Abstract:
An appparatus for confining plasma within a process zone of a substrate processing chamber. In one aspect, an apparatus comprises an annular member having an upper mounting surface, an inner confinement wall, and an outer confinement wall. The apparatus is disposed on or otherwise connected to a gas distribution assembly of the processing chamber to prevent plasma edge effects on the surface of a substrate. The apparatus provides a plasma choke aperture that reduces the volume of the process zone around the periphery of the substrate thereby eliminating uneven deposition of material around the edge of the substrate.

Description:
This application claims priority to Provisional Application No. 60/203,732, filed on May 12, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to semiconductor processing equipment. More specifically, the invention relates to an apparatus and processing chamber for confining plasma gas within a processing zone of a processing chamber. 
     2. Description of the Related Art 
     In the fabrication of integrated circuits (IC) and other electronic devices, multiple layers of conducting, semiconducting, and dielectric materials are deposited on or removed from a surface of a substrate. Integrated circuit devices comprise horizontal and vertical conductive paths. Horizontal conductive paths or interconnects are typically referred to as lines, whereas vertical conductive paths or interconnects are typically referred to as contacts or vias. Contacts extend to a device on an underlying substrate, while vias extend to an underlying metal layer. 
     Thin films of conducting, semiconducting, and dielectric materials may be deposited, formed, or removed by a number of deposition techniques. The common deposition techniques in modern processing are physical vapor deposition (PVD), also known as sputtering, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), and now electroplating. 
     In a chemical vapor deposition (CVD) process, a substrate is exposed to a precursor gas which reacts at the surface of the substrate and deposits a product of the reaction on the substrate to grow a film thereon. This surface reaction can be activated in at least two different ways. In a thermal process, the substrate is heated to a sufficiently high temperature to provide the activation energy necessary to cause the precursor gas adjacent to the substrate to react and deposit a layer on the substrate. In a PECVD process, the precursor gas is subjected to a sufficiently high electromagnetic field that excites the precursor gas into energetic states, such as ions and radicals, which react on the substrate surface to form the desired material. 
     PECVD is one process used in the manufacture of semiconductor devices for depositing silicon carbide (SiC) on various substrates. Silicon carbide is one material useful as a barrier layer, etch stop, and as an anti-reflective coating (ARC), in multiple levels, including the pre-metal dielectric (PMD) level, in IC applications. A PECVD process for depositing SiC involves the introduction of silane gas (SiH 4 ) and methane gas (CH 4 ) into a processing chamber where the gases react and form a film layer of silicon carbide on a substrate positioned in the chamber. Gas distribution assemblies are commonly utilized in PECVD chambers to uniformly distribute gases over the substrate surface upon their introduction into the chamber. Uniform gas distribution is paramount to forming a uniform SiC deposition on the surface of a substrate. 
     FIG. 1 shows a cross-sectional view of a conventional dielectric deposition chamber  30 . The deposition chamber  30  comprises a pedestal  32 , chamber walls  34 , and a gas distribution assembly or showerhead  40 . The showerhead  40  typically presents a planar lower surface which acts as an electrode within the chamber. However, PECVD processes and hardware such as that shown in FIG. 1 have demonstrated problems with deposition uniformity, reproducibility, and reliability in some processes. For example, FIG. 2 shows a typical plasma charge density on a substrate processed using a conventional chamber as shown in FIG.  1 . As shown, the plasma charge density is not uniform across the entire surface of the substrate. Moreoever, the plasma density is greater at the edge of the substrate than the center as indicated by the numerical reference  77 . Typically, deposition uniformity is thicker or greater at the edge of the substrate compared to the center as a result of the increased plasma density around the perimeter of the electrode. Therefore, there exists a need for a cost effective solution to prevent plasma edge effects on deposition processes, thereby vastly improving deposition uniformity, reproducibility, and reliability. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus for confining plasma gas within a processing zone of a substrate processing chamber. In one aspect, an apparatus for confining a plasma within a processing chamber is provided which comprises an upper section having an annular electrode mounting surface, and a lower section integrally formed with the upper mounting section having an inner annular confinement wall and an outer annular confinement wall. The inner annular confinement wall diverges from the vertical at an angle toward the outer annular confinement wall to form a choke aperture. In another aspect, an apparatus is provided comprising an upper section having an annular electrode surface, and a lower section integrally formed with the upper section having an inner confinement wall and an outer confinement wall. In still another aspect, an apparatus for delivering a process gas is provided which comprises a gas distribution assembly having a gas inlet and a gas outlet, and an annular member comprising an upper section having an electrode mounting surface and a lower section integrally formed with the upper section having an inner annular confinement wall and an outer annular confinement wall. 
