Abstract:
A non contact isolation seal assembly for rotary and linear sealing for use in semiconductor manufacturing automation. The noncontact isolation seal assembly employs a seal having an aperture with a shaft extending through the aperture. A gap region is maintained between the outside surface of the shaft and the aperture of the seal. A gas source is connected to the interior of the gap region whereby gas pressure in the gap region is maintained at a higher pressure than gas pressure surrounding the shaft. The flow of gas and differential pressure prevents fluids, gasses, and contaminants from passing through the gap region preventing contamination of the drive mechanism.

Description:
BACKGROUND OF THE INVENTION 
     TECHNICAL FIELD 
     It is well known to use articulated arms to transport semiconductor wafers, plates and flat panel displays between cassettes, load locks, process modules and other work stations. Recent developments in the processing of semiconductors include the introduction of chemical metal polishing (CMP) and copper deposition whereby articulated arms can be exposed to fluids, corrosive liquids and corrosive gasses. These fluids, corrosive liquids and corrosive gasses can infiltrate the drive mechanism for the articulated arm causing premature failure of mechanical and electrical components due to contamination and corrosion. In the past, the drive mechanism has been sealed typically using bellows, lip seals, labarinth seals or ferro-fluid type seals; each of these sealing types has been effective but can be costly or also requiring high precision machining and alignment of sealing components. 
     The apparatus of the present invention relates generally to material transfer devices. The material transferred might include, but is not limited to semiconductor wafers, such as Silicon, Gallium Arsenide, semi conductor packing substrates, such as high density interconnects, semiconductor manufacturing process imaging plates, such as masks or reticles, and large area display panels, such as Active Matrix LCD substrates or Field Emission Diode substrates. 
     The invention further relates to robot drive technologies for handling wafers or flat panels and relates more particularly to improvements in such technologies whereby fluids, gasses, and contaminants can be isolated and excluded from the robot drive mechanism. The invention further relates to seals for rotating and/or reciprocating shafts and, more particularly, to low friction gas and liquid exclusion seals for rotating and/or reciprocating shafts. 
     SUMMARY OF THE INVENTION 
     The invention resides in a seal assembly for use in semiconductor manufacturing automation and more specifically relates to an improvement therefor whereby the robot drive mechanism can be sealed and isolated from fluids, gasses, and contaminants without the use of bellows, lip seals, labarinth seals or ferro-fluid type seals. 
     More specifically, the invention resides in a noncontact isolation seal assembly for rotary and linear sealing for use in semiconductor manufacturing automation. The noncontact isolation seal assembly comprises a seal having an aperture with a shaft extending through the aperture. A gap region is maintained between the outside surface of the shaft and the aperture of the seal. A gas source is connected to the interior of the gap region whereby gas pressure in the gap region is maintained at a higher pressure than gas pressure surrounding the shaft. The flow of gas and differential pressure prevents fluids, gasses, and contaminants from passing through the gap region preventing contamination of the drive mechanism. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and other features of the invention are explained in the following description taken in connection with the accompanying drawings, wherein 
     FIG. 1 is a perspective view of a substrate transfer apparatus incorporating features of the present invention; 
     FIG. 2 is a isolated sectioned perspective view through the substrate transfer apparatus showing the seal assembly of the present invention; 
     FIG. 3 is a isolated sectioned view of a first preferred embodiment of the present invention; 
     FIG. 4 is a isolated sectioned view of a second preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring, now to FIG. 1, there is shown a perspective view of a substrate transfer apparatus  10 . The substrate transfer apparatus  10  includes a drive housing  14 , a drive shaft  22 , driven arm  26  and mounting flange  18 . Mounting flange  18  is fastened to work surface  13 . Contaminants such as fluids, corrosive liquids and corrosive gasses are restricted to the side of work surface  13  and mounting flange  18  which driven arm  26  operates typically by static sealing mounting flange  18  to work surface  13  either by clamping, gasket or o-ring. Work surface  13  tends to act as a barrier to prevent contaminants such as fluids, corrosive liquids and corrosive gasses from exposing the exterior of drive housing  14  to such contaminants. The driven arm  26  includes an end effector  28  which may or may not utilize a vacuum grip when moving substrate  32 . The drive shaft  22  may move in the vertical direction  16  and/or in the rotary direction  12  relative to drive housing  14 . Seal Assembly  34  prevents contaminants such as fluids, corrosive liquids and corrosive gasses from passing from the side of work surface  13  and mounting flange  18  which driven arm  26  operates to the interior of drive housing  14  where the robot drive mechanism for driving driven arm  26  resides. Seal Assembly  34  also prevents contaminants such as particulates from passing from the interior of drive housing  14  to the side of work surface  13  and mounting flange  18  which driven arm  26  operates. A substrate processing apparatus such as disclosed in U.S. Pat. No. 5,270,600 is hereby incorporated by reference in its entirety. The substrate transfer apparatus  10  is adapted for use to process substrates and other articles of similar type, such as, semiconductor wafers or flat panel displays, as is known in the art. In alternative embodiments, other types of housings, flanges and/or arm assemblies could be used in conjunction with the present invention. 
