Abstract:
A method and apparatus for fabricating a wafer spacing mask and a substrate support chuck. Such apparatus is a stencil containing a plurality of dual counterbored apertures that is positioned atop the substrate support chuck while material is deposited onto the stencil and through the apertures&#39; openings onto the chuck. Upon completion of the deposition process, the stencil is removed from the workpiece support chuck leaving deposits of the material of various widths but the same heights to form the wafer spacing mask.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a sputter mask or stencil used to control deposition of material in a physical vapor deposition (PVD) system. More particularly, the invention relates to a method and apparatus for precise formation of features on the surface of a substrate support chuck used in a process chamber.  
           [0003]    2. Background of the Related Art  
           [0004]    Substrate support chucks are widely used to support substrates within semiconductor processing systems. A particular type of chuck is a ceramic electrostatic chuck that is used in high-temperature semiconductor processing systems such as high-temperature physical vapor deposition (PVD). These chucks are used to retain semiconductor wafers or other work pieces in a stationary position during processing. Such electrostatic chucks contain one or more electrodes embedded within a ceramic chuck body. The ceramic material is typically aluminum-nitride or alumina doped with a metal oxide such as titanium oxide (TiO 2 ) or some other ceramic material with similar resistive properties.  
           [0005]    One disadvantage of using a chuck body fabricated from ceramic is that, during manufacture, the support surface is “lapped” to smooth the ceramic material. Such lapping produces particles that adhere to the support surface. These particles are very difficult to completely remove from the support surface. The lapping process may also fracture the chuck body. Consequently, as the chuck is used, particles are continuously produced by these fractures. Additionally, during wafer processing, the ceramic material can abrade a wafer oxide coating from the underside of the wafer resulting in further introduction of particulate contaminants to the process environment. During use of the chuck, the particles can adhere themselves to the underside of the wafer and be carried to other process chambers or cause defects in circuitry fabrication upon the wafer. It has been found that tens of thousands of contaminant particles can adhere to the backside of a given wafer after retention upon a ceramic electrostatic chuck.  
           [0006]    To overcome the disadvantages associated with the workpiece substrate contacting the substrate support chuck, a wafer spacing mask is placed upon the surface of the substrate support chuck. Such a wafer spacing mask is disclosed in commonly assigned U.S. Pat. No. 5,656,093, which is hereby incorporated by reference. The material deposited upon the support surface of the chuck body (i.e., the wafer spacing mask) is a metal such as titanium, titanium nitride, stainless steel and the like. The material supports a semiconductor wafer in such a way that the surface of the wafer that faces the chuck is spaced apart and substantially parallel to the surface of the chuck. Usually the material is deposited to form a plurality of pads, although any wafer spacing pattern deposited on the surface of the substrate support chuck may be used. Thus, the wafer spacing mask reduces the amount of contaminant particles that adhere to the underside of the wafer.  
           [0007]    [0007]FIG. 1 depicts a perspective view of a prior art stencil for depositing support surface features. Such stencil is more fully seen and described in U.S. Pat. No. 5,863,396. The above-referenced device is a plate-shaped stencil  100  having a plurality of apertures  108  and a plurality of slots  106  although various other configurations are possible. Material is deposited through the apertures  108  and slots  106  (e.g., via physical vapor deposition) to create the desired surface features on the support surface. The height of such features (i.e., the pads formed by apertures  108 ) must be within 10% of each other to avoid undue flexing and provide uniform support for the wafer to be processed.  
