Abstract:
A method of making an electrode assembly for a plasma processing apparatus includes securing a backing member to an electrode wherein first fastener members mounted in apertures in the backing member cooperate with second fastener members to hold the electrode assembly to a support member, such as a temperature-controlled top plate in a plasma processing chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. application Ser. No. 10/623,540 entitled ELECTRODE ASSEMBLY FOR PLASMA PROCESSING APPARATUS, filed on Jul. 22, 2003 now U.S. Pat. No. 7,543,547, which claims the benefit of U.S. Provisional Application No. 60/400,451, filed Jul. 31, 2002, the entire contents of each is hereby incorporated by reference. 
    
    
     BACKGROUND 
     Plasma processing apparatuses are used to process substrates by techniques including etching, physical vapor deposition (PVD), chemical vapor deposition (CVD), ion implantation, and resist removal. One type of plasma processing apparatus used in plasma processing includes a reaction chamber containing upper and lower electrodes. An electric field is established between the electrodes to excite a process gas into the plasma state to process substrates in the reaction chamber. 
     SUMMARY 
     A component for a plasma processing apparatus is provided. In a preferred embodiment, the component includes a first member bonded to a second member. The first member includes a plurality of through apertures, each having a first portion, and a wider second portion. The component also includes a plurality of first fastener members adapted to be mounted in the apertures. The first fastener members preferably include a bearing surface facing a surface at least partially defining the second portion of the aperture. 
     In a preferred embodiment, the component is an electrode assembly. 
     In another embodiment, the electrode assembly is attached to a top plate. The top plate is mounted, or adapted to be mounted, inside a reaction chamber of a plasma processing apparatus. The top plate includes through openings aligned with the apertures in the backing member. Second fastener members can each be received in an opening of the top plate and an aligned aperture of the backing member, and attached to a first fastener member to attach the backing member to the top plate. 
     In a preferred embodiment, the electrode assembly is a showerhead electrode assembly. 
     A preferred embodiment of a method of making a component for a plasma processing apparatus comprises securing a first part, such as a backing member to a second part, such as an electrode. The first part includes a plurality of apertures including a first portion and a wider second portion. A first fastener member is mounted in each aperture. The first fastener members preferably include a head in the second portion of the aperture. The head is preferably configured to prevent the first fastener member from being pulled out of the aperture, or from rotating. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an upper electrode assembly and a lower electrode for a plasma reaction chamber. 
         FIG. 2  depicts a fastener including a helicoil used in an upper electrode assembly. 
         FIG. 3  depicts a preferred embodiment of an upper electrode assembly including a fastener member with a T-nut. 
         FIG. 4  is a perspective view of a T-nut. 
         FIG. 5  is a bottom plan view of a preferred embodiment of an upper electrode assembly with the electrode removed to show the backing member. 
         FIG. 6  is a cross-sectional view in the direction of line  6 - 6  in  FIG. 5 . 
         FIG. 7  is a cross-sectional view in the direction of line  7 - 7  in  FIG. 5 . 
         FIG. 8  is a bottom plan view of a preferred embodiment of an upper electrode assembly with the electrode removed to show an exemplary pattern of fastener members. 
         FIG. 9  depicts an aperture in a backing ring. 
         FIG. 10  depicts another preferred embodiment of an upper electrode assembly. 
     
    
    
     DETAILED DESCRIPTION 
     Components for plasma processing apparatuses are provided. In a preferred embodiment, the component is an electrode assembly for a plasma processing apparatus. The electrode assembly can include a backing member secured to an electrode. 
     The electrode can be secured to the backing member by a bonding technique. The bonding material can be a thermally and electrically conductive bonding material, such as an elastomer that provides thermal and electrical attachment of the electrode material to the backing member. The use of elastomers for bonding surfaces together is described, for example, in commonly-owned U.S. Pat. No. 6,073,577, which is incorporated herein by reference in its entirety. 
     The electrode preferably is a solid or a perforated plate of single crystal silicon. The electrode can optionally have through gas passages when used as a showerhead electrode. The backing member is preferably a plate of a material that is chemically compatible with process gases used in the plasma processing chamber, has a coefficient of thermal expansion closely matching that of the electrode material, and is electrically and thermally conductive. Suitable materials for making the backing member include graphite and SiC, for example. 
     In another preferred embodiment of the electrode assembly, the backing member is attached to a top plate. 
       FIG. 1  depicts a preferred embodiment of an upper electrode assembly  10 , which comprises an upper electrode preferably including an inner electrode member  12 , and an outer electrode member  14 . A lower electrode  15  is shown positioned below the upper electrode. In an embodiment, the inner electrode member  12  is preferably a cylindrical plate. The outer electrode member  14  can be continuous member (e.g., a poly-silicon member, such as a ring), or can alternatively include multiple segments (e.g., 2-6 segments). In embodiments including a multiple-segment outer electrode member  14 , contiguous segments preferably overlap each other to protect the underlying joint, such as an elastomeric joint, from exposure to plasma. 
