Patent Publication Number: US-7896974-B2

Title: Chamber for wafer cleaning and method for making the same

Description:
CLAIM OF PRIORITY 
     This application is a divisional application of U.S. patent application Ser. No. 10/404,472, filed on Mar. 31, 2003, now U.S. Pat. No. 7,392,815, the disclosure of which is incorporated in its entirety herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to semiconductor wafer processing. More specifically, the present invention relates to an apparatus in which a semiconductor wafer can be cleaned. 
     2. Description of the Related Art 
     In the manufacture of semiconductor devices, a surface of a semiconductor wafer (“wafer” or “substrate”) must be cleaned to remove chemical and particulate contamination. If the contamination is not removed, semiconductor devices on the wafer may perform poorly or become defective. Particulate contamination generally consists of tiny bits of distinctly defined material having an affinity to adhere to the surface of the wafer. Examples of particulate contamination can include organic and inorganic residues, such as silicon dust, silica, slurry residue, polymeric residue, metal flakes, atmospheric dust, plastic particles, and silicate particles, among others. 
     Wafer cleaning processes are generally performed by applying a fluid to the surface of the wafer. In some instances the fluid is applied to the wafer in a sealed chamber. The method of applying the fluid to the wafer can influence the effectiveness of the wafer cleaning process. For example, a specific fluid flow pattern over the surface of the wafer may provide beneficial cleaning results. Additionally, a specific fluid pressure applied over the surface of the wafer may provide beneficial cleaning results. Traditionally, different wafer cleaning chambers have been required to obtain different fluid flow patterns and fluid pressures over the surface of the wafer. The need to have a different wafer cleaning chambers to satisfy the requirements of a variety of wafer cleaning processes can present problems with respect to overall wafer processing cost and implementation. Also, wafer cleaning processes that require the use of high fluid pressures generally require the use of large wafer cleaning chambers to withstand the high pressure. Larger wafer cleaning chambers correspond to increased overall wafer processing cost. 
     In view of the foregoing, there is a need for a wafer cleaning chamber that allows for variable control of fluid pressures and fluid flow patterns as required to meet the needs of different wafer cleaning processes. The wafer cleaning chamber should also be able to accommodate wafers of different sizes. Furthermore, the wafer cleaning chamber should combine an ability to contain high pressures with an overall minimum size. 
     SUMMARY OF THE INVENTION 
     Broadly speaking, the present invention provides a wafer processing chamber “chamber” that allows a fluid flow and a fluid pressure within the chamber to be controlled in a variable manner. More specifically, the chamber of the present invention utilizes removable plates that can be configured to control the fluid flow and the fluid pressure in an inner volume within the chamber. Also, the removable plates can be used to separate the inner volume within the chamber from an outer volume within the chamber. In this manner, the removable plates can be used to create a pressure differential between the inner volume within the chamber and the outer volume within the chamber. A lower pressure in the outer volume within the chamber requires less outer chamber strength to withstand the lower pressure. A lower outer chamber strength requirement translates into an overall decrease in chamber size. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several embodiments of the present invention are described below. 
     In one embodiment, a wafer cleaning chamber is disclosed. The wafer cleaning chamber includes a lower support having a number of support surfaces. The lower support contains a first volume that exists between the number of support surfaces. The wafer cleaning chamber further includes a plate supported by the number of support surfaces of the lower support. The plate overlies the first volume in the lower support. The plate also has a number of wafer support surfaces to receive and support a wafer. A second volume exists between the number of wafer support surfaces of the plate. Additionally, inlets and outlets are located in a periphery of the plate for introducing a fluid flow. The inlets and outlets are positioned outside a location intended to receive the wafer. The wafer cleaning chamber also includes an upper support overlying the plate. The upper support interfaces with the lower support at a location outside the periphery of the plate. A third volume within the upper support overlies the wafer to be supported by the plate. The third volume is capable of accommodating a fluid flow. The fluid flow can be introduced in a set configuration by the inlets and outlets of the plate. Also, the third volume is in limited fluid communication with the first volume and the second volume. 
     In another embodiment, a wafer processing apparatus is disclosed. The wafer processing apparatus includes a chamber having an upper portion and a lower portion. Support structures are distributed within a first volume that is defined in the lower portion of the chamber. Also, additional support structures are distributed within a second volume that is defined within the upper portion of the chamber. The wafer processing apparatus further includes a lower plate that is configured to be disposed on the support structures of the lower portion of the chamber. When disposed on the support structures, the lower plate overlies the first volume within the lower portion of the chamber. The lower plate includes a number of wafer support structures distributed within a third volume defined within the lower plate. The number of wafer support structures are capable of supporting a wafer. When the wafer is placed on the wafer support structures, the wafer overlies the third volume within the lower plate. The wafer processing apparatus also includes an upper plate configured to be attached to the support structures of the upper portion of the chamber. When the upper plate is attached to the support structures, the upper plate underlies the second volume defined within the upper portion of the chamber. The upper plate serves as an upper boundary of a fourth volume that exists between the upper plate and the wafer to be supported by the lower plate. The fourth volume is capable of containing a fluid. Also, the fourth volume is in limited fluid communication with the first volume, the second volume, and the third volume. 
