Abstract:
A gas injection system includes (a) a side gas plenum, (b) a plurality of N gas inlets coupled to said side gas plenum, (c) plural side gas outlets extending radially inwardly from said plenum, (d) an N-way gas flow ratio controller having N outputs coupled to said N gas inlets respectively, and (e) an M-way gas flow ratio controller having M outputs, respective ones of said M outputs coupled to said tunable gas nozzle and a gas input of said N-way gas flow ratio controller.

Description:
[0001]    BACKGROUND 
         [0002]    1. Technical Field 
         [0003]    The disclosure is related to process gas distribution in a plasma reactor for processing a workpiece such as a semiconductor wafer. 
         [0004]    2. Background Discussion 
         [0005]    Control of process gas distribution in the chamber of a plasma reactor affects process control of etch rate distribution or deposition rate distribution on a workpiece during plasma processing. Gas injection nozzles can be located at the center and periphery of the chamber. It is desirable to control gas injection at both the chamber center and at the periphery. One problem is that systems that control radial distribution of process gas flow rate generally do not control azimuthal distribution of process gas flow rate. As employed in this specification, the term “azimuthal” refers to the circumferential direction in a cylindrical processing chamber. Another problem is that systems that control azimuthal distribution of gas flow rate using gas injectors near the side wall suffer from pressure drops along the azimuthal direction. 
         [0006]    A related problem is how to feed process gas to different zones of gas injectors in such a manner as to avoid asymmetries in gas distribution while at the same time providing full control of both radial and azimuthal gas distributions. 
         [0007]    Another problem is how to provide a gas distribution system that solves all of the foregoing problems in a structure affording rapid disassembly and re-assembly with close-fitting tolerances without damage. 
         [0008]    The formation of gas distribution passages in one layer has generally limited the location of the gas injectors of the chamber to that one layer, which is typically flat and has no particular effect upon gas flow within the chamber. 
       SUMMARY 
       [0009]    A plasma reactor having a chamber interior, a workpiece support and a tunable gas nozzle, includes (a) a side gas plenum, (b) a plurality of N gas inlets coupled to said side gas plenum, (c) plural side gas outlets extending radially inwardly from said plenum, (d) an N-way gas flow ratio controller having N outputs coupled to said N gas inlets respectively, and (e) an M-way gas flow ratio controller having M outputs, respective ones of said M outputs coupled to said tunable gas nozzle and a gas input of said N-way gas flow ratio controller. 
         [0010]    In one embodiment, the tunable gas nozzle has two gas input, and N is four and M is three. The reactor may further include a gas supply panel coupled to a gas input of the three-way gas flow controller. In one embodiment, a process controller is coupled to the M-way gas flow ratio controller and to the N-way gas flow ratio controller, and a user interface is coupled to the process controller. 
         [0011]    In one embodiment, the side gas plenum includes plural sets of gas flow channels, and each one of the sets of gas flow channels includes: (a) an arcuate gas distribution channel having a pair of ends coupled to a corresponding pair of the plural side gas outlets, and (b) an arcuate gas supply channel, one end of the arcuate gas supply channel connected to a corresponding one of the plurality of N gas inlets, and an opposite end of the arcuate gas supply channel coupled to the gas distribution channel proximate a middle point of the gas distribution channel. 
         [0012]    In a related embodiment, the plural sets of gas flow channels are of equal path lengths between respective gas inlet and a respective side gas outlet. 
         [0013]    In one embodiment, the cylindrical side wall includes a liner edge, the plasma reactor further including: (a) a gas delivery ring over the liner edge, the plural sets of gas flow channels being formed in the gas delivery ring, and (b) a top liner ring over the gas delivery ring, the plural side gas outlets extending into the top liner ring, the top liner ring including a top liner ring surface facing the chamber interior. 
