Abstract:
This disclosure relates a system and techniques for adjusting component parts of a Plasma-enhanced processing system. The electric field uniformity generated by plasma processing may be improved by adjusting the distance between a cavity of an upper electrode and an insulating plate that covers, at least a portion of, the cavity. In another embodiment, the electric field uniformity may be improved by adjusting the distance between the substrate and the upper electrode.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to provisional application 61/661,868 filed on Jun. 20, 2012. The provisional application is incorporated by reference in its entirety into this application. 
     
    
       [0002]    TECHNICAL FIELD 
         [0003]    This disclosure generally relates to systems and/or devices used in a plasma-processing chamber. This may include, but is not limited to, plasma-enhanced chemical vapor deposition or plasma etching. More particularly, this disclosure relates to a voltage and electrical field non-uniformity compensation method for large area and/or high frequency plasma reactors. This method is generally applicable to rectangular or square large area plasma processing equipment which for instance is used in LCD and Solar Cell production. 
       BACKGROUND 
       [0004]    Plasma may be generated in a vacuum chamber by providing electrical energy in the radio frequency range to ionize processes gases that may be enclosed in the vacuum chamber at sub-atmospheric pressures. Plasma processing may be used to etch a substrate or deposit a film on the substrate. The quality of the plasma processing may be based, at least in part, on the uniformity of the plasma. In certain instances, controlling the location and uniformity of the plasma in the vacuum chamber may be desirable for substrate processing quality and/or limiting the impact of the plasma to desired regions of the vacuum chamber that may be beneficial for substrate processing or vacuum chamber longevity. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0005]    The features within the drawings are numbered and are cross-referenced with the written description. Generally, the first numeral reflects the drawing number where the feature was first introduced, and the remaining numerals are intended to distinguish the feature from the other notated features within that drawing. However, if a feature is used across several drawings, the number used to identify the feature in the drawing where the feature first appeared will be used. Reference will now be made to the accompanying drawings, which are not necessarily drawn to scale and wherein: 
           [0006]      FIG. 1  illustrates a cross section view of a representative plasma processing system that may include an upper and lower electrode for processing substrates. The upper electrode may include a cavity that may be covered by an insulating plate as described in one or more embodiments of the disclosure. 
           [0007]      FIG. 2  illustrates a cross section view of a representative plasma processing system that may include an upper and lower electrode for processing substrates. The upper electrode may include a cavity that may be covered by an insulating plate that is offset from the upper electrode as described in one or more embodiments of the disclosure. 
           [0008]      FIG. 3  illustrates a cross section view of a representative plasma processing system that may include an upper and lower electrode for processing substrates. The substrate may be offset from the lower electrode as described in one or more embodiments of the disclosure. 
           [0009]      FIG. 4  illustrates a graph showing the shape of the cavity of the upper electrode as described in one or more embodiments of the disclosure. 
       
    
    
