Abstract:
A method and apparatus for depositing a film by chemical vapor deposition comprises a showerhead for dispersing reactant gases into the processing space wherein the showerhead has a first space therein operable for receiving and dispersing the first reacting gas, and has a second space therein, generally isolated from the first space, and operable for receiving and dispersing the second reactant gas separate from the first gas dispersion for maintaining segregation of reactant gases and generally preventing premature mixture of the gases prior to their introduction into the processing space to prevent premature deposition in the system.

Description:
RELATED APPLICATIONS 
     This application is a divisional of patent application Ser. No. 08/940,779, filed Sep. 30, 1997, now U.S. Pat. No. 6,161,500 entitled “Apparatus and Method for Preventing the Premature Mixture of Reactant Gases in CVD and PECVD Reactions.” The parent application is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to chemical vapor deposition (CVD) and plasma-enhanced chemical vapor deposition (PECVD), and more specifically to an apparatus and method for preventing the premature mixture of reactant gas constituents in CVD and PECVD reactions before such mixture is desired in the reaction chamber. 
     BACKGROUND OF THE INVENTION 
     In the formation of integrated circuits (IC&#39;s), it is often necessary to deposit thin films or layers, such as films containing metal and metalloid elements, upon the surface of a substrate, such as a semiconductor wafer. One purpose of such thin films is to provide conductive and ohmic contacts in the circuits and to yield conductive or barrier layers between the various devices of an IC. For example, a desired film might be applied to the exposed surface of a contact or via hole on an insulating layer of a substrate, with the film passing through the insulating layer to provide plugs of conductive material for the purpose of making inter-connections across the insulating layer. 
     One well known process for depositing such films is chemical vapor deposition (CVD) in which a film is deposited using chemical reactions between various constituent or reactant gases. In CVD, reactant gases are pumped into the processing space of a reaction chamber containing a substrate. The gases react in the processing space proximate the substrate, resulting in one or more reaction by-products. The reaction by-products then deposit onto the substrate to form a film on the exposed substrate surface. 
     Another variation of the CVD process which is widely utilized is a plasma-enhanced CVD process or PECVD process in which one or more of the reactant gases is ionized into a gas plasma to provide energy to the reaction process. PECVD is desirable for lowering the temperatures that are usually necessary for a proper reaction with standard CVD. In PECVD, electrical energy is delivered to the gas or gases to form and sustain the plasma. For one such PECVD process, the susceptor containing the substrate and a planar element in the processing space, such as a gas supply element, are electrically biased to operate as RF electrodes for energizing one or more of the reactant gases into an ionized plasma. Such a method is commonly referred to as a parallel plate method because the susceptor and the other biased planar element are maintained generally parallel to one another to simulate biased electrical plates with the substrate positioned therebetween and parallel to the biased elements. 
     The reactant gases for CVD and PECVD processes are delivered to the processing space and substrate through a gas delivery system which provides the proper flow and distribution of the gases for the CVD process. Generally, such gas delivery systems contain gas-dispersing elements in the reaction chamber, such as gas injector rings or flat showerheads, which spread the entering reactant gases around the processing space to insure a uniform distribution and flow of the gases proximate the substrate. Uniform gas distribution and flow is desirable for a uniform and efficient deposition process, a dense plasma, and a uniformly deposited film. Since the gases utilized in CVD and PECVD processes are reactive, it is often necessary to use a separate dispersing element for each constituent gas in order to keep the gases segregated or unmixed prior to the processing space. Otherwise, if the gases mix prior to the processing space, premature deposition occurs inside the dispersing element and inside other sections of the gas delivery system, which hinders a uniform flow of the gas, degrades the deposition process and may contaminate the deposited film. 
     To maintain separate constituent gases, multiple, concentric gas injector rings have been utilized to prevent premature mixture and deposition prior to the processing space. However, multiple gas injector rings in the processing space make it difficult to utilize PECVD techniques because the rings interfere with the placement and action of the RF electrodes necessary for such PECVD techniques. Therefore, the rings detrimentally affect plasma generation. 
     Conventional RF PECVD processes generally utilize a biased, planar gas showerhead opposite a parallel, biased susceptor. One such PECVD process and apparatus is disclosed in U.S. Pat. No. 5,547,243, which is commonly owned with the present application. While such a technique produces suitable PECVD films, directing and dispersing all of the reactant gas constituents through available showerheads will produce premature mixing of the gases before the processing space and yield undesirable deposition inside of the showerhead, or in-line in the system before the showerhead. Therefore, for parallel plate PECVD, it has been necessary to disperse some gases through inlet ports other than the showerhead, yielding non-uniform flow of some of the gas constituents at the substrate, or interfering with plasma generation. 
     Accordingly, it is an objective of the present invention to reduce and generally prevent the premature mixture of reactant gases in CVD and PECVD reactions. 
     It is still another objective of the invention to prevent the deposition of film material in the gas delivery system and to provide a uniform flow and distribution of reactant gases to the processing space for the deposition process. 
     It is another objective of the invention to maintain the separation of the reactant gases and generally prevent their interaction until they are injected and mixed proximate the substrate. 
     It is a further objective generally to prevent such premature interaction and deposition in a PECVD process utilizing parallel plate electrodes without interfering with the RF plasma generation. 
