Abstract:
A shielding system for a physical vapor deposition (PVD) chamber is disclosed. The PVD chamber includes a pedestal supporting a substrate. The shielding system includes a first annular portion and a second annular portion of a pedestal shield. The first annular portion is attached the pedestal at a first location. The first annular portion is located at or below a plane including the substrate. The second annular portion is attached to the pedestal at a second location that is below the first location. The first annular portion is spaced a predetermined distance from the second annular portion and is electrically isolated from the second annular portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/311,655, filed on Mar. 8, 2010. The disclosure of the above application is incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    The present disclosure relates to shields for substrate processing systems, and more particularly to shields for physical vapor deposition (PVD) systems. 
       BACKGROUND 
       [0003]    The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
         [0004]    Physical vapor deposition (PVD) systems are used to deposit metal layers onto substrates such as semiconductor wafers. The metal layers can be used as diffusion barriers, adhesion or seed layers, primary conductors, antireflection coatings, etch stops, etc. 
         [0005]    In PVD systems, a plasma feed gas such as Argon is introduced into a processing chamber. Electrons collide with atoms of the plasma feed gas to create ions. In some applications, magnetic fields are used to increase a residence time of the electrons by causing the electrons to spiral through the plasma. 
         [0006]    A negative potential applied to a cathode attracts the ions towards a target. The ions collide with the target with high energy. Target atoms are dislodged from the surface of the target by direct momentum transfer. The impact of the ions on the target also releases secondary electrons. The dislodged atoms and ions (electrostatically attracted by the secondary electrons) are then deposited on a substrate such as a semiconductor wafer. While deposition on the substrate is desirable, it is important to limit deposition on other components in the processing chamber. One or more shields may be used in the processing chamber to protect components of the processing chamber from undesired deposition. 
         [0007]    Referring now to  FIGS. 1 and 2 , an example of a pedestal shield typically used in PVD systems is shown. In  FIG. 1 , a cross-section of a portion of a processing chamber  10  is shown. In the processing chamber  10 , a substrate such as a semiconductor wafer (hereinafter wafer)  12  is positioned on a wafer holder or a pedestal  14  as shown. The processing chamber  10  includes a wall shield (or a sidewall shield)  16 , which is grounded to the processing chamber  10 . Additionally, a pedestal shield  18  is included to protect a chamber wall of the processing chamber  10  and a ring portion  20  of the pedestal  14  from unwanted deposition of metal particles. The ring portion  20  of the pedestal  14  is made of an electrically insulating material such as ceramic. The pedestal shield  18  and the wall shield  16  are typically made of metal and act as a capacitance C 1 . 
         [0008]    During deposition, a radio frequency (RF) bias is applied to the wafer  12  through the pedestal  14 , and a target mounted on a top wall of the processing chamber  10  is energized to eject metal particles. Plasma distribution along a surface of the wafer  12  is not uniform because a plasma boundary (a boundary condition) is located at an edge of the wafer  12 . 
         [0009]    In addition, when the RF bias is applied to the wafer  12  through the pedestal  14 , an RF level at the edge of the wafer  12  is affected due to the boundary condition. Specifically, RF loss through the pedestal shield  18  to the wall shield  16  causes a lateral RF effect (an edge effect) at the edge of the wafer  12 . 
         [0010]    In  FIG. 2 , an expanded view of a portion of  FIG. 1  is shown to illustrate film accumulation on an inner diameter of the ring portion  20 . The film accumulation occurs because the ring portion  20  slopes downward towards the wafer  12  at the inner diameter of the ring portion  20 . 
       SUMMARY 
       [0011]    A shielding system for a physical vapor deposition (PVD) chamber is disclosed. The PVD chamber includes a pedestal supporting a substrate. The shielding system includes a first annular portion and a second annular portion of a pedestal shield. The first annular portion is attached the pedestal at a first location. The first annular portion is located at or below a plane including the substrate. The second annular portion is attached to the pedestal at a second location that is below the first location. The first annular portion is spaced a predetermined distance from the second annular portion and is electrically isolated from the second annular portion. 
         [0012]    In other features, second annular portion of the pedestal shield includes a straight portion and a curved portion. The straight portion is attached to the second location, is generally perpendicular to the plane including the substrate and extends from the pedestal towards a bottom chamber wall. The curved portion extends from the straight portion towards a side chamber wall. 
