Abstract:
In systems and methods for removing a photoresist film off of a wafer, the wafer is moved into a bath of a process liquid in a process tank. The process liquid removes the photoresist film from the wafer. The process liquid is pumped from the process tank to a filter assembly and moved through filter media to filter out solids from the process liquid, and the filtered process liquid is returned to the process tank. A scraper scrapes the filter media to prevent clogging of the filter media by accumulated solids.

Description:
PRIORITY CLAIM 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 62/350,078, filed Jun. 14, 2016, and now pending. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The field of the invention is processors, systems, and methods for processing semiconductor material wafers, and similar workpieces or substrates for microelectronic devices. 
       BACKGROUND OF THE INVENTION 
       [0003]    Microelectronic devices, such as semiconductor devices, are generally fabricated on and/or in semiconductor material wafers. In wafer level packaging applications, a thick film of photoresist is applied to the wafer and patterned via photolithography. One or more metals are plated through the pattern in the photoresist, to form microelectronic components or interconnections. The photoresist film is then stripped or removed in a using a process liquid, such as a solvent, which chemically reacts with the photoresist film to remove the photoresist film off of the wafer. 
         [0004]    Removing the photoresist can be difficult due to the thickness of the photoresist film. During the removing step, some of the photoresist film, which is typically about 50 to 250 microns thick, often comes off the wafer in relatively large gelatinous or diaphanous-like pieces, referred to here as solids, which are not fully dissolved by the process liquid. This results in a large volume of photoresist pieces accumulating in the process liquid, which can degrade the process liquid, clog filters or other fluid components and require frequent cleaning of the processing system. Engineering challenges remain in providing systems and methods for removing photoresist films. 
       SUMMARY OF THE INVENTION 
       [0005]    A processing system for stripping or removing photoresist off of a wafer has a process tank holding a bath of process liquid. The process liquid is pumped through a self-cleaning filter for filtering solids out of the process liquid. A mechanical scraper mechanically removes the filtered out solids from the filter media. The filter may optionally operate with a local back flush to periodically clean the filter media, with or without using the mechanical scraper. Maintenance requirements, process liquid consumption, and filter consumable costs are reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    In the drawings: 
           [0007]      FIG. 1  is a perspective view of a processing system for removing photoresist and similar films from a wafer. 
           [0008]      FIG. 2  is a section view of the process tank shown in  FIG. 1 . 
           [0009]      FIG. 3  is a schematic diagram of a first embodiment of the filter shown in  FIG. 1 . 
           [0010]      FIG. 4  is a schematic diagram of a second embodiment of the filter shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    As shown in  FIG. 1 , a processing system  20  may have one or more processors  28  within an enclosure  22 . The enclosure  22  may have access openings  24  and  26  to allow workpieces, such as semiconductor wafers, to be moved into and out of the processing system  20 , typically via robots. The access openings  24  and  26  may have closures, such as movable panels or windows, for closing off the access openings  24  and  26  during processing, to better contain vapors or gases within the enclosure  22 . The enclosure  22  may also be provided with air inlets and exhaust connections, to provide a controlled flow of air through the enclosure. 
         [0012]    Referring still to  FIG. 1 , each processor  28  has a head  50  for loading wafers into and out of a process tank  30 . Depending on the specific process performed, a secondary chamber  48 , such as a spin rinser dryer, may be associated with each processor  28  within the enclosure. The process tank  30  of each processor may be connected via fluid a supply line and a return line to a filter assembly  60  in the enclosure  22  or at a location remote from the enclosure. 
         [0013]    Turning to  FIG. 2 , a clean housing  32  may be provided at the top of the process tank  30 . The clean housing  32 , if used, generally includes clean chamber  34  surrounded by a lower or clean chamber drain channel  40 , and a rinse chamber  36  surrounded by an upper or rinse chamber drain channel  38 . The drain channels  38  and  40  are connected to a facility drain and optionally to a vacuum source. The process tank  30  may have a ring section  69  wide enough to accommodate a wafer  100 , and a much narrower central web section  75 . A tank rotor  56  has a plurality of arms  58  extending radially outward from a central hub  61 , with a holder  59  at the outer end of each arm  58 . A tank rotor motor  65  is connected to the tank rotor  56  for rotating the tank rotor  56  in the process tank  30 . One or more nozzles  73  and/or sonic transducers  77  may be provided on or in the outer wall  71  of the ring section  69  of the process tank  30 . 