     In another embodiment, a method for making a wafer processing chamber is disclosed. The method includes forming a lower support plate that has support surfaces distributed within a first volume that is defined within the lower support plate. The first volume is defined to have a first fluid inlet and a first fluid outlet. The method also includes forming a wafer support plate having wafer support surfaces distributed within a second volume that is defined within the wafer support plate. The wafer support surfaces are configured to receive a wafer. Once received, the wafer forms an upper boundary for the second volume defined within the wafer support plate. The second volume is defined to have a second fluid inlet and a second fluid outlet. Additionally, fluid inlets and fluid outlets are provided at a periphery of the wafer support plate and outside a location that is to receive the wafer. The method further includes securing the wafer support plate to the lower support plate. Once secured, the wafer support plate is supported by the support surfaces distributed within the first volume of the lower support plate. Also, the wafer support plate serves as an upper boundary for the first volume defined within the lower support plate. The method continues with the forming of an upper support plate that contains a third volume configured to overlie the wafer to be received by the wafer support surfaces of the wafer support plate. The method also includes securing the upper support plate to the lower support plate to isolate the third volume defined within the upper support plate from an outside environment. The isolation of the third volume from the outside environment is enabled by a seal disposed between the upper support plate and the lower support plate. 
     In another embodiment, a method for performing a wafer cleaning process is disclosed. The method includes providing a chamber in which the wafer cleaning process can be performed. The chamber includes a first volume configured to overlie a wafer to be cleaned. The chamber also includes a plate configured to support the wafer. A second volume is defined within the plate directly below the wafer. The plate includes fluid inlets and fluid outlets defined in a periphery of the plate and outside a portion of the plate defined to support the wafer. The fluid inlets and fluid outlets are oriented to direct a fluid flow through the first volume in a set pattern. Also in the chamber, a support structure is provided to support the plate. The support structure includes a third volume located directly below the plate. The method includes an operation for placing a wafer on the portion of the plate defined to support the wafer. The method further includes pressurizing the first volume to have a higher pressure than the second volume. The method also includes pressurizing the second volume to have a higher pressure than the third volume. The third volume is pressurized to have a pressure between that of the second volume and an environment outside the chamber. Also in the method, a fluid is provided to the first volume through the fluid inlets and is removed from the first volume through the fluid outlets, such that the fluid flows through the first volume in the set pattern. The fluid is formulated to effect the wafer cleaning process. 
     In another embodiment, a method is disclosed for cleaning a wafer. The method includes an operation for placing a wafer on a support plate. The support plate includes a number of fluid inlets and a number of fluid outlets defined in a periphery of the support plate. The periphery of the support plate is defined outside an area of the support plate on which the wafer is placed. The method also includes an operation for flowing a cleaning fluid over the wafer from the number of fluid inlets to the number of fluid outlets in a set fluid flow pattern. The set fluid flow pattern is defined by positions and orientations of the number of fluid inlets and the number of fluid outlets. 
     Other aspects and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention, together with further advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is an illustration showing a vertical cross-section of a wafer processing chamber (“chamber”), in accordance with one embodiment of the present invention; 
         FIG. 2  is an illustration showing a close-up view of a central portion of the chamber as shown in  FIG. 1 , in accordance with one embodiment of the present invention; 
         FIG. 3  is an illustration showing a top view of the lower plate configured to provide a linear fluid flow across the wafer, in accordance with one embodiment of the present invention; 
         FIG. 4  is an illustration showing a top view of the lower plate configured to provide a conical fluid flow across the wafer, in accordance with one embodiment of the present invention; 
         FIG. 5  is an illustration showing a top view of the lower plate configured to provide a spiral fluid flow across the wafer, in accordance with one embodiment of the present invention; 
         FIG. 6  is an illustration showing a vertical cross-section of the chamber incorporating an upper plate, in accordance with one embodiment of the present invention; 
         FIG. 7  is an illustration showing a close-up view of a central portion of the chamber as shown in  FIG. 6 , in accordance with one embodiment of the present invention; 
         FIG. 8A  is an illustration showing an upper plate configured to provide a central fluid feed and a peripheral fluid exhaust, in accordance with one embodiment of the present invention; 
         FIG. 8B  is an illustration showing the use of fluid channels within the upper plate, in accordance with one embodiment of the present invention; 
         FIG. 9  is an illustration showing an upper plate configured to provide a peripheral fluid feed and a central fluid exhaust, in accordance with one embodiment of the present invention; 
         FIG. 10  is an illustration showing an exemplary distribution of the inlets/outlets across the upper plate, in accordance with one embodiment of the present invention; 
         FIG. 11  is an illustration showing a flowchart of a method for making a wafer processing chamber, in accordance with one embodiment of the present invention; 
         FIG. 12  is an illustration showing a flowchart of a method for performing a wafer cleaning process, in accordance with one embodiment of the present invention; and 
         FIG. 13  is an illustration showing a generalized material phase diagram. 
     
    
    
     DETAILED DESCRIPTION 
     An invention is disclosed for a wafer processing chamber “chamber” and a method for making the chamber. Broadly speaking, the present invention provides a chamber that allows a fluid flow and a fluid pressure within the chamber to be controlled in a variable manner. More specifically, the chamber of the present invention utilizes removable plates that can be configured to control the fluid flow and the fluid pressure in an inner volume within the chamber. Also, the removable plates can be used to separate the inner volume within the chamber from an outer volume within the chamber. In this manner, the removable plates can be used to create a pressure differential between the inner volume within the chamber and the outer volume within the chamber. A lower pressure in the outer volume within the chamber requires less outer chamber strength to withstand the lower pressure. A lower outer chamber strength requirement translates into an overall decrease in chamber size. 
     In the following description, 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 or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention. 
