Abstract:
A transport chamber implemented to retrieve a substrate from at least one storage facility that is external to the transport chamber and transition the substrate into at least one processing chamber that is external to the transport chamber is provided. The transport chamber includes a bottom plate having an inner surface that is configured to accept a first O-ring. Further provided is a chamber housing that is defined from a rolled forging. The chamber housing has a top surface, and a bottom surface that is designed to join with the inner surface of the bottom plate such that the first O-ring seal forms a seal. The top surface of the chamber housing is suited to accept a second O-ring seal fastened to the perimeter of the top surface of the chamber housing. The transport chamber further includes a top plate that is configured to sit over the second O-ring seal and thereby form a seal over the top surface of the chamber housing.

Description:
This is a Divisional application of prior Application Ser. No. 08/677,401 filed on Jul. 9, 1996, now U.S. Pat. No. 6,216,328. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to chambers, and more particularly, to substrate transport chambers and methods of efficiently manufacturing the same. 
     Transport modules are generally used in conjunction with a variety of substrate processing modules, which may include semiconductor processing systems, material deposition systems, and flat panel display processing systems. Due to the growing demands for cleanliness and high processing precision, there has been a growing need to reduce the amount of human interaction between processing steps. This need has been partially met with the implementation of transport modules which operate as an intermediate handling apparatus (typically maintained at a reduced pressure, e.g., vacuum conditions). By way of example, a transport module may be physically located between one or more clean room storage facilities where substrates are stored, and multiple substrate processing modules where the substrates are actually processed, e.g., etched or have deposition performed thereon. 
     In this manner, when a substrate is required for processing, a robot arm located within the transport module may be employed to retrieve a selected substrate from storage and place it into one of the multiple processing modules. As is well known to those skilled in the art, the use of a transport module to “transport” substrates among multiple storage facilities and processing modules is typically referred to as a “cluster tool architecture”. 
     FIG. 1 depicts a typical cluster tool architecture  100  illustrating the various chambers that interface with a transport module  106 . Transport module  106  is shown coupled to three processing modules  108   a-   108   c  which may be individually optimized to perform various fabrication processes. By way of example, processing modules  108   a-   108   c  may be implemented to perform transformer coupled plasma (TCP) substrate etching, layer depositions, and sputtering. There may be connected to transport module  106  a load lock  104 , through which substrates may be provided to transport module  106 . 
     As illustrated, load lock  104  is coupled to a clean room  102  where substrates may be stored. In addition to being a retrieving and serving mechanism, load lock  104  also serves as a pressure varying interface between transport module  106  and clean room  102 . Therefore, transport module  106  may be kept at a constant pressure (e.g., vacuum), while clean room  102  is kept at atmospheric pressure. 
     As the demand for larger substrates increases, the need for transport modules capable of transporting these larger substrates also increases. Consequently, as the need for physically larger transport modules increases, existing manufactures of off-the-shelf transport modules have been struggling to develop larger transport modules in a cost effective manner. Unfortunately, existing methods of making these larger transport modules have proved to be extremely inefficient and prohibitively expensive to manufacture. For illustration purposes, the following will illustrate two common methods of manufacturing a transport chamber, which may represent, in one case, the transport module without the electronics. 
     FIG. 2A is a simplified transport chamber  200  assembled using conventional weldment technology. By way of example, transport chambers made by weldment technology generally require machined flat metal plates which are welded together to form boxed enclosures. As illustrated, transport chamber  200  is assembled into a box configuration  202  having four metal plate sides  204 , and a bottom plate  206  welded together at linear intersections  208 . Interface ports  210  will generally be required to form a path for the substrates to be transported into and out of transport chamber  200 , and may be machined out before or after box  202  has been welded together. A top plate (not shown) may then be designed to fit over the top perimeter of side plates  204 . In this manner, a seal may be formed when the top plate is welded or bolted down to box  202 . If the top plate is bolted down, an O-ring seal is typically placed between the top plate and the top surface regions of side plates  204  before being bolted down to box  202 . 
