Abstract:
An adjustable RF coupling ring is capable of reducing a vertical gap between a substrate and a hot edge ring in a vacuum processing chamber. The reduction of the gap reduces polymer deposits on the substrate and electrostatic chuck and improves wafer processing.

Description:
This application is a divisional application of U.S. application Ser. No. 10/251,179 entitled APPARATUS FOR REDUCING POLYMER DEPOSITION ON A SUBSTRATE AND SUBSTRATE SUPPORT, filed on Sep. 20, 2002, now U.S. Pat. No. 7,252,738 the entire content of which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to an apparatus and method for reducing polymer deposition on a substrate and substrate support, and more particularly, the invention relates to the adjustment of a gap between a substrate holder and a substrate to reduce polymer deposition on exposed surfaces of the substrate holder and bottom surfaces of the substrate. 
     DESCRIPTION OF THE RELATED ART 
     Vacuum processing chambers are generally used for chemical vapor depositing (CVD) and etching of materials on substrates by supplying process gas to the vacuum chamber and application of an RE field to the gas. Examples of parallel plate, inductively coupled plasma (TCP˜, also called ICP), and electron-cyclotron resonance (ECR) reactors are disclosed in commonly owned U.S. Pat. Nos. 4,340,462; 4,948,458; and 5,200,232. The substrates are held in place within the vacuum chamber during processing by substrate holders. Conventional substrate holders include mechanical clamps and electrostatic clamps (ESC). Examples of mechanical clamps and ESC substrate holders are provided in commonly owned U.S. Pat. No. 5,262,029 and commonly owned U.S. Pat. No. 5,671,116. Substrate holders in the form of an electrode can supply radio frequency (RF) power into the chamber, as disclosed in U.S. Pat. No. 4,579,618. 
     Substrates which are etched in an oxide etching process generally include an underlayer, an oxide layer which is to be etched, and a photoresist layer formed on top of the oxide layer. The oxide layer may be one of SiO 2 , BPSG, PSG, or other oxide material. The underlayer may be Si, TiN, silicide, or other underlying layer or substrate material. During processing of substrates, unwanted polymer deposition on the surfaces of the chamber can occur. For instance, when the chamber heats up to above 80° C. during oxide etching, a reaction can occur wherein CF 3  forms CF 2  and HF. The formation of CF 2  leads to an increase in polymer deposition on surfaces within the chamber. 
     During etching of a substrate such as a semiconductor wafer in a plasma reactor, the polymer can build up on the cooled, exposed surfaces of the chamber including exposed surfaces of a substrate support such as an electrostatic chuck and other surfaces such as a dielectric annular cap/focus ring surrounding the substrate support. This buildup may cause problems if it flakes off and is carried onto the top surface of the electrostatic chuck. These contaminants on the top surface of the chuck can prevent the chuck from operating properly to hold the wafer securely. In addition, the contaminants can allow helium which is supplied under the wafer as a cooling medium to leak from beneath the wafer and reduce the wafer cooling. The contaminants can also be deposited on and adversely affect the wafer itself. 
     The buildup of polymer can be removed by a cleaning step performed between the processing of successive wafers. Generally, cleaning can be performed by injecting oxygen into the chamber, striking a plasma and reacting the oxygen with the deposited polymer to achieve an aggressive oxygen clean of the processing chamber. 
     The aggressive oxygen cleaning of the processing chamber is undesirable because it adds to the wafer cycle time, reducing through-put of the system. In addition, the aggressive oxygen clean will shorten the lives of members within the processing chamber due to ion bombardment of these members. As such, it would be desirable if substrate processing could be carried out without a need for the aggressive oxygen cleaning step to thereby shorten cycle time and extend the life of chamber components. 
     One example of a vacuum processing chamber  10  is illustrated in  FIG. 1 . The vacuum processing chamber  10  includes a substrate holder  12  including an electrode providing an RE bias to a substrate supported thereon. The substrate holder  12  includes an electrostatic clamp  14  for clamping the substrate. The substrate which is placed on the electrostatic clamp  14  is preferably cooled by helium baekeooling (not shown) provided between the substrate and the electrostatic clamp. A ring  16  surrounds the electrostatic clamp  14 . The ring  16  may be a ceramic focus ring; a combination of a focus ring, coupling ring, and edge ring; or another combination of rings. 