     The upper electrode can be electrically grounded, or it can be powered with radio-frequency (RF) current. The upper electrode can be a showerhead electrode with multiple gas passages for injecting a process gas into a plasma reaction chamber containing the upper electrode and lower electrode  15 . The upper electrode assembly  10  and the lower electrode  15  can be used in various plasma processing operations, such as dry etching, chemical vapor deposition, ion implantation, and resist stripping, in the reaction chamber. 
     Single crystal silicon is a preferred material for plasma exposed surfaces of the inner electrode member  12  and of the outer electrode member  14 . High-purity, single crystal silicon minimizes contamination of semiconductor substrates during plasma processing because it introduces a minimal amount of undesirable elements into the reaction chamber, and also wears smoothly during plasma processing, thereby creating very few particles. Other materials that can be used for plasma-exposed surfaces of the upper electrode include SiC, SiN, AlN, and Al 2 O 3 , for example. 
     The backing member preferably includes a backing plate  18 , which is co-extensive with the inner electrode member  12 , and an outer backing ring  22 . The backing member is preferably made of graphite. The top surface  16  of the inner electrode member  12  is preferably bonded to the backing plate  18 , and the top surface  20  of the outer electrode member  14  is preferably bonded to a continuous backing ring  22 . 
     The backing plate  18  and backing ring  22  are attached to a top plate  24 . The top plate  24  is preferably temperature controlled by flowing a heat transfer fluid (liquid or gas) through it. The top plate  24  is preferably made of a metal having suitable thermal conductivity, such as aluminum, or an aluminum alloy. The top plate  24  preferably provides an electrical ground and a heat sink for the electrode. Preferably, a vacuum seal is provided between the top plate  24  and the backing plate  18  and/or backing ring  22 . For example, a sealing member, such as a sealing ring  26 , can be located between the backing plate  18  and the top plate  24  to minimize gas leakage through an interface between the inner electrode member  12  and the outer electrode member  14 . 
     In the embodiment shown in  FIG. 1 , the backing plate  18  and backing ring  22  are attached to the top plate  24  by fastener members  28 . The fastener members  28  can be threaded screws, bolts, or the like. The fastener members  28  are inserted from the top surface  30  of the top plate  24  into openings  32  and aligned apertures in the backing plate  18  and backing ring  22 .  FIG. 2  shows an embodiment in which the top plate  24  is attached to the backing ring  22  by helicoils  34  inserted in apertures  36  in the backing ring  22  (the backing plate  18 , inner electrode member  12 , and overlying portion of the top plate  24  are not shown for simplicity). The helicoils  34  increase the strength of the threaded connection with the fastener members  28 , as graphite is brittle and has low shear strength. Gas leakage at the apertures  36  can be minimized by a cover plate (not shown) covering the openings  32 . The top plate  24  is shown attached to the backing ring  22  in  FIG. 2 ; however, the same mounting arrangement can be used to attach the backing plate  18  to the top plate  24 . 
     It has been determined that the helicoils  34  are prone to pull out of the backing plate  18  and backing ring  22  at low bolt torque during assembly. Also, the helicoils  34  can back out of the apertures  36  when the fastener members  28  are removed. 
     A stronger connection between the electrode assembly  10  and the top plate  24  is provided by first and second fastener members, where a portion of one of the fastener members faces a bearing surface of the backing member.  FIGS. 3 and 4  show a preferred T-nut configuration of a first fastener member  38 .  FIGS. 5-7  show further views of the fastener member  38 . The fastener member  38  preferably includes a head  40 , shaft  42 , and internal threads  44 . The threads  44  engage with the threads of a second fastener member  28  when the backing member is attached to the top plate  24 . 
     As shown in  FIG. 9 , the apertures  36  in the backing plate  18  and in the backing ring  22  preferably have a stepped configuration, and include a first portion  37  and a wider second portion  45 . The second portion  45  is partially defined by a bearing surface  47 . The head  40  of the fastener member  38  is sized to fit into the second portion  45  of the aperture  36  formed in the backing plate  18 , and the second portion  45  of the aperture  36  formed in the backing ring  22 . In embodiments in which the gas injection holes of the upper electrode are vertical, the fastener member  38  preferably is aligned in the direction of the gas injection holes. 
     Other aperture configurations than a stepped aperture shown in  FIG. 9  can alternatively be used. Such other configurations include multiple-stepped apertures, tapered apertures, and the like. The cross-section of the apertures  36  can be semi-circular, circular, polyhedral, or have other non-circular configurations. Preferably, the apertures  36  are shaped to match the shape of the fastener members  38  to prevent rotation of the fastener members  38  when they are inserted in the apertures  36 . 
