Abstract:
Embodiments of the invention generally relate to a grounding kit for a semiconductor processing chamber, and a semiconductor processing chamber having a grounding kit. More specifically, embodiments described herein relate to a grounding kit which creates an asymmetric grounding path selected to significantly reduce the asymmetries caused by an off center RF power delivery.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims benefit of U.S. Provisional Application Ser. No. 61/441,186, filed Feb. 9, 2011 (Attorney Docket No. APPM/15759L), which is incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Embodiments of the invention generally relate to a grounding kit for a semiconductor processing chamber, and a semiconductor processing chamber having a grounding kit. More specifically, embodiments of the invention relate to a grounding kit capable of producing a uniform plasma in a physical vapor deposition chamber having asymmetrical RF power delivery. 
         [0004]    2. Description of the Related Art 
         [0005]    Physical vapor deposition (PVD), or sputtering, is one of the most commonly used processes in the fabrication of electronic devices. PVD is a plasma process performed in a vacuum chamber where a negatively biased target is exposed to a plasma of an inert gas having relatively heavy atoms (e.g., argon (Ar)) or a gas mixture comprising such inert gas. Bombardment of the target by ions of the inert gas results in ejection of atoms of the target material. The ejected atoms accumulate as a deposited film on a substrate placed on a substrate support pedestal disposed within the chamber. The support pedestal usually includes an electrostatic chuck (ESC) to support and retain substrates within the processing chamber during processing. 
         [0006]    A grounding kit may be disposed in the chamber to create a return path for the RF power, which is used to create the plasma, to travel back to the RF power source. Due to process chamber complexity and size constraints, not all of the chamber components can be coaxially aligned with the substrate support pedestal. This offset of components can cause uniformity issues in the plasma created within the chamber. For instance, it has been found by the inventors that using a conventional grounding kit in a chamber having an offset RF power delivery site can cause the RF power to be distributed asymmetrically, especially at RF power frequencies greater than 13.56 MHz. Thus, the plasma created is distributed asymmetrically across the substrate being processed which can cause the substrate to be processed unevenly. 
         [0007]    Although conventional grounding kit designs have a robust processing history at 13.56 MHz of RF power, processes performed using conventional kits at higher frequencies exhibit asymmetries beyond desirable limits. Therefore, there is a need in the art for an improved grounding kit. 
       SUMMARY OF THE INVENTION 
       [0008]    Embodiments of the invention generally provide a grounding kit for use in a physical vapor deposition (PVD) chamber and a PVD chamber having a grounding kit. 
         [0009]    In one embodiment, a grounding kit is provided for use in a substrate processing chamber. The substrate processing chamber has a target disposed thereon and an RF power source operable to provide RF power at frequencies greater than 13.56 MHz to the target in a manner that produces an RF power delivery asymmetry. The processing chamber also includes a substrate support electrically coupled thereto and a shield surrounding the target and the substrate support. The shield is selectively electrically coupled to the substrate support when the substrate support is in an elevated position. The grounding kit has a plurality of conductors electrically coupling the shield to the substrate support and selectively positioned to compensate for the power delivery asymmetry by providing an asymmetrical grounding path between the shield and the substrate support. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of 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 considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0011]      FIG. 1  is a simplified cross-sectional view of a semiconductor processing system having one embodiment of a grounding kit. 
           [0012]      FIG. 2  is a simplified cross-sectional view of the semiconductor processing system of  FIG. 1  during processing of a substrate. 
           [0013]      FIGS. 3-5  are illustrative plasma distributions under different RF circuit conditions. 
           [0014]      FIG. 6A  is an overhead view of one embodiment of a grounding kit. 
           [0015]      FIG. 6B  is an overhead view of one embodiment of a grounding kit. 
           [0016]      FIG. 7  is a sectional view of one embodiment of a ground path contact. 
           [0017]      FIG. 8  is a partial sectional view of one embodiment of a contact ring assembly. 
       
    
    
       [0018]    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 disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
       DETAILED DESCRIPTION 
       [0019]    Embodiments of the invention generally provide a process kit for use in a physical deposition (PVD) chamber. In one embodiment, the process kit has reduced effects on the electric fields within the process cavity, which promotes greater process uniformity and repeatability. 
