Abstract:
A plasma generation device has a plasma containment vessel comprising integral cast cooling elements. A casting mold is placed over a foundation, leaving at least one surface of the foundation exposed. At least one cooling tube is then placed over the foundation, and a casting material is then poured into the casting mold over the foundation and the cooling tubes. The foundation portion of the assembly is machined and anodized to become an interior and vacuum surface of a plasma chamber with integral cooling elements.

Description:
RELATED APPLICATIONS  
       [0001]     This is a continuation-in-part of U.S. patent application Ser. No. 10/395,585, filed Mar. 24, 2003. 
     
    
     BACKGROUND  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates generally to plasma containment vessels, and more specifically to plasma chambers comprising integral cast cooling elements.  
         [0004]     2. Brief Description of the Prior Art  
         [0005]     A chamber for containment of a subatmospheric plasma typically requires three key features. First, the chamber must be able to seal a vacuum created within the chamber, which may be in the 10 −9  Torr range. Second, the interfaces and materials of the chamber need to be able to withstand the heat and chemistry of the plasma environment. Finally, plasma chambers ordinarily must be cooled for extraction of the internal heat generated by the plasma. Aluminum alloys are often materials of choice for construction of interior vacuum surfaces of plasma chambers as they are vacuum compatible and can be anodized to offer the necessary resistance from corrosive gases and from the plasma itself. Cooling may be accomplished for example by providing copper water tubing in contact with or impressed into the aluminum walls of the chamber. One limitation of this approach is the attachment between the cooling tubes and the metal plate. If the tubes are soldered, brazed, welded or epoxied to the aluminum plate, then the attachment point will limit the flow of heat from the plate to the cooling tubes.  
         [0006]     Alternatively, attempts have been made to cast cooling tubes inside of the walls of a containment vessel to eliminate the degradation in heat transfer through the soldered, brazed, welded or epoxied connection. Typical cast materials, however, are not appropriate for many applications. In vacuum chambers, the porosity of cast materials can hamper the establishment of a vacuum, significantly slowing production times. Cast materials can also become impregnated with undesired impurities, and typically cannot be anodized to a level that is acceptable for corrosion resistance in a plasma environment.  
       SUMMARY OF THE INVENTION  
       [0007]     The invention features a plasma generation device having a plasma containment vessel comprising integral cast cooling elements. In one aspect of the invention, a core material serves as a foundation for a cast cooling assembly. The core material is selected for its suitability as a vacuum containment material and for its tolerance to a plasma environment. A cooling assembly is then cast upon the foundation material using a casting mold. In one embodiment, the cooling assembly comprises metallic cooling tubes embedded in a casting disposed conformally to the exterior surface of the chamber wall. After the cooling assembly is cast upon the core material, the solid chamber wall assembly is machined and anodized to become an interior vacuum surface of a chamber with integral cooling elements.  
         [0008]     In another aspect of the invention, one or more of the integral cooling elements of a plasma chamber vessel serves as a coldplate for mounting of heat generating electrical components. The cooling element thus serves to extract heat from both the plasma as well as from electrical components of the plasma generation device.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     Embodiments of the present invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to similar elements and in which:  
         [0010]      FIG. 1  illustrates a cast coldplate within general embodiments of the invention;  
         [0011]      FIG. 2  is a flowchart illustrating a method for making a cast coldplate within general embodiments of the invention;  
         [0012]      FIG. 3  illustrates a vacuum chamber using a cast coldplate of general embodiments of the invention on one side of the vacuum chamber; and  
         [0013]      FIG. 4  illustrates a vacuum chamber using a cast coldplate of general embodiments of the invention on multiple sides of the vacuum chamber.  
     