     In yet another aspect, a processing chamber is provided for confining a plasma within a processing chamber. The processing chamber comprises a chamber body defining a processing cavity, a substrate support member disposed in the processing cavity, a gas distribution assembly having at least one gas inlet and at least one gas outlet, and an annular member having an upper section comprising an upper section having an electrode mounting surface and a lower section integrally formed with the upper section having an inner annular confinement wall and an outer annular confinement wall. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. 
     It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be conconfinementred limiting of its scope, for the invention may admit to other equally effective embodiments. 
     FIG. 1 is a cross-sectional view of a conventional dielectric deposition chamber of the prior art. 
     FIG. 2 is a plasma charge density pattern on a substrate processed using a conventional dielectric deposition chamber as shown in FIG.  1 . 
     FIG. 3 is a cross-sectional view of a CVD D x Z Chamber commercially available from Applied Materials, Inc., of Santa Clara, Calif., having an electrode extension member. 
     FIG. 4 is an exploded cross-sectional view of the gas delivery assembly shown in FIG.  3 . 
     FIG. 5 is a cross-sectional view of a gas delivery system showing an alternative embodiment of an electrode extension member. 
     FIG. 6 is a plasma charge density pattern on a substrate using an annular electrode extension apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention generally relates to an electrode extension member that forms a choke aperture in a plasma zone of a substrate processing chamber. The choke aperture reduces the volume of the plasma zone at the edge of the substrate where greater plasma density is typically formed. The extension member extends at least partially into the periphery of the plasma zone, reducing the volume of the plasma around the edge of the substrate. Further, the electrode extension member provides a downwardly extending portion, which better defines the lateral boundaries of the plasma. Consequently, the electrode extension member confines the plasma away from the grounded confinement wall of the processing chamber to prevent losses to the confinement wall. As a result, a more uniform layer deposition is obtained across the entire surface of the substrate. 
     Many substrate processing chambers are commercially available. For clarity and ease of description however, the following description refers primarily to a processing chamber commercially available from Applied Materials, Inc., of Santa Clara, Calif., known as a CVD D x Z Chamber, and described by Zhao et al. in U.S. Pat. No. 5,558,717, which is incorporated herein by reference. 
     FIG. 3 is a cross-sectional confinement view of a CVD D x Z Chamber. The CVD D x Z chamber  20  comprises a chamber body  22 , typically made of aluminum, which defines an inner vacuum chamber  23  that has a plasma processing region  24 . The chamber  20  includes a pedestal  32  having a supporting surface  34  on which a substrate  36  is supported for chemical vapor deposition of a desired material thereon. Vertically movable lift pins  38  facilitate the delivery of the substrate  36  to and from the supporting surface  34 . The chamber  20  further includes a gas delivery assembly  40  that introduces process gas and purging gas to the chamber  20 , and an RF power supply  50  for creating and sustaining a process gas plasma to effect deposition onto the substrate  36 . 
     The gas delivery assembly  40  is disposed on a base plate  60  at an upper end of the chamber body  22  and includes a gas distribution faceplate  42 , often referred to as a showerhead, an electrode extension member  44 , a blocker plate  45 , and a gas-feed drum  46 . The gas is provided to the gas delivery assembly  40  by a central gas inlet  80  formed in the gas-feed drum  46 . Although not shown, the process gas inlet  80  is coupled to one or more upstream gas sources and/or other gas delivery components, such as gas mixers. The process gas inlet  80  is in fluid communication with a gap  261  defined by a lower face  263  of the gas-feed drum  46  and an upper surface  255  of the showerhead  42 . 