     As can be appreciated, the welding process may be very labor intensive in that the weld must be uniform and provide a vacuum-tight seal where the various plates meet. In addition, large amounts of machining time may be spent in preparing the various plates in order to generate smooth meeting surfaces for subsequent welding steps. By way of example, plates  204  must be precisely machined to smoothly match bottom plate  206 . In this manner, less time is consumed adjusting plates that fail to meet up with each other. Finally, once box  202  has been welded together, additional time must be spent performing post-weldment machining to cure any heat generated warping that may have been introduced during the welding process. As is well known in the art, the intensity of the thermal heat introduced during a welding process may tend to cause extensive distortions that further increase the time and expenses associated with post-weldment machining processes used to face-off warped regions. 
     One disadvantage associated with a weldment-type transport chamber  200  is that it may have structural deficiencies due to the vast amount of linear inches requiring welding. For illustration purposes, relatively long regions of welding are required for large transport chambers having dimensions between 60 and 100 inches. The structural weakness introduced at welding interfaces therefore produces well known step-down regions. By way of example, if a welding interface were magnified and examined closely, a thinner plate dimension would result at weld interfaces. Therefore, in order to prevent the introduction of structural weaknesses, more time and expense must be invested to assure that typical loads up to about 75,000 pounds are withstood. Further, welded structures may cause failures associated with long term fatigue. 
     In addition, once all post weldment machining is complete, additional cleaning steps must be performed to remove any surface metal contamination introduced during welding. Consequently, further time, effort and expense must be invested in cleaning the finished transport chamber before being spun into operation. 
     FIG. 2B illustrates another conventional manufacturing process used to make transport chamber  250 . The manufacturing process is sometimes referred to as a “hogout” process since transport chamber  250  is formed from an initial solid billet  254  of aluminum. Solid billet  254  is typically machined-out from one side in order to generate a hollow region in the center (e.g., thereby forming a box similar to that of FIG.  2 A). A hogout transport chamber does provide certain advantages over weldment-type transport chambers, but other disadvantages are introduced. By way of example, the machining required to define a hollow region  256  in a large billet of aluminum tends to be very labor-intensive, and the machining process also tends to generate large quantities of unusable aluminum scraps. 
     Once the machining process is complete, hollow region  256  must be polished down to produce smooth sides and eliminate any contaminating materials or scrap. A top plate may then be designed to fit over the box structure generated from the machining process. Next, interface ports  258  are defined to provide the passageways for substrates to be introduced into and out of transport chamber  250 . 
     In addition to being a very labor intensive process, generating transport chamber  250  from solid billet  254  is very expensive. As can be appreciated, solid billet  254  is remarkably heavy and must be paid for by the pound. Therefore, once the scrap is machined out, about 80 percent of the aluminum is wasted since industry does not pay well for recycled scraps. 
     There are entities that provide ready-made transport chambers of the weldment type and hogout type. By way of example, Brooks Automation of Lowell, Mass. is a supplier of ready-made chambers. Although there are companies that make custom transport chambers, the traditional method used to build weldment type or hogout type chambers is typically very expensive. 
     In view of the forgoing, what is needed is a transport chamber that employs a cost efficient manufacturing method for generating large transport chambers, without producing warping and structural deficiencies of a weldment, and without expending large amounts of time machining hollow regions in large solid billets which produce useless waste. 
     SUMMARY OF THE INVENTION 
     The present invention fills this need by disclosing a method of making a transport chamber having a robot arm installed within the transport chamber. In this embodiment, the robot arm may be implemented to retrieve a substrate from at least one storage facility that is external to the transport chamber, and insert the substrate into at least one processing chamber that is external to the transport chamber. 
     Preferably, the method of making the transport chamber includes: (a) providing a bottom plate having an inner surface; (b) defining a robot drive mounting port at about the center of the bottom plate, applying a first o-ring seal around the perimeter of the inner surface of the bottom plate; (c) generating a chamber housing from a rolled forging, the chamber housing having a top surface, and a bottom surface designed to meet the inner surface of the bottom plate such that the first o-ring seal forms a substantially vacuum-tight seal, and the top surface of the chamber housing having a second o-ring seal around the perimeter; and (d) providing a top plate having an underlip portion around the perimeter designed to sit over the second o-ring seal in order to form a substantially vacuum-tight seal against the top surface of the chamber housing. 
     Advantageously, one embodiment provides a fast and efficient method for installing and removing the transport chamber robot arm from at least one access window defined in the top plate. In addition, the interior portions of the transport chamber may be efficiently accessed through at least one viewport window in order to perform periodic maintenance. 