     The vacuum processing chamber  10  includes a source of energy for maintaining a high density (e.g. 10t1˜1012 ions/cm 3 ) plasma in the chamber such as an antenna  18  (such as a planar spiral coil or other suitable design) which is positioned above the chamber and powered by a suitable RE source. A suitable RE impedance matching circuit, inductively couples RE into the chamber  10  so as to provide a high density plasma. The chamber  10  also includes a suitable vacuum pumping apparatus for maintaining the interior of the chamber at a desired pressure (e.g. below 50 mTorr, typically 1-20 mTorr). A dielectric window  20  (such as a uniformly thick and planar sheet of quartz, alumina, silicon nitride, etc.) is provided between the antenna  18  and the interior of the processing chamber  10  and forms the vacuum chamber wall at the top of the processing chamber  10 . A dielectric gas distribution plate, commonly called a showerhead  22 , may be provided beneath the window  20  and includes a plurality of openings such as circular holes (not shown) for delivering process gas supplied by a gas supply to the processing chamber  10 . However, the gas distribution plate  22  can be omitted and process gas can be supplied to the chamber by other arrangements such as gas rings, etc. 
     One area in which deposits of polymer can occur in a processing chamber is a narrow gap  30  between the wafer supported on the electrostatic chuck  14  and the surrounding ring(s)  16 . Specifically, a gap  30  is provided beneath the edge of the wafer which overhangs the surrounding ring. This gap  30  allows for manufacturing tolerances, thermal expansion and wear of the parts. However, process gas and volatile byproducts within the chamber  10  may migrate into the gap  30  and cause undesirable polymer deposits in the gap and on the underside edge of the wafer which may flake off and cause contamination of the wafer and/or chamber. 
       FIG. 2  is an enlarged cross sectional view of an outer portion of an electrostatic chuck  14 ′ and surrounding rings including a focus ring  16 ′, a coupling ring  40 , and a hot edge ring  42 . 
     As shown in the enlarged view of  FIG. 3 , when a substrate S in the form of a semiconductor wafer is positioned on the electrostatic chuck  14 ′ and held in place by a suitable electrostatic clamping force a small vertical gap  30 ′ is provided between an overhanging edge of the substrate S and a groove  44  provided in the edge of the hot edge ring  42 . This vertical clearance gap  30 ′ is designed to prevent the overhanging edge of the substrate S from being lifted and thereby avoid a reduction in clamping force applied by the electrostatic chuck  14 ′. However, this additional vertical clearance gap  30 ′ provides additional opportunity for polymer buildup which may flake off and contaminate the substrate S or the electrostatic chuck  14 ′. 
     Thus, it would be desirable to reduce the vertical gap  30 ′ between the hot edge ring  42  or other surrounding ring and the overhanging substrate edge. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an apparatus for adjusting a gap between a ring surrounding substrate support and a substrate. 
     In accordance with one aspect of the invention the plasma processing apparatus comprises a processing chamber, a power source which energizes process gas in an interior of the processing chamber into a plasma state for processing a substrate, a substrate support which supports a substrate within the interior of the processing chamber, the substrate support having an upper surface, an upper ring surrounding the substrate support, the upper ring having a portion extending under a substrate when the substrate is located on the substrate support, and a coupling ring surrounding the substrate support, the coupling ring having a first ring rotatable with respect to a second ring to adjust height of the coupling ring and adjust a gap between the upper ring and the substrate. 
     In accordance with another aspect of the invention the plasma processing apparatus comprises a processing chamber, a process gas which energizes process gas in an interior of the processing chamber into a plasma state for processing a substrate, a substrate support which supports a substrate within the interior of the processing chamber, the substrate support having an upper surface, an upper ring surrounding the substrate support, the upper ring having a portion extending under a substrate when the substrate is located on the substrate support, and a coupling ring surrounding the substrate support, the coupling ring having a first ring rotatable with respect to a second ring to adjust height of the coupling ring and adjust a gap between the upper ring and the substrate. 
