Abstract:
A method and apparatus is provided for clamping and shielding the edge of a substrate useful in electronic device fabrication. A shadow ring is formed by an inward radial extension of the top surface of a generally annular shaped clamp ring. The shadow ring portion overhangs but does not contact the top surface of a substrate being processed. A smoothly tapered substrate contact surface extending from the outer diametrical extent of the shadow ring bottom surface to the bottom surface of the clamp ring is sized and adapted to engage the outer edge of a substrate. The substrate contact surface aligns the clamp ring to a substrate support member and a substrate to the substrate support member and the clamp ring as the substrate is lifted vertically.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to improvements in semiconductor processing equipment. More particularly, the invention relates to methods and apparatus for clamping and shielding the edge of a substrate with minimal edge exclusion. 
     BACKGROUND OF THE RELATED ART 
     The fabrication of semiconductor devices on substrates typically requires the deposition of multiple metal, dielectric and semiconductive layers on the surface of substrates. These layers are typically deposited onto substrates in vacuum processing chambers. Some processing operations may require the deposition of additional layers while others may require the etching, or partial removal, of a previously deposited film layer. 
     One commonly used vacuum deposition process is physical vapor deposition (PVD), also referred to as sputtering. In a typical PVD process, a target comprised of the desired deposition material is exposed to a plasma and bombarded by ions from the plasma. This bombardment causes atoms or larger particles to be sputtered from the target and deposited on the substrate being processed. Typically in PVD processes, the geometry of the chamber and the spacing of the target from the substrate being processed is important in order to control the even distribution of the target material onto the substrate. 
     During processing, a substrate support member, often referred to as a pedestal, susceptor, or heater, is disposed in the processing chamber to support the substrate. A clamp ring is typically supported in the chamber above the support member on a shield. When a substrate is introduced into the chamber and supported on the support member, the support member and substrate are moved in the chamber relative to the clamp ring to pick up the clamp ring so that the clamp ring contacts the edge of the substrate and holds the substrate on the support member. As a result of the contact of the clamp ring with the edge of the substrate, the clamp ring shields the edge of the substrate from deposition material, thereby minimizing the usable area on the surface of the substrate. 
     Clamp rings have been provided having a seat portion which engages the top surface of the substrate and an overhanging roof portion which does not contact the top portion of the substrate. The purpose of the roof portion in some applications is to shield the edge of the substrate from deposition. The roof is typically spaced from the upper surface of the substrate to prevent deposition material from being deposited at points where the clamp ring contacts the substrate. If deposition material deposits at these contact points, the substrate can adhere to the clamp ring following deposition which can lead to other difficulties including particle generation or even system shut down to remove the substrate. 
     Clamp rings are generally formed as a continuous annular shaped member or an interrupted metal ring. As shown in FIG. 2, part of the ring  56  engages the substrate surface and exerts a downward force on the top, outer edge of the substrate  12  which is positioned on the support member. The weight of the clamp ring  30  holds the substrate in position for processing and assists in preventing substrate warpage. The fact that the clamp ring contacts the top surface of the substrate presents several problems. First, as previously mentioned, the clamp ring is likely to receive material deposits thereon as deposition processes are performed. This can cause adherence of the substrate to the clamp ring. Such adherence can hinder the removal of the substrate from the chamber following processing. Secondly, the clamp ring seat or contacting portion  56  shields a portion of the outer perimeter of the substrate surface. This reduces the useable surface area of the substrate on which electronic devices may be formed. This problem is generally referred to as edge exclusion. 
     Much effort has been directed at developing clamp rings that shield the edge of the substrate and control or prevent sticking of substrates to the clamp ring without the loss of excess usable surface area on the substrate. Typically, clamp rings adequately secure the substrate to the support member, but achieve this holding force at the expense of the outer perimeter of the substrate. 
     The trend in metallization is to provide as much coverage on the substrate surface as possible. This can be seen in full coverage deposition systems which do not utilize clamp rings or shadow rings during deposition. Further, the trend is to utilize copper as the material of choice in metallization and electroplating as the process of choice to deposit copper. However, copper deposited on the beveled edge of a substrate tends to flake or peel off during chemical mechanical polishing. As a result, edge exclusion has continued to be a requirement of some deposition schemes. 
     As shown in FIG. 2, one common approach to edge exclusion has involved extending the clamp ring across the gap between the edge of the substrate and the edge of the support member and forming a lip or seat extending over the edge of the substrate. Attempts to minimize loss of usable surface area have also required moving the inner terminus of the clamp ring lip which overhangs the edge of the substrate outwardly to more closely approach the edge of the substrate. To maintain a good aspect ratio (ratio of lip overhang width to height above the substrate) to minimize loss of usable surface area on the substrate has proven difficult. One successful approach in this regard is disclosed in U.S. Pat. No. 5,810,931 which is assigned to the assignee of the present invention and incorporated herein by reference. 
