Abstract:
A vacuum seal arrangement comprising a one-piece elastomeric gasket having at least first and second O-rings interconnected by a planar web, a first part having a first planar sealing surface with a dove-tail groove therein holding the first O-ring and a square walled groove therein holding the second O-ring, the first part further including at least one passage in the first planar sealing surface surrounded by the first O-ring or second O-ring.

Description:
BACKGROUND 
     O-rings used for vacuum sealing applications such as plasma etching reactors require appropriately designed grooves to position the O-rings against the sealing surfaces. See, for example, commonly-owned U.S. Pat. Nos. 6,010,133 and 6,536,777, the disclosures of which are hereby incorporated by reference. A single or double dove-tailed groove is typically used to position the O-ring and to prevent the O-ring from falling out during the installation process. However, when multiple small O-rings need to be placed close to each other, there might be insufficient distance to accommodate the O-ring grooves on the parts to be sealed. 
     SUMMARY 
     Disclosed herein is a vacuum seal arrangement comprising a one-piece elastomeric gasket having at least first and second O-rings interconnected by a planar web, a first part having a first planar sealing surface with a dove-tail groove therein holding the first O-ring and a square walled groove therein holding the second O-ring, the first part further including at least one passage in the first planar sealing surface surrounded by the first O-ring or second O-ring. 
     In one embodiment, the first and second O-rings are concentric and the square walled groove is inside the dove-tail groove. Preferably, the first and second O-rings have the same wall thickness, the dove-tail groove is a single dove-tail groove having an inner straight wall and an outer inclined wall and the square walled groove has inner and outer walls oriented 90° to the first planar sealing surface, the open grooves having a depth less than the O-ring wall thickness and a central axis coincident with the central axis of the passage. 
     In another embodiment, the gasket includes three, four or five additional O-rings mounted in grooves in square walled grooves in the first planar sealing surface. For example, there can be five additional O-rings identical in shape and having the same diameters and wall thickness as the first and second O-rings, the first O-ring arranged as a central O-ring surrounded by the second O-ring and the five additional O-rings arranged at radial positions 60° apart around the central O-ring, adjacent surfaces of the six O-rings being separated by a distance less than the wall thickness of the O-rings. 
     In a further embodiment, the O-rings have a thickness of about 0.1 to about 0.25 inch and the web is a flat interconnecting section between the O-rings and/or the first and second O-rings have the same size with an inner diameter of about 0.5 to about 2 inches. For example, the first and second O-rings can have a thickness of about 0.1 to about 0.25 inch and the dove-tail groove can be a single dove-tail groove with an inner straight wall and an outer inclined wall. Alternatively, the first and second O-rings can have a thickness of about 0.1 to about 0.25 inch and the dove-tail groove can be a double dove-tail groove with an inner inclined wall and an outer inclined wall. 
     The O-rings can be concentric or laterally offset. For example, an inner surface of the second O-ring can surround the at least one passage and the second O-ring can be inside the first O-ring. Alternatively, the at least one passage can comprise a central passage surrounded by the first O-ring and the first planar sealing surface can include six additional passages having centers thereof equidistant from the center of the central passage, the gasket including five additional O-rings and the first planar sealing surface including five additional square walled grooves, the square walled grooves holding the second O-ring and the five additional O-rings. 
     In one arrangement, a second part is attached to the first part and the second part includes a passage aligned with the passage in the first part. In another arrangement, a second part is attached to the first part and the second part includes seven passages aligned with the passages in the first part. In a further arrangement a second planar sealing surface is clamped against the first O-ring and a third part having a third planar sealing surface is clamped against the second O-ring. 
     The dove-tail groove can be separated from the square walled groove by an annular wall having an annular surface coplanar with the first planar sealing surface and the web extends over the annular surface. An outer wall of the dove-tail groove can be at an angle of 60° to 80° and the bottom of the dove-tail groove can be wider than the opening of the dove-tail groove. Preferably, the bottom of the dove-tail groove and the bottom of the square walled groove are coplanar. 
     In a preferred embodiment, the vacuum sealing arrangement is located in a plasma processing chamber such as a plasma etching chamber wherein the passage delivers a reactant gas to the chamber. Alternatively, the passage can be a vacuum passage or a liquid passage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a vacuum seal arrangement according to a first embodiment. 
         FIG. 2  is a top view of the multiple O-ring gasket shown in  FIG. 1 . 
         FIG. 3  is a cross-sectional view of a vacuum seal arrangement according to a second embodiment. 
         FIG. 4  is a top view of the multiple O-ring gasket shown in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed herein is a novel O-ring gasket which attaches multiple O-rings to each other using a thin web of O-ring elastomer thereby reducing the number of O-ring grooves required in the sealing parts of a plasma processing chamber. The O-ring gasket can be used for gas, liquid or vacuum seals where passages are spaced close together and/or minimize particle generation due to metal on metal contact of sealing surfaces. 