     Accordingly, the present invention addresses these objectives and the shortcomings of the various CVD and PECVD apparatuses and processes currently available in the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention prevents premature mixture of reactant gases in CVD and PECVD reactions and maintains a separation of reactant gases to prevent their interaction until they are injected and mixed in the processing space proximate a substrate. The present invention further provides a uniform flow and distribution of the reactant gases and is suitable for use with RF plasmas and PECVD processes without interfering with the plasma. Particularly, the present invention provides the necessary gas separation while being suitable for parallel plate PECVD processes. 
     The present invention comprises a generally circular, planar gas-dispersing manifold, preferably in the form of a planar showerhead, which is coupled to at least two different reactant gas lines for dispersing reactant gases into a chamber proximate a substrate. The showerhead has a first space therein which is operable for receiving and dispersing a first reactant gas, and further comprises a second space, which is isolated from the first space, and is also operable for receiving and dispersing a second gas independently of the dispersion of the first gas. The showerhead of the invention maintains a segregation between the reactant gases in the first and second spaces, and prevents a premature mixture of the gases before the gases enter the processing space. In that way, premature deposition in the gas delivery system and prior to the processing space is generally prevented. 
     To disperse the reactant gases passing through the inventive showerhead, the showerhead includes two separate pluralities of gas-dispersing passages, which are in communication with each of the respective gas spaces within the showerhead, but are isolated from each other. The dispersing passages have outlets which open at a face surface of the showerhead opposite the substrate. When the separate reactant gases are directed through the showerhead, no mixture occurs within the showerhead, and each of the reactant gases is dispersed independently to thus mix proximate the substrate, as desired. The gas-dispersing passages for each of the respective first and second spaces are positioned in cooperating grids around the lower face surface of the showerhead to uniformly disperse and mix the gases proximate the substrate. 
     In accordance with another aspect of the present invention, the showerhead has a generally planar, and thus compact, design which functions electrically as a parallel plate when biased with RF energy. Therefore, the inventive showerhead may be utilized for parallel plate PECVD processes without interfering with the plasma. As such, the reactant gases are dispersed separately and uniformly for a stable, uniform plasma and a uniform deposition of the film. 
     The showerhead of the invention has a planar first space positioned in a plane generally parallel with a planar second space and below the second space. That is, the second space is stacked above the first space in the showerhead. Gas is introduced into each of the respective spaces through ports that communicate with the spaces, and the reactant gases spread through the planar spaces to be uniformly dispersed proximate the substrate by the grids of dispersing passages. 
     In one embodiment of the invention, the first gas space comprises a plurality of elongated cylindrical passages which extend through the showerhead. The passages originate at one area on the periphery of the circular showerhead and extend to another peripheral area on an opposite side of the showerhead. The elongated passages are generally isolated from each other along their lengths, but are co-planar and extend next to each other to define the planar first space. The opposite ends of the elongated first space passages are each coupled to a peripheral coupler which has a single inlet port and a wide outlet port for simultaneously interfacing with each of the ends of the elongated passages. The two couplers provide gas simultaneously to each of the ends of the elongated passages so that gas introduced at the periphery of the circular showerhead is distributed uniformly in the first space and around the showerhead. The elongated passages generally angle out from each coupler to reach a maximum area of the showerhead face surface and then angle back to the opposite coupler. 
     The second space is an open cylindrical space above the first space elongated passages. A second reactant gas is introduced into the second space through two inlet ports positioned at opposite peripheral points on the showerhead. The ports for introducing the second gas are positioned at approximately a 90° offset on the showerhead periphery from the peripheral first gas couplers so as not to interfere with the couplers for the first space. 
     One set of gas dispersing passages is arranged in a grid on the showerhead and communicates between the second gas space and the face of the showerhead so that the second gas may be delivered to the processing space. Each passage from the set extends from the second space, past the elongated first space passages, and opens at the showerhead face without intersecting the first space passages. In that way, the gases are kept segregated in the showerhead. Another set of dispersing passages, also in a grid arrangement, communicates with the elongated passages of the first space to deliver the gas therefrom. 
     In another embodiment of the present invention, the reactant gases are introduced into the center of the showerhead rather than at the periphery thereof. To that end, the showerhead includes a center stem having two passages and two inlet ports for the respective first and second gases. The center stem extends generally perpendicular to the plane of the showerhead and one of the gas inlet ports opens directly into the second space. Preferably a 90° coupler is used to direct the incoming second gas parallel to the plane of the second space. The center stem may be biased with RF energy when desired for PECVD processing. 
     The first gas port communicates with a diametrical passage, located above the first and second spaces in the showerhead, which directs the gas out to the periphery of the showerhead. The first gas space comprises a peripheral channel which distributes the first gas around the periphery of the showerhead. Gas distribution fingers, each opened at one end thereof, are coupled to the channel and extend toward a diameter line of the showerhead to terminate proximate the diameter line. The fingers are co-planar and are generally parallel to one another, with one set of fingers distributing gas to one half of the showerhead and another set of fingers distributing gas to the other half of the circular showerhead. 
     Sets of gas dispersing passages are arranged in interacting grids, similar to the embodiment previously described, and the dispersing passages communicate between the respective first and second gas spaces and the showerhead face. The second space passages extend between the fingers of the first space so as not to mix the reactant gases prior to their dispersion at the face of the showerhead and proximate the substrate. 