     Therefore, it would be desirable to provide a clamp ring which minimizes edge exclusion (maximizes die area) and also prevents copper (or other) metal deposition on the substrate backside and on the substrate bevel. 
     SUMMARY OF THE INVENTION 
     The present invention generally provides a clamp ring having a tapered seat design to secure the substrate to a supporting surface. The tapered surface of the clamp ring preferably aligns the clamp ring and the substrate to each other as well as to the supporting surface. 
     In one aspect of the invention, the clamp ring includes a lower tapered surface which rests on an edge of a substrate, such as a beveled edge of a substrate, during processing. The upper surface of the clamp ring forms an inner lip of the clamp ring which overhangs a portion of the substrate surface above the plane of contact between the clamp ring and the substrate edge. 
     In another aspect of the invention, the lower tapered surface of the clamp ring aligns the substrate on the support member as the clamp ring is lifted to engage the clamp ring. Any misalignment of the substrate on the support member can be corrected by lateral movement of the substrate as the substrate comes into contact with the lower tapered surface of the clamp ring. The lower tapered surface of the clamp ring is adapted to rest on the edge of the substrate and acts as a hard stop for any material deposition beyond the diameter of this plane of contact, thereby preventing edge and backside deposition of material on the substrate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above recited features and advantages of the present invention are understood with better clarity and are best understood by reference to the following detailed description when taken in conjunction with the appended drawings. 
     It is to be noted, however, that the appended drawings illustrate only one typical embodiment of the invention and are therefore not considered limiting of its scope, for the invention may admit to other equally affective embodiments. 
     FIG. 1 is a side view, partially in section of a PVD substrate processing chamber system employing concepts of the present invention. 
     FIG. 2 is a partial cross sectional view showing a typical prior art clamp ring. 
     FIG. 3 is a partial cross sectional view showing one embodiment of a clamp ring of the invention. 
     FIG. 4 is a partial sectional view of an another embodiment of the invention. 
     FIG. 5 is a substantially bottom perspective view of a clamp ring of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A clamp ring according to the present invention generally provides a tapered lower surface at its inner terminus which is adapted to contact the outer edge of a substrate to prevent deposition material from being deposited on the edge and backside of a substrate and on the adjacent surfaces of a substrate support member. The clamp ring of the invention also provides improved edge exclusion and prevents the formation of a bridging layer between the clamp ring and the substrate. The invention is useful in deposition chambers for semiconductor device manufacture, such as PVD or chemical vapor deposition (CVD) chambers. The system will be described in more detail below in a typical PVD chamber for depositing a metal film, such as copper (Cu), on a substrate. While this preferred embodiment is described as an annular member, the shape is not limiting of the scope of the invention. 
     FIG. 1 is a simplified sectional view of a conventional PVD chamber  20  having one embodiment of a clamp ring  30  of the invention supported in the upper portion of the chamber  20 . The chamber  20  generally includes a chamber enclosure wall  24  having at least one gas inlet  27  and an exhaust outlet  28  connected to a vacuum pumping system (not shown). A substrate support member  26  is disposed at the lower end of chamber and a target  22  is received at the upper end of the chamber. Target  22  is electrically isolated from the enclosure wall  24  and the enclosure wall is preferably grounded. A negative voltage is applied to the target  22  with respect to the enclosure wall  24  to generate a plasma in the chamber. A shield  40  is disposed within the chamber  20  and includes an annular upturned wall  41  on which the clamp ring  30  may be suspended over a substrate support member  26  when the support member  26  is retracted downwardly in the chamber as shown in FIG.  1 . 
     In preparation for receiving a substrate into the chamber, the substrate support member  26  is lowered by a drive mechanism  42  to a position well below the clamp ring  30 . The bottom of support member  26  approaches a pin positioning platform  36  when in its lowered position. Support member  26  includes three or more vertical bores (not shown) each of which contains a vertically slidable pin  34 . When the support member  26  is in the lowered position, the bottom tip of each pin  34  rests on the platform  36 , and the upper tip of each pin protrudes above the upper surface of the support member  26 . The upper tips of the pins define a plane generally parallel to the upper surface of the support member  26  for receipt of a substrate to be processed. 
     A conventional robot arm (not shown) carries a substrate  12  into the chamber  20  and places the substrate above the upper tips of pins  34 . A lift mechanism  43  moves the pin platform upwardly to place the pins against the under side of the substrate and to lift the substrate off the robot arm. The robot blade (not shown) retracts from the chamber  20  and the lift mechanism raises the support member and the pins slide downward through the support member  26  to position the substrate thereon. The lift mechanism continues to raise the support member  26  so that the periphery of the substrate contacts the inner portion of the annular clamp ring  30  which is resting on the upturned wall portion  41 . 