         [0020]      FIG. 1  depicts an exemplary semiconductor processing chamber  100  having one embodiment of a grounding kit  150 . In the embodiment shown, the processing chamber  100  comprises a sputtering chamber, also called a physical vapor deposition (PVD) chamber, capable of depositing metal or ceramic materials, such as for example, Si, SiN, Er, Yb, Y, Hf, HfO, Ru, Co, AlN, Ti, TiAl, TiN, AlO, Al, Cu, Ta, TaN, TaC, W, WN, La, LaO, Ni, a nickel alloy, such as NiPt, NiTi, or NiYb, among others. One example of a processing chamber that may be adapted to benefit from the invention is the ALPS® Plus and SIP ENCORE® PVD processing chambers, available from Applied Materials, Inc. of Santa Clara, Calif. It is contemplated that other processing chambers including those from other manufacturers may be adapted to benefit from the invention. 
         [0021]    The processing chamber  100  includes a chamber body  101  having upper adapters  102  and sidewall adapters  104 , a chamber bottom  106 , and a lid assembly  108  that enclose an interior volume  110  or plasma zone. The chamber body  101  is typically fabricated by machining and welding plates of stainless steel or by machining a single mass of aluminum. In one embodiment, the sidewall adapters  104  comprise aluminum and the chamber bottom  106  comprises stainless steel. The chamber bottom  106  generally contains a slit valve (not shown) to provide for entry and egress of a substrate  105  from the processing chamber  100 . 
         [0022]    The lid assembly  108  generally includes a target backing plate  130 , a target  132 , and a magnetron  134 . The target backing plate  130  is supported by the upper adapters  102  when in a closed position. A ceramic ring seal  136  is disposed between the target backing plate  130  and upper adapters  102  to prevent vacuum leakage therebetween. 
         [0023]    The target  132  is coupled to the target backing plate  130  and exposed to the interior volume  110  of the processing chamber  100 . The target  132  provides material which is deposited on the substrate  105  during a PVD process. The target  132  may contain Si, SiN, Er, Yb, Y, Hf, HfO, Ru, Co, AlN, Ti, TiAl, TiN, AlO, Al, Cu, Ta, TaN, TaC, W, WN, La, LaO, Ni, a nickel alloy, such as NiPt, NiTi, or NiYb, or other suitable material. An isolator ring  198  is disposed between the target  132 , target backing plate  130 , and chamber body  101  to electrically isolate the target  132  from the target backing plate  130  and the upper adapter  102  of the chamber body  101 . 
         [0024]    A RF power source  140  and a DC power source  147  are coupled to the target  132  to provide a RF and/or DC bias thereto to drive the plasma process. The RF power source  140  is coupled by an RF feed terminal  143  to the target  132 . The RF feed terminal  143  is offset from a centerline  141  of the target  132 . The centerline  141  of the target  132  is also the centerline of the chamber  100 . The target  132  may be biased relative to ground, e.g., the chamber body  101 . The RF power source  140  and DC power source  147  may be positioned adjacent the chamber  100  and may be connected to the target  132  at off center locations in consideration for other chamber components which need to be centrally located. In one embodiment, the RF power source  140  provides power to the target  132  at a frequency greater than 13.56 MHz of power, for example at about 27.12 MHz or greater. 
         [0025]    A gas, such as argon, is supplied to the interior volume  110  from a gas source  142  via conduits  144 . The gas source  142  may comprise a non-reactive gas such as argon or xenon, which is capable of energetically impinging upon and sputtering material from the target  132 . The gas source  142  may also include a reactive gas, such as one or more of an oxygen-containing gas, a nitrogen-containing gas, a methane-containing gas, that are capable of reacting with the sputtering material to form a layer on a substrate. 
         [0026]    Spent process gas and byproducts are exhausted from the chamber  100  through exhaust ports  146  that receive spent process gas and direct the spent process gas to an exhaust conduit  148  having a throttle valve to control the pressure of the gas in the chamber  100 . The exhaust conduit  148  is connected to one or more exhaust pumps  149 . Typically, the pressure of the sputtering gas in the chamber  100  is set to sub-atmospheric levels, such as a vacuum environment, for example, gas pressures of 0.6 mTorr to 400 mTorr. 
         [0027]    A plasma is formed from the gas between the substrate  105  and the target  132 , as seen in  FIG. 2 . Ions within the plasma are accelerated toward the target  132  and cause material to become dislodged from the target  132 . The dislodged target material is deposited on the substrate  105 . A match circuit  145  may be incorporated to compensate for fluctuations in the plasma during processing of the substrate  105 . 