         [0013]    In other features, the first annular portion of the pedestal shield and the straight portion of the second annular portion of the pedestal shield are adjacent to a ring portion of the pedestal. An upper surface of the ring portion slopes downwardly from a radially inner diameter to a radially outer diameter. 
         [0014]    In other features, the shielding system further includes a wall shield. The wall shield extends inwardly from the side chamber wall towards the pedestal. The wall shield overlaps a radially outer portion of the second annular portion of the pedestal shield. 
         [0015]    In other features, the curved portion of the second annular portion of the pedestal shield is concave relative to a top chamber wall, and the wall shield is concave relative to the top chamber wall. 
         [0016]    In other features, the first annular portion includes a first portion and a second portion. The first portion is attached to the pedestal and is parallel to the plane including the substrate. The second portion extends in a perpendicular direction from the first portion. 
         [0017]    In other features, the second annular portion includes a third portion and a first curved portion. The third portion is attached to the pedestal at the second location and is parallel to the plane including the substrate. The first curved portion extends from the third portion towards a side chamber wall. 
         [0018]    In other features, the first curved portion is concave relative to a top chamber wall. 
         [0019]    In other features, the first, second, and third portions surround a ring portion of the pedestal. An upper surface of the ring portion slopes downwardly from a radially inner diameter of the ring portion to a radially outer diameter of the ring portion. 
         [0020]    In other features, the shielding system further includes a wall shield. The wall shield includes a fourth portion and a second curved portion. The fourth portion is attached to the side chamber wall. The second curved portion extends from the first portion and that is concave relative to a bottom chamber wall. 
         [0021]    In other features, a first end of the first curved portion is located inside the second curved portion. A second end of the second curved portion is located inside the first curved portion. 
         [0022]    In still other features, a method for shielding in a physical vapor deposition (PVD) chamber. The PVD chamber includes a pedestal supporting a substrate. The method includes attaching a first annular portion of a pedestal shield to the pedestal at a first location at or below a plane including the substrate. The method further includes attaching a second annular portion of the pedestal shield to the pedestal at a second location that is below the first location. The method further includes spacing the first annular portion a predetermined distance from the second annular portion. The method further includes electrically isolating the first annular portion from the second annular portion. 
         [0023]    In other features, the method further includes attaching a straight portion of the second annular portion of the pedestal shield to the second location, where the straight portion is generally perpendicular to the plane including the substrate. The method further includes extending the straight portion from the pedestal towards a bottom chamber wall. The method further includes extending a curved portion of the second annular portion of the pedestal shield from the straight portion towards a side chamber wall. 
         [0024]    In other features, the method further includes disposing the first annular portion of the pedestal shield and the straight portion of the second annular portion of the pedestal shield adjacent to a ring portion of the pedestal. The method further includes inclining an upper surface of the ring portion to slope downwardly from a radially inner diameter to a radially outer diameter. 
         [0025]    In other features, the method further includes extending a wall shield inwardly from the side chamber wall towards the pedestal to overlap a radially outer portion of the second annular portion of the pedestal shield. 
         [0026]    In other features, the curved portion of the second annular portion of the pedestal shield is concave relative to a top chamber wall. The wall shield is concave relative to the top chamber wall. 
         [0027]    In other features, the method further includes attaching a first portion of the first annular portion to the pedestal, disposing the first portion parallel to the plane including the substrate, and extending a second portion of the first annular portion in a perpendicular direction from the first portion. 
         [0028]    In other features, the method further includes attaching a third portion of the second annular portion to the pedestal at the second location, disposing the third portion parallel to the plane including the substrate, and extending a first curved portion of the second annular portion from the third portion towards a side chamber wall. 
         [0029]    In another feature, the first curved portion is concave relative to a top chamber wall. 
         [0030]    In other features, the method further includes disposing the first, second, and third portions to surround a ring portion of the pedestal. The method further includes inclining an upper surface of the ring portion to slope downwardly from a radially inner diameter of the ring portion to a radially outer diameter of the ring portion. 
