Abstract:
Vacuum processing chambers having provisions for thermal expansion and contraction. Specific embodiments provide a plasma processing chamber having a showerhead that enables thermal expansion and contraction without imparting structural stress on the chamber body and without breaking any vacuum seal.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of and claims priority from U.S. Provisional Application Ser. No. 61/285,505, filed on Dec. 10, 2009, the entire content of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The invention concerns a vacuum processing apparatus, such as plasma chambers used for etching or forming thin films on substrates or other workpieces. 
         [0004]    2. Related Art 
         [0005]    Manufacturing processes in the fields of semiconductor, flat panel displays, solar panels, etc., involve processing in vacuum chambers. For example, vacuum chambers are used for plasma-enhanced chemical vapor deposition (PECVD), plasma etching and various other processes for forming thin films on substrates (workpieces) and etching structures on the substrates. In such chambers, various gases are flowed into the chamber, either via injectors or via a showerhead. For uniform plasma processing in large chambers, a showerhead is preferable over injectors. The showerhead would generally cover substantially the entire ceiling of the chamber, so that even amount of gas is injected everywhere within the chamber. 
         [0006]    As gas is flowed into the chamber, plasma is ignited and sustained using radio frequency or microwave energy. This heats up the chamber. Also, for many processes active heaters are used to heat the substrates, which further add to heating of the chamber. Of course, when the processed substrates are removed from the chamber and fresh ones are introduced into the chamber, the chamber cools down until plasma is ignited again. These changes in temperatures cause various parts of the chamber to expand and contract. Parts made of different material would expand and contract at different rates. Also, large parts in large chamber would expand considerably. This is especially true for showerheads of large processing chambers, such as those used for fabrication of flat panel displays or solar cell. 
       SUMMARY 
       [0007]    The following summary of the invention is included in order to provide a basic understanding of some aspects and features of the invention. This summary is not an extensive overview of the invention and as such it is not intended to particularly identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented below. 
         [0008]    Embodiments of the invention provide vacuum processing chambers having provisions for thermal expansion and contraction. Specific embodiments of the invention provide a plasma processing chamber having a showerhead that enables thermal expansion and contraction without imparting structural stress on the chamber body and without breaking any gas seal. 
         [0009]    According to an embodiment of the invention, a plasma chamber is provided wherein the showerhead assembly anchors the showerhead at one point, while allowing sliding of the shower at other points in order to allow for thermal expansion and contraction. According to another embodiment, no anchoring is provided, and the showerhead may slide in all directions while maintaining gas seal. 
         [0010]    According to an embodiment of the invention, a vacuum processing chamber is provided, comprising: a chamber body; a showerhead assembly coupled to top portion of the chamber body and comprising: a back plate rigidly attached to the chamber body; a perforated showerhead plate having a plurality of oval holes; and, a plurality of fastening assemblies that slidingly attach the showerhead plate to the back plate to thereby allow sliding of the showerhead plate relative to the back plate while gas seal is maintained between the showerhead plate and the back plate. According to one embodiment, at least one bolt rigidly attaches the showerhead plate to the back plate. 
         [0011]    According to an embodiment of the invention, a method for securing a showerhead assembly onto a vacuum processing chamber is provided, comprising: fixedly attaching a back plate to the vacuum processing chamber; coupling a perforated showerhead plate to the back plate by using a plurality of fastening assemblies to slidingly attach the perforated showerhead plate to the back plate; and, providing a gas seal between the perforated showerhead plate and the back plate. According to one embodiment, the method further comprises fixedly attaching at least one location of the perforated showerhead plate to the back plate. 
         [0012]    Other aspects and features of the invention will become apparent from the description of various embodiments described herein, and which come within the scope and spirit of the invention as claimed in the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]    The accompanying drawings, which are incorporated in and constitute a part of this specification, exemplify the embodiments of the present invention and, together with the description, serve to explain and illustrate principles of the invention. The drawings are intended to illustrate major features of the exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of actual embodiments nor relative dimensions of the depicted elements, and are not drawn to scale. 
           [0014]      FIG. 1  is a schematic illustrating major elements of a plasma processing chamber implementing an embodiment of the invention. 
           [0015]      FIG. 2  is a cross section illustrating one example of anchoring one side of the showerhead, according to an embodiment of the invention. 
           [0016]      FIG. 3  is a cross section illustrating one example of floating one side of the showerhead, according to an embodiment of the invention. 