       FIG. 1  is an illustration showing a vertical cross-section of a wafer processing chamber (“chamber”)  100 , in accordance with one embodiment of the present invention. In one embodiment, the chamber  100  can serve as a wafer cleaning chamber. The chamber  100  includes a lower support plate  101  having a number of support surfaces  102 . The support surfaces  102  are distributed within an intermediate volume  113  defined within a top portion of the lower support plate  101 . The support surfaces  102  are capable of supporting a lower plate  109  at discrete locations in a substantially uniform manner. The number and location of the support surfaces  102  depends on a pressure differential between the two sides of the lower plate  109 . When placed on the support surfaces  102 , the lower plate  109  serves as an upper boundary to the intermediate volume  113 . 
     The lower plate  109  can be secured to the lower support plate  101  by a number of bolts  111 . The lower plate  109  includes a number of wafer support surfaces  110  distributed to provide substantially uniform support to a wafer  117  to be disposed within the chamber  100 . The lower plate  109  can be sized to allow the chamber  100  to process wafers of different sizes (e.g., 200 mm diameter, 300 mm diameter, etc. . . . ). The wafer support surfaces  110  are separated to form a lower volume  115 . The lower volume  115  is located beneath the wafer  117  to be disposed on the lower plate  109 . Hence, with respect to the wafer  117 , the lower volume  115  is also referred to as an underlying volume  115 . 
     The chamber  100  also includes an upper support plate  103  that is configured to interface with a top section of the lower support plate  101 . The upper support plate  103  includes a wafer processing volume  119 . The wafer processing volume  119  is configured to overlie the wafer  117  when the upper support plate  103  is attached to the lower support plate  101 . When the wafer  117  is present in the chamber  100 , the top surface of the wafer  117  is exposed to the wafer processing volume  119 . Hence, with respect to the wafer  117 , the wafer processing volume  119  is also referred to as an overlying volume  119 . 
     A seal  107  is disposed between the upper support plate  103  and the lower support plate  101  at a peripheral location where the upper support plate  103  and the lower support plate  101  are in contact. The seal  107  traverses the periphery of the wafer processing volume  119  and serves to isolate the wafer processing volume  119  from an outside environment. To enable the seal  107 , the upper support plate  103  and lower support plate  101  are forced together by a number of bolts  105  located outside a periphery of the seal  107 . Some wafer processes must be performed at extremely high pressures. Thus, the upper support plate  103 , the lower support plate  101 , and the bolts  105  provide sufficient strength to withstand a pressure which may exist within the wafer processing volume  119 . 
     Additionally, some wafer processes must be performed at specific temperatures. In order to provide temperature control within the wafer processing volume  119 , thermal control devices can be disposed within the upper support plate  103  and the lower support plate  101 . In one embodiment, the thermal control devices can include heat exchanger fluid pathways. In another embodiment, the thermal control devices can include electric heating elements. In either embodiment, conduction through the upper support plate  103 , the lower support plate  101 , and the lower plate  109  provide a transfer mechanism to move heat from the thermal control devices to the wafer processing volume  119 . 
       FIG. 2  is an illustration showing a close-up view of a central portion of the chamber  100  as shown in  FIG. 1 , in accordance with one embodiment of the present invention. The close-up view shows a vertical cross-section of half of the chamber  100 , including the upper support plate  103 , the wafer processing volume  119 , the wafer  117 , the underlying volume  115 , the lower plate  109 , the intermediate volume  113 , and the lower support plate  101 . 
     As discussed with respect to  FIG. 1 , the lower plate  109  serves to support the wafer  117  by providing the wafer support surfaces  110  upon which the wafer  117  will be secured during wafer processing. Each of the wafer support surfaces  110  is a part of a discrete support structure. The discrete support structures corresponding to the wafer support surfaces  110  are distributed in a substantially uniform manner throughout the underlying volume  115 . Therefore, the underlying volume  115  exists between the discrete support structures corresponding to the wafer support surfaces  110  and below the wafer  117 . An inlet  207  is provided for introducing fluids into the underlying volume  115 . An outlet  205  is provided for removing fluids from the underlying volume  115 . In other embodiments, the inlet  207  and the outlet  205  can be disposed at other locations within the lower plate  109 . A number of inlets/outlets  209  are also provided within the lower plate  109  to introduce and remove fluids from the wafer processing volume  119 . 
     As discussed with respect to  FIG. 1 , the lower support plate  101  serves to support the lower plate  109  by providing the support surfaces  102  upon which the lower plate  109  will be secured during wafer processing. Each of the support surfaces  102  is a part of a discrete support structure. The discrete support structures corresponding to the support surfaces  102  are distributed in a substantially uniform manner throughout the intermediate volume  113 . Therefore, the intermediate volume  113  exists between the discrete support structures corresponding to the support surfaces  102  and below the lower plate  109 . An inlet  201  is provided for introducing fluids into the intermediate volume  113 . An outlet  203  is provided for removing fluids from the intermediate volume  113 . In other embodiments, the inlet  201  and the outlet  203  can be disposed at other locations within the lower support plate  101 . 
     The wafer processing volume  119  is formed within the upper support plate  103  to overlie the wafer  117  when the upper support plate  103  is joined with the lower support plate  101 . Since the wafer  117  is not hermetically sealed to the lower plate  109  during wafer processing, the wafer processing volume  119  will be in fluid communication with the underlying volume  115  through a limited fluid communication pathway  211  at the periphery of the wafer  117 . The limited fluid communication pathway  211  is essentially the area between the wafer  117  and the peripheral wafer support surface  110  of the lower plate  109 . 