     The invention thus provides a segregated, and uniform distribution of the reactant gases while reducing deposition of film material prior to entry of the reactant gases into the processing space containing the substrate. In that way, an efficient gas flow is achieved, premature deposition is prevented, and the likelihood of contamination from deposition within the showerhead is reduced. Furthermore, gas segregation may be maintained during RF PECVD process. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given below, serve to explain the principles of the invention. 
     FIG. 1 is a cross-sectional view of the reaction chamber equipped with the manifold of the present invention. 
     FIG. 2 is a top plan view in partial cross-section, of one embodiment of the present invention taken along lines  2 — 2  of FIG. 1, with the cover removed for clarity. 
     FIG. 2A is a cross-sectional view of an embodiment of the invention taken along lines  2 A— 2 A of FIG.  2 . 
     FIG. 2B is a cross-sectional view of an embodiment of the invention taken along lines  2 B— 2 B of FIG.  2 . 
     FIG. 2C is a partial cross-sectional view taken along lines  2 C— 2 C of FIG.  2 B. 
     FIG. 3 is the top plan view of an embodiment of the present invention, illustrating coupling of reactant gas lines to the manifold, as seen along line  3 — 3  of FIG.  1 . 
     FIG. 3A is a side view taken along lines  3 A— 3 A of FIG.  3 . 
     FIG. 3B is a side view taken along lines  3 B— 3 B. 
     FIGS. 4A and 4B are bottom sectional views of an embodiment of the invention illustrating the gas-dispersing outlets for the various reactant gases dispersed through the invention. 
     FIG. 5 illustrates a top plan view, and partial cross section, of an alternative embodiment of the showerhead of the present invention. 
     FIG. 6 is a cross sectional view along lines  6 — 6  of FIG.  5 . 
     FIG. 7 is a cross sectional view along lines  7 — 7  of FIG.  6 . 
     FIG. 8A is a top plan view of one quadrant of the showerhead illustrating gas-dispersing openings. 
     FIG. 8B is a top plan view of one quadrant of the showerhead illustrating gas-dispersing openings. 
     FIG. 9 is a partial cross-sectional view illustrating the showerhead mounted in a reaction chamber. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     FIG. 1 is a cross sectional view of the reaction chamber equipped with the gas segregating or “no-mix” gas manifold or showerhead of the present invention. Reaction chamber  10  includes a housing  12  formed of a suitable material such as stainless steel, which defines a processing space  14  therein. A susceptor  16 , which may be rotating or stationary, supports a substrate  18  within the processing space  14  to receive a material layer or film through CVD and/or PECVD processes. Reaction chamber  10  will further comprise other systems, such as a vacuum system (not shown) for providing a vacuum pressure within processing space  14 , which is generally necessary for CVD processes. The manifold or showerhead  20  of the invention is illustrated supported around its peripheral edges by supports  21  such that the bottom face surface  22  of the showerhead faces into the processing space  14  toward substrate  18 . In a preferred embodiment, showerhead  20  is generally parallel to substrate  18 , which is desired for RF parallel plate PECVD processes. 
     In accordance with the principles of the present invention, separate reactant gases are provided to showerhead  20  by gas delivery system  26  and system  28 , respectively. Furthermore, for PECVD processes, showerhead  20  is coupled through an appropriately constructed RF shaft or line  30  to an RF energy source  32  for biasing the showerhead and creating a plasma within processing space  14  for plasma-enhanced deposition of PECVD, as understood by a person of ordinary skill in the art. The embodiments of the invention disclosed herein are configured for two separate reactant gases. However, as will be understood by a person of ordinary skill in the art, the present invention might be utilized for introducing more than two separate reactant gases through showerhead  20 . 
     FIGS. 2,  2 A, and  2 B, illustrate plan and sectional views of one embodiment of the showerhead  20  of the invention, illustrating separate reactant gas spaces therein. Showerhead  20  may be formed of stainless steel or other suitable materials, and is preferably conductive to be used in PECVD processes. As illustrated in FIGS. 2A and 2B, showerhead  20  includes a first planar space  36  for containing a first reactant gas, and a second planar space  38 , physically isolated from the first gas space  36 , so as to provide separation and segregation of the reactant gases until they are dispersed from showerhead  20  in accordance with the principles of the invention. For ease of reference, the first reactant gas injected into first space  36  will be referred to as gas A, while the second reactant gas injected into second space  38  will be referred to as gas B. As will be understood in accordance with the principles of the invention, other embodiments might utilize more than two reactant gases. 
     The first space  36  comprises a plurality of gas distribution passages  40  which collectively form first space  36 . The passages  40  extend from one gas port inlet  42 A at a peripheral area of the showerhead to another gas inlet  42 B at another peripheral area of the showerhead  20 , positioned approximately 180° from the port  42 A. In that way, gas is introduced into the passages  40  from both ends thereof. The passages  40  are generally co-planar and span across the showerhead from inlet port  42 A to port  42 B to define planar first space  36 . 
     Showerhead  20  further includes peripheral coupler pieces or couplers  44 A,  44 B, which define the respective inlets  42 A and  42 B. The coupler pieces  44 A,  44 B, each interface with a respective notch  45  formed in the showerhead  20  and include a main inlet port  46  which branches into a wide outlet port  48 . The end of the wide outlet port  48  of each of the couplers communicates with the respective ends of the elongated passages  40 , which make up the first space  36 . In that way, gas A introduced into port  46  is distributed through ports  48  and simultaneously through the first space passages  40 . The couplers direct gas A to each of the ends of the passages  40  so that gas introduced at the periphery of the circular showerhead is distributed uniformly in the first space and around the showerhead. 
     Referring to FIG. 2, it may be seen that a majority of the elongated passages  40  are formed in showerhead  20  to angle outwardly from one coupler  44 A to a diametrical centerline  49  and then back to the other coupler  44 B in a similar fashion. In that way, the passages  40  reach a maximum area around the face  22  of showerhead  20  to provide an even and uniform distribution of gas A. The passages  40  are isolated from each other along their lengths, but couple together at the couplers  44 A,  44 B. 