         [0028]    The magnetron  134  is coupled to the target backing plate  130  on the exterior of the processing chamber  100 . One magnetron which may be utilized is described in U.S. Pat. No. 5,953,827, issued Sep. 21, 1999 to Or et al., which is hereby incorporated by reference in its entirety. 
         [0029]    A pedestal assembly  120  is supported by and electrically coupled to the chamber bottom  106 . The pedestal assembly  120  supports the substrate  105  and the deposition ring  180  during processing. The pedestal assembly  120  is coupled to the chamber bottom  106  of the chamber  100  by a lift mechanism  122  that is configured to move the pedestal assembly  120  between a lower position as illustrated in  FIG. 1  and an elevated position for processing as illustrated in  FIG. 2 . Additionally, in the lower position, lift pins (not shown) are moved through the pedestal assembly  120  to space the substrate from the pedestal assembly  120  to facilitate exchange of the substrate with a wafer transfer mechanism disposed exterior to the processing chamber  100 , such as a single blade robot (not shown). A bellows  124  is typically disposed between the pedestal assembly  120  and the chamber bottom  106  to isolate the interior volume  110  of the chamber body  101  from the interior of the pedestal assembly  120  and the exterior of the chamber. The bellows is conductive to provide an electrical connection between the pedestal assembly  120  and the chamber body  101 . 
         [0030]    The pedestal assembly  120  generally includes a substrate support  126  sealingly coupled to a base plate  128  which is coupled to a ground plate  125 . The substrate support  126  may be comprised of aluminum or ceramic. The substrate support  126  may be an electrostatic chuck, a ceramic body, a heater or a combination thereof. In one embodiment, the substrate support  126  is an electrostatic chuck that includes a dielectric body having electrodes  138  embedded therein. The ground plate  125  is typically fabricated from a metallic material such as stainless steel or aluminum. The base plate  128  may be coupled to the ground plate by a plurality of connectors  137 . The connectors  137  may be one of a bolt, screw, rivet, weld or other suitable connector. The base plate  128  may be removable from the ground plate  125  for facilitating easier replacement and maintenance of the substrate support  126  and base plate  128 . The substrate support  126  has a substrate receiving surface  127  that receives and supports the substrate  105  during processing, the surface  127  having a plane substantially parallel to a sputtering surface  133  of the target  132 . 
         [0031]    A ground shield  160 , a cover ring  170 , and a deposition ring  180  are used to confine a plasma  201  formed in the interior volume  110  to a region above the substrate  105 , as seen in  FIG. 2 . The cover ring  170  interleaves with the ground shield  160  and cooperates with the deposition ring  180  to create pathways which prevent the plasma from leaving the interior volume  110 . 
         [0032]    The ground shield  160  is supported by the chamber body  101  and encircles the sputtering surface  133  of the sputtering target  132  that faces the substrate support  126 . The shield  160  also surrounds the substrate support  126 . The shield  160  covers and shadows the sidewall adapters  104  of the chamber  100  to reduce deposition of sputtering deposits originating from the sputtering surface  133  of the sputtering target  132  onto the components and surfaces behind the shield  160 . For example, the shield  160  can protect the surfaces of the substrate support  126 , the overhanging edge of the substrate  105 , sidewall adapters  104  and chamber bottom  106  of the chamber  100 . 
         [0033]    The grounding kit  150  is used to provide a ground path for the RF and/or DC power delivered to the processing chamber  100 . The grounding kit  150  includes at least a ground plate  152  and one or more ground path contacts  154 . The ground plate  152  may be made of a highly conductive material, such as, for example, stainless steel. The ground plate  152  may be coupled to the ground plate  125  of the pedestal assembly  120  by a mounting ring  158 . The mounting ring  158  may have a plurality of mounting holes  159  to allow connectors  156  to pass therethrough and couple to the ground plate  152  of the pedestal assembly  120 . The connectors  156  may be one of a bolt, screw, rivet, weld or other suitable connector. The mounting ring  158  may be may be made of a highly conductive material, such as, for example, stainless steel, and in one embodiment, is formed with the ground plate  152  as a unitary body. 
         [0034]    The ground path contacts  154  are adapted to contact a lower portion of the ground shield  160  thereby forming the ground path coupling the shield  160  to the pedestal assembly  120 . The ground path contacts  154  may be made of a highly resilient and conductive material, such as, for example, beryllium copper or stainless steel. The ground path contacts  154  may have a spring form and may be adapted to compress when placed in contact with the ground shield  160  to ensure good electrical contact between the ground shield  160  and the pedestal assembly  120 . 