         [0031]    In other features, the method further includes attaching a fourth portion of a wall shield to the side chamber wall, and extending a second curved portion of the wall shield from the fourth portion, where the second curved portion is concave relative to a bottom chamber wall. 
         [0032]    In other features, the method further includes disposing a first end of the first curved portion inside the second curved portion, and disposing a second end of the second curved portion inside the first curved portion. 
         [0033]    In still other features, a physical vapor deposition (PVD) chamber includes a pedestal supporting a substrate, where the pedestal includes a ring portion, and where an upper surface of the ring portion slopes downwardly from a radially inner diameter of the ring portion to a radially outer diameter of the ring portion. The PVD chamber further includes a first annular portion of a pedestal shield and a second annular portion of the pedestal shield. The first annular portion is attached to the pedestal and is located at or below a plane including the substrate. The second annular portion includes a straight portion and a first curved portion. The straight portion is generally perpendicular to the plane including the substrate and extends from the first annular portion towards a bottom chamber wall. The first curved portion extends from the straight portion towards a side chamber wall. The first annular portion and the straight portion are adjacent to the ring portion of the pedestal. 
         [0034]    In other features, the PVD chamber further includes a wall shield. The wall shield includes a first portion that is attached to the side chamber wall and a second curved portion that extends towards the pedestal. 
         [0035]    In another feature, the first curved portion of the pedestal shield overlaps the second curved portion of the wall shield. 
         [0036]    In other features, the first curved portion of the pedestal shield is concave relative to a top chamber wall, and the second curved portion of the wall shield is concave relative to the top chamber wall. 
         [0037]    In still other features, a method for shielding in a physical vapor deposition (PVD) chamber includes arranging a pedestal configured to support a substrate in the PVD chamber. The method further includes configuring an upper surface of a ring portion of the pedestal to slope downwardly from a radially inner diameter of the ring portion to a radially outer diameter of the ring portion. The method further includes attaching a pedestal shield including a first annular portion and a second annular portion to the pedestal, where the second annular portion includes a straight portion and a first curved portion. The method further includes arranging the first annular portion of the pedestal shield at or below a plane including the substrate. The method further includes arranging the straight portion generally perpendicular to the plane including the substrate, where the straight portion extends from the first annular portion towards a bottom chamber wall. The method further includes arranging the first curved portion to extend from the straight portion towards a side chamber wall. The first annular portion and the straight portion are adjacent to a ring portion of the pedestal. 
         [0038]    In another feature, the method further includes attaching a wall shield to the side chamber wall, where the wall shield includes a first portion that is attached to the side chamber wall and a second curved portion that extends towards the pedestal. 
         [0039]    In another feature, the method further includes overlapping the first curved portion of the pedestal shield with respect to the second curved portion of the wall shield. 
         [0040]    In other features, the first curved portion of the pedestal shield is concave relative to a top chamber wall, and the second curved portion of the wall shield is concave relative to the top chamber wall. 
         [0041]    Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0042]    The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0043]      FIG. 1  illustrates a pedestal shield according to the prior art; 
           [0044]      FIG. 2  illustrates film accumulation on an inner diameter of a ring portion of a pedestal; 
           [0045]      FIG. 3  illustrates a split pedestal shield according to the present disclosure; 
           [0046]      FIG. 4  illustrates another pedestal shield according to the present disclosure; and 
           [0047]      FIG. 5  illustrates another implementation of a split pedestal shield according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0048]    The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical OR. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
         [0049]    The present disclosure relates to reducing the lateral RF effect at the edge of the wafer and improving plasma uniformity across the wafer. The lateral RF effect at the edge of the wafer can be reduced, and the plasma uniformity can be improved across the wafer in different ways disclosed herein. 
         [0050]    For example, the pedestal shield can be split into two shield portions. The geometry and arrangement of the two shield portions relative to other components of the processing chamber can be selected to reduce the lateral RF effect at the edge of the wafer and to improve plasma uniformity across the wafer. Alternatively or additionally, the pedestal shield can be lowered and arranged approximately at or below a level of the wafer to improve plasma uniformity across the wafer. 
