W and the process fluid  38  corresponding to the exposed portion of the electrode  42  within finger  18 . The particular portions of conductors  42  which are exposed may be varied to adjust the calibration (i.e., distance between the workpiece W and process fluid  38  at the moment the reference signal passes through conductor  42 ). Alternatively, adjustments of calibration may be implemented by software. 
     Lowering and contacting the semiconductor workpiece W with process fluid  38  wets the lower surface S 1  thereof with the fluid  38 . In one embodiment, the lowering of workpiece W results in the spreading of the meniscus  39  of process fluid  38  over the entire lower surface S 1  of the semiconductor workpiece W. 
     Responsive to receiving a logical “true” state of the position indication signal from position sensor  60 , control system  80  knows the exact position of semiconductor workpiece W with respect to the surface  39  of process fluid  38 . Subsequent movement of process head  16  and semiconductor workpiece W following the reception of the indication signal may be variable depending upon the particular application. For example, after the lower surface S 1  of the semiconductor workpiece W has been driven to contact the meniscus  39  of process fluid  38 , control system  80  may operate the drive motor  22  to retract or raise the semiconductor workpiece W a predetermined distance to provide the column  35  of process fluid  39  between semiconductor workpiece W and the remaining process fluid  38  within fluid compartment  36 . The lower surface S 1  of semiconductor workpiece W preferably remains wetted during the retraction of process head  16  and workpiece W. An adhesive force or tension overcomes the gravitational force and maintains the process fluid  38  in contact with the lower surface S 1  during retraction of the workpiece W thereby forming column  35 . As noted above, the formed column  35  of process fluid  38  may be a few millimeters in height. The positioning of semiconductor workpiece W with respect to process fluid  38  may vary and is dependent upon the specific type of plating coverage desired. 
     FIG. 10 is a flowchart illustrating one manner of operating the control system  80 . Central processing unit  82  is configured via software code stored in, for example, memory  84  according to the illustrated flow chart. The control operations described in the depicted flow chart may be implemented in hardware according to alternative embodiments of the invention. 
     As illustrated in FIG. 10, control system  80  asserts a start signal that step  90 . The start signal is preferably asserted prior to the lowering of the semiconductor workpiece W toward the meniscus  39  of process fluid  38 . Assertion of the start signal sets second latch  74  thereby electrically coupling position sensor  60  and process module  10  via relay  64 . 
     At step  92 , control are  80  scans or reads the output of first latch  73  of position sensor  60  according to timing of the control system  80  (e.g., at predetermined time intervals). Following the scanning, control system  80  analyzes the detected signal to determine whether it has gone to a logical “true” state. As noted above, die logical “true” state indicates that the lower surface S 1  of semiconductor workpiece W is a predetermined distance from surface  39  of process fluid  38 . If the indication signal is not at a logical “true” state, control system  80  continues to scan the output of first latch  73  of signal logic  72  at predetermined time intervals. 
     The control system  80  proceeds to step  96  of FIG. 10 if the position indication signal goes to a logical “true” state. At that time, the control system asserts the reset signal at step  96  that clears the first latch  73 . Thereafter, control system  80  proceeds to step  98  to adjust the vertical spacing between the semiconductor workpiece W and meniscus  39  of the process fluid  38 . For example, referring to FIG. 2, semiconductor workpiece W may be lowered a distance d 1  at step  98  depending upon the calibration of the process module  10  corresponding to the distance between the lower surface S 1  and surface  39  of process fluid  38 . Alternatively, semiconductor workpiece W may be lowered a distance d 2  at step  98  if the process head  16  shown in FIG.  3  and the fingers  18  associated therewith are utilized. The process described with reference to FIG. 10 may be repeated when a subsequent semiconductor workpiece W is to be processed. 
     Adjusting the positioning of semiconductor workpiece W relative to process fluid  38  preferably coats or wets the lower surface S 1  of the semiconductor workpiece with the process fluid  38 . Processing of the semiconductor workpiece W in accordance with the described method eliminates the need for covering the edges or upper surface S 2  of the semiconductor workpiece inasmuch as process fluid  38  is not applied to the sides or upper surface of the workpiece. 
     In addition, the semiconductor workpiece W may be subsequently raised following the coating of the lower surface S 1  thereof. An attractive force draws the process fluid upward forming a column  35  of process fluid between the semiconductor workpiece W and the process fluid bath  38 . Such raising of semiconductor workpiece W reduces the chance of exposure of the sides or edges and upper surface S 2  of workpiece W to the process fluid  38 . The edges and upper surface S 2  of workpiece W preferably remain free of plating solution during the processing and unwanted plating or processing of various portions of workpiece W is minimized. 
     In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the apparatus herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.