         [0014]    In a related embodiment, each of the plural side gas outlets includes: (a) a side gas injection nozzle extending radially in the top liner ring toward the chamber interior and including an axially extending gas delivery insert-receiving hole, and (b) a gas delivery insert extending from the gas delivery ring into the axially extending gas delivery insert-receiving hole. 
         [0015]    The plasma reactor may further include an axial internal gas flow passage in the gas delivery insert and a radial internal gas flow nozzle passage through a side wall of the axially extending gas delivery insert hole, the axial internal gas flow passage being in registration with the radial internal gas flow nozzle passage. 
         [0016]    In one embodiment, the top liner ring includes plural nozzle pockets in the top liner ring surface, the side gas injection nozzle extending into a corresponding one of the nozzle pockets. Moreover, the side gas injection nozzle includes plural O-ring nozzle grooves concentric with the side gas injection nozzle, the plasma reactor further including first plural O-rings in the plural O-ring nozzle grooves compressed against an interior side wall of a corresponding one of the nozzle pockets. 
         [0017]    In one embodiment, the side gas injection nozzle further includes: (a) a cylindrical outer nozzle surface, wherein the O-ring nozzle grooves define nozzle groove surfaces indented with respect to the cylindrical outer nozzle surface, and (b) an axial evacuation slot including slot sections in the cylindrical outer nozzle surface beginning at an end of the side gas injection nozzle inside the nozzle pocket, and slot sections in the nozzle groove surfaces. 
         [0018]    In further embodiment, there is a gap between the cylindrical outer nozzle surface and the interior side wall of a corresponding one of the nozzle pockets, the slot sections in the nozzle groove surfaces providing an evacuation path around the first plural O-rings, the slot sections in the cylindrical outer nozzle surface providing an evacuation path to the gap. 
         [0019]    In one embodiment, the top liner ring further includes plural gas delivery insert pockets facing the gas delivery ring, a portion of the gas delivery insert extending into a corresponding one of the gas delivery insert pockets. In the same embodiment, the gas delivery inert includes plural O-ring insert grooves concentric with the gas delivery insert, the plasma reactor further including second plural O-rings in the plural O-ring insert grooves compressed against an interior side wall of a corresponding one of the plural gas delivery insert pockets. 
         [0020]    In one embodiment, each of the plural gas outlets further includes an axial port in the gas delivery ring extending to the axial internal gas flow passage of the gas delivery insert. 
         [0021]    In an embodiment, the side gas injection nozzle includes a ceramic material, and the gas delivery ring and the gas delivery insert include steel, and the top liner surface and the cylindrical side wall includes a protective layer including an anodized material or Yttria. 
         [0022]    In a further aspect, a side gas injection kit is provided, including: a top liner ring including plural nozzle pockets, plural side gas injection nozzles extending into the nozzle pockets, each of the plural side gas injection nozzles including: (a) an outer nozzle surface and plural O-ring nozzle grooves in the outer nozzle surface and concentric with the side gas injection nozzle, and (b) first plural O-rings in the plural O-ring nozzle grooves compressed against an interior side wall of a corresponding one of the nozzle pockets. 
         [0023]    In one embodiment, the side gas injection nozzle further includes: (a) nozzle groove surfaces indented with respect to the outer nozzle surface and formed in the O-ring nozzle grooves, and (b) an axial evacuation slot including slot sections in the cylindrical outer nozzle surface beginning at an end of the side gas injection nozzle inside the nozzle pocket, and slot sections in the nozzle groove surfaces. 
         [0024]    In a related embodiment, the side gas injection kit further includes a gap between the cylindrical outer nozzle surface and an interior side wall of a corresponding one of the nozzle pockets, the slot sections in the nozzle groove surfaces providing an evacuation path around the first plural O-rings, the slot sections in the cylindrical outer nozzle surface providing an evacuation path to the gap. 