         [0051]    The present disclosure is organized as follows. In  FIG. 3 , a first arrangement of a split pedestal shield is shown. In  FIG. 4 , a pedestal shield arranged approximately in level with the wafer is shown. In  FIG. 5 , a second arrangement of a split pedestal shield is shown. 
         [0052]    Referring now to  FIG. 3 , a cross-section of a portion of a processing chamber  100  including a pedestal shield according to the present disclosure is shown. The pedestal shield according to the present disclosure includes an upper shield portion  102  and a lower shield portion  104 . The upper shield portion  102  and the lower shield portion  104  are annular. The upper shield portion  102  may be located at approximately the same height or level as the wafer  12 . Alternatively, the upper shield portion  102  may be located below the level of the wafer  12 . Leveling a top surface of the upper shield portion  102  relative to the wafer  12  in this manner improves plasma uniformity across the wafer  12 . 
         [0053]    The lower shield portion  104  is separated and electrically isolated from the upper shield portion  102  by a ring portion  106  of the pedestal  14 . Specifically, the upper shield portion  102  and the lower shield portion  104  are attached to the ring portion  106 . A gap separates the upper shield portion  102  and the lower shield portion  104 . The ring portion  106  of the pedestal  14  is made of an electrically insulating material such as ceramic. The ring portion  106  electrically isolates the upper shield portion  102  from the lower shield portion  104 . 
         [0054]    As a result, a capacitance C 2  is created between upper and lower shield portions  102  and  104 . The gap between the upper shield portion  102  and the lower shield portion  104  allows the upper shield portion  102  to closely match a floating potential of the wafer  12 , especially in RF biased processes. 
         [0055]    The gap between the upper shield portion  102  and the lower shield portion  104  also reduces RF loss through the lower shield portion  104 . Reducing RF loss through the lower shield portion  104  increases a center-to-edge RF uniformity at the wafer  12 . 
         [0056]    More specifically, splitting the pedestal shield into the upper shield portion  102  and the lower shield portion  104  and lowering the top surface of the upper shield portion  102  to approximately the same height as the wafer  12  can expand the plasma boundary. Consequently, the plasma distribution at the edge of the wafer  12  tends to be the same as the plasma distribution at the center of the wafer  12  as shown. 
         [0057]    Further, the upper shield portion  102  can be biased such that a bias difference between the upper shield portion  102  and the wafer  12  can be significantly reduced. Reducing the bias difference between the upper shield portion  102  and the wafer  12  can decrease or eliminate the lateral RF effect due to the RF bias at the edge of the wafer  12 . Consequently, wafer uniformity tends to improve. 
         [0058]    The ring portion  106  of the pedestal  14  is newly designed according to the present disclosure. For example, the ring portion  20  in  FIG. 1  slopes downward towards the wafer  12  at the inner diameter of the ring portion  20 . In contrast, the ring portion  106  slopes downward away from the wafer  12  at the inner diameter of the ring portion  106 . 
         [0059]    Further, as compared to the ring portion  20 , the ring portion  106  has a greater slope at the inner diameter of the ring portion  106 . The increased downward slope away from the wafer  12  at the inner diameter of the ring portion  106  tends to reduce film accumulation on the ring portion  106 . Consequently, the ring portion  106  tends to have an increased life relative to the ring portion  20 . 
         [0060]    Additionally, a predetermined distance separates the ring portion  106  from the wafer  12 . The predetermined distance depends on the type of material used to construct the ring portion  106 . 
         [0061]    More specifically, the upper shield portion  102  is attached to the ring portion  106  and is located at or below a plane including the wafer  12 . The lower shield portion  104  includes a straight portion  104 - 1  and a curved portion  104 - 2 . The straight portion  104 - 1  is perpendicular to the plane including the wafer  12 . The straight portion  104 - 1  is attached to the ring portion  106  at a different location than the upper shield portion  102 . The straight portion  104 - 1  extends away from the wafer  12  and toward the pedestal  14 . The curved portion  104 - 2  extends from the straight portion  104 - 1  and extends away from the wafer  12  and the pedestal  14 . 
         [0062]    The upper shield portion  102  and the straight portion  104 - 1  of the lower shield portion  104  surround the ring portion  106 . The wall shield  16  is electrically isolated from the pedestal shield and is attached to the processing chamber  100 . 