     In accordance with a further aspect of the invention the method of reducing polymer deposition on a substrate support in a plasma processing system comprises providing an adjustment mechanism for adjusting a gap between a substrate and a surrounding ring in a plasma processing apparatus, and adjusting the gap between the substrate and the surrounding ring by rotating a first ring with respect to a second ring of the adjustment mechanism. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The invention will now be described in greater detail with reference to the preferred embodiments illustrated in the accompanying drawings, in which like elements bear like reference numerals, and wherein: 
         FIG. 1  is a cross sectional view of a vacuum processing chamber; 
         FIG. 2  is an enlarged cross sectional view of a portion of  FIG. 1  showing the electrostatic chuck and surrounding rings; 
         FIG. 3  is an enlarged cross sectional view of portion A of  FIG. 2 ; 
         FIG. 4  is an enlarged cross sectional view of a portion of a vacuum processing chamber according to the present invention including an adjustable coupling ring; 
         FIG. 5  is an exploded schematic prospective view of the adjustable coupling ring of  FIG. 4 ; and 
         FIG. 6  is an enlarged cross sectional view of a portion of an electrostatic chuck and focus ring showing a gap between the focus ring and substrate. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A portion of a substrate support for a vacuum processing chamber according to one embodiment of the present invention is illustrated in  FIG. 4 . The substrate support  100  illustrated in  FIG. 1  includes an electrostatic chuck  102 , a focus ring  104 , a coupling ring  106 , and a hot edge ring  108 . 
     As is well known to those familiar with the plasma processing art, the rings surrounding the electrostatic chuck including the focus ring  104 , coupling ring  106 , and hot edge ring  108  help focus the ions from the RE induced plasma region on the surface of the substrate to improve process uniformity, particularly at the edge of the substrate. This is because when RE power is supplied to substrate holding chuck  102 , equipotential field lines are set up over substrate and bottom electrode. These field lines are not static but change during the RE cycle. The time averaged field results in the bulk plasma being positive and the surface of the substrate and electrostatic chuck negative. Due to geometry factors, the field lines are not uniform at the edge of the substrate. The focus, coupling, and hot edge rings help direct the bulk of the RE coupling through substrate to the overlying plasma by acting as a capacitor between the plasma and the powered electrode (e.g., RE-powered chuck). 
     The hot edge ring  108  overlays an adjustable RF coupling ring  106 . The hot edge ring  108  is a sacrificial edge ring surrounding the electrostatic chuck  102 . The hot edge ring  108  is a replaceable component which tends to become hot during processing of a substrate and thus is referred to as a hot edge ring. The hot edge ring  108  may be made from conductive electrode materials such as SiC and silicon or from dielectric materials such as quartz. By changing the edge ring material, the degree of coupling through the plasma can be tailored to provide a desired localized “edge” etch rate at the outer portion of a substrate being processed. SiC, having a lower capacitive impedance, will generally produce a faster edge etch rate than silicon. Quartz and other dielectrics will have a lesser effect on the edge etch rate. 
     In the described embodiment a gap  130 , shown in  FIG. 6 , is formed between an over hanging edge of the substrate S and the silicon hot edge ring  108 . The gap  130  has a vertical dimension d controlled by the adjustable RE coupling ring  106 . The adjustable RF coupling ring  106  is capable of controlling the vertical dimension d of the gap by moving the silicon hot edge ring  108  in a vertical direction as appropriate. It should be noted that vertical direction is any direction substantially parallel to a Y axis, as shown in  FIGS. 1 and 6 . 
     In accordance with one embodiment of the invention, the adjustable RE coupling ring  106  moveably supports the silicon hot edge ring  108 . The adjustable RE coupling ring  106  provides mechanical support for the silicon hot edge ring  108  as well as the capability to control the gap distance d to within a specified range. In one aspect of the invention, the adjustable RE coupling ring  106  is capable of forming the gap with an associated gap distance d ranging between approximately 0.5 mils to less than 6 mils. 