     To disperse gas A, showerhead  20  further comprises a plurality of gas dispersing passages  50  which have outlets at the face surface  22  of showerhead  20 . Referring to FIGS. 2 and 2A, gas dispersing passages  50  communicate between the first space passages and face  22  surface to direct gas A in the first space to the substrate  18  in processing space  14 . The passages  50  are generally perpendicular to the planes of showerhead  20 , first space  36  and substrate  18  to direct gas A directly at substrate  18  and thereabove. The passages  50  are arranged in a grid on face surface  22  of showerhead  20  as illustrated in FIGS. 2 and 4A and discussed further hereinbelow. 
     Turning now to FIG. 2B, second space  38  is defined between surface  51  above passages  40  and the lower surface  53  of a cover  54 . A cylindrical space formed in the showerhead is sealed by a cover  54  (see FIG. 2B) to define a generally cylindrical second space for the gas B to disperse within the showerhead. Cover  54  rests on a circumferential lip  55 , and is further held up by a plurality of spacers  56 . Gas inlet ports  58 A and  58 B are formed on opposite sides of showerhead  20  proximate the outer peripheral edge of the showerhead. Referring to FIGS. 2 and 3, it may be seen that gas inlet ports  58 A and  58 B are generally shifted by approximately 90° around the periphery of the showerhead from ports  42 A and  42 B. Distribution passages  59  communicate between the ports  58 A,  58 B, and second space  38 . In that way, gas B introduced into the ports is dispersed throughout space  38 . 
     A second plurality of gas-dispersing passages  60  are formed in showerhead  20  and communicate between the second space  38  and showerhead face  22 . The passages  60  generally have a greater length than gas A passages  50  since they must travel from second space  38  which is above first space  36  and must open at the bottom face  22  of the showerhead  20  along with passages  50 . Gas B passages  60  are positioned in a grid in the showerhead such that none of the passages will intersect the first space elongated passages  40  to prevent mixture of the gases. Referring to FIG. 2C, gas B passages  60  have a first larger diameter D of approximately 0.06 inches, and then narrow to a second, smaller diameter d of approximately 0.018 inches. Therefore gas B, introduced through ports  58 A,  58 B, is directed into space  38  and then out through the passages  60  into the processing space  14  to mix with gas A above the substrate. As may be seen in FIG. 2, passages  60  are also generally perpendicular to the plane of showerhead  20  and form a grid over the bottom face surface  22  of showerhead  20  which cooperates with the grid formed by openings  50  such that gas A and gas B are dispersed generally uniformly into the processing space  14  over the substrate  18 . Since second space  38  is isolated from the first space  36 , gas A and gas B are segregated in the showerhead and only mix when dispersed into processing space  14 . 
     FIGS. 3,  3 A, and  3 B disclose a plan view, and side views of a first gas delivery system  26  and a second gas delivery system  28  which contain gas A and gas B, respectively, for introduction into showerhead  20 . Referring to FIG. 3A, gas system  28  for gas B includes a single inlet  65  which feeds into lines  64 A and  64 B, which are, in turn, coupled with inlets  58 A and  58 B, respectively. Referring to FIG. 3B, gas A is similarly introduced and system  26  includes the single inlet port  67  which couples to lines  62 A and  62 B to deliver gas to the inlets  42 A and  42 B, respectively. Each of the lines may include one or more filter elements  69  for filtering the reactant gases introduced to the showerhead. Systems  26 ,  28  are coupled to gas supplies (not shown) through appropriate openings in the reaction chamber depending upon the structure of the chamber. 
     While the showerhead of the present invention may be utilized in traditional CVD environments, it may also be utilized for PECVD environments utilizing an RF plasma. In the past, dispersing different reactant gases with gas rings did not provide a suitable environment for parallel-plate RF plasma systems. With the present invention, a parallel plate system may be maintained wherein the showerhead  20  is biased with RF energy to form an RF electrode and create an electric field in the processing space  14  to form and sustain an ionized plasma. To that end, the cover  54  of showerhead  20  is coupled to a conductive metal hub or stem  66  which in turn couples with a receiving shoulder  68  when the cover  54  is in position on the showerhead. Stem  66  in turn, is coupled to RF source  32  through an appropriately conductive line  30  such that the showerhead may be biased with RF energy to act as an RF electrode. It has been found that maintaining a biased planar showerhead in close proximity and parallel to a substrate (e.g., one inch spacing) provides a uniformly dense plasma for a PECVD process as discussed in U.S. Pat. No. 5,567,243, which is incorporated herein by reference in its entirety. In that way, a parallel plate RF system may be maintained while keeping the reactant gases segregated until they are introduced above the substrate  18  in space  14 . The present invention has thus been found to reduce or eliminate pre-mixing of the reactant gases and deposition upstream of the processing space  14  while maintaining the parallel plate configuration necessary for PECVD. 
     For one preferred embodiment of the invention, FIG. 4A illustrates a portion of the grid of passages  50  for gas A. Similar quadrants are essentially duplicated on face surface  22 . FIG. 4B, on the other hand, illustrates a portion of the grid of passages  60  for introducing gas B also with duplication of the quadrant illustrated in  4 B around the remainder of the showerhead. 
     Table 1 below lists the X-Y coordinates of the various gas A passage openings of one embodiment of the invention, with the origin  0 , 0  defined from the physical center of the circular showerhead face surface  22 . Table 2 illustrates similar X-Y coordinates for the gas B passages. It will be readily understood that different coordinates might also be utilized to form a grid of gas-dispersing openings in the showerhead as will be readily understood by a person of ordinary skill in the art. The openings in the embodiment of FIGS. 2,  4 A and  4 B, will provide a uniform distribution of the reactant gases in the processing space above substrate  18  for efficient and uniform deposition of gases over the substrate  18 . 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Gas A Passage Coordinates 
               