         [0063]    Referring now to  FIG. 4 , a cross-section of a portion of a processing chamber  200  utilizing a different arrangement of a pedestal shield  19  is shown. The pedestal shield  19  in the processing chamber  200  is different than the pedestal shield in the processing chamber  100  shown in  FIG. 3 . Unlike the pedestal shield in the processing chamber  100 , the pedestal shield  19  in the processing chamber  200  is not split into the upper shield portion  102  and the lower shield portion  104 . 
         [0064]    Further, the pedestal shield  19  in the processing chamber  200  is arranged differently than the pedestal shield  18  in the processing chamber  10  shown in  FIG. 1 . Specifically, the pedestal shield  19  in the processing chamber  200  is positioned lower than the pedestal shield  18  in the processing chamber  10  such that the top surface of the pedestal shield  19  is approximately at the same height or level as the wafer  12 . By leveling the pedestal shield  19  relative to the wafer  12 , plasma uniformity is improved at the edge of the wafer  12  through the electrical field across the wafer  12 . 
         [0065]    The processing chamber  200  also includes the pedestal  14  having a newly designed ring  202  portion. The ring portion  202  has a different profile than the ring portion  20  used in the processing chamber  10 . For example, the ring portion  20  in  FIG. 1  slopes downward towards the wafer  12  at the inner diameter of the ring portion  20 . In contrast, the ring portion  202  slopes downward away from the wafer  12  at the inner diameter of the ring portion  202 . 
         [0066]    Additionally, as compared to the ring portion  20 , the ring portion  202  has an increased downward slope at the inner diameter of the ring portion  202 . The profile (i.e., the slope characteristics) of the ring  202  portion decreases film accumulation on the inner diameter of the ring portion  202 . Decreasing film accumulation on the inner diameter of the ring portion  202  tends to extend the life of the ring portion  202 . 
         [0067]    In  FIG. 4 , the pedestal shield  19  includes first, second, and third portions  19 - 1 ,  19 - 2 ,  19 - 3 . The first and second portions  19 - 1 ,  19 - 2  are straight portions, and the third portion  19 - 3  is a curved portion. The first portion  19 - 1  is on the same plane as the wafer  12  and is therefore level with the wafer  12 . 
         [0068]    The second portion  19 - 2  extends perpendicularly from the first portion  19 - 1 . The second portion  19 - 2  extends away from the wafer  12  and toward the pedestal  14 . The third portion  19 - 3  extends from the second portion  19 - 2  and extends away from the wafer  12  and the pedestal  14 . The first and the second portions  19 - 1 ,  19 - 2  are adjacent to the ring portion  202  as shown. The wall shield  16  is electrically isolated from the pedestal shield  19  and is attached to the processing chamber  200 . 
         [0069]    Referring now to  FIG. 5 , a cross-section of a processing chamber  300  including a pedestal shield  301  is shown. The pedestal shield  301  has a different geometry than the pedestal shield  18 . In addition, the pedestal shield  301  can be split and arranged in different ways. For example, the pedestal shield  301  can be split into a lower shield portion  302  and an upper shield portion  304 . The lower shield portion  302  and the upper shield portion  304  are annular. The arrangement of the lower shield portion  302  and the upper shield portion  304  relative to other components of the processing chamber  300  is described below. The lower shield portion  302  can be grounded to the processing chamber  300 . 
         [0070]    The processing chamber  300  further includes a wall shield  306 . The wall shield  306  is grounded to the processing chamber  300 . The pedestal  14  includes a ring portion  308 . The ring portion  308  is made of an electrically insulating material such as ceramic. 
         [0071]    In the example shown, the lower shield portion  302  generally has a shape of a curve (e.g., a semicircle or an arc). Specifically, the lower shield portion  302  includes a curved portion  302 - 1  and a straight portion  302 - 2 . The curved portion  302 - 1  is concave relative to a top wall of the processing chamber  300 . The straight portion  302 - 2  of the lower shield portion  302  is attached to the pedestal  14 . The upper shield portion  304  includes first and second straight portions  304 - 1 ,  304 - 2  that are joined at right angle. The first straight portion  304 - 1  of the upper shield portion  304  is attached to the ring portion  308  and is located at or below a plane including the wafer  12 . 
         [0072]    The wall shield  306  includes a curved portion  306 - 1  that is similar to the curved portion  302 - 1  of the lower shield portion  302 . The curved portion  306 - 1  of the wall shield  306  is concave relative to a bottom wall of the processing chamber  300 . Additionally, the wall shield  306  includes first, second, and third straight portions  306 - 2 ,  306 - 3 ,  306 - 4 . The third straight portion  306 - 4  of the wall shield  306  is attached to the processing chamber  300 . 
         [0073]    The geometry of the pedestal shield  301  and the manner of splitting and arranging the pedestal shield shown are for example only. The pedestal shield  301  can have a different geometry than that shown and can be split and arranged in a different manner than that shown. 
         [0074]    In general, a capacitance C formed by two parallel conductive plates separated by a dielectric with permittivity ε can be determined as: 
         [0000]    
       