         [0025]    In a further related embodiment, the side gas injection kit further comprises: (a) plural gas delivery insert pockets in the top liner ring, (b) plural gas delivery extending into the gas delivery insert pockets, and (c) each of the gas delivery inserts including plural O-ring insert grooves concentric with the gas delivery insert, and second plural O-rings in the plural O-ring insert grooves compressed against an interior side wall of a corresponding one of the plural gas delivery insert pockets. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    So that the manner in which the exemplary embodiments of the present invention are attained can be understood in detail, a more detailed description of the invention, briefly summarized above, may be obtained by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be appreciated that certain well known processes are not discussed herein in order to not obscure the invention. 
           [0027]      FIG. 1  is a simplified block diagram of one embodiment. 
           [0028]      FIG. 2  is an elevational view corresponding to  FIG. 1 . 
           [0029]      FIG. 3  depicts an embodiment having eight gas outlets. 
           [0030]      FIG. 4  depicts a side gas delivery kit for the embodiment of  FIG. 3 . 
           [0031]      FIG. 5  is a cut-away cross-sectional view of the side gas delivery kit of  FIG. 4 . 
           [0032]      FIG. 6  is an enlarged view of a portion of  FIG. 5 . 
           [0033]      FIG. 7  depicts the bottom liner. 
           [0034]      FIG. 8  illustrates the workpiece support pedestal enclosed by the bottom liner. 
           [0035]      FIG. 9  depicts a view of the top liner ring from the top. 
           [0036]      FIG. 10  depicts a view of the top liner ring from the bottom. 
           [0037]      FIG. 11  is an enlarged view of a portion of  FIG. 10 . 
           [0038]      FIGS. 12 and 13  are top and bottom views, respectively, of the gas delivery ring. 
           [0039]      FIG. 14  is an enlarged cross-sectional view taken along lines  14 - 14  of  FIG. 12 . 
           [0040]      FIG. 15  is an enlarged view of the injection nozzle of  FIG. 6 . 
           [0041]      FIG. 16  is a cross-sectional view corresponding to  FIG. 15 . 
           [0042]      FIG. 17  is an enlarged view of the gas delivery insert of  FIG. 6 . 
           [0043]      FIG. 18  is a cross-sectional view corresponding to  FIG. 17 . 
           [0044]      FIG. 19  depicts a gas delivery block employed in the embodiment of  FIG. 4 . 
           [0045]      FIG. 20  is a cross-sectional view corresponding to  FIG. 19 . 
           [0046]      FIG. 21  depicts an exploded assembly of the gas distribution ring, the top liner ring  144 , the injection nozzles and the gas distribution inserts of  FIG. 4 . 
           [0047]      FIG. 22  is an enlarged view of a portion of  FIG. 21 . 
       
    
    
       [0048]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
       DETAILED DESCRIPTION 
       [0049]      FIG. 1  is a simplified block diagram of one embodiment. A plasma reactor chamber  100 , depicted in elevational view in  FIG. 2 , is enclosed by a cylindrical side wall  102  defining a chamber volume  104 . A workpiece support pedestal  106  is inside the chamber volume and rests on a pedestal lift mechanism  108  shown in  FIG. 2 . As depicted in  FIG. 2 , a tunable gas nozzle  110  is mounted on a ceiling  112  of the chamber  100 , and has a center gas nozzle  114  and a side gas nozzle  116  that inject gas toward the center and side, respectively, of the chamber  100 . The center and side gas nozzles  114 ,  116  are independently fed by gas supply lines  114   a,    116   a  which are labeled “nozzle 1” and “nozzle 2”, respectively, in  FIG. 1 . A circular side gas injection plenum  118  receives process gas at four gas inlets  120  and injects process gas into the chamber at plural gas outlets  122 . As shown in  FIG. 1 , the four gas inlets  120  are connected respectively to four supply lines labeled “side gas 1”, “side gas 2”, “side gas 3” and “side gas 4” in  FIG. 1 , which are fed by four outputs of a four-way gas flow ratio controller  124 . The input of the four-way gas flow ratio controller  124  and the gas supply lines  114   a  and  116   a  receive process gas from respective outputs of a three-way gas flow ratio controller  126 . A gas supply panel  128  furnishes process gas to the input of the three-way gas flow ratio controller  126 . A controller  130  having a user interface  132  governs the gas flow ratio controllers  124  and  126 . 