     Referring now to FIG. 2, there is shown an isolated sectioned perspective view through the substrate transfer apparatus. The seal assembly  34  includes a seal  38  in mounting flange  18  held in place either loosely or fixed by capture plate  40 . Shaft  22  may move in the vertical direction  16  and/or in the rotary direction  12  relative to mounting flange  18 . A gas source  42  is connected to mounting flange  18  with tubing  44  and fitting  46 . The gas source can be compressed air, nitrogen, argon or other gas species compatible with the drive mechanism contained within drive housing  14  of FIG.  1 . 
     Referring now to FIG. 3, there is shown an isolated sectioned view of a first preferred embodiment of the present invention. The first preferred embodiment of the seal assembly  50  includes a seal  54  in mounting flange  18  held in place by capture plate  40 . Shaft  22  may move in the vertical direction  16  and/or in the rotary direction  12  relative to mounting flange  18 . Shaft  22  includes an outer surface  80  and can be made of aluminum, stainless steel or other suitable material. Mounting flange  18  includes a port  52 , a lower seating surface  78  and an outer seating surface  66 . Capture plate  40  includes an upper seating surface  74 . Seal  54  includes a first sealing surface  56 , a second sealing surface  58 , recess  60 , lower sealing surface  76 , upper sealing surface  72 , outside surface  62  and vents  64  and  65 . Alternately, recess  60  can be eliminated effectively making first sealing surface  56  and second sealing surface  58  the same surface while still maintaining functionality of the seal assembly. Seal  54  can be made from a variety of metals, plastics or other suitable materials but is preferably machined from PVDF resin such as KYNAR. KYNAR is a registered trademark of PENNWALT CORPORATION for its polyvinylidene flouride resin. 
     Lower seal gap  88  is the space between lower sealing surface  76  and lower seating surface  78 . Upper seal gap  90  is the space between upper seating surface  74  and upper sealing surface  72 . Preferably the sum of lower sealing gap  88  and upper sealing gap  90  is maintained at between about 0.001 inches to 0.005 inches which allows seal ring  54  to float in mounting flange  18  such that seal  54  stays substantially concentric with shaft  22 ; however other distances could be provided and any range that works for the purpose intended is usable. This feature compensates for misalignment, eccentricity and deflection of shaft  22  relative to flange  18 . Alternately, lower sealing gap  88  and upper sealing gap  90  can be zero or less effectively fixing seal  54  relative to flange  18 ; in this case shaft  22  must be precisely guided so as not to contact first sealing surface  56  and second sealing surface  58  of seal  54 . Outer play gap  86  is the space between outside surface  62  and outer seating surface  66 . Outer play gap is preferably maintained higher than the sum of expected values for misalignment, eccentricity and deflection of shaft  22  relative to flange  18  in order to prevent seal  54  from bottoming out on flange  18 . Upper shaft seal gap  82  is the space between first sealing surface  56  and shaft  22 . Lower shaft seal gap  84  is the space between second scaling surface  58  and shaft  22 . Preferably, upper shaft seal gap  82  and Lower shaft seal gap  84  is maintained at between about 0.001 inches to 0.005 inches; however other distances could be provided and any range that works for the purpose intended is usable. 
     A gas source  42  is connected to mounting flange  18  with tubing  44  and fitting  46 . The gas source can be compressed air, nitrogen, argon or other gas species compatible with the drive mechanism contained within drive housing  14  of FIG.  1 . Gas pressure is preferably maintained between about five and ten pounds per square inch; however other pressure could be provided and any range that works for the purpose intended is usable. Gas is introduced into the seal assembly through port  52  in order to maintain outer pressurized region  70 , vents  64 ,  65  and gap region  68  at a pressure preferably between about five and ten pounds per square inch; however other pressure could be provided and any range that works for the purpose intended is usable. Gas flows through Upper shaft seal gap  82 , Lower shaft seal gap  84  at a higher rate than through Lower seal gap  88  and Upper seal gap  90  because of the higher clearance of Upper shaft seal gap  82  and Lower shaft seal gap  84  as well as the lower surface area of first sealing surface  56  and second sealing surface  58 . The combination of gas pressure and gas flow prevents seal  54  from contacting shaft  22  while acting as a barrier to prevents fluids, gasses, and contaminants from passing by the seal assembly as previously set forth. 