     The blocker plate  45  is located within the gap  261  and is mounted to the gas-feed cover plate  46 . The blocker plate  45  is preferably made of an aluminum alloy and includes passageways or holes  47  formed therein which are adapted to disperse the gases from the gas inlet  80  to the showerhead  42 . 
     The showerhead  42  has a plurality of holes  48  adapted to distribute the gas flow into the process region  24 , and an annular flange  49 , which is an integral component of the showerhead  40 , disposed on an isolation ring  70  to support the gas delivery assembly  40 . The showerhead  42  is substantially disc-shaped and is constructed of a material having a high thermal conductivity and low thermal contact resistance (Rc) such as an aluminum alloy with a highly finished surface. Preferably, a seal  275  is disposed in the annular mounting flange  49  to ensure a fluid-tight contact with the isolation ring  70 . The isolation ring  70  is comprised of a non-conductive material, such as a ceramic or polymer material, and isolates the RF power from the grounded base plate  60 . 
     The gas-feed drum  46  includes an annular mounting flange  273  formed at a perimeter of the gas-feed drum  46 . The annular mounting flange  273  is sized to rest on a perimeter of the showerhead  42 . Preferably, a seal  271  is disposed in the annular mounting flange  273  to ensure a fluid-tight contact with the showerhead  40 . The gas-feed drum plate  46  is preferably made of aluminum or an aluminum alloy. The gas-feed drum  46  may also include a multi-turn, cooling/heating channel (not shown) containing water or other fluid to maintain the gas delivery assembly  40  at a desired temperature. The gas-feed drum  46  is disposed on the showerhead  42  and in thermal communication therewith. The power source  50  supplies power, which may be direct current (DC) or radio frequency (RF), to the showerhead  42  to facilitate the generation of a plasma. 
     The electrode extension member  44  is an annular member or a ring-shaped member. In one embodiment, the electrode extension member  44  is disposed on the periphery of the showerhead  40  as shown in FIG.  3 . Alternatively, the electrode extension member  44  may be shaped to conform to either or both a surface of a substrate or a lower surface of a gas delivery assembly as described below in the discussion of FIG.  5 . 
     In operation, a film, such as a silicon carbide (SiC) film for example, may be deposited on a substrate  36  that is positioned on the pedestal  32  through cooperation of a robot (not shown) and the lift pins  38 . The pedestal  32  raises the substrate  36  into close proximity to the showerhead  42 . A process gas comprising, for example, trimethylsilane and a noble gas, such as helium or argon, is then injected into the chamber  20  through the central gas inlet  80  where the gas flows through the holes  47  of the blocker plate  45 , and to the back of the showerhead  42 . The process gas passes through the holes  48  of the showerhead  42  into the processing region  24  and towards the substrate  36 , as indicated by the arrows. Upon reaching the substrate  36 , the process gases react on the upper surface thereof. Subsequently, the process gas byproducts flow radially outwardly across the edge of the substrate  36 , into a pumping channel  23 , and are exhausted from the chamber  20  by a vacuum system (not shown). During the deposition of the SiC film, the chamber pressure is between about 3 to 10 Torr, more preferably about 6 to 10 Torr. A single 13.56 MHz RF power source applies about 300 to 700 watts with a power density of about 4.3 to 10 watts/cm 2 , more preferably about 400 to 600 watts with a power density of about 5.7 to 8.6 watts/cm 2 , to the anode and cathode to form the plasma in the chamber with the silicon based gas. The RF power source may be a mixed-frequency RF power supply that typically supplies power at a higher RF frequency of 13.56 MHz and at a lower RF frequency of 360 kHz to enhance decomposition of the reactive species introduced into the chamber. The substrate surface temperature is between about 200° to 400° C., more preferably about 300° to 400° C. 
     In addition to SiC deposition, it is believed that the deposition hardware described herein may be used with any deposition material such as other dielectric anti-reflective coating (DARC) materials, oxides (Si X O Y ), carbon-doped silicon oxide (Si X O Y :C), carbon-doped silicon nitride (Si x n y :C), or low dielectric materials, for example. 