     In the embodiment shown in  FIG. 4 , the head  40  of the fastener member  38  has at least one transverse dimension, d, which exceeds the maximum transverse dimension (e.g., the diameter) of the first portion  37  of the aperture  36 . The configuration of the head  40  prevents the fastener member  38  from being pulled out of the aperture  36  toward the top plate  24 . Consequently, the fastener member  38  provides a significantly greater pull-out force than the helicoil  34 . Also, because the head  40  prevents the fastener member  38  from turning in the aperture  36 , the fastener member  38  does not back out of the aperture  36  when the fastener member  28  is disengaged from the fastener member  38 . 
     To prevent rotation of the fastener member  38 , the head  40  preferably has a non-circular shape. The second portion  45  of the aperture  36  preferably is shaped to mate with the head  40  when T-nuts are used as the fastener member  38 . The configuration of the head  40  provides a bearing surface  48  facing the bearing surface  47  of the second portion  45 . This arrangement increases the failure bolt force, and prevents rotation of the fastener member  38  relative to the backing plate  18  and the backing ring  22  when the head  40  is received in the second portion  45  of the aperture  36 . 
     The fastener member  38  is not limited to a T-nut configuration. The head  40  of the fastener member  38  can alternatively have other non-circular shapes, such as semi-circular, D-shaped, oval, polygonal shapes, including triangular, rectangular, square, trapezoidal, hexagonal, and the like. For such other shapes, the second portion  45  of the apertures  36  in the backing plate  18  and in backing ring  22  preferably have a matching shape to prevent rotation of the fastener member  38  relative to the backing plate  18  and to the backing ring  22 . 
     Alternatively, the head  40  can have a circular shape, but also include a key in the axial direction, which is received in a mating portion of the aperture  36 . 
     In another embodiment, the head  40  of the fastener member  38  can be circular and non-concentric with respect to the shaft  42 . Such configuration prevents rotation of the fastener member  38  in the mating aperture. 
     The upper electrode assembly can include fastener members  38  having the same, or a different, head configuration from each other. 
     The aperture  36  can be formed in the backing plate  18  and in the backing ring  22  by any suitable technique, such as milling, drilling, casting, molding, and the like. If desired, the backing plate  18  can include two or more layers bonded together, with each layer including an aperture corresponding to a portion of the aperture  36 . 
     In a preferred embodiment, the fastener member  38  is bonded to the bearing surface  47  using an adhesive, such as an elastomer, or the like. The adhesive prevents the fastener member  38  from coming out of the recess  44  during assembly, and also provides a cushion to spread the bearing and torsional loads. After the backing plate  18  and backing ring  22  have been bonded to the inner electrode member  12  and outer electrode member  14 , respectively, the fastener member  38  is trapped between the upper electrode and backing member. 
     The fastener member  38  can be made of any suitable material. The fastener member  38  can be made of metals and metal alloys including, for example, stainless steels, such as Nitronic-60, or molybdenum. Nitronic-60 provides resistance to galling in a vacuum environment. Molybdenum has a coefficient of thermal expansion that closely matches the coefficient of thermal expansion of graphite, which is preferably used for the backing plate  18  and backing ring  22 . Alternatively, the fastener member  38  can be made of a non-metallic material, such as a ceramic, polymer, or composite. 
       FIG. 8  is a bottom view of the upper electrode assembly  10  with the inner electrode member  12  and the outer electrode member  14  removed to show an exemplary concentric arrangement of fastener members  38  installed in the backing plate  18  and backing ring  22 . The upper electrode assembly  10  preferably includes from about 8 to 32 fastener members  38 . Concentrically arranged gas injection holes  48  formed in the backing plate  18  are also shown in  FIG. 8 . The gas injection holes  48  are preferably aligned with gas passages in the inner electrode member  12 . 
       FIG. 10  depicts another preferred embodiment of an upper electrode assembly including an alternative fastening arrangement. A fastener member  128  is received in an aperture  136  in the backing ring  22 , and in an opening  132  in the top plate  24  (the backing plate  18 , inner electrode member  12 , and associated portion of the top plate  24  are not shown for simplicity). The fastener member  128  includes a head  129  and a shaft  130 . The shaft  130  preferably includes external threads  131  at an upper portion  131 . A fastener member  140 , such as a threaded nut, engages the threads  131  to secure the top plate  24  to the backing ring  22  and to the outer electrode member  14 . 
     In the embodiment shown in  FIG. 10 , the fastener member  128  preferably is bonded to a bearing surface  147  of the backing ring  22  with a suitable adhesive, as described above. 
     While the invention has been described in detail with reference to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made, and equivalents employed, without departing from the scope of the appended claims.