           [0008]    [0008]FIG. 2 depicts a cross-section as seen along lines  2 - 2  of FIG. 1 of the prior art stencil as placed on top of a surface  210  of a ceramic electrostatic chuck  200  following deposition of the surface features by physical vapor deposition (PVD). As can be seen, some deposited material  206  forms on the stencil. Some deposited material forms support surface features  204  that have larger dimensions than other features  202 . Some features are taller in profile as a result of the “shadowing” effect. The “shadowing” effect is a condition by which PVD material approaching the stencil at angles that are not nearly perpendicular to the stencil is deposited on the sidewalls of the aperture instead of the support surface. Accordingly, this will cause some features to protrude above a desired height “d” from the surface  210 . By mapping the inconsistencies in pad height, it has been ascertained that pads over the outer areas of the substrate support are higher than those radially inward. Unfortunately, this condition is undesirable as it leads to non-uniform substrate support, i.e.; the point of contact of the various features with the wafer will be at different heights. A non-uniform substrate support condition alters the critical temperature profile on the wafer and results in excessive bowing of the wafer during chucking. These undesirable conditions eventually alter the quality of the final product.  
           [0009]    Therefore, a need exists in the art for a method and apparatus for fabricating a wafer spacing mask having a plurality of features wherein the plurality of features are formed simultaneously, uniform in profile and wherein the wafer spacing mask can easily be removed from the chuck assembly.  
         SUMMARY OF THE INVENTION  
         [0010]    The disadvantages heretofore associated with the prior art are overcome by a method and apparatus for forming features on a substrate support chuck. The apparatus is a stencil containing a plurality of apertures, each of said apertures having a dual counterbore. The stencil comprises a plate-shaped one-piece structure having a central opening with a plurality of apertures radiating from the central opening outward about the plate-shaped structure. The stencil is preferably fabricated from a ceramic material such as alumina.  
           [0011]    A method of forming features on a surface of a substrate support chuck with the stencil comprises the steps of positioning the stencil on the surface of the substrate support chuck; depositing the material onto the stencil and through a plurality of dual counterbored apertures provided in the stencil to form said features upon the surface of the substrate support chuck; removing said stencil and leaving said features upon said surface of said substrate support chuck. The method uses a stencil having a central opening and a plurality of dual counterbored apertures disposed about the plate. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with accompanying drawings, in which:  
         [0013]    [0013]FIG. 1 depicts a perspective view of a prior art stencil for depositing support surface features;  
         [0014]    [0014]FIG. 2 depicts a cross-sectional view as seen along lines  2 - 2  of FIG. 1 of the prior art stencil;  
         [0015]    [0015]FIG. 3 depicts a perspective view of a sputter mask in accordance with the present invention;  
         [0016]    [0016]FIG. 4 depicts a cross-sectional view of the sputter mask positioned on the surface of a substrate support chuck within a physical vapor deposition system;  
         [0017]    [0017]FIG. 5A depicts a plan view of a sputter mask in accordance with the present invention; and  
         [0018]    [0018]FIG. 5B depicts a cross-sectional view along lines  5 B- 5 B of FIG. 5A of the sputter mask according to the present invention.  
         [0019]    [0019]FIG. 6 depicts a flow chart for producing a sputter mask according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    One solution to forming features having uniform profiles (heights) is shown in FIG. 3. FIG. 3 shows a sputter mask  300  having a plurality of dual counterbored apertures  308 . For best understanding of the invention, the reader should simultaneously refer to both FIGS. 3 and 4 while reading the following. The sputter mask  300  comprises a plurality of dual counterbored apertures  308 . The plurality of dual counterbored apertures  308  are each comprised of a center bore  306 , a forming aperture  310  on the top of the sputter mask  300  and a release counterbore aperture  312  formed on the bottom  324  of the sputter mask  300 . All of the release apertures  312  along the bottom of the sputter mask  300  are formed having the same dimensions. The release apertures  312  all have the same diameter and the same depth. The forming apertures  310  disposed on the top  323  of the sputter mask  300  penetrate to different depths. Each aperture  308  is created by forming a central bore  306  and disposing a counterbored aperture  310 , also known as the top counterbored hole on the top  323  of the sputter mask  300 . The depth of the top counterbored hole  310  varies as a function of distance beginning at the geometric center  301  of the sputter mask  300  and radiating outward. Illustratively, each of the dual counterbored apertures  308  has on its upper surface  323  a top counterbored hole known as the forming aperture  310  having a diameter of approximately 0.165 inches. Opposite each top counterbored holes  310  on the bottom surface  324  is a bottom counterbored hole known as the release aperture  312  having a diameter of approximately 0.090 inches and a depth of 0.008 inches. Many other sizes and arrangements of apertures are available and all such variations are considered within the scope of the present invention.  