         [0035]    Processes performed in the chamber  100  are controlled by a controller  190  that comprises program code having instruction sets to operate components of the chamber  100  to facilitate processing of substrates in the chamber  100 . For example, the controller  190  can comprise program code that includes a substrate positioning instruction set to operate the pedestal assembly  120 ; a gas flow control instruction set to operate gas flow control valves to set a flow of sputtering gas to the chamber  100 ; a gas pressure control instruction set to operate a throttle valve to maintain a pressure in the chamber  100 ; a temperature control instruction set to control a temperature control system (not shown) in the pedestal assembly  120  or sidewall adapter  104  to set temperatures of the substrate or sidewall adapters  104 , respectively; and a process monitoring instruction set to monitor the process in the chamber  100 . 
         [0036]    Referring now to  FIG. 2 , in operation, RF power at a frequency greater than 13.56 MHz, for example at about 27.12 MHz or greater, is delivered from the RF power source  140  through the match circuit  145  to the sputtering target  132 . The RF power is coupled to the gases within the interior volume  110  to form the plasma  201  therein. The RF current is coupled from the plasma  201  to the ground shield  160 , and travels along a first ground path GP 1  and a second ground path GP 2  back to the match circuit  145 . The grounding kit  150  is part of the first ground path GP 1 . The first and second ground paths GP 1 , GP 2  work in concert to maintain the plasma  201  at a substantially central location between the sputtering target  132  and substrate  105  within the interior volume  110 . 
         [0037]    Referring now to  FIGS. 3-5 ,  FIG. 3  is an illustrative distribution of plasma  302 , shown above the substrate  105 , formed using an off center RF power delivery and a symmetric ground return path. The off center RF power delivery may provide power to the interior volume  110  of the chamber  100  asymmetrically at RF frequencies above 13.56 MHz, for example about 27.12 MHz or greater, thereby causing an asymmetric distribution of plasma  302  above the substrate  105 . It has been found by the inventors that the use of an asymmetric ground path can be used to compensate for the off-set distribution of the plasma  302 . 
         [0038]      FIG. 4  is an illustrative distribution of plasma  402  formed using a centered RF power delivery and an asymmetric ground path created by a non-symmetrical azimuthal distribution of contacts  154  relative to the centerline of the chamber body  101  and ground shield  160 . Even though the RF power is delivered symmetrically above the center of the substrate  105 , the asymmetric ground path causes the plasma to distribute asymmetrically around the substrate  105 , with a larger distribution near the portion of the ground path that has more contact area (i.e., more current carrying capacity) resulting from a greater number of contacts  154  in that region. The portion of the ground path having more current carrying capacity can be tuned by repositioning the contact  154  such that the asymmetry caused by an off center RF power delivery is substantially canceled out by the asymmetry caused by the ground path. For example, the distribution of the plasma  402  shown in  FIG. 4 , which is created by the asymmetric ground path, is tuned to be a mirror image of the distribution of the plasma  302  shown in  FIG. 3 . 
         [0039]    Combining the off center RF power delivery with the tuned asymmetric ground path causes the plasma to become evenly distributed across the substrate  105 , as shown in  FIG. 5 . For example, the plasma distribution may be azimuthally symmetrical to within 5 percent using an asymmetric grounding kit tuned for an offset delivery of power at a frequency of about 27.12 MHz of power delivery to the target  132 . 
         [0040]    The portion of the ground path with the most current carrying capacity is located opposite from the RF power delivery site across the center of the substrate. The ground path can be tuned by adjusting the specific amount of contact are to accurately compensate for the specific RF power delivery asymmetry using the position of the contacts  154 , i.e., having more contacts  154  in one region or side of the substrate  105  or shield  160  relative the other. Determining the amount of contact area (i.e., contacts  154 ) needed in one region relative another can be done through computer modeling, empirical data, and trial and error, among other methods. 
         [0041]      FIG. 6A  is an overhead view of one embodiment of the grounding kit  150  which may be used to provide a tuned asymmetric grounding path to compensate for an off center RF power delivery. The grounding kit  150  has a plurality of ground path contacts  154  distributed asymmetrically along the perimeter of the ground plate  152 . As discussed above, the ground path contacts  154  are located radially outward of the outermost diameter of the pedestal assembly  120  to provide sufficient clearance to allow the contacts  154  to interface with the ground shield  160 . The ground plate  152  shown in  FIG. 6A  is configured to only partially surround the pedestal assembly  120  to allow space for other components of the processing chamber  100 . However, the ground plate  152  may be configured to completely surround the pedestal assembly  120  if desired, as shown in  FIG. 6B . 