         [0014]    In use, the head  50  holding a wafer  100  is lowered down into a load port  54  at the top of the process tank  30 , as shown in  FIG. 2 . The head  50  hands the wafer  100  off to a holder  59  on the tank rotor  56 . The tank rotor motor  65  rotates the tank rotor  56  moving the wafer  100  in a circular path through the process liquid contained in the process tank  30 , and simultaneously moving a subsequent holder  59  to the load port  54  to receive a subsequent wafer  100 . The process liquid may be a solvent, optionally heated to e.g., 80 to 120° C. Process liquid may optionally be jetted or sprayed from nozzles  73 , which may be submerged in or above the surface of the process liquid. As the tank rotor  56  continues to rotate, the processed wafer  100  returns to the load port  54  and is removed from the process tank  30  via the head  50 . Subsequent wafers  100  are similarly processed sequentially. The tank rotor  56  rotates about a rotation axis which is substantially horizontal, i.e., within 15 degrees of horizontal. 
         [0015]    As shown in the example of  FIG. 3 , the filter assembly  60  has a filter chamber  68  surrounding the filter media  66 . A return chamber  70  is formed to the outside of the filter media  66 , between the filter media and a housing  62 . In the example shown, the filter chamber  68  is a vertically oriented cylindrical and the filter media  66  and the collection chamber are annular and concentric with the filter chamber  68 . However, other shapes may of course be used as well. An inlet  64  on the housing  62  leads into the filter chamber  68 . Process liquid is pumped from the process tank  30  to the inlet  64  and into the filter chamber  68 . An outlet  72  outlet adjacent to a lower end of the return chamber is connected to a return line for returning filtered process liquid back to the process tank  30 . 
         [0016]    A collector  74  at the bottom of the filter chamber  68  may funnel solids towards a purge valve  82  and a recovery unit  84 . A mechanical scraper has a scraper head  76  on a shaft  78  movable linearly via an actuator  80 . The scraper head  76  may include one or more disks or blades contacting the filter media to scrape off solids accumulated on the filter media. The filter media is typically a metal screen or mesh, although other forms of filter media may also be used. 
         [0017]    During processing, a pump  92  pumps process liquid from the process tank  30  into the filter chamber  68  via the inlet  64 . The pump  92  may be a self cleaning pump, such as a semi-enclosed impeller pump, for pumping the process liquid through the system. Process liquid moves from the filter chamber  68 , through the filter media  66 , and into the return chamber  70  via the pump  92  exerting positive fluid pressure on the process liquid within the filter assembly. 
         [0018]    The solids deposit out on or in the filter media  66 . The process liquid in the return chamber  70 , largely free of filtered out solids, is pumped back to the process tank  30  via the outlet for reuse. 
         [0019]    Periodically, or on an as needed basis, the actuator  80  moves the scraper head  76  linearly through the filter chamber  68 . The scraper head  76  slides along the inner annular surface of the filter media  66  scraping off solids and pushing them down into the collector  74 . This prevents solids  90  from building up and clogging the filter media. After a specified amount of solids  90  accumulates in the collector  74 , the purge valve  82  is opened and the solids  90  are purged to a waste drain. 
         [0020]    Alternatively, the purge valve  82  may connect to a recovery unit  84  adapted for separating excess process liquid from the solids  90  and routed back to the inlet  64  via a recovery line  88 , and the solids  90  are routed to a recovery unit drain  86  or to a storage vessel for disposal. The recovery unit  84  may also be adapted to recover dissolved or entrained materials, such as precious metals. Opening the purge valve  82  may also allow solids to be purged from the filter media  66  via flushing by rapid movement of the process liquid through the filter chamber  68 . 
         [0021]      FIG. 4  shows an alternative self-cleaning filter assembly  101  which operates in the same way as the filter assembly  60  shown in  FIG. 3 , except that the scraper head  76 , shaft  78  and actuator  80  are replaced with a rotary scraper having a filter rotor  102  rotated by a rotary actuator  104 . One or more blades or other surfaces of the filter rotor  102  scrape solids off of the filter media  66 . 
         [0022]    A single self cleaning filter assembly  60  or  101  may be used to filter the process liquid of multiple processors  28  simultaneously to reduce the cost of the processing system  20 . Alternatively, two self cleaning filter assemblies  60  or  101  may be used in parallel to prevent down time for maintenance. The self cleaning filter assembly  60  or  101  allows the process liquid to be used for a longer time and reduces the cost of operating the processing system  20 . 
         [0023]    Operations of the processing system  20 , including the pumps, valves, motors, actuators, and head movements described may be controlled via a computer electrically linked to these elements. 
         [0024]    The term wafer as used here includes semiconductor material wafers, as well as other substrates on which micro-scale components are formed. The term connected as used relative to fluid components means connected via a pipe or hose, with or without any other physical connection. Thus, novel methods and systems have been shown and described. Various changes and substitutions may of course be made without departing from the spirit and scope of the invention. The invention, therefore, should not be limited, except by the following claims and their equivalents.