     In another embodiment, a transport chamber implemented to retrieve a substrate from at least one storage facility that is external to the transport chamber, and insert the substrate into at least one processing chamber that is external to the transport chamber is disclosed. The transport chamber includes: (a) a bottom plate having an inner surface; (b) a first O-ring seal fastened to the perimeter of the inner surface of the bottom plate; (c) a chamber housing machined from a rolled forging, the chamber housing having a top surface, and a bottom surface designed to join with the inner surface of the bottom plate such that the first o-ring seal forms a seal, and the top surface of the chamber housing having a second o-ring seal fastened to the perimeter of the top surface of the chamber housing; and (d) a top plate configured to sit over the second o-ring seal thereby forming a seal over the top surface of the chamber housing. 
     These and other advantages of the present invention will become apparent upon reading the following detailed descriptions and studying the various figures of the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is diagrammatic illustration of a typical cluster tool architecture which illustrates how various processing modules may be coupled to a transport module. 
     FIG. 2A is a simplified transport chamber assembled using conventional weldment technology. 
     FIG. 2B is another conventional transport chamber defined from a solid billet of aluminum. 
     FIG. 3 is a side-view of a transport chamber manufactured in accordance with one embodiment of the present invention. 
     FIG. 4 is a magnified top-view of the top plate of the transport chamber of FIG. 3 in accordance with one embodiment of the present invention. 
     FIG. 5A is a representative rolled forging which is used to make the chamber housing of the transport chamber of FIG. 3 in accordance with a preferred embodiment of the present invention. 
     FIG. 5B is a three-dimensional perspective view of a chamber housing after being machined from the rolled forging of FIG. 5A in accordance with a preferred embodiment of this invention. 
     FIG. 6 is a three-dimensional top view of a bottom plate which forms part of the transport chamber of FIG. 3 in accordance with a preferred embodiment of this invention. 
     FIG. 7 is an exploded view of FIG. 3 in accordance with a preferred embodiment of this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As described above, FIG. 1 schematically illustrates a typical cluster tool architecture and the relative positioning of transport module  106 . FIGS. 2A and 2B illustrate a weldment-type and a hogout-type transport chamber respectively, and their associated manufacturing inefficiencies. 
     An invention is described for improving the efficiency of manufacturing large transport chambers through the implementation of a rolled forging. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be obvious, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known manufacturing steps have not been described in detail in order not to unnecessarily obscure the present invention. 
     FIG. 3 is a side-view of a transport chamber  300  manufactured in accordance with one embodiment of the present invention. Transport chamber  300  generally includes a chamber housing  302 , a bottom plate  306 , and a top plate  304  all assembled to form a vacuum-tight chamber. In one embodiment, chamber housing  302  may have any number of facets  305  and interface ports  316 . By way of example, there are seven facets  305  and seven interface ports  316  in this embodiment. As is well known in the art, facets  305  provide a surface area for other chambers to meet up against chamber housing  302 . In this manner, a vacuum-tight seal may be formed between the various processing chambers and load lock chambers interconnected to transport chamber  300  as described in FIG.  1 . 
     In this embodiment, at least one facet surface area  305  may be joined up against a load lock unit (e.g., load lock  104  of FIG. 1) to provide a pressure interface between a clean room storage facility and chamber housing  302 . In this manner, transport chamber  300  may be maintained at a constant vacuum pressure which eliminates the need to pump down transport chamber  300  each time a new substrate is placed into or out of the chamber. By way of example, the pressure inside transport chamber  300  is preferably maintained at a pressure of between about 1 mTorr and about 150 mTorr, and more preferably between about 5 mTorr and about 100 mTorr, and preferably, at about 10 mTorr. 
     As shown, top plate  304  sits over a top surface of chamber housing  302 , and an O-ring seal  312  is positioned such that a vacuum-tight seal is made when top plate  304  is bolted down to chamber housing  302 . Similarly, bottom plate  306  may be bolted up against chamber housing  302  such that a vacuum-tight seal is made when O-ring seal  314  is positioned between chamber housing  302  and bottom plate  306 . It should be appreciated that although top plate  304  and bottom plate  306  have been described as being bolted to chamber housing  302 , any other suitable method of joining the respective plates may be substituted therefor. By way of example, suitable securing methods may include implementing clamps, straps, atmospheric force alone, threaded male and female connections, etc. 