             
          
           
               
                   
                 HOLE 
                 x 
                 y 
               
               
                   
                   
               
               
                   
                 A1 
                 0.000 
                 0.300 
               
               
                   
                 A2 
                 0.524 
                 0.252 
               
               
                   
                 A3 
                 1.056 
                 0.234 
               
               
                   
                 A4 
                 1.602 
                 0.215 
               
               
                   
                 A5 
                 2.166 
                 0.195 
               
               
                   
                 A6 
                 2.757 
                 0.174 
               
               
                   
                 A7 
                 3.383 
                 0.153 
               
               
                   
                 A8 
                 4.052 
                 0.129 
               
               
                   
                 A9 
                 0.000 
                 0.795 
               
               
                   
                 A10 
                 0.489 
                 0.763 
               
               
                   
                 A11 
                 0.989 
                 0.711 
               
               
                   
                 A12 
                 1.508 
                 0.656 
               
               
                   
                 A13 
                 2.051 
                 0.599 
               
               
                   
                 A14 
                 2.625 
                 0.539 
               
               
                   
                 A15 
                 3.239 
                 0.474 
               
               
                   
                 A16 
                 3.906 
                 0.404 
               
               
                   
                 A17 
                 0.000 
                 1.367 
               
               
                   
                 A18 
                 0.452 
                 1.287 
               
               
                   
                 A19 
                 0.920 
                 1.204 
               
               
                   
                 A20 
                 1.410 
                 1.118 
               
               
                   
                 A21 
                 1.928 
                 1.027 
               
               
                   
                 A22 
                 2.483 
                 0.929 
               
               
                   
                 A23 
                 3.084 
                 0.823 
               
               
                   
                 A24 
                 3.745 
                 0.706 
               
               
                   
                 A25 
                 0.000 
                 1.932 
               
               
                   
                 A26 
                 0.414 
                 1.829 
               
               
                   
                 A27 
                 0.847 
                 1.721 
               
               
                   
                 A28 
                 1.306 
                 1.607 
               
               
                   
                 A29 
                 1.797 
                 1.484 
               
               
                   
                 A30 
                 2.329 
                 1.352 
               
               
                   
                 A31 
                 2.914 
                 1.206 
               
               
                   
                 A32 
                 3.566 
                 1.043 
               
               
                   
                 A33 
                 4.306 
                 0.859 
               
               
                   
                 A34 
                 0.000 
                 2.518 
               
               
                   
                 A35 
                 0.374 
                 2.396 
               
               
                   
                 A36 
                 0.770 
                 2.268 
               
               
                   
                 A37 
                 1.195 
                 2.130 
               
               
                   
                 A38 
                 1.658 
                 1.975 
               
               
                   
                 A39 
                 2.160 
                 1.816 
               
               
                   
                 A40 
                 2.723 
                 1.633 
               
               
                   
                 A41 
                 3.363 
                 1.425 
               
               
                   
                 A42 
                 4.102 
                 1.185 
               
               
                   
                 A43 
                 0.000 
                 3.131 
               
               
                   
                 A44 
                 0.332 
                 2.997 
               
               
                   
                 A45 
                 0.688 
                 2.853 
               
               
                   
                 A46 
                 1.074 
                 2.697 
               
               
                   
                 A47 
                 1.498 
                 2.526 
               
               
                   
                 A48 
                 1.971 
                 2.335 
               
               
                   
                 A49 
                 2.507 
                 2.118 
               
               
                   
                 A50 
                 3.128 
                 1.867 
               
               
                   
                 A51 
                 3.861 
                 1.571 
               
               
                   