         [0050]    The gas injection pattern in the chamber  100  has three concentric zones including a center zone governed by the center gas nozzle  114 , an inner zone governed by the side gas nozzle  116  and a peripheral zone governed by the gas outlets  122 . The user may adjust the gas flow ratios among the three concentric zones by controlling the three-way gas flow ratio controller  126 . In addition, the user may govern azimuthal (circumferential) gas distribution by controlling the four-way gas flow ratio controller  124 . An advantage is that the gas flow ratio controllers  124  and  126  provide simultaneous independent control of both radial distribution of gas flow and azimuthal distribution of gas flow. A further advantage is that the gas outlets  122  at the chamber periphery are fed in parallel, and the pressure losses are uniformly distributed in the azimuthal direction. 
         [0051]      FIG. 3  depicts an embodiment in which there are eight gas outlets  122 . Any other suitable number of gas outlets may be employed in other embodiments. In the embodiment of  FIG. 3 , the plenum  118  of  FIG. 1  is embodied in four pairs of recursive gas flow channels, each pair including an arcuate gas distribution channel  136  and an arcuate gas supply channel  138 . The four pairs of recursive gas flow channels  136 ,  138  provide parallel paths between the gas inlets  120  and the gas outlets  122 . Each pair of the eight gas outlets  122  of  FIG. 3  is fed from a corresponding gas inlet  120  via a corresponding pair of the recursive gas flow channels  136 ,  138 . Each gas distribution channel  136  has a pair of ends connected to the corresponding pair of gas outlets  122 , and is fed at its center by one end of the corresponding arcuate gas supply channel  138 , the other end of the gas supply channel  138  connected to the corresponding gas inlet  120 . 
         [0052]      FIG. 4  depicts a side gas delivery kit for the embodiment of  FIG. 3 , including a top liner ring  140 , a bottom liner  142 , and a gas delivery ring  144  between the top liner ring  140  and the bottom liner  142 . The bottom liner  142  includes the side wall  102  of  FIG. 3 . The gas delivery ring  144  contains the recursive gas flow channels  136 ,  138  of  FIG. 3 , as will be described below in greater detail.  FIG. 5  is a cut-away cross-sectional view of the side gas delivery kit of  FIG. 4 , showing a gas delivery insert  146  extending from the gas delivery ring  144  into the top liner ring  140 , and further showing a injection nozzle  148  in the top liner ring  140 . 
         [0053]      FIG. 6  is an enlarged view of a portion of  FIG. 5 , showing in greater detail the gas delivery insert  146  and the injection nozzle  148 . The gas delivery insert  146  is supported on the gas delivery ring  144 . The gas delivery insert  146  has an internal axial insert gas flow passage  150  coupled to one end of a corresponding gas distribution channel  136 , as will be described in greater detail below. The top of the gas delivery insert  146  is received inside the injection nozzle  148  near a radially outer end of the injection nozzle  148 . The injection nozzle  148  has an internal radial nozzle gas flow passage  152  in communication with the internal axial insert gas flow passage  150 . The radially inner end of the injection nozzle  148  is open to the interior of the chamber  100 . Each gas outlet  122  in the embodiment of  FIG. 3  is implemented by a corresponding injection nozzle  148  and a corresponding gas delivery insert  146  of  FIG. 6 . 
         [0054]      FIG. 7  depicts the bottom liner  142 .  FIG. 8  shows how the workpiece support pedestal is enclosed by the bottom liner  142 . The bottom liner  142  has three symmetrically disposed slit openings  154  for wafer transfer. 
