Abstract:
The present invention is directed to a valve seal assembly for use in multi-chamber vacuum devices. The seal assembly comprises a door and a deformable seal ring running along the periphery of the door, wherein the seal ring is held in place by a reversibly mounted securing means such as a disk, ring or clamp.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of U.S. application Ser. No. 10/346,833, filed Jan. 17, 2003 which claims the benefit of U.S. Provisional Application No. 60/353,400, filed Jan. 31, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to a seal assembly for valves and in particular to a gate valve or pendulum valve seal assembly having a replaceable deformable seal ring, said assembly finding particular use in forming a seal between chambers in vacuum equipment employed in the semiconductor industry for chip manufacture.  
         BACKGROUND OF THE INVENTION  
         [0003]    Integrated circuit (IC) chips are typically manufactured in multi-chambered vacuum equipment. Each chamber may contain a different environment, e.g. atmosphere, temperature, and pressure, than adjacent chambers. Chambers are typically isolated from each other by gate valves (or slit valves). Such valves may be utilized for moving semiconductor wafers from one chamber to another. In addition, pendulum valves may be employed to separate chambers from a vacuum source and for the feeding or exhausting of gases. In both gate valves and pendulum valves, sealing is affected by closing a sealing member, also referred to as a disk or door, portion of the valve. Generally, the door comprises a metal plate, sized and shaped for covering the opening within the valve, and a deformable seal, or O-ring, mounted on the sealing surface of the door, near its periphery. The deformable seal is typically made from an elastomeric or thermoplastic polymer.  
           [0004]    During use in the manufacture of IC chips, the deformable door seal is exposed to high temperatures and to corrosive plasmas. The latter conditions, coupled with repeated opening and closing of the door, causes the deformable seal ring to deteriorate and, eventually need to be replaced. Deformable seal replacement has been problematic.  
           [0005]    Early door designs featured a dovetail-shaped groove running along the periphery of the door sealing surface. The groove was used to hold a deformable O-ring seal or a modified O-ring (U.S. Pat. No. 5,482,297). However, in use, the deformable seal ring could undesirably pop out of the groove when the gate valve door was opened. It could also be difficult and time consuming to install a replacement seal ring within the groove without damaging the seal.  
           [0006]    A more recent door design is disclosed in U.S. Pat. No. 6,089,543 wherein the gate valve door comprises a mounting member and a seal plate attached thereto, wherein a deformable seal ring is mounted onto the outer surface of the seal plate. In this design, the deformable seal ring is preferably bonded, by molding in place, onto the seal plate. When it is desired to replace a worn deformable seal ring, the seal plate/deformable seal assembly is readily detached from the mounting member and discarded. A new seal plate/deformable seal assembly is then attached to the mounting member. This design has the economic and environmental disadvantage of not re-using the old seal plate.  
           [0007]    U.S. Pat. No. 5,579,718 discloses a slit valve door having a removable O-ring seal that is held in place within a groove that is partially formed by the door and partially formed by a removable wedge insert. However, it may be difficult to install the O-ring seal in this door groove without twisting the O-ring. Twisting can cause premature seal failure.  
           [0008]    It is an object of the present invention to provide a valve door having a securely mounted deformable seal element which may be quickly replaced when desired, without the need for replacing a large portion of the door and without damaging the seal element.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention is directed to a valve seal assembly for use in sealing an opening in a chamber employed in vacuum equipment, particularly in semiconductor manufacturing equipment.  
           [0010]    Specifically an aspect of the invention is a valve seal assembly for use in vacuum chambers of semiconductor manufacturing equipment, said valve assembly comprising:  
           [0011]    a) a door having a groove for receiving a seal ring, said groove formed on a sealing surface near a periphery of said door, and wherein a first portion of said groove is formed of a base, an outer sidewall and outer lip in said door;  
           [0012]    b) a securing means for holding a seal ring within said groove on said door, said securing means having an outer sidewall and lip which forms a second portion of said groove;  
           [0013]    c) fastening means for attaching said securing means to said door; and  
           [0014]    d) a deformable seal ring shaped and sized to complementarily fit within said groove, said seal ring comprising a first thin portion for complementarily engaging said first portion of said groove and a second thin portion for complementarily engaging said second portion of said groove, and said seal ring having a thick portion located between said first and second thin portions and sized to extend beyond said door lip. 
       
    
    
     BRIEF DESCRIPTIONS OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a plan view of an embodiment of the seal assembly of this invention.  
         [0016]    [0016]FIG. 2 is a cross-section view of an embodiment of the seal assembly of this invention taken along lines  2 - 2  of FIG. 1.  
         [0017]    [0017]FIG. 3 is a cross-section view of another embodiment of the seal assembly of this invention taken along lines  2 - 2  of FIG. 1.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    [0018]FIG. 1 shows a plan view of the valve door seal assembly  10  of this invention wherein a deformable seal ring  12  is mounted in a groove near the periphery of the sealing surface of door  14  and held in place by securing means  16 . By “sealing surface” is meant the surface of the door which covers the opening that is sealed when the valve is closed.  