     In the described embodiment, the adjustable RE coupling ring  106  includes two rings  110 ,  112  as shown in  FIG. 5 . The first ring  110  or top ring includes three projections  114  extending from the ring in a direction parallel to a Y axis of the ring. The second ring  112  or bottom ring includes three sets of a plurality of graduated steps  116  around the circumference of the ring. Rotation of the first ring  110  clockwise with respect to the second ring  112  decreases an overall vertical height of the coupling ring  106  and adjusts the gap between the substrate and the hot edge ring  108 . 
     In the described embodiment, the adjustable coupling ring  106  preferably includes graduated steps  116  that vary in height increments of about 0.0001-0.01 inches and preferably about 0.001 inches. Although the illustrated embodiment includes six graduated steps  116  in each of the three sets of steps, other numbers of steps may also be used depending on the amount of adjustment and graduation of adjustment desired. According to another embodiment twelve graduated steps  116  are provided for twelve adjustment heights. 
     In the described embodiment, the top ring  110  of an adjustable coupling ring  106  includes the projections  114  with a height which is equal to approximately the total height of all the steps  116  in one of the three sets of plurality of graduated steps. In a preferred embodiment, the projections  114  have a height of about 0.012 inches. In the described embodiment, the adjustable coupling ring  106  can be formed of quartz. 
     The adjustable RE coupling ring  106  according to the present invention, allows the precise adjustment of the gap  130  between the substrate S and the hot edge ring  108  in a plurality of individual steps. The coupling ring  106  allows an operator to readjust the coupling ring at any time between processing of substrates or during set up of the vacuum processing chamber. The RE coupling ring  106  also ensures that the hot edge ring  108  is adjusted evenly on all sides of the substrate and that a top surface of the coupling ring remains substantially horizontal. 
     The adjustable RE coupling ring  106  may be installed in new vacuum processing chambers or used to retrofit existing vacuum processing chambers to provide adjustability of the hot edge ring  108 . 
     A process for installing and adjusting the adjustable RE coupling ring  106  is easily implemented as follows. The bottom ring  112  of the coupling ring  106  is placed on the step of the electrostatic chuck  102  with the plurality of graduated steps  116  facing upward. The top ring  110  is then placed onto the bottom ring  112  with the three projections  114  each aligned on the highest of the graduated steps. The hot edge ring  108  is then placed on top of the assembled coupling ring  106  and the gap is measured with a measuring device. One example of a measuring device is a vertical mount dial indicator which is placed on the substrate holding chuck  102  and measures a vertical distance from the top of the chuck to the top of the edge of the hot edge ring  108 . Preferably, the gap  130  is measured at 90 degrees apart around the electrostatic chuck. The measurement is taken at a location on the hot edge ring  108  close to the electrostatic chuck  102 . Due to deterioration or wear of the hot edge ring, just outside the edge of the substrate, the area of the hot edge ring  108  closest to the chuck  102  should be the highest location in the hot edge ring groove. The measurement will generally indicate that the hot edge ring  108  is higher than the electrostatic chuck  102  and that the hot edge ring needs to be adjusted downward. The hot edge ring  108  is then removed. The coupling ring  106  is then adjusted by rotating the top ring  110  clockwise and thus reducing the height of the coupling ring. The hot edge ring  18  is then replaced and the adjustment is then repeated until a minimum gap distance d is achieved. 
     According to one preferred embodiment of the invention, the rings  110  and  112  of the coupling ring  106  include a locking feature (not shown) which locks the rings in an aligned radial position. One example of a locking mechanism includes an detent on the top ring  110  which interlocks with grooves on each step of the bottom coupling ring  112 . 
     It should be appreciated that in a specific system, the specific shape of the focus ring  104 , the coupling ring  106 , and the hot edge ring  108  may vary depending on the arrangement of chuck  102 , substrate and/or others. Therefore, the exact shape of the rings surrounding the chuck in  FIGS. 4-6  are shown for illustration purposes only and are not limiting in any way. Although the invention has been illustrated with a coupling ring arranged to adjust a hot edge ring, other rings may also be adjusted using the coupling ring. 
     While the invention has been described in detail with reference to the preferred embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made and equivalents employed, without departing from the present invention.