         
           
             C 
             = 
             
               
                 ɛ 
                  
                 
                     
                 
                  
                 A 
               
               d 
             
           
         
       
     
         [0000]    where C is the capacitance, A is a surface area of the conductive plates, and d is a distance between the conductive plates. 
         [0075]    In an RF circuit comprising a capacitor C, an impedance Z of the capacitor C can be determined as: 
         [0000]    
       
         
           
             Z 
             = 
             
               - 
               
                 j 
                 
                   2 
                    
                   
                       
                   
                    
                   π 
                    
                   
                       
                   
                    
                   fC 
                 
               
             
           
         
       
     
         [0000]    where, j is an imaginary unit, and f is an RF frequency. 
         [0076]    The lateral RF effect at the edge of the wafer  12  (i.e., the edge effect) can be reduced if the capacitance C 2  between the upper and lower pedestal shield portions is less than the capacitance C 1  between the pedestal shield and wall shield. That is, the lateral RF effect at the edge of the wafer  12  can be reduced if the following equation is satisfied: 
         [0000]      C 2 &lt;C 1    
         [0077]    The capacitance C 2  between the upper and lower shield portions of the pedestal shield can be decreased by increasing the distance d between the upper and lower shield portions. For example, in  FIG. 3 , capacitance C 2  between the upper and lower shield portions  102  and  104  can be decreased by increasing the distance d between the upper and lower shield portions  102  and  104 . In  FIG. 5 , capacitance C 2  between the upper and lower shield portions  302  and  304  can be decreased by increasing the distance d between the upper and lower shield portions  302  and  304 . 
         [0078]    Alternatively, the capacitance C 2  between upper and lower shield portions of the pedestal shield can be decreased by decreasing the surface area A of the upper and lower shield portions. For example, in  FIG. 3 , capacitance C 2  between the upper and lower shield portions  102  and  104  can be decreased by decreasing the surface area A of the upper and lower shield portions  102  and  104 . In  FIG. 5 , capacitance C 2  between the upper and lower shield portions  302  and  304  can be decreased by decreasing the surface area A of the upper and lower shield portions  302  and  304 . 
         [0079]    For a split pedestal shield, the distance between upper shield and lower shield portions should not be very large due to constraints on space available in the processing chamber. Moreover, deposition on a ceramic trench area may short-circuit the pedestal shield. Therefore, the surface area A should be smaller in order to satisfy the equation: 
         [0000]      C 2 &lt;C 1    
         [0080]    For example, in  FIG. 1 , capacitance C 1  is formed by the wall shield  16  and the pedestal shield  18 . The distance d between the wall shield  16  and the pedestal shield  18  is about 0.4 in, and the area A is about 140 in 2 . The capacitance C 1  formed by the wall shield  16  and the pedestal shield  18  is: 
         [0000]    
       