           [0017]      FIG. 4  is an explosive view illustrating a floating mechanism according to an embodiment of the invention. 
           [0018]      FIG. 5  is an isometric view of the assembled floating attachment. 
           [0019]      FIG. 6  is a lower elevation of the cover plate  176 , showing its underside. 
           [0020]      FIG. 7  illustrates a sliding fastening mechanism according to another embodiment of the invention. 
           [0021]      FIGS. 8A and 8B  are bottom elevation view of the back plate and the showerhead plate according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIG. 1  is a schematic illustrating major elements of a plasma processing chamber  100  implementing an embodiment of the invention. The chamber  100  includes a chamber body  102 , generally made of metal, such as aluminum, stainless steel, etc. A pedestal  105  is provided for holding one or more substrates. The pedestal  105  may support a susceptor, a chuck, and/or a heater. The pedestal may be attached to a lift mechanism  115 , so that it is lowered to the illustrated position for substrates loading via the valve  110 , and then lifted up for processing. At its top, the chamber has a showerhead assembly that includes a showerhead plate  120  attached to a back plate  125 . The back plate  125  is secured hermetically to the chamber body  102 . Gas is supplied to the showerhead from source  130 , via conduit  135 . The showerhead plate  120  has many perforations that allow the gas to disperse into the chamber. 
         [0023]      FIG. 2  is a cross section illustrating one example of anchoring one location of the showerhead plate  120  to the back plate  125 , according to an embodiment of the invention. According to an embodiment of the invention, at least one point of the shower plate  120  is anchored to the back plate  125 , such that it is sealed to the back plate  125  to avoid gas leaks, and such that it cannot move relative to the back plate  125  at that point. This point may be, for example, one of the corners or the center of the showerhead plate. The illustration of  FIG. 2  shows the example of anchoring at one corner of the showerhead plate. 
         [0024]      FIG. 3 , on the other hand, shows example of the sliding fastening assemblies used to slidingly attach the showerhead to the backplate, according to an embodiment of the invention. That is, in this embodiment, at least the diametrically opposing side of the showerhead plate  120  is attached to the back plate  125  in a floating manner, such that it is sealed to the back plate  125 , but can slide with respect to the back plate  125  at that location. In this manner, expansion and contraction of the showerhead plate  120  is enabled, as it is free to slide with respect to the back plate  125 , while still keeping the seal to it to avoid processing gas escaping from between the showerhead plate and the back plate. 
         [0025]    As shown in  FIGS. 2 and 3 , an o-ring  140  is provided between the showerhead plate  120  and back plate  125 , so as to provide gas seal between the showerhead plate  120  and the back plate  125 . A Teflon block or spacer  145  is also provided between the showerhead plate  120  and the back plate  125 , such that it maintains a small gap between the showerhead plate  120  and the back plate  125 , enabling sliding motion therebetween. In  FIG. 2 , the showerhead plate  120  is securely bolted to the back plate  125  using bolt  150  and washer  155 . A cover  160  is provided to cover the bolt  150 . 
         [0026]      FIG. 3  illustrate the sliding fastening assembly that is used to attach the showerhead plate  120  to the back plate  125  in a manner providing gas seal but allowing sliding of the showerhead plate  120  for thermal expansion and contraction. While in  FIG. 2  a hole  152  having a diameter just sufficient to accommodate the bolt  150  is drilled in the showerhead plate, for the sliding fastening assembly illustrated in  FIG. 3  the hole  154  is of oval shape and includes a step  156 . An insert  170  is inserted into the hole  154 , such that it is seated against the step  156 . The insert may be made of ceramic or other material. 
         [0027]      FIG. 4  is an exploded view of the sliding fastening mechanism according to one embodiment of the invention. As shown in  FIG. 4 , the insert  170  has a hole  172  that is of slightly larger diameter than the diameter of the bolt  150  and is oval in shape. Also, as shown in  FIG. 4 , the insert  170  includes a key  171 , so that it can be inserted into hole  154  in only one orientation, such that the long axis of the oval hole  172  is in the direction of expansion of the showerhead plate  120  at that location. 