                 A52 
                 0.000 
                 3.780 
               
               
                   
                 A53 
                 0.287 
                 3.640 
               
               
                   
                 A54 
                 0.599 
                 3.488 
               
               
                   
                 A55 
                 0.941 
                 3.321 
               
               
                   
                 A56 
                 1.323 
                 3.134 
               
               
                   
                 A57 
                 1.668 
                 3.073 
               
               
                   
                 A58 
                 1.841 
                 2.787 
               
               
                   
                 A59 
                 2.258 
                 2.679 
               
               
                   
                 A60 
                 2.759 
                 2.493 
               
               
                   
                 A61 
                 2.935 
                 2.300 
               
               
                   
                 A62 
                 3.568 
                 2.040 
               
               
                   
                 A63 
                 0.000 
                 4.475 
               
               
                   
                 A64 
                 0.239 
                 4.337 
               
               
                   
                 A65 
                 0.501 
                 4.185 
               
               
                   
                 A66 
                 0.794 
                 4.016 
               
               
                   
                 A67 
                 1.126 
                 3.825 
               
               
                   
                 A68 
                 1.509 
                 3.603 
               
               
                   
                 A69 
                 1.848 
                 3.520 
               
               
                   
                 A70 
                 2.069 
                 3.182 
               
               
                   
                 A71 
                 2.394 
                 3.179 
               
               
                   
                 A72 
                 2.622 
                 2.888 
               
               
                   
                 A73 
                 3.202 
                 2.626 
               
               
                   
                 A74 
                 1.605 
                 4.145 
               
               
                   
                 A75 
                 2.033 
                 3.926 
               
               
                   
                 A76 
                 2.236 
                 3.613 
               
               
                   
                 A77 
                 2.608 
                 3.576 
               
               
                   
                 A78 
                 2.871 
                 3.217 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Gas B Passage Coordinates 
               
             
          
           
               
                   
                 HOLE 
                 x 
                 y 
               
               
                   
                   
               
               
                   
                 B1 
                 0.300 
                 0.000 
               
               
                   
                 B2 
                 0.795 
                 0.000 
               
               
                   
                 B3 
                 1.367 
                 0.000 
               
               
                   
                 B4 
                 1.932 
                 0.000 
               
               
                   
                 B5 
                 2.518 
                 0.000 
               
               
                   
                 B6 
                 3.131 
                 0.000 
               
               
                   
                 B7 
                 3.780 
                 0.000 
               
               
                   
                 B8 
                 4.475 
                 0.000 
               
               
                   
                 B9 
                 0.252 
                 0.524 
               
               
                   
                 B10 
                 0.763 
                 0.489 
               
               
                   
                 B11 
                 1.287 
                 0.452 
               
               
                   
                 B12 
                 1.829 
                 0.414 
               
               
                   
                 B13 
                 2.396 
                 0.374 
               
               
                   
                 B14 
                 2.997 
                 0.332 
               
               
                   
                 B15 
                 3.640 
                 0.287 
               
               
                   
                 B16 
                 4.337 
                 0.239 
               
               
                   
                 B17 
                 0.234 
                 1.056 
               
               
                   
                 B18 
                 0.711 
                 0.989 
               
               
                   
                 B19 
                 1.204 
                 0.920 
               
               
                   
                 B20 
                 1.721 
                 0.847 
               
               
                   
                 B21 
                 2.268 
                 0.770 
               
               
                   
                 B22 
                 2.853 
                 0.688 
               
               
                   
                 B23 
                 3.488 
                 0.599 
               
               
                   
                 B24 
                 4.185 
                 0.501 
               
               
                   
                 B25 
                 0.215 
                 1.602 
               
               
                   
                 B26 
                 0.656 
                 1.508 
               
               
                   
                 B27 
                 1.118 
                 1.410 
               
               
                   
                 B28 
                 1.607 
                 1.306 
               
               
                   
                 B29 
                 2.130 
                 1.195 
               
               
                   
                 B30 
                 2.697 
                 1.074 
               
               
                   
                 B31 
                 3.321 
                 0.941 
               
               
                   
                 B32 
                 4.016 
                 0.794 
               
               
                   
                 B33 
                 0.195 
                 2.166 
               
               
                   
                 B34 
                 0.599 
                 2.051 
               
               
                   
                 B35 
                 1.027 
                 1.928 
               
               
                   
                 B36 
                 1.484 
                 1.797 
               
               
                   
                 B37 
                 1.975 
                 1.658 
               
               
                   
                 B38 
                 2.526 
                 1.498 
               
               
                   
                 B39 
                 3.134 
                 1.323 
               
               
                   
                 B40 
                 3.825 
                 1.126 
               
               
                   
                 B41 
                 0.174 
                 2.757 
               
               
                   
                 B42 
                 0.539 
                 2.625 
               
               
                   
                 B43 
                 0.929 
                 2.483 
               
               
                   
                 B44 
                 1.352 
                 2.329 
               
               
                   
                 B45 
                 1.816 
                 2.160 
               
               
                   
                 B46 
                 2.335 
                 1.971 
               
               
                   
                 B47 
                 2.787 
                 1.841 
               
               
                   
                 B48 
                 3.073 
                 1.668 
               
               
                   