     As illustrated, bottom plate  306  has two support beams  310  positioned below bottom plate  306  which provide additional structural support to transport chamber  300 . Although support beams  310  may be constructed of any type of rigid material, preferably a mild steel which is readily available and may be used to provide a rigid structural base. However, it should be understood that the support beams  310  may be eliminated if bottom plate  306  is made sufficiently thick to withstand any operational pressures and structural requirements. 
     Preferably, chamber housing  302  may have an outer diameter of between about 12 inches and 400 inches, and more preferably, a outer diameter of between about 30 inches and 200 inches, and preferably about 90 inches from one corner of one facet to a diagonal corner of another facet. Further, the vertical height of transport chamber  302  may preferably be between about 3 inches and about 50 inches, and more preferably, between about 5 and about 25 inches, and preferably about 10 inches. 
     Further, interface ports  316  may have a horizontal width opening of between about 400 millimeters and 1,050 millimeters, and more preferably, between about 500 millimeters and 800 millimeters, and preferably about 650 millimeters. The opening height of each interface port  316  may preferably be between about 1,200 millimeters and 50 millimeters, and more preferably between about 500 millimeters and 65 millimeters, and preferably about 75 millimeters. When interface ports  316  are selected within these ranges, larger substrates having dimensions of about 1,000 millimeters by 1,000 millimeters may be transported in and out of transport chamber  300  when chamber housing  302  is designed large enough to accommodate the motion path of the largest substrate being transported. 
     Still referring to FIG. 3, top plate  304  is also shown having view ports  308  designed to provide viewing and access capabilities into transport chamber  300 . By way of example, view ports  308  may provide an efficient passage for maintaining mechanical components (e.g., a gate drive valve) and cleaning particles. As is well known in the art, small atmospheric particles resulting from general use, small substrate particles and/or large substrate fragments may occasionally end up inside transport chamber  300 . In such cases, it is typically desired that those particles be removed in order to prevent product defects or an obstruction for a robot arm (not shown for ease of illustration) that is responsible for transporting substrates. Further, view ports  308  may also provide time saving maintenance access for replacing various consumable O-ring seals that surround insert plates (not shown) that fit into interface ports  316 . 
     FIG. 4 is a magnified top-view of top plate  304  which illustrates some of the advantageous features associated with one embodiment of the present invention. By way of example, top plate  304  may include an access window  410  for installing and removing the aforementioned robot arm into transport chamber  300 . Access window  410  may be of any suitable dimensional such that a robot arm may easily fit into transport chamber  300 . As will be described in greater detail with reference to FIG. 6 below, once the robot arm is brought into transport chamber  300  through access window  410 , the robot arm is attached to a robot arm drive which comes up through bottom plate  306 . 
     Once the robot arm has been installed, access window may be closed. It should be appreciated that since access window may be a solid aluminum plate sealed down by O-rings, opening and closing may be difficult without a hinge (not shown for ease of illustration) designed to mechanically reduce the weight of access window  410 . Although any type of lifting mechanism may be employed (or none at all), one type of hinge may be a Counterbalance™ which may be obtained from Counterbalance Corporation of Warminster, Pa. 
     Although viewport windows  308  are shown positioned over each interface port  316  as described with reference to FIG. 3, it should be understood that viewport windows  308  may be optional. Further, the positioning and shape of viewport windows  308  may be modified without departing from the spirit and scope of this embodiment. By way of example, viewport windows  308  may be circular, hexagonal, rectangular, etc., and there may be a greater or fewer number of viewport windows  308  than interface ports  316 . In one embodiment, viewport windows  308  may be a clear two inch thick polycarbonate plastic which may be sealed down to top plate  304  by an O-ring. In this manner, a vacuum-tight seal may be maintained when transport chamber  300  is brought down to vacuum conditions. In this embodiment, Lexan® plastic which is available from General Electric Plastics of Pittsfield, Mass., may be used to make viewport windows  308 . 