         [0021]    As shown in FIG. 4, the specific shape of the sputter mask  300  depends on the shape of the substrate support chuck  402 . Typically, a substrate support chuck  402  is circular, i.e., disk or plate shaped, in plan form, matching the shape of a typical semiconductor wafer as commonly known in the art. The substrate support chuck  402  is generally supported upon a support apparatus  408 . The support apparatus  408  supports the chuck  402  and allows for heating, cooling and retaining a workpiece or substrate upon the surface  404  of the substrate support chuck  402 . To retain a workpiece on the chuck surface  404 , the chuck  402  contains one or more elements  406  for electrostatically clamping the workpiece upon connection to an appropriate power source (not shown). The chuck  402  may also employ a mechanical system for preventing movement or the workpiece (i.e., circumferencially disposed clamp ring or integrated vacuum parts (not shown)). The present invention is applicable to any of the commonly used chuck types. Therefore, the specific nature of the chuck  402  and its operation is irrelevant to the present invention.  
         [0022]    The sputter mask  300  is shaped such that when it is placed on the surface of the substrate support chuck  402 , the bottom surface  324  of the sputter mask  300  is supported by the surface  404  of a chuck  402 . In the depicted embodiment, the substrate support chuck  402  contains a flange  416  that extends radially from the central body  401  of the chuck  402  and circumscribes the entire chuck body  401 . As such, the circumferential edge  418  of the chuck body  401  is used to center the sputter mask  300  upon the chuck  402 . Although the sputter mask  300  rests upon the chuck surface  404 , there are areas of the sputter mask  300  that do not contact the surface  404  of the substrate support chuck  402 . In particular, the sputter mask  300  does not contact a surface  420  of the flange  416 . A gap  414  is formed between the flange of the substrate support and the sputter mask  300 . The sputter mask  300  extends beyond the edge of the flange  416  of the support surface to form an overhang  432 . In use, this overhang  432  supports a conventional cover ring  434 .  
         [0023]    The sputter mask  300  contains approximately  372  dual counterbored apertures  308  that are arrayed in a pattern of concentric rings. FIGS. 5A and 5B each depict a different view of a sputter mask according to the present invention and it may be helpful to the reader to view both figures simultaneously. FIG. 5A depicts a plan view of a sputter mask in accordance with the present invention. FIG. 5B depicts a vertical cross-sectional view along line  5 B- 5 B of FIG. 5A. The present embodiment shows the dual counterbored apertures  308  arranged in a plurality of concentric circular patterns  302  radiating from the center  301 . The dual counterbored apertures  308  have forming apertures  310  that vary in depth from approximately 0.062″ in a first circular pattern  302   1 , to approximately 0.065″ in a ninth circular pattern  302   9 . The concentric circular patterns are equidistantly spaced from each other and begin in an area located a distance from the central point  301 . The present embodiment features nine concentric circular patterns. The first concentric circular pattern  302   1  has twelve equally spaced dual counterbored apertures  308  arranged within it. The forming apertures  310  of the first concentric circular pattern  302   1  are bored to a depth of approximately 0.062 inches (see FIG. 5B for detail). Second, third and fourth concentric circular patterns  3022 ,  3023  and  3024  respectively, each have twenty-four equally spaced dual counterbored apertures  308  arranged within them. The forming apertures  310  of the second, third and fourth concentric circular patterns are bored to a depth of approximately 0.063 inches respectively. Fifth, sixth and seventh concentric circular patterns  302   5 ,  302   6  and  302   7  respectively, each have forty-eight equally spaced dual counterbored apertures  308  arranged within them. In the fifth concentric circular pattern the depth of the forming apertures  310  is approximately 0.063 inches while the depth of the forming apertures  310  for the sixth and seventh concentric circular patterns is approximately 0.064 inches. Lastly, the eighth and ninth concentric circular patterns  302   8  and  302   9  respectively each have 72 equally spaced dual counterbored apertures  308  arranged within them. Both the eighth and ninth concentric circular patterns have forming apertures  310  bored to a depth of approximately 0.065 inches.  