         [0042]    The ground plate  152  also has a plurality of holes  153  formed therethrough to facilitate fastening of the ground path contacts  154  to the ground plate  152 . The holes  153  may be distributed in around the ground plate  152  to define mounting positions that allow the ground path contacts  154  to be selectively positioned around the pedestal assembly  120  to tune out the azimuthal asymmetry created by the offset RF power delivery or other condition. Depending on the number of holes  153  utilized to define a contact mounting position for coupling a single contact  154  to the ground plate  152 , the ground plate  152  has at least N+1 contact mounting positions for number of contacts  154 . In one embodiment, the holes  153  are located radially outward of the outermost diameter of the pedestal assembly  120  to provide sufficient clearance for the ground path contacts  154  to clear the pedestal assembly  120  to interface with the ground shield  160 . The greater number of holes  153  allows the ground path contacts  154  to be repositionable on the ground plate  152  to allow the azuthmal symmetry of the ground path between the pedestal assembly  120  and shield  160  to be changed to match changes in the plasma symmetry do to the addition/replacement of chamber components and/or processing conditions. 
         [0043]      FIG. 7  is a sectional view of one embodiment of a ground path contact  154  coupled to the ground plate  152 . The ground path contact  154  is coupled to the ground plate  152  by one or more fasteners  702 , for example two fasteners  702 . The fasteners  702  may be one of a bolt, screw, rivet, weld or other suitable connector. In one embodiment, the fasteners  702  are bolts and pass through a first fastening plate  704  and threadingly engage with a second fastening plate  706 . The fastening plates  704 ,  706  are positioned to clamp the ground path contact  154  and ground plate  152  together when the fasteners  702  are tightened. A contact point  708  may be adapted to contact the ground shield  160 . The ground path contact  154  is adapted to compress when the pedestal assembly  120  is raised into the upper position for processing the substrate  105 . The compressed ground path contact  154  generates a spring force that ensures good electrical contact between the ground path contact  154  and the ground shield  160 . The height and/or width of the ground path contact  154  may be adjusted to tune the amount of contact between the ground path contact  154  and the ground shield  160 . The ground path contact  154  may also be lengthened or shortened to further tune the amount of contact between the ground path contact and the ground shield  160 . 
         [0044]      FIG. 8  illustrates a partial sectional view of one embodiment of a contact ring assembly  850 . The contact ring assembly  850  is coupled to a substrate support assembly  820  disposed in a processing chamber  800 . The substrate support assembly  820  is sealed to the chamber  800  by a bellows  824 . The contact ring assembly  850  generally consists of a ring  852  mounted to the substrate support assembly  820  by a plurality of fasteners  856  disposed through mounting holes  859  of the ring  852  and threadingly engaged with threaded holes  827  of the substrate support assembly  820 . The ring  852  comprises an attachment flange  858 , an inner connecting wall  851 , an upper ground plane member  853 , an outer connecting wall  855 , and a lower ground plane member  857 . The upper ground plane member  853  and inner connecting wall  851  may be in close proximity with the substrate support assembly  820  to minimize arcing therebetween. Supported on the lower ground plane member  857  are a number of spring contacts  854  adapted to contact a ground shield  860  thereby creating a ground path for energy provided to the chamber  800  to be returned to the energy source. The spring contacts  854  may be positioned on the lower ground plane member  857  as described above to create an asymmetric ground path that may compensate for asymmetric RF power application. The spring contacts  854  may be made of a highly resilient and conductive material, such as, for example, beryllium copper or stainless steel. The spring contacts  854  may have a spring form and may be adapted to compress when placed in contact with the a bottom wall  810  of the ground shield  860  to ensure good electrical contact between the ground shield  860  and the substrate support assembly  820 . 
         [0045]    The ground shield may be supported on an upper adapter  802  of the chamber  800  by a mounting flange  838 . The ground shield  860  generally consists of the mounting flange  838 , an outer vertical wall  839 , a step  840 , a middle vertical wall  841 , the bottom wall  810 , and an inner vertical wall  842 . The middle vertical wall  841  may have a plurality of apertures  843  formed therethrough. The apertures  843  accommodate high gas flow and do not allow plasma to flow therethrough. 
         [0046]    Thus, a grounding kit has been provided that removes the asymmetries in a plasma caused by an off center RF power source. 
         [0047]    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.