     SUMMARY 
       [0010]    Embodiments described in this disclosure may relate to the arrangement or design of plasma processing components used to etch a substrate or deposit a film on a substrate. Broadly, the plasma process chamber may include a vacuum chamber that may be held at sub-atmospheric pressure. The plasma process chamber may also include a gas distribution system to provide process gases that may be used to generate plasma. Plasma may be ignited by a radio frequency (RF) power system that may include one or more electrodes that may be used to ionize the process gases using RF power that is provided to the one or more electrodes. For example, a substrate may be placed below or adjacent to an electrode. The electrode may be placed a certain distance above or near the substrate to adjust or control the uniformity of the plasma above or around the substrate. A higher degree of plasma uniformity may result in a more uniform film deposition across the substrate. 
         [0011]    In one embodiment, the electrode may include a sloped cavity along at least a portion of the electrode. The slope of the cavity may be optimized based, at least in part, on whether the cavity is maintained at vacuum, includes a dielectric material, or one or more gases. An insulating plate may cover at least a portion of the cavity. The geometry of the cavity may be optimized based, at least in part, on a lens distance and a substrate distance. In one instance, the lens distance may be the maximum distance that separates the electrode and the insulating plate over the cavity portion of the electrode. The substrate distance may be a distance between the insulating plate and the substrate placed below the electrode. In this embodiment, the insulating plate may be placed flush with the electrode such that the lens distance is approximate to the maximum depth of the cavity. 
         [0012]    In another embodiment, the insulating plate may be offset from the cavity such that the lens distance is greater than the maximum depth of the cavity. In one instance, offset spacer may be placed between the insulating plate and the electrode to increase the lens distance. In this embodiment, the lens distance may also be referred to as the offset distance. Broadly, the offset distance may be less than or equal to 3 mm. In one particular embodiment, the offset distance may be approximately 0.3 mm. 
         [0013]    The offset distance may vary on desired process conditions or process performance requirements. For example, the offset distance may be based, at least in part, on an applied frequency of the RF power system, a size of the electrode, and/or the substrate distance. 
         [0014]    In another embodiment, the placement of the substrate may be used to optimize process conditions instead of the placement of the insulating plate. For example, the substrate distance may be optimized by placing spacers below the substrate instead of placing spacers between the electrode and the insulating plate. 
         [0015]    Example embodiments of the disclosure will now be described with reference to the accompanying figures. 
       DETAILED DESCRIPTION 
       [0016]    Embodiments of the invention are described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the disclosure are shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. 
         [0017]      FIG. 1  illustrates a cross section view of a representative plasma processing system  100  that may be used for processing substrates using plasma. The system  100  may include an upper electrode  102 , a lower electrode  104 , and a radio frequency source  106  that provides power to the upper electrode  102 . A gas distribution system (not shown) may also provide process gases to the upper electrode  102 , which are distributed by a plurality of gas portals  108 . In this embodiment, the upper electrode  102  and the lower electrode  104  may be separated by a plasma-processing region  110 . A substrate  112  may be placed on the lower electrode  104  adjacent to the plasma-processing region  110 . In this instance, the lower electrode  104  may be coupled to an electrical ground  114 . 
         [0018]    In one embodiment, the upper electrode  102  may include a cavity  116  that may be at least partially covered by an insulating plate  118 . The cavity  116  may be used to obtain a more uniform electrical field that may be generated when power is applied to the upper electrode  102 . Broadly, the cavity  116  may be a concave cavity within the upper electrode, as shown in  FIG. 1 . The cavity  116  may be sloped from an exterior surface of the upper electrode  102  to a maximum distance or lens distance  120  that may be near the center of the upper electrode  102 . The slope of the cavity  116  depends mainly on the electrode size, the generator frequency and the plasma gap. As an example for a 1.1×13 m electrode at 40 Mhz and a plasma gap of &lt;10 mm the cavity may be approximately 1.2 mm deep. 
         [0019]    The contents of the cavity  116  may vary depending on the desired process conditions to etch or deposit on the substrate  112 . The contents of the cavity  116  may impact the uniformity of the electric field generated during plasma processing. In one embodiment, the cavity  116  may be held under sub-atmospheric pressure conditions which may or may not include process gases. In another embodiment, the cavity  116  may also include a dielectric material that may be flush with the insulating plate  118  and/or the cavity  116  of the upper electrode  102 . 
         [0020]    The insulating plate  118  may cover the cavity  116  and may be separated from the substrate  112  by a processing distance  122 . This distance may be measured from the exterior surface of the insulating plate  118  that may be facing the substrate  112  to a surface of the substrate  112  that may be facing the insulating plate  118 . In this embodiment, the electrode separation distance  124  may be measured between the surfaces of the upper electrode  102  and the lower electrode  104  that may be facing each other. In the  FIG. 1  embodiment, the electrode separation distance  124  may be the thickness of the substrate  112  plus the processing distance  122 . In one embodiment, the thickness of the substrate may be less than 5 mm. In one particular embodiment, the thickness of the substrate  112  may be approximately 3 mm. 
         [0021]    The system  100  may also be varied further to optimize or control the uniformity of the electrical field in the region of the upper electrode and/or plasma-processing region  110 . The optimization may include, but is not limited to, varying the lens distance and/or the processing distance  122 . 
         [0022]      FIG. 2  illustrates a cross section view a representative plasma processing system  200  that may increase the lens distance  202  by adding spacers  204  between the insulating plate  118  and the upper electrode  102 . In contrast to  FIG. 1 , the lens distance  202  is larger and the plasma-processing distance  206  is smaller. For example, the lens distance  120  in  FIG. 1  may be approximately 0.5 mm. In contrast to  FIG. 2 , the spacers  204  between the upper electrode  102  and the insulating plate  118  may increase the lens distance to approximately 2.5 mm. In this embodiment, the electrode separation distance  124 , as shown in  FIG. 2 , may be similar to the electrode separation distance  124  shown in  FIG. 1 . 
         [0023]    In one embodiment, the spacer  204  may be a dielectric material that may be coupled to the upper electrode  102 . The spacer  204  may be continuous along the perimeter of the cavity  116 . In this way, the spacer  204  may form a leak tight seal between the upper electrode  102  and the insulating plate  118 . For example, the leak tight seal may be applicable when sub-atmospheric pressure is desired between the upper electrode  102  and the insulating plate  118 . 
         [0024]    In another embodiment, the spacer  204  may be integrated into dielectric material that may fill, at least a portion of, the cavity  116 . In this way, the dielectric material may fill at least a portion of the cavity  116  while offsetting the insulating plate  118  from the upper electrode  102 . 
         [0025]      FIG. 3  illustrates a cross section view of a representative plasma processing system  300 . In this embodiment, the processing distance  302  between the insulating plate  118  and the substrate  112  may be adjusted by placing substrate spacers  304  below the substrate  112 . The substrate spacer distance  306  being at most approximately 3 mm. As shown in  FIG. 3 , the insulating plate  118  may be placed flush with the upper electrode  102 . In this embodiment, the insulating plate may cover the cavity  116  to enable a sub-atmospheric pressure within the cavity  116 . 
         [0026]    In one embodiment, the substrate spacers  304  may include, but are not limited to, three separate ridges that are placed on a surface of the lower electrode  104 . In this instance, there may be a gap between the substrate  112  and the lower electrode  104 . However, in other embodiments, the substrate spacers  304  may be arranged to minimize the size of the gap or eliminate the gap to prevent process gases or plasma from reaching the backside of the substrate  112 . 
         [0027]      FIG. 4  illustrates a graph  400  showing one embodiment of the shape of the cavity  116  of the upper electrode  102  as shown  FIG. 1 . For example, the x-axis represents the distance from the center of the reactor or cavity  116  and the y-axis represents the distance from a surface of the cavity  116  to the insulating plate  118 . In this instance, the center of the reactor may have the largest distance between the cavity  116  surface and the insulating plate  118 . 
         [0028]    In this instance, the  FIG. 1  embodiment may be represented in the 0 mm offset line  402  which reflects a gap distance of 0.6 mm at the center of the cavity  116  and a minimum gap distance of approximately zero at the edge of the cavity at 0.75 m. In contrast, the offset  404  increase, as illustrated in the system  200  in  FIG. 2 , may be represented by the 1.5 mm offset line  406 . The center gap distance may be approximately 2.5 mm and the edge gap distance may be approximately 1.5 mm. 
         [0029]    In other embodiments, the offset line  406  may vary between 0.6 mm and 3 mm depending on the impact of the electrical field uniformity desired for the plasma process using system  200 .