     Referring now to FIG. 4, there is shown a isolated sectioned view of a second preferred embodiment of the present invention. The second preferred embodiment of the seal assembly  100  includes a first seal  138 , a second seal  132  and a spacer  136  in mounting flange  18  held in place capture plate  40 . Shaft  22  may move in the vertical direction  16  and/or in the rotary direction  12  relative to mounting flange  18 . Shaft  22  includes an outer surface  80  and can be made of aluminum, stainless steel or other suitable material. Mounting flange  18  includes a port  52 , a lower seating surface  78  and an outer seating surface  66 . Capture plate  40  includes an upper seating surface  74 . First seal  138  includes a first sealing surface  130 , first lower surface  124 , first upper sealing surface  122 , and first outside surface  120 . Second seal  132  includes a second sealing surface  114 , second lower sealing surface  112 , second upper surface  110 , and second outside surface  104 . Spacer  136  includes a spacer inner surface  128 , spacer lower surface  108 , spacer upper surface  126 , spacer outside surface  118 , backcut  119  and vents  106  and  134 . First seal  138 , second seal  132  and spacer  136  can be made from a variety of metals, plastics or other suitable materials but are preferably machined from PVDF resin such as KYNAR. KYNAR is a registered trademark of PENNWALT CORPORATION for its polyvinylidene flouride resin. 
     Lower seal gap  140  is the space between second lower sealing surface  112  and lower seating surface  78 . Upper seal gap  148  is the space between upper seating surface  74  and first upper sealing surface  122 . Lower spacer gap  142  is the space between second upper surface  110  and spacer lower surface  108 . Upper spacer gap  146  is the space between first lower surface  124  and spacer upper surface  126 . Preferably the sum of lower sealing gap  140 , upper sealing gap  148 , lower spacer gap  142  and upper spacer gap  146  is preferably maintained at between about 0.001 inches to 0.005 inches which allows first seal  138  and second seal  132  to float in mounting flange  18  such that first seal  138  and second seal  132  stay substantially concentric with shaft  22 ; however other distances could be provided and any range that works for the purpose intended is usable. This feature compensates for misalignment, eccentricity and deflection of shaft  22  relative to flange  18 . First outer play gap  156  is the space between first outside surface  120  and outer seating surface  66 . First outer play gap is preferably maintained higher than the sum of expected values for misalignment, eccentricity and deflection of shaft  22  relative to flange  18  in order to prevent first seal  138  from bottoming out on flange  18 . Second outer play gap  154  is the space between second outside surface  104  and outer seating surface  66 . Second outer play gap is preferably maintained higher than the sum of expected values for misalignment, eccentricity and deflection of shaft  22  relative to flange  18  in order to prevent second seal  132  from bottoming out on flange  18 . Outer spacer gap  158  is the space between spacer outer surface  118  and outer seating surface  66 . Preferably outer spacer gap  158  is preferably maintained between about 0.0005 and 0.001 inches; however other distances could be provided and any range that works for the purpose intended is usable. Inner spacer gap  152  is the space between outer surface  80  of shaft  22  and spacer inner surface  128 . Inner spacer gap  152  is preferably maintained higher than the sum of expected values for misalignment, eccentricity and deflection of shaft  22  relative to flange  18  in order to prevent shaft  22  from contacting spacer  136 . Upper shaft seal gap  150  is the space between first sealing surface  130  and shaft  22 . Lower shaft seal gap  144  is the space between second sealing surface  114  and shaft  22 . Preferably upper shaft seal gap  150  and Lower shaft seal gap  144  is preferably maintained at between about 0.001 inches to 0.005 inches; however other distances could be provided and any range that works for the purpose intended is usable. 
     A gas source  42  is connected to mounting flange  18  with tubing  44  and fitting  46 . The gas source can be compressed air, nitrogen, argon or other gas species compatible with the drive mechanism contained within drive housing  14  of FIG.  1 . Gas pressure is preferably maintained between about five and ten pounds per square inch; however other pressure could be provided and any range that works for the purpose intended is usable. Gas is introduced into the seal assembly through port  52  in order to maintain outer pressurized region  102 , vents  106 ,  134  and gap region  116  at a pressure preferably between about five and ten pounds per square inch; however other pressure could be provided and any range that works for the purpose intended is usable. Gas flows through Upper shaft seal gap  150 , Lower shaft seal gap  144  at a higher rate than through lower seal gap  140  and upper seal gap  148  because of the higher clearance of Upper shaft seal gap  150  and Lower shaft seal gap  144  as well as the lower surface area of first sealing surface  130  and second sealing surface  114 . The combination of gas pressure and gas flow prevents first seal ring  138  and second seal ring  132  from contacting shaft  22  while acting as a barrier to prevents fluids, gasses, and contaminants from passing by the seal assembly as previously set forth. 
     While the present invention has been particularly described with respect to certain elements in its preferred embodiment, it will be understood that the invention is not limited to these particular methods and/or apparatus described in the preferred embodiments, the process steps, the sequence or the final structures depicted in the drawings. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention defined by the appended claims. In addition, other methods and or devices may be employed in the apparatus of the instant invention.