    
     DETAILED DESCRIPTION  
       [0014]      FIG. 1  illustrates a cast coldplate applicable to embodiments of the invention. The cast coldplate  100  has a foundation  102  with a top surface  104 , a bottom surface  106 , and side surfaces  108 ,  110 . The foundation can be made of any of a variety of materials. In one embodiment, the material is selected for use as an interior wall of a plasma chamber. Such materials include machined aluminum and aluminum alloys such as aluminum  6601 .  
         [0015]     The coldplate also has a casted component  112  with at least one cooling tube  114 ,  116 ,  118 ,  120  within it. The cooling tubes can be completely or partially surrounded by the casted component, depending upon the application. The cooling tubes can be made of conventional copper water piping or of any of a variety of other materials depending upon the cooling fluid used and the heat exchange properties that are desired. Alternatively, the cooling device is a heat pipe device. An aluminum structure surrounding copper pipes provides for good heat conduction for many applications.  
         [0016]      FIG. 2  illustrates a method for making a cast coldplate. The method begins at block  200  and continues to block  202  where a casting mold is placed over the foundation  102 , surrounding at least the top surface  104  of the foundation  102 . In illustrated embodiments of the invention (see  FIG. 1 ), the casting mold surrounds the top surface  104  of the foundation  102 , as well as the side surfaces  108 ,  110  of the foundation. However, the casting mold may alternatively surround just the top surface  104  of the foundation  102 .  
         [0017]     At block  204 , cooling tubes  114 ,  116 ,  118 ,  120  are placed over the foundation  102 . Cooling tubes  114 ,  116 ,  118 ,  120  that are placed over the foundation  102  may be placed directly on the foundation material or suspended off the surface of the foundation material using a fixture. At block  206 , casting material is poured over the foundation  102  and the cooling tubes  114 ,  116 ,  118 ,  120  to create a layer of casting material. The casting material, in one embodiment is poured so that is completely surrounds the exterior of each tube. This maximizes the heat transfer surface. The number and placement of the cooling tubes will depend on the particular application and a variety of factors such as heat flow demands, fluid flow and pressure drop tolerances. Coolant, such as water, may then be run through the cooling tubes  114 ,  116 ,  118 ,  120  to keep the cast coldplate cool, thereby keeping components, such as electronics mounted to the plate, cool. The method ends at block  208 .  
         [0018]     In another aspect of the invention, the foundations of one or more cast coldplates are used as an inner wall of a vacuum chamber, for example, a plasma chamber. The foundation material is particularly well suited for use as a chamber wall and the cast material, in intimate contact with the foundation conducts heat away from the foundation and toward the cooling pipes.  
         [0019]     In one embodiment, the bottom surface of the foundation is placed over a top surface of a vacuum chamber, such that one side of the vacuum chamber comprises the bottom surface  106  of the foundation  102 , as illustrated in  FIG. 3 . The vacuum chamber  300  comprises a cast coldplate  100  on one side of the vacuum chamber, a housing  302  such as aluminum or aluminum alloy on a plurality of sides of the vacuum chamber, and a chamber  304  in which plasma is maintained. The housing  302  and bottom surface  106  of the foundation  102  of the cast coldplate  100  surround the chamber  304  in which plasma is maintained. The coldplate also serves as a heat sink upon which components of the power supply, match, or other electronics of the plasma generation device are mounted. In another embodiment, as illustrated in  FIG. 4 , the vacuum chamber  300  comprises a cast coldplate  100  on each of its sides.  
         [0020]     As plasma moves through the vacuum chamber  304 , the plasma source body  302  and cast coldplate  100  increase in temperature. To keep the vacuum chamber  300  cool, water is run through the cooling tubes  114 ,  116 ,  118 ,  120 .  
         [0021]     The plasma source body  302  and foundation  102  may comprise a metal such as aluminum, copper, nickel, or steel, or a coated metal such as anodized aluminum or nickel-plated aluminum. The casting material used to create the casted component  112  of the cast coldplate  100  may comprise an aluminum alloy, or a tin alloy, for example.  
         [0022]     In the description above, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. In other instances, well-known circuits, structures, devices, and techniques have been shown in block diagram form or without detail in order not to obscure the understanding of this description.  
         [0023]     The present invention includes various steps, but steps can be added to or deleted from any of the methods and signal or messages can be added or subtracted from any of the described steps or control lines without departing from the basic scope of the present invention. It will be apparent to those skilled in the art that many further modifications and adaptations can be made. The particular embodiments are not provided to limit the invention but to illustrate it. The scope of the present invention is not to be determined by the specific examples provided above but only by the claims below.  
         [0024]     Furthermore, while the invention has been illustrated in the context of a coldplate used in a plasma chamber, the invention is not so limited. It can be applied to coldplates in general, as well as to any application in which a component needs cooling and requires that a specific foundation material surface be exposed.  
         [0025]     It should also be appreciated that reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature may be included in the practice of the invention. Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this invention.