       FIG. 1  shows an embodiment of a gasket  10  having an outer O-ring  12  and an inner O-ring  14  which fit in an outer dove-tail groove  16  and a square walled groove  18  in a planar sealing surface  20  of a first part  22  of metal or ceramic material. A passage  24  in part  22  opens into the groove  18 . A planar sealing surface  25  of a second part  26  can be clamped against the inner O-ring  14  such that a passage  28  in the second part  26  is in fluid communication with the first passage  24 . A planar sealing surface  29  of a third part  30  surrounding the second part  26  can be clamped against the outer O-ring  12 . In this particular embodiment, there is insufficient room to allow for putting a dove-tail groove  16  for sealing part  22  to part  26 . However, by attaching the smaller inner O-ring  14  to the larger outer O-ring  12  by a thin web  32 , the smaller inner O-ring  14  can be retained in position by the outer O-ring  12  thereby allowing easier assembly. As shown in  FIG. 2 , the gasket  10  has a single passage formed by the inner periphery of the inner O-ring  14 . 
     Those skilled in the art will recognize that the above mentioned scheme can be used for a multitude of O-ring designs that are used for sealing applications wherein passages are in close proximity. 
     Further, some of these O-rings may have other functions in addition to or instead of sealing. For example, in one embodiment the outer O-ring  12  acts as a vacuum seal while the inner O-ring  14  acts as a soft surface to prevent rubbing of hard surfaces against each other. 
       FIGS. 3 and 4  show another embodiment of a vacuum seal arrangement utilizing a multi-orifice gasket  40  for sealing parts that allow separate fluids such as liquids or gases to flow through discrete passages. The gasket  40  includes seven O-rings with seven passages through the gasket as shown in  FIG. 3 . As shown in  FIG. 3 , the gasket includes a center O-ring  42  surrounded by six O-rings  44 ,  46 ,  48 ,  50 ,  52 ,  54  connected to each other and the center O-ring  42  by web  56 . The O-rings  42 - 56  have identical sizes and the distance between opposed surfaces of the O-rings is less than a wall thickness of the O-rings. As shown in  FIG. 4 , the center O-ring  42  fits in a dove-tail groove  58  in a first planar surface  60  of a first part  62  and the outer O-rings  44 - 52  fit in square walled grooves  64  in the first part  62 . A second planar surface  66  of a second part  68  is held against the gasket  40  to allow fluid communication between a center passage  70  in the first part  62  and a center passage  72  in the second part  68 . Likewise, passages  74   a ,  74   b , etc. in the first part  62  are in fluid communication with passages  76   a ,  76   b , etc. in the second part  68 . Each fluid is thus separated from the other fluids and the atmosphere using the gasket  40 . Using the attached O-ring concept, only the center O-ring  42  uses a dove-tail groove  58  for retaining the seven attached O-rings  42 - 52 . The other six O-rings  44 - 54  merely sit in the open square walled grooves  64 . As can be observed in  FIG. 3 , this arrangement allows placement of the O-rings closer to each other compared to the configuration in which each O-ring is separately held by dove-tail groove. 
     A preferred cross-sectional diameter of the O-rings is about 0.1 to about 0.25 inch and a preferred outside diameter of the O-rings is about 0.5 to about 2 inches. The dove-tail groove can have single inclined inner or outer wall or the inner and outer walls can be inclined towards each other such that the opening of the groove is smaller than the O-ring cross-section. Preferred materials for the O-rings include semiconductor processing comparable comparable perfluoroelastomers or fluorosilicone with or without fillers such as CaO and MgO, e.g., “VITON”, “CHEMRAZ”, “PERLAST”, “KALREZ” or other suitable material. 
     It should be observed that since O-rings are typically fabricated using a mold, manufacture of the attached O-rings is not significantly more difficult compared to manufacture of a single O-ring. 
     Typical O-ring sealing applications require one groove per O-ring used. For applications requiring multiple O-rings in close proximity, the gasket  10 ,  40  reduces the number of dove-tailed O-ring grooves in the sealing parts needed compared to using separate O-rings thereby increasing the design flexibility, reducing the cost associated with dove-tailed grooves, and allowing for closer packing of hardware features, if required. 
     While various embodiments have been described, it is to be understood that variations and modifications may be resorted to as will be apparent to those skilled in the art. Such variations and modifications are to be considered within the purview and scope of the claims appended hereto. 
     All of the above-mentioned references are herein incorporated by reference in their entirety to the same extent as if each individual reference was specifically and individually indicated to be incorporated herein by reference in its entirety.