     During operation, a pressure in the wafer processing volume  119  will be maintained at a higher level than a pressure in the underlying volume  115 , thus creating a pressure differential through the wafer  117  from top to bottom. The pressure differential serves to push the wafer  117  toward the lower plate  109  with sufficient force to secure the wafer  117  to the wafer support surfaces  110 . Since the pressure in the wafer processing volume  119  is higher than the pressure in the underlying volume  115 , some fluid will pass from the wafer processing volume  119  through the limited fluid communication pathway  211  to the underlying volume  115 . The outlet  205  can be used to remove fluid from the underlying volume  115  as necessary. 
     The dimensions of the wafer processing volume  119 , the underlying volume  115 , and the wafer support surfaces  110  can vary depending upon the requirements (e.g., pressure, fluid flow rate, fluid composition, etc. . . . ) of the wafer process to be performed. In one embodiment, a separation distance D 1  between the upper support plate  103  and the wafer  117  top surface is about 0.04 inch. As used herein, the term “about” means within ±10% of a specified value. However, in other embodiments different values for D 1  may be used. In one embodiment, a depth D 2  of the underlying volume  115  between the wafer  117  and the lower plate  109  can be within a range extending from about 0.005 inch to about 0.04 inch. In a particular embodiment, the depth D 2  is about 0.02 inch. In one embodiment, an overlap distance D 3  between the wafer  117  and the peripheral wafer support surface  110  can be within a range extending from about 0.1 inch to about 0.5 inch. In a particular embodiment, the overlap distance D 3  is about 0.25 inch. The overlap distance D 3  is a key factor in establishing the pressure drop between the wafer processing volume  119  and the underlying volume  115 , through the limited fluid communication pathway  211 . In one embodiment, a wafer positioning tolerance D 4  (i.e., nominal distance between the wafer  117  edge and a wafer pocket perimeter within the lower plate  109 ) can be within a range extending from about 0.025 inch to about 0.1 inch. The wafer positioning tolerance D 4  may be dictated by a precision of a robot handling device. 
     The wafer support surfaces  110  are configured to contact a percentage of the wafer  117  commensurate with the pressure differential to be applied through the wafer  117 . A higher pressure differential requires a higher percentage of the wafer  117  to be in contact with the wafer support surfaces  110 . In one embodiment, the wafer support surfaces  110  can be in contact with a percentage of the wafer  117  surface within a range extending from about 5% to about 80%. In another embodiment, the wafer support surfaces  110  can be in contact with a percentage of the wafer  117  surface within a range extending from about 15% to about 25%. In yet another embodiment, the wafer support surfaces  110  can be in contact with about 20% of the wafer  117  surface. With a differential pressure within a range extending from about 1 atm to about 1.5 atm, the wafer support surfaces  110  can be in contact with a percentage of the wafer  117  surface within a range extending up to about 10%. With a differential pressure within a range extending from about 3 atm to about 4 atm, the wafer support surfaces  110  can be in contact with a percentage of the wafer  117  surface within a range extending from about 50% to about 70%. 
     It is preferable to minimize the percentage of the wafer  117  in contact with the wafer support surfaces  110  (i.e., wafer backside contact area). Minimization of the wafer backside contact area, however, should be performed in a manner that provides sufficient support for the particular pressure differential to be applied between the wafer processing volume  119  and the underlying volume  115 . Minimizing the wafer backside contact area serves to reduce the potential for wafer  117  contamination. Also, minimizing the wafer backside contact area reduces the potential for particles becoming lodged between the wafer  117  and the wafer support surfaces  110 , which could cause difficulty in securing the wafer  117 . 
     Pressures in each of the wafer processing volume  119 , the underlying volume  115 , and the intermediate volume  113  can be controlled independently by controlling fluid introduction to and removal from each volume. The lower plate  109  allows the wafer processing volume  119  pressure to be adjusted relative to the intermediate volume  113  pressure. In this manner, the lower plate  109  allows a high pressure to be constrained within the wafer processing volume  119 . In an alternate embodiment, the intermediate volume  113  can be over-pressurized to cause a fluid to be introduced into the wafer processing volume  119  from the intermediate volume  113 . Regardless, of the particular embodiment, however, the pressure differential between the two sides of the lower plate  109  dictates the required thickness of the lower plate  109 . A larger pressure differential across the lower plate  109  requires the lower plate  109  to have a larger thickness. For the lower plate  109  to be thinner, the pressure differential between the wafer processing volume  119  and the intermediate volume  113  should be lower. 
     It is desirable to minimize the thickness of the lower plate  109  in order to reduce the volume of outer chamber  100  material and the chamber  100  overall size. However, a balance exists when determining the lower plate  109  thickness to use and the minimum intermediate volume  113  pressure to allow. A thinner lower plate  109  will reduce the overall chamber  100  size, but a lower intermediate volume  113  pressure will allow the use of a thinner lower support plate  101 , by reducing a pressure differential between the intermediate volume  113  and an outside environment. 
     With an effective variation in pressure differential from the wafer processing volume  119  to the intermediate volume  113  to the outside environment, the chamber  100  size can be optimized. Thus, the use of multiple chamber internal volumes allows for a more compact chamber  100  design. Also, minimizing the size of the wafer processing volume  119  allows both the chamber size and the wafer processing cycle time to be reduced. A smaller wafer processing volume  119  requires less material to constrain the pressure within the wafer processing volume  119 . Furthermore, a smaller wafer processing volume  119  requires less time to reduce the high pressure within the wafer processing volume  119  to a pressure at which the wafer  117  can be safely transferred, thus reducing the wafer processing cycle time. 