         [0055]      FIG. 9  depicts a view of the top liner ring  140  from the top, while  FIG. 10  depicts a view of the top liner ring  140  from the bottom. The top liner ring  140  has an annular bottom surface  156  from which the injection nozzles  148  open into the chamber  100 . The annular bottom surface  156  is concave and provides a transition between the radius of a ridge  158  conforming to the bottom liner  142  and an inner radius of an opening  160  at the top of the top liner ring  140 . The curvature of the annular bottom surface  156  can promote gas flow from each injection nozzle  148  toward the workpiece. 
         [0056]      FIG. 11  is an enlarged view of a portion of  FIG. 10 , showing one of eight hollow nozzle pockets  164  formed in the top liner ring  140  and one of eight hollow gas delivery insert pockets  166  formed in the top liner ring  140 . The injection nozzle  148  shown in  FIG. 6  is held inside the nozzle pocket  164 , as will be described below. A portion of the gas delivery inert  146  shown in  FIG. 6  is held inside the gas delivery insert pocket  166 , as will be described below. As shown in  FIG. 11 , the nozzle pocket  164  is cylindrically shaped, extends in a radial direction and forms an opening  164   a  in the annular bottom surface  156 . The gas delivery insert pocket  166  is formed in a shelf  170  extending outwardly from a circumferential periphery  172  of the top liner ring  140 . 
         [0057]      FIGS. 12 and 13  are top and bottom views, respectively, of the gas delivery ring  144 .  FIG. 12  shows the formation of the four gas distribution channels  136  and the four gas supply channels  138  in the gas delivery ring  144 . Each gas supply channel  138  receives gas from the corresponding gas inlet  120 . Each gas inlet  120  ( FIG. 3 ) includes an axial port  120 - 1  ( FIG. 13 ) formed in a tab  144 - 1  extending from a periphery  144 - 2  of the gas delivery ring  144 . The axial port  120 - 1  opens through a bottom surface of the tab  144 - 1 . A radially extending gas inlet channel  120 - 2  ( FIG. 12 ) is coupled between the axial port  120 - 1  and one end  138 - 1  of the gas supply channel  138 . An opposite end  138 - 2  of the gas supply channel  138  is coupled to the middle of the gas distribution channel  136 . Each end  136 - 1  and  136 - 2  of the gas distribution channel  136  terminates at an axial gas outlet  122 ′. The axial gas outlet  122 ′ is coupled to the bottom of the internal axial insert gas flow passage  150  of a gas delivery insert  146 , as shown in  FIG. 6 . In this manner, the four gas distribution channels  136  feed eight gas delivery inserts  146 . In the illustrated embodiment, there are two axial gas ports  120 - 1  in each tab  144 - 1  feeding respective sets of the gas flow channels  136 ,  138 . In the illustrated embodiment, the gas distribution channels  136  and the gas supply channels  138  follow arcuate paths that are concentric with the cylindrical side wall  102 . The gas distribution channels  136 , the gas supply channels  138  and the radial gas inlet channel  120 - 2  provide respective paths between the gas inlets  120  and the gas outlets  122  that are of equal length. An advantage of the equal path lengths is a reduction in non-uniformity in gas flow resistance among the various paths, affording better process control. 
         [0058]      FIG. 14  is an enlarged cross-sectional view taken along lines  14 - 14  of  FIG. 12 , and shows one of the gas distribution channels  136  formed in the gas delivery ring  144  and covered by a gas channel cover  171 .  FIG. 14  further shows the intersection between one end of the gas distribution channel  136  and the gas outlet  122 ′. 