     Further, top plate  304  is shown having an underlip  402  which is designed to sealably sit over O-ring seal  312  which lies around the top surface of chamber housing  302  as illustrated in FIG.  3 . In this manner, underlip  402  will fit over O-ring seal  312  as illustrated in FIG.  3 . Top plate  304  may also have a reduced diameter protrusion  303  which is designed to fit into chamber housing  302 , and further assures a more accurate positioning of top plate  304  into chamber housing  302  on axis. 
     In one embodiment, the thickness of top plate  304  may be between about 2 inches and 6 inches, and more preferably, between about 3 and 5 inches, and preferably about 4 inches. This thickness is preferably selected to withstand anticipated pressures of about 15 pounds per square inch. In this embodiment, anticipated deflections are typically not more than between about 1 inch and 0 inches, and more preferably, between about 0.5 inches and 0.1 inches, and preferably not more than about 0.2 inches. By way of example, the described deflections define the approximate degree by which the center region of top plate  304  may drop. That is, if the center region of top plate  304  does drop, a dish-like shape may be formed. 
     However, it should be appreciated that the above described deflections may vary depending upon the selected thickness, material and diameter of top plate  304 . In this embodiment, top plate  304  may have a diameter of between about 12 inches and 400 inches, and more preferably, between about 30 inches and 200 inches, and preferably about 80 inches. Therefore, it should be appreciated that top plate  304  may be quite heavy when formed to, e.g., a thickness of about 4 inches. The weight further assures that underlip  402  seals tightly up against O-ring  312 . 
     FIG. 5A is a representative rolled forging  500  which depicts a ring having an outer diameter, an inner diameter and a vertical height. In this embodiment, rolled forging  500  may be a solid aluminum ring which advantageously increases the manufacturing efficiency of chamber housing  302 . Therefore, rolled forging  500  will be the starting point from which chamber housing  302  is machined. Although any dimension may be specially selected to meet particular needs, rolled forging  500  is preferably selected to have a raw inner diameter of about 79 inches, a raw outer diameter of about 93 inches, and a vertical raw height of about 11 inches. Although rolled forgings may be obtained from any suitable supplier, a suitable rolled forging may be obtained from Jorgenson Forge, of Seattle, Wash. 
     FIG. 5B is a three-dimensional perspective view of chamber housing  302  after being machined from a rolled forging as described above. It should be appreciated that substantial cost savings are realized due to the reduced amount of machining required to form the various facets  305  of chamber housing  302  and interface ports  316 . As compared to weldment and hogout type transport chambers, there may be approximately about a 40 percent time savings in generating a finished transport chamber  300  (e.g., of FIG.  3 ). By way of example, substantially no welding is required to generate transport chamber  300  which eliminates warping and distortions problems. In addition, very little aluminum is wasted as compared to hogout type chambers. 
     In this embodiment, top surface  506  of chamber housing  302  is shown having an O-ring seal  312  surrounding the inner diameter of chamber housing  302 . As described above, when top plate  304  is placed over chamber housing  302 , a vacuum-tight seal is formed when underlip  402  of FIG. 4 sits over O-ring seal  312 . In this embodiment, chamber housing  302  may have an outermost diameter of between about 12 inches and 400 inches, and more preferably, between about 30 and 200 inches, and preferably about 91 inches. 
     Chamber housing  302  also includes a sealing surface lip  504  which is shown to be an underneath surface region of chamber housing  302 . As will be better appreciated after bottom plate  306  has been fully described in FIG. 6 below, sealing surface lip  504  will advantageously provide a sealing surface when O-ring seal  314  is sandwiched between bottom plate  306  and chamber housing  302 . 
     FIG. 6 is a three-dimensional top view  600  of bottom plate  306 . As shown, bottom plate  306  has a robot drive mounting port  602  designed to allow a robot arm drive (not shown for ease of illustration) to be installed from beneath bottom plate  306 . In this manner, the robot arm drive may seal up against an O-ring sealing surface lip  604  which surrounds robot drive mounting port  602  and provides a sealing surface for an O-ring seal. Further, in this embodiment, O-ring seal  314  is shown provided around the perimeter of the top surface of bottom plate  306 . In this manner, when bottom plate  306  is secured up against chamber housing  302 , O-ring  314  may from a vacuum-tight seal. 