         [0028]    A sliding plate  173  is provided over the insert  170 . The sliding plate  173  has four oval holes  174 , which are also oriented in the direction of sliding. In each of the holes, a ball  175  is inserted. Each ball  175  can ride freely inside its respective oval hole  174 . A cover plate  176  is provided over the assembly of the sliding plate  173  and balls  175 . It can be appreciated that the insert  170 , sliding plate  173 , balls  175  and cover plate  176 , essentially form a “linear” ball bearing arrangement. Two optional washers  177 ,  178  are provided over the cover plate  176 , and a bolt  150  tightens the entire assembly onto the back plate  125 . As can be understood, under proper tightening of the bold  150 , the showerhead plate  120  can be sealed to the backplate  150 , but also be able to expand by sliding with respect to the backplate  125 . When this occurs, the assembly of showerhead plate  120  and insert  170  “ride” on balls  175 , since the hole  172  provided in the insert  170  is oval in the direction of expansion motion. In this embodiment, all of the parts, except for the bolt  150 , are made of ceramic, but other materials may be used for the various parts, such as aluminum, anodized aluminum, Teflon, etc. 
         [0029]      FIG. 5  illustrates the entire sliding fastening arrangement with bolt  150  inserted thorough the washers  177 / 178 , the cover plate  176 , the sliding plate  173 , and the insert  170 . This entire assembly is inserted into the hole  154 , shown in  FIG. 3 , and the bolt is tightened so as to form a seal with o-ring  140 , but allow sliding of the showerhead plate  120 , assisted by the Teflon block. 
         [0030]      FIG. 6  is a lower elevation of the cover plate  176 , showing its underside. As shown in  FIG. 6 , according to one embodiment, four races are provided on the bottom face of the cover plate, such that the balls  175  can freely roll in one linear direction dictated by the race. 
         [0031]      FIG. 7  illustrate a sliding fastening mechanism according to another embodiment of the invention. The sliding fastening mechanism according to this embodiment is similar to that shown in  FIGS. 3 and 4 , except that balls  175  are eliminated and the sliding is enables by simple friction. According to one embodiment, cover  176  “rides” on insert  170  and sliding there-between occurs at interface  175 ′. According to another embodiment, the surfaces of the cover  176  and insert  170  which form interface  175 ′ are treated to provide reduce friction and avoid or reduce particle generation caused by the sliding. This can be done by, for example, by coating the surfaces with, e.g., Teflon, anodization, etc. According to yet another embodiment, a disk made of smooth material, such as Teflon, is provided at the interface  175 ′. 
         [0032]    According to another embodiment, the showerhead plate is not fixedly attached to the back plate. Rather, a plurality of sliding fastening assemblies are used to attach the showerhead plate to the back plate, so that it is free to expand in all directions. However, the plurality of sliding fastening assemblies are oriented such that the center of the showerhead plate remains at the same location regardless of expansion or contraction of the showerhead plate. This is illustrated in  FIGS. 8A and 8B . 
         [0033]      FIGS. 8A and 8B  are bottom elevation views of the back plate  125  (shown in broken line) and the showerhead plate  120  according to an embodiment of the invention. The broken-line arrows illustrate straight-line directions from the center of the showerhead plate, extending radially and passing through the center of each point where a fastening assembly is provided. As illustrated, each of the oval holes  154  of the fastening assembly is oriented such that its long axis lies along the straight line extending radially from the center of the showerhead plate. As explained above, each of the inserts  170  includes a key, such that when it is inserted into a hole  154  it assumes an orientation so that the long axis of its oval hole  172  is also oriented along the straight line extending radially from the center of the showerhead plate. In this manner, at each point where a fastening assembly is provided, the showerhead can slide only along the direction of the straight line extending radially from the center of the showerhead plate and passes through that point. Consequently, it can be understood that the showerhead can expand and contract in all directions by sliding or riding on the fastening assemblies, but because of the orientation of the fastening assemblies the center of the showerhead remains at the same location regardless of the expansion and contraction of the showerhead plate. That is, the orientations of the fastening mechanisms prevent any rotation or translation of the showerhead plate, other than radial expansion and contraction. 
         [0034]      FIG. 8A  illustrate the showerhead plate in its expanded position. As shown, the showerhead plate has expanded such that the bolts  150  are on the inner-radial side of the oval holes  154 . Conversely, in  FIG. 8B , illustrating the contracting position, the bolts  150  are shown at the outer-radial side of the oval holes  154 . 
         [0035]    While the invention has been described with reference to particular embodiments thereof, it is not limited to those embodiments. Specifically, various variations and modifications may be implemented by those of ordinary skill in the art without departing from the invention&#39;s spirit and scope, as defined by the appended claims. Additionally, all of the above-cited prior art references are incorporated herein by reference.