     FIG. 4 is an exploded cross-sectional view of the gas delivery assembly  40  as shown in FIG.  3 . The gas delivery assembly  40  includes a showerhead  42  having an electrode extension member  280  disposed on the periphery thereof. The electrode extension member  280  includes an upper section  282  integrally formed with a lower section  284 . The upper section  282  has an upper mounting surface  283 , an inner wall  288  and an outer wall  286 . The lower section  284  comprises an inner confinement wall  289 , and an outer confinement wall  287 . The diameter of the outer confinement wall  287  is the same or substantially the same as the diameter of the outer wall  286  of the upper section  282 . The diameter of the inner confinement wall  289  is the same or substantially the same as the diameter of the inner wall  288  of the upper section  282  and diverges from the vertical toward the dimension of the outer confinement wall  287  of the lower section  282 . The inner confinement wall  289  diverges at an angle from about 30 degrees to about 70 degrees. Preferably, the inner confinement wall  289  diverges at an angle of about 45 degrees. 
     The inner confinement wall  288  of the upper section  282  is coupled to the periphery of the showerhead  42  by fasteners  298 ,  299 , which are preferably bolts, to ensure good electrical communication therewith. The upper section  282  has a substantially planar upper mounting surface  283  that conforms to the lower face  256  of the isolation ring  70 . In mating abutment, the upper mounting surface  283  and lower face  256  define an interface that is parallel to the radial axis  291  of the gas delivery assembly  40 . 
     FIG. 5 is an exploded cross-sectional view showing an alternative embodiment of an electrode extension member  380 . The electrode extension member  380  is preferably used with processing chambers having limited lateral expansion capability. The electrode extension member  380  includes an upper mounting surface  386 , an inner confinement wall  384 , and an outer confinement wall  382 . The diameter of the outer confinement wall  382  is the same or substantially the same as a diameter of a showerhead  42 . The diameter of the inner confinement wall  384  is the same or substantially the same as a diameter of a substrate (not shown), and diverges from the vertical toward the outer confinement wall  382 . The inner confinement wall  384  diverges toward the outer confinement wall  382  at an angle from about 30 degrees to about 70 degrees. Preferably, the inner confinement wall  384  diverges at an angle of about 45 degrees toward the outer confinement wall  382 . 
     The electrode extension member  380  is disposed on a lower face  354  of the showerhead  42 . The substantially planar upper mounting surface  386  of the electrode extension member  380  is coupled to the lower face  354  of the showerhead  42  by bolts or a similar fastener (not shown) to ensure good electrical communication therewith. In mating abutment, the upper mounting surface  386  and the lower face  354  define an interface which is parallel to the radial axis  391  of the gas delivery assembly  349 . 
     The electrode extension members  280  and  380  are constructed of a material having a high thermal conductivity and low thermal contact resistance (Rc) such as an aluminum alloy with a highly finished surface. The electrode extension members  280  and  380  are typically constructed of the same material as the showerhead  42  disposed thereto. Alternatively, in a further embodiment, the showerhead  42  may be milled from a single piece of aluminum or other suitable material to include the downward extension portion of the electrode extension member  280  and  380  as described herein. 
     The gas delivery assembly  40  as shown in FIGS. 3,  4 , and  5  are described as being an annular member or a ring-shaped member. However, the invention is not limited to a particular shape. Other geometric configurations such annular parallelograms and other shapes are contemplated. 
     The invention will be further described in the following non-limiting example. 
     EXAMPLE 1 
     A substrate was processed using the processing chamber shown in FIG. 3. A film of silicon carbide having a mean thickness of 923 angstroms was deposited on a silicon substrate. The deposition uniformity was measured by a UV-145SE® Thin Film Measurement System. The deposition thickness had a measured standard deviation of 1.6 percent across the surface of the substrate. As can be seen from FIG. 6, the substrate did not exhibit the doughnut shaped configuration and deposition was uniform across the surface of the substrate. 
     Comparison Example 
     A deposition process was carried out using a conventional chamber as shown in FIG. 1. A film of silicon carbide having a mean thickness of 977 angstroms was deposited on a silicon substrate. As shown in FIG. 2, the doughnut shaped configuration was present across the surface of the substrate as represented by numerical indication  77 . The deposition uniformity was measured by the same UV-145SE® Thin Film Measurement System. The deposition thickness had a measured standard deviation of 3.8 percent. 
     While foregoing is directed to the preferred embodiment 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.