     Also shown are bores  606  which are defined around the perimeter of bottom plate  306  in order to provide a passage for inserting a shaft portion of a gate drive unit (not shown for ease of illustration). As is well known in the art, gate drives units are generally used to mechanically open and close a gate up against the various interface ports  316  which may lead to processing chambers, load locks and clean rooms. For more information on gate drive units, reference may be made to U.S. patent application Ser. No. 08/679,357 filed on the same day as the instant application, naming Trace L. Boyd and Martin F. Yeoman as inventors, and entitled “Vacuum Chamber Gate Valve and Method for Making Same”. This application is hereby incorporated by reference. 
     In addition, for more information on consumable-type O-rings that may be placed within interface ports  316 , reference may be made to U.S. patent application Ser. No. 08/675,994 filed on the same day as the instant application, naming Trace L. Boyd, Richard D. Beer, Eric A. Terbeek and Vernon W. H. Wong as inventors, and entitled “Chamber Interfacing O-Rings and Method for Implementing Same”. This application is hereby incorporated by reference. 
     For illustration purposes, two parallel support beams  310 , as described above, are shown traversing the under region of bottom plate  306 . Support beams are generally used to provide bottom plate  306  with additional structural support. Although support beams  310  may be eliminated if bottom plate  306  is made thicker, support beams  310  may be used for preferred bottom plate  306  thicknesses of between about 1 and 6 inches, and more preferably, between about 1.5 and 4 inches, and preferably about 2 inches. In this manner, the structural support provided by support beams  310  will be sufficient to withstand the anticipated structural stresses and operational pressures. In addition, since support beams  310  are primarily used to provide structural support, a mild steel which is stronger and stiffer than aluminum may be used. In this embodiment, the preferred diameter of bottom plate  306  may be between about 12 inches and 400 inches, and more preferably, between about 30 and 200 inches, and preferably about 80 inches. 
     FIG. 7 is an exploded view  700  of FIG. 3 illustrating how top plate  304  may be placed over and into chamber housing  302 , and how chamber housing  302  may receive bottom plate  306 . Once the three-part structure is bolted together using any suitable bolting mechanism, the resulting transport chamber may form a vacuum-tight chamber which may be maintained under vacuum conditions during operation. 
     To maximize throughput, transport chamber  300  may be equipped with two or more IN-ports for receiving substrates, and the remaining interface ports may be used to connect up to processing modules. In this manner, a greater number of substrates may be processed throughout the chambers of the cluster architecture. By way of example, when one IN-port is waiting for a load lock to be pressured down, a previously pressured down load lock may introduce a new substrate into the transport chamber. Further, it should be appreciated that each load lock may hold a multiplicity of substrates which are stacked in a cassette arrangement. A representative load lock must therefore be large enough to hold cassettes of substrates so that once the load lock is pressured down, the transport chamber robot arm may be able to access all the substrates in the pressured down load lock without having to sit idle during a pressure down operation each time a substrate is needed. 
     Structurally, transport chamber  300  is rather heavy and may be supported off the ground so that the aforementioned robot arm, gate drive, and accompanying electronics may be installed from below bottom plate  306 . There may be situations where bottom plate  306  may need to be disengaged from chamber housing  302  in order to maintenance transport chamber  300 . Advantageously, a support structure may preferably be made of mild steel (not shown) and mounted to an outer under surface  706  of chamber housing  302 . In this manner, bottom plate  306  may be partially or completely removed without having to disassemble the entire transport chamber  300 . 
     Initially, substrates being transported into transport chamber  300  are in a pre-processed stage. In one embodiment, the substrates may be further processed in order to generate flat panel displays (FPDs) which are typically exposed to number of etching processes. By way of example, the assignee of this application identifies this cluster architecture by the trademark name “Continuum”. However, it should be borne in mind that the transport chamber  300  and its associated processing modules may be used in any processing system to fabricate a variety of different articles of manufacture. By way of example, transport chamber  300  may be used to transport semiconductor wafers, disk drives, items needing metal plating and etching. Broadly speaking, the disclosed embodiments may also be used for depositing films, freeze drying foods and any other application implementing a vacuum transport chamber and associated processing modules. 
     Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. In addition, although the preferred materials used to make chamber housing  302 , top plate  304 , and bottom plate  306  is aluminum, any other suitable material such as stainless steel, etc., may be substituted therefor. Therefore, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.