         [0059]    The injection nozzle  148  of  FIG. 6  is depicted in detail in  FIG. 15  and in cross-section in  FIG. 16 . The injection nozzle  148  has a cylindrical body  180  through which the internal radial nozzle gas flow passage  152  extends to a gas injection passage  182  forming an orifice  184  at the radially inner end  180   a  of the cylindrical body  180 . An axially extending gas delivery insert hole  186  is formed through the cylindrical body  180  near its radially outer end  180   b.  The gas delivery insert  146  is received in the gas delivery insert hole  186 . A first O-ring groove  188  concentric with the cylindrical body  180  is formed near the radially outer end  180   b  of the cylindrical body  180  and defines a first O-ring groove inner surface  188   a.  A second O-ring groove  190  concentric with the cylindrical body  180  is formed in the cylindrical body  180  between the first O-ring groove  188  and the radially inner end  180   a,  and defines a second O-ring groove inner surface  190   a.  An axial evacuation slot  192  is formed in the surface of the cylindrical body  180 , and includes a first slot section  192 - 1  between the radial outer end  180   b  and the first O-ring groove  188 , a second slot section  192 - 2  between the first and second O-ring grooves  188  and  190 , and a third slot section  192 - 3  extending for a short distance from the second O-ring groove  190  toward the radially inner end  180   a.  The axial slot  192  further includes a first groove axial slot section  192 - 4  in the first O-ring groove inner surface  188   a  and a second groove axial slot section  192 - 5  in the second O-ring groove inner surface  190   b.  As shown in  FIGS. 6 , O-rings  194  are inserted into the first and second O-ring grooves  188  and  190 . There is a small nozzle-to-pocket clearance or gap between the cylindrical body  180  and the interior surface of the nozzle pocket  164 . The axial slot  192  enables the evacuation through the nozzle-to-pocket gap of gas trapped between the radial outer end  180   b  of the injection nozzle  148  and the back wall  164   b  ( FIG. 11 ) of the nozzle pocket  164 . The axial slot  192  enables the evacuated air to bypass the O-rings  194 . 
         [0060]      FIG. 17  depicts the gas delivery insert  146  shown in  FIG. 6 .  FIG. 18  is a cross-sectional view corresponding to  FIG. 17 . Referring to  FIGS. 17 and 18 , the gas delivery insert  146  includes a cylindrical insert post  202  supported on a generally flat insert base  204 . The internal axial insert gas flow passage  150  shown in  FIG. 6  extends through the cylindrical insert post  202 . Gas outlets  205   a  and  205   b  through the cylindrical insert post  202  intersect the internal axial insert gas flow passage  150 . In forming the assembly of  FIG. 6 , the cylindrical insert post  202  ( FIG. 18 ) is inserted into the gas delivery insert hole  186  of the injection nozzle  148  of  FIG. 16  until the gas outlets  205   a  and  205   b  are in registration with the internal radial nozzle gas flow passage  152  of  FIG. 6 . 
         [0061]    The cylindrical insert post  202  has O-ring grooves  206 ,  208  concentric with the cylindrical insert post  202  in which O-rings  209  ( FIG. 6 ) are received. Interior surface  186   a  of the gas inlet hole  186  ( FIG. 16 ) is an O-ring sealing surface against which the O-ring  209  is pressed upon insertion of the insert post  202  into the gas inlet hole  186 . An O-ring groove  210  ( FIG. 18 ) is formed in the top surface of the insert base  204  around the bottom of the cylindrical insert post  202 . An O-ring groove  212  ( FIG. 18 ) is formed in the bottom surface of the insert base  204  concentric with the cylindrical insert post  202 . An O-ring  216  ( FIG. 6 ) is held in the O-ring groove  212  for fitting the gas delivery insert  146  against the top liner ring  140 . An O-ring  214  ( FIG. 6 ) is held in the O-ring groove  210  for fitting the insert base  204  onto the gas delivery ring  144 . 