         [0019]    [0019]FIG. 2 shows, in cross-section along  2 - 2 , the door assembly of this invention. Seal ring  12  is reversibly mounted on the base  18  of a groove on the sealing surface of door  14 . The groove has an outer side wall  20  and an outer lip  22  for complementarily engaging a relatively thin outer portion  30  of deformable seal ring  12 . Securing means  16  has an outer side wall  24  and outer lip  26  for complementarily engaging a relatively thin inner portion  32  of deformable seal ring  12 . Seal ring  12  has a relatively thick portion  34  located between thin portions  30  and  32 . Thick portion  34  is generally parabolic-shaped and it is sized to extend above the lips of both door  14  and securing means  16  for sealing engagement with the surface (i.e. mating flange) surrounding the opening in the valve (not shown). The shape of seal ring  12  results in the requirement for only a relatively minor compressive force in order to form an effective seal under high vacuum. Much more force would be required if seal ring  12  were an O-ring.  
         [0020]    Although securing means  16  is shown as a solid disk or wedge in the figures, one skilled in the art would readily recognize that the securing means could equally be a continuous ring, a non-continuous ring, or a series of brackets. Such alternate embodiments are contemplated in this invention. Securing means  16  is reversibly attached to door  14  by fastening means  28 .  
         [0021]    Fastening means  28  may include bolts (as shown in FIG. 2), screws, pins, adhesives, etc. Such alternative embodiments are included in the present invention. The number and location of fastening means required to adequately attach securing means  16  to door  14  depends upon the shape and size of the securing means and may be readily determined by the skilled practitioner. Optionally, second seal  36  may be used with fastening means  28  (FIG. 3) to form an airtight seal between the fastening means and the door. This ensures that a vacuum leak does not occur due to poor mating between door  14 , seal ring  12  and securing means  16 . Second seal  36  may be a washer, O-ring, square gasket, or the like.  
         [0022]    Door  14  and securing means  16  can be fabricated from metals such as stainless steel, aluminum, or other non-deformable metal. The door and securing means may be made of the same material or of different material. Securing means  16  can also be made from polymers having either a modulus or a hardness much greater than that of the material used as the seal ring  12 . Polymers, useful for preparation of the securing means include, but are not limited to nylon, polyether ether ketone (PEEK), polyether sulfone (PES), polytetrafluoroethylene (PTFE), polyimide, or an organic or inorganic composite. Preferably the door and securing means are made of steel or aluminum, most preferably a stainless steel such as 316L, or anodized aluminum.  
         [0023]    Seal ring  12  may be fashioned out of elastomer (preferably) or other deformable material such as a thermoplastic resin (e.g. copolymers of tetrafluoroethylene) that is thermally stable and inert to the plasma which is employed in the chip manufacturing equipment. Suitable elastomers include silicone rubber, nitrile rubber, hydrogenated nitrile rubber, EPDM, copolymers of ethylene and an alpha olefin having at least four carbon atoms, and fluoroelastomers, including perfluoroelastomers. For applications requiring seals that may be exposed to high temperatures, harsh chemicals or require very low extractables, a perfluoroelastomer is the preferred elastomer. By “perfluoroelastomer” is meant copolymers comprising copolymerized units of tetrafluoroethylene and copolymerized units of a perfluoro(alkyl vinyl ether) or a perfluoro(alkoxy vinyl ether). Such copolymers may also contain a minor amount (preferably less than 7 mole percent, based on the total number of moles of comonomers) of a cure site such as Br, I, CN, or H. Perfluoroelastomers have been extensively described in the prior art. See, for example, U.S. Pat. Nos. 4,035,565; 4,281,092; 4,529,784; 4,487,903; 5,789,489; 5,936,060; 6,140,437; 6,211,319 B1 and 6,281,296 B1.  
         [0024]    Optional second seal  36  may be fashioned out of any of the materials mentioned above as suitable for seal ring  12 . However, since second seal  36  is never exposed to plasmas, it need not be made from expensive perfluoroelastomer or other plasma inert material.  
         [0025]    Worn seal ring  12  may easily be replaced in the present invention by the steps of a) disengaging fastening means  28 , b) removing securing means  16 , c) replacing the worn seal ring with a new seal ring, d) repositioning securing means  16  and e) engaging fastening means  28 . The new seal ring easily slides into the groove without twisting.  
         [0026]    Finite Element Analysis (FEA) studies of 1) the valve seal assembly of the present invention in the embodiment of a slit valve and 2) the door seal assembly of U.S. Pat. No. 5,579,718 indicate that the door seal of the present invention has a higher contact pressure against the mating flange (while under the same compressive load) than does the U.S. Pat. No. 5,579,718 door seal assembly. This results in better vacuum sealing performance for the seal assembly of the present invention.  
         [0027]    The present valve seal assembly finds use in vacuum sealing applications, particularly in gate or slit valves and in pendulum valves utilized in the sealing of vacuum chambers in semiconductor chip manufacturing equipment. Besides the preferred embodiments of the invention illustrated in the drawings and described in detail above, the skilled artisan will readily understand that the invention is capable of alternative embodiments. For example, in order to provide space for thermal expansion of the seal ring, the groove sidewall radius, seal ring width and the undercut geometry of the securing means may be adjusted. Accordingly the invention should not be strictly limited in scope to the preferred embodiments.