     As previously mentioned, the lower plate  109  includes the number of inlets/outlets  209  for introducing fluids to and removing fluids from the wafer processing volume  119 . The inlets/outlets  209  are located near the periphery of the lower plate  109  and outside a location intended to receive the wafer  117 . The inlets/outlets  209  can be configured to control a fluid flow through the wafer processing volume  119  over a top surface of the wafer  117 . It is likely that different fluid flow patterns and pressures will work better for different wafer processing applications. The inlets/outlets  209  in the lower plate  109  can be configured to provide numerous fluid flow patterns within the wafer processing volume  119 . In following, numerous lower plates  109  can be designed and manufactured to provide a selection of fluid flow patterns, thus allowing a suitable fluid flow pattern to be selected for a specific wafer process. Since the lower plates  109  are interchangeable, the fluid flow pattern through the wafer processing volume  119  can be changed without requiring other aspects of the chamber  100 , beyond the lower plate  109 , to be altered. 
       FIG. 3  is an illustration showing a top view of the lower plate  109  configured to provide a linear fluid flow across the wafer  117 , in accordance with one embodiment of the present invention. The lower plate  109  is defined to have a number of inlets  209 B distributed in a substantially uniform manner around a 180 degree segment of the lower plate  109  periphery. The lower plate  109  is further defined to have a number of outlets  209 A distributed in a substantially uniform manner around a 180 degree segment of the lower plate  109  periphery that is opposite the 180 degree segment containing the number of inlets  209 B. The fluid is introduced into the wafer processing volume  119  through the number of inlets  209 B. The fluid is removed from the wafer processing volume  119  through the number of outlets  209 A. The disposition of the number of inlets  209 B and the number of outlets  209 A causes the fluid to flow in a linear pattern across the top surface of the wafer  117  as indicated by arrows  301 . 
       FIG. 4  is an illustration showing a top view of the lower plate  109  configured to provide a conical fluid flow across the wafer  117 , in accordance with one embodiment of the present invention. The lower plate  109  is defined to have a number of inlets  209 B distributed in a substantially uniform manner around a segment of the lower plate  109  periphery that subtends an angle less than 180 degrees. The lower plate  109  is further defined to have a number of outlets  209 A distributed in a substantially uniform manner around a segment of the lower plate  109  periphery that subtends an angle less than that subtended by the number of inlets  209 B. The number of outlets  209 A are positioned at a location opposite the number of inlets  209 B. The fluid is introduced into the wafer processing volume  119  through the number of inlets  209 B. The fluid is removed from the wafer processing volume  119  through the number of outlets  209 A. The disposition of the number of inlets  209 B and the number of outlets  209 A causes the fluid to flow in a conical pattern across the top surface of the wafer  117  as indicated by arrows  401 . The conical pattern can be optimized to allow the fluid flow to maintain a constantly accelerating velocity across the top surface of the wafer  117 . 
       FIG. 5  is an illustration showing a top view of the lower plate  109  configured to provide a spiral fluid flow across the wafer  117 , in accordance with one embodiment of the present invention. The lower plate  109  is defined to have a number of inlets  209 B distributed in a substantially uniform manner around the lower plate  109  periphery. The fluid is introduced into the wafer processing volume  119  through the number of inlets  209 B. The number of inlets  209 B are configured to direct the fluid in a tangential direction with respect to the wafer  117 . The configuration of the number of inlets  209 B causes the fluid to flow in a spiral pattern across the top surface of the wafer  117  as indicated by arrows  501 . In one embodiment, the fluid is removed from the wafer processing volume  119  through one or more outlets located in the upper support plate  103 . 
       FIG. 6  is an illustration showing a vertical cross-section of the chamber  100  incorporating an upper plate  601 , in accordance with one embodiment of the present invention. The chamber  100  incorporates the lower plate  109 , the lower support plate  101 , the bolts  111 , the bolts  105 , and the seal  107  as previously described with respect to  FIG. 1 . The chamber  100  embodiment illustrated in  FIG. 6 , however, incorporates a different upper support plate  103 A. 
     The upper support plate  103 A is configured to interface with the top section of the lower support plate  101 . The upper support plate  103 A includes a number of support surfaces  602 . The support surfaces  602  are distributed within an intermediate volume  605  defined within a bottom portion of the upper support plate  103 A. The support surfaces  602  are capable of supporting the upper plate  601  at discrete locations in a substantially uniform manner. The number and location of the support surfaces  602  depends on a pressure differential between the two sides of the upper plate  601 . The upper plate  601  can be secured to the upper support plate  103 A by a number of bolts  603 . When secured to the upper support plate  103 A, the upper plate  601  serves as a lower boundary to the intermediate volume  605 . 
     The upper support plate  103 A further includes the wafer processing volume  119 . The wafer processing volume  119  is configured to overlie the wafer  117  when the upper support plate  103 A is attached to the lower support plate  101 . The wafer processing volume  119  is also configured to underlie the upper plate  601  when the upper plate  601  is secured to the upper support plate  103 A. In this manner, the upper plate  601  serves as an upper boundary to the wafer processing volume  119 . 
       FIG. 7  is an illustration showing a close-up view of a central portion of the chamber  100  as shown in  FIG. 6 , in accordance with one embodiment of the present invention. The close-up view shows a vertical cross-section of half of the chamber  100 , including the upper support plate  103 A, the upper plate  601 , the intermediate volume  605 , the wafer processing volume  119 , the wafer  117 , the underlying volume  115 , the lower plate  109 , the intermediate volume  113 , and the lower support plate  101 . 