         [0062]    The description of  FIGS. 12 and 13  above refers to two tabs  144 - 1  of the gas delivery ring  144 , each tab  144 - 1  supporting a pair of gas inlet ports  120 - 1  open at the bottom surface of the tab  144 - 1 .  FIGS. 19 and 20  depict a gas delivery block  220  for fastening to the bottom surface of a tab  144 - 1  and having a pair of gas inlet stems  222  that meet the pair of gas inlet ports  120 - 1  upon joining of the gas delivery block  220  to the tab  144 - 1 . The illustrated pair of gas inlet stems  222  provide connection to two outputs of the four-way gas flow ratio controller  124 . 
         [0063]    Radial distribution of gas flow is adjusted by controlling the three-way gas flow ratio controller  126 . Independently, azimuthal gas distribution is adjusted controlling the four-way gas flow ratio controller  124 . An advantage is that the gas flow ratio controllers  124  and  126  provide simultaneous independent control of both radial distribution of gas flow and azimuthal distribution of gas flow. A further advantage is that the gas outlets  122  at the chamber periphery are fed in parallel, and the pressure losses are uniformly distributed in the azimuthal direction. This latter feature simplifies control of azimuthal gas distribution. 
         [0064]    The gas injection inserts  146  facilitate the location of the injection nozzles  148  in the concave surface  156  of the top gas ring  140 . Gas injection from the side is optimized because the injection nozzles  148  are located in the concave surface  156  of the top liner ring  140 , and the injected gas is guided by the concave surface  156 . The top gas ring  140  and the injection nozzles  148  are located in a plane above the gas delivery ring  144  containing the four pairs of recursive gas flow channels  136 ,  138 . Gas flow paths spanning the gap between the plane of the injection nozzles  148  and the gas delivery ring  144  are provided by the gas delivery inserts  146 . 
         [0065]    Referring to  FIGS. 21 and 22 , the top liner ring  140 , the gas delivery ring  144 , the eight gas delivery inserts  146  and the eight injection nozzles  148  are separate pieces, which enables the selection of materials to be optimized for each individual piece, and facilitates an efficient modular assembly. In an embodiment, the gas delivery ring  144  comes into contact with process gases but not with plasma. They are therefore formed of a ceramic material (or stainless steel or other suitable material) that is compatible with process gases employed in plasma processes such as a plasma enhanced reactive ion etch process, or plasma enhanced chemical vapor deposition process, as some examples. The injection nozzles  148  face the plasma processing zone of the chamber, and therefore are formed of a material, such as a ceramic material, that is compatible with exposure to plasma. The top liner ring  140  and the bottom liner  142  may be formed of a material which is not generally compatible with exposure to plasma. To avoid exposure of the material to plasma, the interior surface of the side wall  102  and the annular bottom surface  156  of the top liner ring  140  are covered with a protective layer compatible with exposure to plasma. The side wall  102  and the top liner ring  140  may be formed of aluminum, and their protective coatings may comprise Yttria or may be formed by anodization. 
         [0066]    The modular parts may be conveniently and repetitively assembled and disassembled in the manner depicted in  FIGS. 21 and 22  without damage to the various parts, while permitting a close fitting between parts, due in part to the protection afforded by the O-rings referred to above. Specifically, the O-rings  194  of  FIG. 6  protect the injection nozzles  148  during their insertion in the nozzle pockets  164 . The O-rings  209  on the gas delivery inserts  146  protect the injection nozzles  148  from the gas delivery inserts during insertion of the inserts  146  into the insert-receiving holes  186  in the injection nozzles  148 . The O-rings  194  and  209  are elastically compressible in one embodiment. 
         [0067]    Assembly procedure in  FIGS. 21 and 22  entails inserting the injection nozzles  148  into the nozzle pockets  164  in the top liner ring  140 , mounting the gas delivery inserts  146  on the gas delivery ring  140 , and then bringing the gas delivery ring  144  and the top liner ring  144  together so as to insert the gas delivery inserts  146  into the respective insert-receiving holes  186 . 
         [0068]    While the illustrated embodiment exemplifies four-way symmetry involving eight injection nozzles  148 , other symmetries may be employed involving a different number of injection nozzles  148 . 
         [0069]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.