     FIG. 3 is a partial cross sectional view of one embodiment of a clamp ring  30  and the edge of a substrate  12 . The clamp ring generally includes an upper roof portion  54  which extends partially over and above the upper surface of the substrate  12  to provide shielding of the contact point between the clamp ring and the edge of the substrate and an outer flange portion  50 . In one embodiment, at least a portion of the lower surface of the clamp ring  30  has a generally flat tapered surface  58  to contact a substrate. Alternatively, the surface  58  may be concave or convex. The tapered surface  58  engages the beveled edge  57  or other outer edge of substrate  12  as the clamp ring  30  engages the substrate on relative movement between the substrate and the clamp ring in the chamber. The tapered surface is preferably disposed at an angle comparable to the angled edge of a substrate, generally between about 5 and 85 degrees from the longitudinal axis of the clamp ring. The tapered surface  58  is preferably disposed at an angle which would allow the clamp ring to rest at least partially on the edge of the substrate to hold the substrate in position for processing. The substrate  12  supports the clamp ring  30  as the substrate support member is moved through the clamp ring on its travel in the chamber. Preferably, the clamp ring is supported by the beveled edge of substrate  12  uniformly about its circumference and stabilizes the substrate position relative to the support member and the clamp ring. The clamp ring  30  is heavy enough to prevent the clamp ring and/or the substrate from sliding across the surface of the support member  26  once the clamp ring engages the substrate and is supported by its own weight on the substrate. As the substrate moves through the clamp ring, any lateral offset of the substrate is eliminated because the angled surface of the clamp ring urges the substrate into alignment on the support member and within the inner diameter of the clamp ring. The tapered surface of the clamp ring thereby reduces the mechanical tolerances, i.e., variations in substrate size, which must be taken into account when defining the inner diameter of the clamp ring. While the tapered surface is shown as a generally flat surface, it is contemplated by the present invention that the surface could be concave or convex. 
     Once clamp ring  30  is positioned on the substrate, the PVD process is started. The tapered surface  58  provides minimal surface area exclusion on the substrate during the deposition process. The tapered surface  58  also forms a solid barrier or stop to prevent vapor or particle escape from the support member  26  area during deposition. When the process is complete, the processed substrate  12  is removed from chamber  20  by a reversal of the process steps previously described. 
     As described previously, any premature contact between the edge  57  of a substrate  12  and the tapered edge surface  58  of clamp ring  30  of the invention as the substrate  12  is raised into processing position by the support member, results in lateral movement of the substrate  12  along the top surface of the support member into an aligned position. This aligning movement can continue until the opposite side of the tapered edge  58  also contacts the opposite side bevel edge  57  of the substrate  12 . Thus, the clamp ring  30  of the invention is self aligning with the substrate  12 . 
     FIG. 4 shows an alternative embodiment of a clamp ring of the invention. The lower surface of the clamp ring may include an angled recess  55  which defines a generally flat tapered surface  58  and a generally flat lower roof surface  59  disposed over the substrate in a manner generally parallel to the upper surface of a substrate disposed on the support member  26  which provides a roof aspect ratio which can be proportioned to provide good edge exclusion while also preventing sticking of the clamp ring to the substrate. A tapered seating surface  58  is provided to contact the edge of the substrate similar to the embodiment shown in FIG.  3 . However; the plane of the roof portion disposed inwardly of the seating portion is generally disposed parallel with the substrate surface. A roof aspect ratio (height:width) can be selected to minimize edge exclusion and/or deposition at the contact area between the clamp ring and the substrate. In addition, the generally parallel lower surface could be stepped to provide an effective roof aspect ratio which is greater than a generally planar lower surface. FIG. 5 is a substantially bottom perspective view of the clamp ring showing the tapered surface  58  and the lower roof surface  59  which define the angled recess  55 . 
     The clamp ring is preferably made of a compatible material such as aluminum, ceramics such as aluminum oxide or alumina, quartz, and the like. Other materials may be known or become known in the art and may be used as well. 
     The clamp ring of the present invention may be used in PVD, CVD, etch or any other processing system to improve edge exclusion. Such systems typically include a chamber and a substrate support pedestal which lifts a substrate vertically to engage a clamp ring in accordance with the concepts of the invention. Once engaged, the clamp ring seals the bevel edge surface of the substrate and maintains the position of the substrate during processing. 
     While the forgoing is directed to the preferred embodiment of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims which follow.