     The lower plate  109 , having the wafer support surfaces  110  distributed within the underlying volume  115  and containing the inlet  207 , the outlet  205  and the inlet/outlet  209 , is the same as previously described with respect to  FIG. 2 . Also, the lower support plate  101 , having the support surfaces  102  distributed within the intermediate volume  113  and containing the inlet  201  and the outlet  203 , is the same as previously described with respect to  FIG. 2 . 
     As discussed with respect to  FIG. 6 , the upper support plate  103 A serves to support the upper plate  601  by providing the support surfaces  602  upon which the upper plate  601  will be secured during wafer processing. Each of the support surfaces  602  is a part of a discrete support structure. The discrete support structures corresponding to the support surfaces  602  are distributed in a substantially uniform manner throughout the intermediate volume  605 . Therefore, the intermediate volume  605  exists between the discrete support structures corresponding to the support surfaces  602  and above the upper plate  601 . An inlet  701  is provided for introducing fluids into the intermediate volume  605 . An outlet  703  is provided for removing fluids from the intermediate volume  605 . In other embodiments, the inlet  701  and the outlet  703  can be disposed at other locations within the upper support plate  103 A. 
     Pressures in each of the wafer processing volume  119  and the intermediate volume  605  can be controlled independently by controlling fluid introduction to and removal from each volume. The upper plate  601  allows the wafer processing volume  119  pressure to be adjusted relative to the intermediate volume  605  pressure. In this manner, the upper plate  601  allows a high pressure to be constrained within the wafer processing volume  119 . In an alternate embodiment, the intermediate volume  605  can be over-pressurized to cause a fluid to be introduced into the wafer processing volume  119  from the intermediate volume  605 . Regardless, of the particular embodiment, however, the pressure differential between the two sides of the upper plate  601  dictates the required thickness of the upper plate  601 . A larger pressure differential across the upper plate  601  requires the upper plate  601  to have a larger thickness. For the upper plate  601  to be thinner, the pressure differential between the wafer processing volume  119  and the intermediate volume  605  should be lower. 
     It is desirable to minimize the thickness of the upper plate  601  in order to reduce the volume of outer chamber  100  material and the chamber  100  overall size. However, a balance exists when determining the upper plate  601  thickness to use and the minimum intermediate volume  605  pressure to allow. A thinner upper plate  601  will reduce the overall chamber  100  size, but a lower intermediate volume  605  pressure will allow the use of a thinner upper support plate  103 A, by reducing a pressure differential between the intermediate volume  605  and an outside environment. With an effective variation in pressure differential from the wafer processing volume  119  to the intermediate volume  605  to the outside environment, the chamber  100  size can be optimized. 
     The upper plate  601  includes a number of inlets/outlets  705  for introducing fluid to and removing fluid from the wafer processing volume  119 , as indicated by arrows  707 . The inlets/outlets  705  are distributed across the upper plate  601  and are configured to control the fluid flow through the wafer processing volume  119  over the top surface of the wafer  117 . As previously mentioned, it is likely that different fluid flow patterns and pressures will work better for different wafer processing applications. The inlets/outlets  705  in the upper plate  601  can be configured to provide numerous fluid flow patterns within the wafer processing volume  119 . Additionally, the inlets/outlets  705  in the upper plate  601  can be configured to work in conjunction with the inlets/outlets  209  in the lower plate  109  to provide fluid flow patterns within the wafer processing volume  119 . In following, numerous upper plates  601  can be designed and manufactured to provide a selection of fluid flow patterns, thus allowing a suitable fluid flow pattern to be selected for a specific wafer process. As with the lower plates  109 , the interchangeability of the upper plates  601  allows the fluid flow pattern through the wafer processing volume  119  to be changed without requiring other aspects of the chamber  100  to be changed. 
       FIG. 8A  is an illustration showing an upper plate  601 A configured to provide a central fluid feed and a peripheral fluid exhaust, in accordance with one embodiment of the present invention. The upper plate  601 A includes a number of inlets  705 A distributed in a location near a center of the upper plate  601 A. In one embodiment, the upper plate  601 A includes a number of outlets  705 B distributed about periphery of the upper plate  601 A at a location near the periphery of the wafer  117 . In another embodiment, the lower plate  109  includes a number of outlets  209 A distributed in a substantially uniform manner around the periphery of the lower plate  109 . In yet another embodiment, the upper plate  601 A includes the number of outlets  705 B and the lower plate  109  includes the number of outlets  209 A. In either embodiment, the fluid is introduced into the wafer processing volume  119  through the number of inlets  705 A and removed from the wafer processing volume  119  through the number of outlets  705 B and/or  209 A. The configuration of the number of inlets  705 A and the number of outlets  705 B and/or  209 A causes the fluid to flow from a central region to a peripheral region of the wafer  117 . 
       FIG. 8B  is an illustration showing the use of fluid channels within the upper plate  601 A, in accordance with one embodiment of the present invention. Fluid channels  801  are provided for transferring fluid to the number of inlets  705 A. Fluid channels  803  are provided for transferring fluid from the number of outlets  705 B. Use of fluid channels to independently control different inlets and outlets within the upper plate  601 A allows for pressure equalization and flow pattern control within the wafer processing volume  119 . Additionally, the use of fluid channels provides flexibility in changing flow patterns within the wafer processing volume  119  and in varying the pressure differential between the wafer processing volume  119  and the intermediate volume  605 . 