                 B49 
                 3.603 
                 1.509 
               
               
                   
                 B50 
                 0.153 
                 3.383 
               
               
                   
                 B51 
                 0.474 
                 3.239 
               
               
                   
                 B52 
                 0.823 
                 3.084 
               
               
                   
                 B53 
                 1.206 
                 2.914 
               
               
                   
                 B54 
                 1.633 
                 2.723 
               
               
                   
                 B55 
                 2.118 
                 2.507 
               
               
                   
                 B56 
                 2.679 
                 2.258 
               
               
                   
                 B57 
                 3.182 
                 2.069 
               
               
                   
                 B58 
                 3.520 
                 1.848 
               
               
                   
                 B59 
                 4.145 
                 1.605 
               
               
                   
                 B60 
                 0.129 
                 4.052 
               
               
                   
                 861 
                 0.404 
                 3.906 
               
               
                   
                 B62 
                 0.706 
                 3.745 
               
               
                   
                 B63 
                 1.043 
                 3.566 
               
               
                   
                 B64 
                 1.425 
                 3.363 
               
               
                   
                 B65 
                 1.867 
                 3.128 
               
               
                   
                 B66 
                 2.300 
                 2.935 
               
               
                   
                 B67 
                 2.493 
                 2.759 
               
               
                   
                 B68 
                 2.888 
                 2.622 
               
               
                   
                 B69 
                 3.179 
                 2.394 
               
               
                   
                 B70 
                 3.613 
                 2.236 
               
               
                   
                 B71 
                 3.926 
                 2.033 
               
               
                   
                 B72 
                 0.859 
                 4.306 
               
               
                   
                 B73 
                 1.185 
                 4.102 
               
               
                   
                 B74 
                 1.571 
                 3.861 
               
               
                   
                 B75 
                 2.040 
                 3.568 
               
               
                   
                 B76 
                 2.626 
                 3.202 
               
               
                   
                 B77 
                 3.217 
                 2.871 
               
               
                   
                 B78 
                 3.576 
                 2.608 
               
               
                   
                   
               
             
          
         
       