         
           
             
               C 
               1 
             
             = 
             
               
                 
                   
                     ɛ 
                      
                     
                         
                     
                      
                     A 
                   
                   d 
                 
                 ≈ 
                 
                   
                     ɛ 
                     × 
                     140 
                   
                   0.4 
                 
               
               = 
               
                 350 
                  
                 
                     
                 
                  
                 ɛ 
               
             
           
         
       
     
         [0081]    On the other hand, in  FIG. 3 , capacitance C 2  is formed by the upper and lower shield portions  102 ,  104  of the split pedestal shield. The area A is about 8 in 2 , and the separation d between the upper and lower shield portions  102 ,  104  is about 0.07 in. The capacitance C new  is: 
         [0000]    
       
         
           
             
               C 
               2 
             
             = 
             
               
                 
                   
                     ɛ 
                      
                     
                         
                     
                      
                     A 
                   
                   d 
                 
                 ≈ 
                 
                   
                     ɛ 
                     × 
                     8 
                   
                   0.07 
                 
               
               = 
               
                 
                   114 
                    
                   
                       
                   
                    
                   ɛ 
                 
                 &lt; 
                 
                   C 
                   1 
                 
               
             
           
         
       
     
         [0082]    In general, the capacitance C 2  can be reduced by selecting the surface area A and the distance d and by selecting the geometry of the pedestal shield. In addition, film deposition (e.g., thickness of film) can be changed by selecting the geometry of the pedestal shield. 
         [0083]    The arrangement of the lower shield portion  302 , the upper shield portion  304 , and the wall shield  306  shown in  FIG. 5  is now described in detail. The curved and straight portions of the lower shield portion  302 , the upper shield portion  304 , and the wall shield  306  each has first and second ends. 
         [0084]    The first end of the curved portion  302 - 1  of the lower shield portion  302  is collinear to a center of the curved portion  306 - 1  of the wall shield  306 . A line joining the first end of the curved portion  302 - 1  and the center of the curved portion  306 - 1  is perpendicular to a plane along which the wafer  12  lies. 
         [0085]    The second end of the curved portion  302 - 1  of the lower shield portion  302  is joined at a first junction to the first end of the straight portion  302 - 2  of the lower shield portion  302 . The first junction is separated by a predetermined distance from the first end of the first straight portion  304 - 1  of the upper shield portion  304 . 
         [0086]    The second end of the first straight portion  304 - 1  of the upper shield portion  304  is joined at a second junction to the first end of the second straight portion  304 - 2  of the upper shield portion  304 . The second junction surrounds the ring portion  308 . The second straight portion  304 - 2  of the upper shield portion  304  is approximately level with the wafer  12  and is parallel to the wafer  12 . That is, the second straight portion  304 - 2  of the upper shield portion  304  is coplanar to the wafer  12 . The second end of the second straight portion  304 - 2  is attached to the ring portion  308 . 
         [0087]    The straight portion  302 - 2  of the lower shield portion  302  intersects a tangent drawn at the second end of the curved portion  302 - 1  of the lower shield portion  302  at right angle. The tangent is perpendicular to a diameter of the curved portion  302 - 1  of the lower shield portion  302 . The diameter of the curved portion  302 - 1  of the lower shield portion  302  is parallel to the straight portion  302 - 2  of the lower shield portion  302 . 
         [0088]    The second end of the straight portion  302 - 2  of the lower shield portion  302  extends toward the pedestal  14 . The second end of the straight portion  302 - 2  of the lower shield portion  302  is grounded to the processing chamber  300 . 