         [0024]    Typically, the material of the sputter mask  300  is titanium. Other materials can be used such as silicon, ceramic, aluminum, aluminum nitride and the like. The choice of material depends on the type of system the sputter mask  300  will be used in. For example, in PVD systems, materials that minimize differential thermal expansion such as titanium are the most desirable materials for the sputter mask  300 . Another consideration in choosing sputter mask material is the material that will be sputtered in the system to form deposits on the surface of the substrate support. For example, it is impossible to clean and reuse a titanium mask that has been sputtered with titanium. Therefore, if a reusable mask is desirable, the mask  300  should be fabricated from a different material than that which is being sputtered, e.g., a silicon mask would be appropriate for sputtering titanium.  
         [0025]    A method of making the sputter mask  300  is shown in FIG. 6 as a series of method steps  600 . The method begins at step  602  with a blank disk of suitable material such as but not limited to aluminum. In the present embodiment the disk is approximately 0.120 inches thick and approximately eight inches in diameter. It is appreciated by those skilled in the art that these dimensions may vary widely. In step  604 , a plurality of dual counterbored apertures is formed having the characteristics as previously described. The sputter mask is then mounted on a test e-chuck at step  606 . A layer of material is then deposited onto the sputter mask in step  608 . After the deposition process is complete the sputter mask is removed from the test e-chuck at step  610  and measurements are taken at step  612  to determine the non-uniformity distribution parameters. The data taken from the measurements is used to develop and adjust the depth of the forming aperture  310  of the dual counterbored apertures  308  at step  614  as they radiate from the central point. This final adjustment counteracts any of the non-uniformities in the features from the deposition process.  
         [0026]    A method of forming deposits on the surface  404  of the substrate support chuck  402  begins with placement of the sputter mask  300  onto the substrate support surface within a PVD system  50  as seen in FIG. 4. In addition to the chuck  402 , the PVD system contains a chamber  126  (vacuum chamber) containing a vacuum, a cover ring assembly  128  for confining the deposition proximate the chuck, and a target  130 . The PVD system is a conventional system that is operated in a conventional manner to cause sputtering of the target material upon the sputter mask  300  and the exposed support surface  404  of the chuck  402 . The deposition material is a material that bonds to and is thermally compatible with the chuck material. For example, for ceramic chucks, deposition materials include boron-nitride, diamond, oxides, such as aluminum oxide, and metals such as titanium. In general, this technique for patterned deposition of materials is known as liftoff deposition.  
         [0027]    To fabricate a sufficient plurality of features, the PVD system deposits a 1 micron layer of material on the substrate support chuck  402  while the sputter mask  300  is positioned on the support surface  404  of the chuck  402 . Deposition material passes through the apertures  308  of the sputter mask  300  onto the surface of the substrate support  404 . Additionally, a second layer of material may be deposited over the first layer for example, an insulator may be first deposited and a conductor deposited thereover. Any number of layers comprising various materials can be deposited using this process. Following the deposition, the target  130  is removed from the chamber  126  such that the sputter mask  300  can be removed from the chuck surface  404  through the top of the PVD system enclosure. The bottom counterbores  312  prevent sticking of the sputter mask  300  to the deposited material of the chuck  402  and provide material deposits having convex (domed) surfaces. The result is a pattern of deposition material atop the chuck surface  404  and the flange surface  420 . The combination of the dual counterbored holes  310  and  312  ensures a uniform (±10% of height of all fixtures) layer of deposited material during the deposition process.  
         [0028]    While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.