       FIG. 9  is an illustration showing an upper plate  601 B configured to provide a peripheral fluid feed and a central fluid exhaust, in accordance with one embodiment of the present invention. The upper plate  601 B includes a number of outlets  705 C distributed in a location near a center of the upper plate  601 B. In one embodiment, the upper plate  601 B includes a number of inlets  705 D distributed about periphery of the upper plate  601 B at a location near the periphery of the wafer  117 . In another embodiment, the lower plate  109  includes a number of inlets  209 B distributed in a substantially uniform manner around the periphery of the lower plate  109 . In yet another embodiment, the upper plate  601 B includes the number of inlets  705 D and the lower plate  109  includes the number of inlets  209 B. In either embodiment, the fluid is introduced into the wafer processing volume  119  through the number of inlets  705 D and/or  209 B and removed from the wafer processing volume  119  through the number of outlets  705 C. The configuration of the number of inlets  705 D and/or  209 B and the number of outlets  705 C causes the fluid to flow from a peripheral region to a central region of the wafer  117 . 
       FIG. 10  is an illustration showing an exemplary distribution of the inlets/outlets  705  across the upper plate  601 , in accordance with one embodiment of the present invention. The number and distribution of inlets/outlets  705  will depend upon the desired fluid flow pattern to be applied within the wafer processing volume  119 . The distribution of inlets/outlets  705  as shown in  FIG. 10  provides an example of possible inlet/outlet  705  locations across the upper plate  601 . Other inlet/outlet  705  numbers and distributions can be employed to satisfy the fluid flow pattern requirements of a particular wafer processing operation. 
       FIG. 11  is an illustration showing a flowchart of a method for making a wafer processing chamber, in accordance with one embodiment of the present invention. The method includes an operation  1101  in which a lower support plate is formed. In one embodiment, the lower support plate is formed from stainless steel. In other embodiments, the lower support plate can be formed from other materials that are compatible with the processes to be performed within the wafer processing chamber. The forming can be accomplished by pouring molten material into a mold or by machining a block of material. The lower support plate is formed to have support surfaces distributed within a first volume defined within the lower support plate. The first volume is defined to have a first fluid inlet and a first fluid outlet. The lower support plate is capable of withstanding a pressure differential to be applied between volumes located at each side of the lower support plate. 
     The method also includes an operation  1103  in which a wafer support plate is formed. In one embodiment, the wafer support plate is formed from stainless steel. In other embodiments, the wafer support plate can be formed from other materials that are compatible with the processes to be performed within the wafer processing chamber. The forming can be accomplished by pouring molten material into a mold or by machining a block of material. The wafer support plate is formed to have wafer support surfaces distributed within a second volume defined within the wafer support plate. The wafer support surfaces are configured to receive a wafer. Once received, the wafer forms an upper boundary for the second volume defined within the wafer support plate. The second volume is defined to have a second fluid inlet and a second fluid outlet. Additionally, fluid inlets and fluid outlets are provided at a periphery of the wafer support plate and outside a location that is to receive the wafer. The peripheral fluid inlets and fluid outlets of the wafer support plate can be configured to create a fluid flow pattern within the third volume. In some embodiments, the fluid flow pattern can be either a linear pattern, a conical pattern, or a spiral pattern. In other embodiments, different fluid flow patterns can be created to satisfy the requirements of a wafer processing operation. The wafer support plate is capable of withstanding a pressure differential to be applied between volumes located at each side of the wafer support plate. 
     The method further includes an operation  1105  in which the wafer support plate is secured to the lower support plate. Once secured, the wafer support plate is supported by the support surfaces distributed within the first volume of the lower support plate. Also, the wafer support plate serves as an upper boundary for the first volume defined within the lower support plate. 
     The method continues with an operation  1107  in which an upper support plate is formed. In one embodiment, the upper support plate is formed from stainless steel. In other embodiments, the upper support plate can be formed from other materials that are compatible with the processes to be performed within the wafer processing chamber. The forming can be accomplished by pouring molten material into a mold or by machining a block of material. The upper support plate is formed to contain a third volume that is configured to overlie the wafer to be received by the wafer support surfaces of the wafer support plate. The upper support plate is capable of withstanding a pressure differential to be applied between volumes located at each side of the upper support plate. 
     In one embodiment, support surfaces are formed within the upper support plate. The support surfaces are distributed within a fourth volume. The fourth volume can have a fluid inlet and a fluid outlet. The support surfaces formed within the upper support plate are configured to receive and support an upper plate. In accordance with this embodiment, the method includes an optional operation  1109 , in which the upper plate is formed. In one embodiment, the upper plate is formed from stainless steel. In other embodiments, the upper plate can be formed from other materials that are compatible with the processes to be performed within the wafer processing chamber. The forming can be accomplished by pouring molten material into a mold or by machining a block of material. The upper plate is formed to have fluid inlets and fluid outlets capable of introducing fluid to and removing fluid from third volume. The fluid inlets and fluid outlets of the upper plate can be configured to create a fluid flow pattern within the third volume. In some embodiments, the fluid flow pattern can be either a linear pattern, a conical pattern, a spiral pattern, a center feed with peripheral exhaust pattern, or a peripheral feed with center exhaust pattern. In other embodiments, different fluid flow patterns can be created to satisfy the requirements of a wafer processing operation. Also in accordance with this embodiment, the method includes an optional operation  1111 , in which the upper plate is secured to the support surfaces of the upper support plate. In this manner, the upper plate serves as a lower boundary to the fourth volume and an upper boundary to the third volume. The upper plate is capable of withstanding a pressure differential between the fourth volume and the third volume. 