         [0089]    The straight portion  302 - 2  of the lower shield portion  302  is parallel to the wafer  12  and the second straight portion  304 - 2  of the upper shield portion  304 . The straight portion  302 - 2  of the lower shield portion  302  is perpendicular to the first straight portion  304 - 1  of the upper shield portion  304 . 
         [0090]    The first end of the curved portion  306 - 1  of the wall shield  306  is collinear to a center of the curved portion  302 - 1  of the lower shield portion  302 . A line joining the first end of the curved portion  306 - 1  and the center of the curved portion  302 - 1  is perpendicular to the plane along which the wafer  12  lies. 
         [0091]    The second end of the curved portion  306 - 1  of the wall shield  306  is joined to the first end of the first straight portion  306 - 2  of the wall shield  306 . The first straight portion  306 - 2  of the wall shield  306  intersects a tangent drawn at the second end of the curved portion  306 - 1  of the wall shield  306  at right angle. The tangent is perpendicular to a diameter of the curved portion  306 - 1  of the wall shield  306 . The diameter of the curved portion  306 - 1  of the wall shield  306  is parallel to the first straight portion  306 - 2  of the wall shield  306 . 
         [0092]    The first straight portion  306 - 2  of the wall shield  306  is parallel to the wafer  12 , the straight portion  302 - 2  of the lower shield portion  302 , and the second straight portion  304 - 2  of the upper shield portion  304 . The first straight portion  306 - 2  of the wall shield  306  is perpendicular to the first straight portion  304 - 1  of the upper shield portion  304 . The first straight portion  306 - 2  of the wall shield  306  extends away from the first and second ends of the curved portion  306 - 1  of the wall shield  306 . 
         [0093]    The second end of the first straight portion  306 - 2  of the wall shield  306  is joined to the first end of the second straight portion  306 - 3  of the wall shield  306 . The first straight portion  306 - 2  of the wall shield  306  is joined to the second straight portion  306 - 3  of the wall shield  306  at right angle. The second straight portion  306 - 3  of the wall shield  306  is parallel to the first straight portion  304 - 1  of the upper shield portion  304 . 
         [0094]    The second straight portion  306 - 3  of the wall shield  306  is perpendicular to the wafer  12 , the second straight portion  304 - 2  of the upper shield portion  304 , and the straight portion  302 - 2  of the lower shield portion  302 . The second straight portion  306 - 3  of the wall shield  306  extends in a direction along a line drawn from the pedestal to the wafer  12 . 
         [0095]    The second end of the second straight portion  306 - 3  of the wall shield  306  is joined to the first end of the third straight portion  306 - 4  of the wall shield  306 . The second end of the third straight portion  306 - 4  of the wall shield  306  is grounded to the processing chamber  300 . The second straight portion  306 - 3  of the wall shield  306  is joined to the third straight portion  306 - 4  of the wall shield  306  at right angle. 
         [0096]    The third straight portion  306 - 4  of the wall shield  306  is parallel to the wafer  12 , the straight portion  302 - 2  of the lower shield portion  302 , the second straight portion  304 - 2  of the upper shield portion  304 , and the first straight portion  306 - 2  of the wall shield  306 . The third straight portion  306 - 4  of the wall shield  306  is perpendicular to the first straight portion  304 - 1  of the upper shield portion  304 . The third straight portion  306 - 4  of the wall shield  306  extends away from the wafer  12  and the pedestal  14 . 
         [0097]    In summary, the split pedestal shield with electrically isolated upper and lower shield portions protects the chamber wall and other components of the processing chamber from undesired deposition. The plasma boundary can be expanded from the edge of the wafer to an edge of the upper shield portion of the pedestal shield without impairing the ability of the lower shield portion to adequately protect the chamber wall and the ring portion from undesired deposition. The split pedestal shield tends to eliminate the lateral RF effect at the wafer edge by reducing lateral RF coupling and harmonizing an RF power vector to be vertical. Lowering the pedestal shield to the wafer level tends to improve plasma uniformity across the wafer. 
         [0098]    Further, the life of the ring portion tends to improve by changing the profile (i.e., the slope characteristics) of the ring portion as disclosed herein. Compared to prior designs, the new designs take nearly the same amount of manufacturing time and costs. Although the new designs are developed for PVD systems, the principles described herein can be utilized in other processing chambers used to process substrates. 
         [0099]    The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims.