Patent Publication Number: US-2017365449-A1

Title: Rf return strap shielding cover

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Application Ser. No. 62/352,871, filed Jun. 21, 2016, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Field 
     Embodiments described herein generally relate to a substrate support assembly, and more specifically, to a substrate support assembly having at least one shield cover configured to prevent plasma arcing. 
     Description of the Related Art 
     Flat panel displays (FPD) are commonly used for active matrix displays such as computer and television monitors, personal digital assistants (PDAs), and cell phones, as well as solar cells and the like. Plasma enhanced chemical vapor deposition (PECVD) may be employed in flat panel display fabrication to deposit thin film on a substrate supported within a vacuum processing chamber on a substrate support assembly. PECVD is generally accomplished by energizing a precursor gas into a plasma within the vacuum processing chamber, and depositing a film on the substrate from the energized precursor gas. 
     When the precursor gas in energized, an RF current return path is formed in the processing chamber. The RF current travels from the showerhead, through the substrate support assembly, down the RF current return straps to the chamber bottom, and back up to the chamber lid along the sidewalls of the processing chamber. As processing chambers increase in size, the path length of the RF current return path increases. The long length of the RF current return path results in a large voltage drop between the substrate support assembly and the sidewalls of the processing chamber. The large voltage drop may undesirably induce arching between the sidewall and the substrate support assembly. 
     Moreover, since the RF current return straps have generally looped shape, the RF current running through the strap can under certain conditions energize gases present below the substrate support assembly through inductive coupling to form a parasitic plasma. The parasitic plasma may promote unwanted deposition below the substrate support assembly which may later become a source of contamination and undesirably decrease the time between chamber cleans, and may also attack chamber components through plasma induced erosion and electrical arcing, thereby reducing their service life. 
     Thus, there is a need for an improved substrate support assembly. 
     SUMMARY 
     Embodiments described herein generally relate to a substrate support assembly having a shield cover. In one embodiment, a substrate support assembly includes a support plate, a plurality of RF return straps, at least one shield cover, and a stem. The support plate is configured to support a substrate and is coupled to the stem. The plurality of RF return straps are coupled to the support plate and extend below a bottom surface of the support plate. At least one shield cover is coupled to the support plate and covers at least a portion of a side of at least one of the plurality of RF return straps closest a perimeter of the support plate. 
     In another embodiment, a processing chamber is disclosed herein. The processing chamber includes a chamber body and a substrate support assembly. The chamber body includes a lid, a sidewall, and a bottom defining a processing region in the chamber body. The substrate support assembly is disposed on the processing region. The substrate support assembly includes a support plate, a plurality of RF return straps, at least one shield cover, and a stem. The support plate coupled to the support plate and is configured to support a substrate. The plurality of RF return straps are coupled to between the support plate and the bottom of the chamber body. At least one shield cover is coupled to the support plate. The least one shield cover is deposed between at least one of the plurality of RF return straps and the sidewall of the chamber body. 
     In another embodiment, a method of processing a substrate is disclosed herein. The method includes placing a substrate on a substrate support assembly disposed in a processing chamber. Generating a plasma within the processing chamber, wherein RF current utilized to generate the plasma travels through an RF return strap coupling the substrate support assembly and a body of the processing chamber. The substrate support assembly having a shield cover disposed between chamber body and a portion of the RF return strap. The method further includes depositing a layer of material on the substrate disposed on the substrate support assembly while the substrate is exposed to the plasma. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, 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 disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. 
         FIG. 1  illustrates a cross-sectional view of a processing chamber, according to one embodiment. 
         FIG. 2  illustrates a bottom view of the substrate support assembly of  FIG. 1 , according to one embodiment. 
         FIG. 3  is partial cross-sectional view of the processing chamber with the shield cover illustrated in phantom to reveal an RF current return strap, according to one embodiment. 
         FIG. 4  is a partial cross-sectional side view of the processing chamber illustrating gas flow around the shield cover illustrated in  FIG. 3 , according to one embodiment. 
     
    
    
     For clarity, identical reference numerals have been used, where applicable, to designate identical elements that are common between figures. Additionally, elements of one embodiment may be advantageously adapted for utilization in other embodiments described herein. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a cross-sectional view of a processing chamber  100  having a substrate support assembly  118  with a shield cover  150 , according to one embodiment. The shield cover  150  is utilized to reduce the probability of arcing within the processing chamber, and inhibit plasma formation below the substrate support assembly  118  within the processing chamber  100 . 
     The processing chamber  100  includes a chamber body  102  having sidewalls  104 , a bottom  106 , and a showerhead  108  that define a processing volume  110 . The processing volume  110  is accessed through a slit valve opening  109  formed through the sidewalls  104  to allow entry and egress of a substrate  101  that is processed within the processing volume  110  while disposed on the substrate support assembly  118 . 
     The showerhead  108  is coupled to a backing plate  112 . For example, the showerhead  108  may be coupled to the backing plate  112  by a suspension  114  at the periphery of the backing plate  112 . One or more coupling supports  116  may be used to couple the showerhead  108  to the backing plate  112  to aid in controlling sag of the showerhead  108 . 
     The substrate support assembly  118  is disposed in the processing volume  110  of the processing chamber  100 . The substrate support assembly  118  includes a support plate  120  and a stem  122 . The stem  122  is coupled to a bottom surface  190  of the support plate  120 . An upper surface  192  of the support plate  120  is configured to support the substrate  101  during processing. The support plate  120  includes temperature control elements  124 . The temperature control elements  124  are configured to maintain the substrate support assembly  118  at a desired temperature. 
     A lift system  126  may be coupled to the stem  122  to raise and lower the support plate  120 . Lift pins  128  are moveably disposed through the support plate  120  to space the substrate  101  from the support plate  120  to facilitate robotic transfer of the substrate  101  though the slit valve opening  109 . 
     The substrate support assembly  118  also includes at least one RF return strap  130 . The RF return straps  130  are coupled between the support plate  120  and the chamber body  102 . For example, one end of the RF return straps  130  may be coupled to the bottom surface  190  of the support plate  120  while the opposite end of the RF return straps  130  may be coupled to the bottom  106  of the chamber body  102 . In one embodiment, the RF return straps  130  have a substantially vertical orientation. The RF return straps  130  provide an RF current path from the periphery of the substrate support assembly  118  to the bottom  106  of the chamber body  102 . 
     The shield cover  150  is fabricated from a dielectric material. For example, the shield cover  150  may formed from ceramic or other suitable plasma resistant dielectric material. The shield cover  150  is coupled to the support plate  120  and covers at least a portion of at least one of the RF return straps  130  that is coupled to the support plate  120 . The shield cover  150  covers at least a portion of an upper end  180  (shown in phantom in  FIG. 1 ) of the RF return strap  130  that is attached to a perimeter  182  of the support plate  120 . Thus, the position of the shield cover  150  disposed between the RF return strap  130  and the sidewall of the chamber body  102  substantially prevents arcing of the substrate support assembly and RF return strap  130  with the sidewalls of the chamber body  102 . 
     In one example, the RF return strap  130  is coupled to the bottom surface  190  or perimeter  182  of the support plate  120 . In another example, a plurality of shield covers  150  may be coupled to the support plate  120 . For example, the plurality of shield covers  150  may be spaced about an outer edge of the bottom surface  190  (i.e., around the perimeter  182  of the support plate  120 . In another embodiment, the plurality of shield covers  150  may be continuous about the outer edge of the bottom surface  190 . The shield cover  150  may be positioned on the bottom surface  190  of the support plate  120  in a substantially horizontal orientation and extend below the bottom surface  190  of the support plate  120  to cover the upper end  180  of the RF return strap  130  that faces the sidewall of the chamber body  102 . The shield cover  150  has a length, L, that the shield cover  150  extends below the support plate  120  that is short enough to accommodate the movement of the support plate  120  by the lift system  126  to a position that enable substrate transfer through the slit valve opening  109  without the shield cover  150  contacting the bottom  106  of the processing chamber  100 . In yet another embodiment, the shield cover  150  may be coupled to a side of the support plate  120 . 
     In one example, the shield cover  150  is in the form of a substantially flat plate. The shield cover  150 , when fixed to the support plate  120 , has a substantially vertical orientation that is parallel to the edge of the support plate  120  to which the shield cover  150  is attached. The shield cover  150  is to the support plate  120  in a manner that allows the shield cover  150  to extend below the bottom surface  190  of the support plate  120 , thereby shielding the upper end  180  of the RF return strap  130 . 
     Continuing to refer to the other components of the processing chamber  100 , a gas source  132  may be coupled to the backing plate  112  to provide processing gas through a gas outlet  134  in the backing plate  112 . The processing gas flows from the gas outlet  134  through gas passages  136  in the showerhead  108 . A vacuum pump  111  may be coupled to the processing chamber  100  to control the pressure within the processing volume  110 . 
     An RF power source  138  may be coupled to the backing plate  112  and/or to the showerhead  108  to provide RF power to the showerhead  108 . The RF power creates an electric field between the showerhead  108  and the substrate support assembly  118  so that a plasma may be generated from the gases between the showerhead  108  and the substrate support assembly  118 . 
     A remote plasma source  140 , such as an inductively coupled remote plasma source, may also be coupled between the gas source  132  and the backing plate  112 . Between processing substrates, a cleaning gas may be provided to the remote plasma source  140  so that a remote plasma is generated and provided into the processing volume  110  to clean chamber components. The cleaning gas may be further excited while in the processing volume  110  by power applied to the showerhead  108  from the RF power source  138 . Suitable cleaning gases include but are not limited to NF 3 , F 2 , and SF 6 . 
     The RF power from the RF power source  138  provided to the showerhead  108  and transferred across the plasma to the substrate support assembly  118 , follows an RF return path from the substrate support assembly  118 , to the bottom  106  of the processing chamber  100  through the RF return straps  130 , and back up to the RF power source  138  via the sidewalls  104 . Because the path of the RF return path is large, there is a large drop in voltage between the perimeter  182  of the support plate  120  (and RF return straps  130 ) and the sidewalls  104  of the chamber body  102 . Under certain conditions, arcing may occur between the perimeter  182  of the support plate  120  (and RF return straps  130 ) and the sidewalls  104  of the chamber body  102  in processing chambers in which the shield cover  150  is not present. The dielectric insulation provided by the shield cover  150  between the perimeter  182  of the support plate  120  (and RF return straps  130 ) and the sidewalls  104  of the chamber body  102  substantially prevents arcing even though these components may have a high voltage drop along the RF return path. Additionally, the shield cover  150  inhibits gas flow directly between the upper end  180  of the shielded RF return straps  130  the perimeter  182  of the support plate  120  proximate the RF return straps  130 . The inhibited gas flow further reduces the probability of undesirable plasma formation beneath the support plate  120  and proximate the RF return straps  130 . Thus, presence of the shield cover  150  decreasing the chances of plasma arcing, and inhibits plasma formation below the support plate  120 , which extends the mean time between chamber cleans and service life of the shielded RF return straps  130 . 
       FIG. 2  illustrates a bottom view of the substrate support assembly  118  having at least one shield cover  150 , according to one embodiment. As illustrated in  FIG. 2 , a plurality of shield covers  150  is coupled to the support plate  120 . In one embodiment, the shield covers  150  may be coupled to an outer edge  202  of the support plate  120 . For example, a single shield cover  150  may be coupled to the outer edge  202  of the support plate  120  such that the shield cover  150  covers at least a portion of a side  204  (i.e., the upper end  180 ) of at least two RF return straps  130  that are closest to the support plate  120 . For example, a plurality of shield covers  150  may be coupled to the outer edge  202  of the support plate  120  such that the each shield cover  150  covers the side  204  and upper end  180  of a single RF return strap  130  in a one-to-one correspondence. Alternatively, each shield cover  150  may cover at least two RF return straps  130 . 
     In another embodiment, the shield covers  150  (as shown in phantom) may be positioned along the outer edge  202  of the support plate  120  and circumscribe the entire perimeter  182  of the support plate  120 . In another embodiment, the shield covers  150  may be positioned along one or more portions of the outer edge  202 . For example, the shield covers  150  may be positioned along a short side  204  of the support plate  120 , adjacent the slit valve opening  109  in the sidewalls  104 , as the portion of the sidewalls  104  adjacent the slit valve opening  109  may have a high longer RF return path resulting in a larger voltage drop between the short side  204  of the support plate  120  and sidewalls  104  having the slit valve opening  109  formed therein. 
     The shield cover  150  is configured to shield the RF return straps  130  from the sidewall  104  of the chamber body  102  so that the sidewalls  104  and RF return straps  130  are not damaged from arcing. Thus, the shield cover  150  acts as an insulator between the sidewalls  104  and the RF return straps  130 . 
     Thus, the shield cover  150  provides protection for the chamber sidewalls  104  from potential arcing due to the voltage drop between the substrate support assembly and the sidewalls of the processing chamber from the RF current loop. 
       FIG. 3  is partial cross-sectional view of the processing chamber  100  illustrating the shield cover  150 , according to one embodiment. The RF return strap  130  is coupled to the support plate  120  and the bottom  106  of the processing chamber  100  via clamps  304 . The shield cover  150  is shown coupled to a side  182  of the support plate  120 , such that at least an upper portion  306  of the RF return strap  130  is covered by the shield cover  150 . The shield cover  150  is configured to block, or decrease, the amount of gas flowing (as depicted by flow arrows  402 ) beneath the support plate  120  in the vicinity, of the RF return strap  130 , thereby forming a gas depleted area  302  immediately next to the upper portion  306  of the RF return strap  130 . When RF current is provided to the support plate  120 , the RF current runs through the support plate  120 , down the RF return straps  130 , along the bottom  106  of the chamber, up the sidewalls  104 , and back to the RF power source  138 . Because the upper portion  306  of the RF return straps  130  is in the gas depleted area  302 , there is no gas to which the RF current running through the RF return straps  130  can inductively couple to, thereby reducing, if not eliminating, parasitic plasma below the support plate  120  in the vicinity of the upper portion  306  of the RF return strap  130 . By creating the gas depleted area  302  beneath the support plate  120  and proximate the RF return strap  130 , the shield cover  150  reduces the likelihood of parasitic plasma formation from inductive coupling beneath the support plate  120 . 
       FIG. 4  is a partial cross-sectional side view of the processing chamber  100  illustrating the shield cover  150  in phantom to reveal the RF return strap  130 , according to one embodiment. As discussed above, RF current travels up the sidewall  104  of the chamber  100  back to the RF power source  138  which may result in a substantial voltage potential between the upper portion  306  of the RF return strap  130  and the sidewall  104  of the processing chamber  100 . The position of the shield cover  150  between the sidewall  104  and the RF return strap  130  inhibits the formation of parasitic plasma due to capacitive coupling between the sidewall  104  and the RF return strap  130 . Moreover, the position of the shield cover  150  causes the gases within the processing chamber  100  to be shielded from the upper portion  306  of the RF return strap  130  as shown by gas flow arrows  402 , thus forming the gas depleted area  302  immediately adjacent the upper portion  306  of the RF return strap  130 . Because there is substantially less gas in the gas depleted area  302  as compared to conventional processing chambers, the likelihood of parasitic plasma formation from inductive coupling as current flows through the RF return strap  130 . Moreover, as there is less gas in the gas depleted area  302 , the potential for deposition on the underside of the support plate  120  is also substantially reduced, thereby advantageously reducing the probability of potential chamber contamination. 
     Thus, the shield cover  150  substantially reduces the potential for parasitic plasma formation beneath the support plate  120  and around the RF return strap  130 , as well as reducing the potential for plasma arcing to the sidewalls  104  of the chamber  100   
     While the foregoing is directed to specific embodiments, other and further embodiments may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.