     
     FIGS. 5-8B illustrate an alternative embodiment of the present invention wherein the reactant gases are introduced into the center of the showerhead rather than at the periphery thereof. Referring to FIG. 5, showerhead  70  includes a center hub or stem  72  having a gas A inlet port  74  and a gas B inlet port  76 . Showerhead  70  is generally planar and has a circular cross section similar to the showerhead  20  previously described. Stem  72  extends generally perpendicular to the plane of showerhead  70  (see FIG.  6 ). 
     Referring now to FIG. 6, showerhead  70  comprises a lower body section  78  which interacts with a cover section  80  which rests on the body section  78 . The body section  78  is formed with a plurality of gas distribution fingers  82  as discussed further hereinbelow. Body section  78  also forms part of a peripheral channel  84 . Cover section  80  includes an annular rim  86  which rests on an annular surface  87  of body section  78 . Rim  86  provides a stand-off above top surface  89  of the bottom section so that body section  78  and cover section  80  cooperate to define a second space  90  for distribution of gas B. Cover section  80  also forms part of the peripheral channel  84 . A metal band  92  extends around the periphery of showerhead  70  and is attached to the cover section  80  and body section  78  such as by welding, to enclose channel  84 . Channel  84  is utilized to distribute and disperse gas A as further described hereinbelow. 
     Gas B is introduced into second space  90  through port  76 . Port  76  terminates in a shunt or cap structure  94  which includes a plurality of openings  96  to distribute gas B in space  90 . Gas B is directed through port  76  generally perpendicular to the plane of space  90 . However, the cap  94  directs the gas in a direction generally parallel with space  90  to provide uniform distribution around space  90  and uniform dispersal of gas B. Gas B is dispersed through a plurality of gas-dispersing passages  98  which are formed in the showerhead body section  78  and communicate between a lower face surface  99  of the showerhead  70  and gas B space  90 . Similar to the gas B passages of the previously described embodiment, the passages  98  have a first diameter D 1  of approximately 0.06 inches, and then narrow down to the second diameter d 1  of approximately 0.018 inches to direct the gas out of space  90  at the face surface  99 . 
     Turning now to FIGS. 5 and 7, the first space comprises a plurality of gas distribution passages, such as gas distribution fingers  82  which disperse gas A throughout the showerhead for even, uniform distribution thereof. Referring to FIG. 5, one set of gas distribution fingers  82  extends from peripheral channel  84  to approximately one side of a diametrical line  101 , while another set of fingers extends from the peripheral channel on the other side of the showerhead  70  to proximate the other side of the diametrical line  101 . In that way, one set of gas distribution fingers directs gas to one side of the showerhead and another set of fingers directs gas to the other side of the showerhead. Gas distribution fingers are each open at one end into the peripheral channel  84  for receiving gas A therefrom. The fingers are co-planar and extend generally parallel to each other and have varying lengths depending upon where they open into the peripheral channel, as clearly illustrated in FIG.  5 . The fingers  82  are elongated with a cylindrical shape, and are shown having a circular cross section, although various other shapes of cross-sections might also be utilized. 
     Gas A is directed from inlet  74 , which is plugged at its lower end by a plug  75 , to channel  84  via a diametrical bore  104  in cover section  80  plugged at each end by plugs  106 . The bore  104 , at each end, feeds peripheral channel  84  through axial ports  108 . In this way, the channel  84  receives gas A at two places 180° apart and from the channel gas A is directed into the distribution fingers  82  and to the passages  102 . A second set of gas-dispersing passages  102  communicates between the gas distribution fingers  82  and the face surface  99  of the showerhead  70  to disperse gas A. As illustrated in FIG. 7, the gas dispersing passages  98 , which communicate with gas B space  90 , extend through the showerhead body section  78  without intersecting fingers  82 . In that way, the reactant gases are not mixed within the showerhead in accordance with the principles of the present invention. Passages  102  have a diameter of approximately 0.018 inches. 
     Referring to FIGS. 8A and 8B, various locations of the openings for the gas dispersing passages are shown referenced to one quadrant of the showerhead. The respective grids are formed by duplication of the quadrants illustrated in FIGS. 8A and 8B. FIG. 8A illustrates the location of gas A openings  102  which communicate with the gas distribution fingers  82 . FIG. 8B, on the other hand, illustrates the gas dispersing openings  98  which communicate with the gas B space  90 . On showerhead  70 , the gas dispersing openings are arranged in equally spaced rows and columns, as opposed to the openings in the previously disclosed embodiment of showerhead  20 . 
     FIG. 9 illustrates another feature of the present invention wherein a showerhead as illustrated in FIGS. 5-8B is mounted for use within a CVD reaction chamber. Showerhead  70  is surrounded by a ceramic shield  124  formed with a suitable ceramic, such as alumina. Stem  72  supports the showerhead  70  within the reaction chamber  126  and also provides electrical connections as discussed further hereinabove. The showerhead is appropriately coupled to a gas A supply  127  and a gas B supply  128 . To suppress plasma discharge within the gas lines leading to the showerhead, the showerhead  70  is coupled to the appropriate gas supplies through plasma suppressors  130 . Plasma suppressor  130  is shown coupled in line between the gas B supply  128  and the showerhead  70 . In accordance with the principles of the present invention, a similar suppressor (not shown) will be utilized between the gas A supply  127  and the showerhead  70 . Ceramic shield  124  is supported in reaction chamber  126  by a support ring  132  which is suspended about the metal lid  133  of reaction chamber  126  by appropriate bolts  134 . The bolts are tightened in a downward direction, and threaded holes formed in the support ring  132  and bear against a washer  136  coupled to metal lid  133  to lift the support ring  132  in a vertically upward direction. A shoulder  137  of support ring  132  bears against an appropriately formed shoulder  138  of the ceramic shield  124  to thus lift the ceramic shield against the inner surface  139  of metal lid  133 . A seal  140  is coupled between the upper surface of the ceramic shield  124  and lid surface  139  to provide for a seal where a portion of the shield  124  and stem  72  pass through an opening in lid  133 . 
     A clamp ring  142  engages an upper portion of stem  72  for lifting the stem  72  with respect to ceramic shield  124 . As illustrated in FIG. 9, the clamp ring includes a plurality of screws or bolts  144  therearound which bear against a metal washer  146  positioned on the upper surface of shield  124 . When the bolts  144  are tightened down in appropriately threaded openings of clamp ring  142 , they drive the clamp ring  142  vertically upward, and thus pull the stem  72  upward with respect to shield  124 . Stem  72  includes a flange  148  which engages an inside shoulder  150  of shield  124 . A seal  152  is positioned between flange  148  and shoulder  150  for proper sealing between the stem  72  and shield  124 . In that way, support ring  132  lifts shield  124  for sealing and clamp ring  142  lifts stem  72  for sealing. Therefore, the inner environment of reaction chamber  126  is sealed against the outer environment as is necessary in CVD processes. The gas passages  74  and  76  are coupled to the appropriate gas supplies by VCR fittings  154  which are commercially available and well known in the art. As illustrated in FIG. 9, a quartz spacer cylinder  156  is positioned between shield  124  and stem  72  proximate showerhead  70  to suppress secondary plasmas. 
     Turning now to the plasma suppressors  130 , the suppressors provide a generally nonconductive ceramic material between gas line section  158   a  which is directed to the showerhead  70  and gas line section  158   b,  which is directed to the appropriate gas supply, such as gas B supply  128 . The suppressor  130  includes a ceramic, cylindrically formed body  160  which is preferably also formed of alumina. The respective gas line sections  158   a  and  158   b  are coupled to body  160  by nickel end plates  164 ,  166  which couple the gas line sections  158   a,    158   b  to body  160 . A plurality of small parallel channels or passages  170  are formed in body  160  to align and connect with the respective line sections  158   a,    158   b.  The passages are preferably dimensioned to allow the passage of gas to the showerhead  70 , but are small enough to prevent the creation of a plasma discharge therein. Accordingly, any plasma discharge from chamber  126  is suppressed to prevent any discharge to the right of suppressor  130 , as illustrated in FIG.  9 . In one embodiment, the passages are cylindrical, having a diameter of approximately 0.050 inches. In that way, plasma discharge is generally prevented from existing within the gas lines past the suppressor  130 . 
     While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of applicant&#39;s general inventive concept.