     The method also includes an operation  1113  in which the upper support plate is secured to the lower support plate. Securing the upper support plate to the lower support plate causes the third volume defined within the upper support plate to be isolated from an outside environment. Isolation of the third volume from the outside environment is enabled by a seal disposed between the upper support plate and the lower support plate. 
       FIG. 12  is an illustration showing a flowchart of a method for performing a wafer cleaning process, in accordance with one embodiment of the present invention. The method includes an operation  1201  for providing a chamber in which the wafer cleaning process can be performed. The chamber includes a first volume configured to overlie a wafer to be cleaned. The chamber also includes a plate configured to support the wafer. A second volume is defined within the plate directly below the wafer. Also in the chamber, a support structure is provided to support the plate. The support structure includes a third volume located directly below the plate. The method further includes an operation  1203  for pressurizing the first volume to have a higher pressure than the second volume. Also in the method, an operation  1205  is provided for pressurizing the second volume to have a higher pressure than the third volume. The third volume is pressurized to have a pressure between that of the second volume and an environment outside the chamber. The method also includes an operation  1207  for providing a fluid to the first volume that overlies the wafer to be cleaned. The fluid is formulated to effect the wafer cleaning process. In one embodiment, the fluid is a supercritical fluid. 
     The wafer processing chamber of the present invention is well suited for use in a wafer process that utilizes a supercritical fluid. As previously described, the wafer processing chamber is suited for controlling the pressure within the wafer processing volume. Additionally, the wafer processing chamber is capable of controlling the pressure differentials that exist between the wafer processing volume, the intermediate volume of the chamber, and the outside environment. Having an ability to adjust the wafer processing volume pressure relative to the chamber intermediate volume pressures, as afforded by the present invention, can be valuable in designing a supercritical fluid processing chamber that is minimal in size. Also, in supercritical fluid wafer processing, the pressure within the wafer processing volume must be controlled to maintain the supercritical state of the fluid. 
       FIG. 13  is an illustration showing a generalized material phase diagram. The phase of the material is represented as regions of solid, liquid, and gas, wherein the presence of a particular phase is dependent on pressure and temperature. The gas-liquid phase boundary follows an increase in both pressure and temperature up to a point called the critical point. The critical point is delineated by a critical pressure (P c ) and a critical temperature (T c ). At pressures and temperatures beyond P c  and T c , the material becomes a supercritical fluid. 
     Wafer cleaning operations can be performed using the supercritical fluid. The supercritical fluid shares the properties of both a gas phase and a liquid phase. The supercritical fluid has near zero surface tension. Therefore, the supercritical fluid can reach into and between small features on the wafer surface. Also, the supercritical fluid has a diffusivity property similar to a gas. Therefore, the supercritical fluid can get into porous regions of wafer materials, such as low-K dielectric material, without becoming trapped. Additionally, the supercritical fluid has a density similar to a liquid. Therefore, more supercritical fluid can be transported to the wafer in a given amount of time as compared to a gas. 
     Wafer processing with the supercritical fluid must be performed at high pressures to maintain the supercritical state of the fluid. For example, supercritical fluid processing can be performed at pressures ranging from about 68 atm to about 273 atm. Therefore, the wafer processing chamber must be able to withstand the associated high pressures. The wafer processing chamber of the present invention is capable of withstanding and controlling the high pressures associated with supercritical fluids. 
     Generally speaking, in supercritical fluid processes, the wafer processing volume is pressurized and the temperature within the wafer processing volume is controlled. The wafer processing volume pressure and temperature are controlled to maintain a supercritical fluid state. In an exemplary embodiment, the wafer processing volume can be pre-pressurized with CO 2  only or with a mixture of CO 2  and an appropriate chemistry. The critical pressure and temperature for CO 2  is approximately 73 atm and 31° C., respectively. It should be noted that the supercritical fluid used in combination with the wafer processing chamber of the present invention is not restricted to CO 2 . Other suitable supercritical fluids can also be used. Additionally, the chemistry of the supercritical fluid may include additives such as co-solvents, co-chelating agents, surfactants, or any combination thereof. The additives contained within the supercritical fluid can be useful for performing specific functions, such as dissolving and removing photoresist, dissolving and removing organic residue, and chelating metals, among others. 
     The advantages of the wafer processing chamber of the present invention are numerous. One advantage is that the wafer processing chamber is completely configurable. By interchanging the upper and lower plates, the chamber can be converted to several different configurations without changing the main chamber body. This advantage allows one type of chamber to be used for several potential wafer processing applications. Also, the interchangeability of the upper and lower plates allows the wafer processing volume pressure and flow pattern to be appropriately selected for a particular wafer processing application. Additionally, during a wafer cleaning process, there is a potential that material being cleaned from the wafer can become trapped in cavities within the chamber. Since the upper and lower plates are removable, both the chamber and the upper and lower plates can be more easily cleaned. 
     The wafer processing chamber of the present invention can be incorporated into a wafer processing cluster architecture. In one example, the wafer processing cluster architecture can incorporate separate modules for performing wafer cleaning operations, wafer etching operations, CMP operations, and wafer rinsing operations. Additionally, in the wafer processing cluster architecture, the wafer can be transferred between different modules using a robotic wafer handling mechanism or a track mechanism. 
     While this invention has been described in terms of several embodiments, it will be appreciated that those skilled in the art upon reading the preceding specifications and studying the drawings will realize various alterations, additions, permutations and equivalents thereof. It is therefore intended that the present invention includes all such alterations, additions, permutations, and equivalents as fall within the true spirit and scope of the invention.