Abstract:
An apparatus and method used to selectively etch materials from the edge and bevel areas of a silicon wafer are provided. In one configuration, a bevel etch spin chuck, for use in a device for removing unwanted material from an edge and bevel area of a wafer, includes a fluid channel, a separation barrier, and a gas channel that are substantially circular and concentric. A fluid, such as an etching solution, is provided to the fluid channel and contacts one or more areas at the edge and bevel area of the wafer. A stream of continuously flowing gas, such as nitrogen, is provided to the gas channel and purges an active side of the wafer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 11/294,644, filed Dec. 5, 2005, which claims priority to U.S. provisional patent application Ser. No. 60/633,061, filed Dec. 3, 2004. This application also claims priority to U.S. provisional patent application Ser. No. 60/936,216, filed Jun. 18, 2007. These three related patent applications in their entirety are hereby incorporated by reference into this application. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention generally relates to the manufacture of devices employing wet etching processes. More specifically, this invention relates to a method and apparatus for removing and reducing contaminants present in, or introduced during, the wet etching process, wherein the devices produced by such processes are produced without a substantial decrease in performance of the resulting device. 
       BACKGROUND OF THE INVENTION 
       [0003]    The continued decrease in the sizes of devices being produced from silicon or other substrate wafers in wet etching processes has made the wafers more vulnerable to contamination from particles and debris. Semiconductor manufactures utilize a number of cleaning procedures throughout the process of wafer manufacture to remove undesirable debris from the wafer surface. 
         [0004]    Loss analysis studies have indicated that a significant source of debris that leads to a reduction in wafer yield is the presence of undesirable substances on the wafer backside and on the outer several millimeters of the feature, active or top side or surface of the wafer. These debris may comprise both contamination from foreign particles and desired and/or undesired materials and/or layers which are present in, or introduced during, the wafer manufacturing process. In one instance, desired materials may be deposited or collected at or near this edge of the wafer without the benefit of tight control due to the location at the edge of the wafer. An etching process that removes all materials on the wafer backside and on the feature side along the edge of the wafer without adversely impacting the ultimate performance of the devices being produced will generally remove the source of contamination, and thus increase wafer yield. 
         [0005]    These materials may be removed from the backside and outer feature side edges through the application of a barrier layer, followed by a thin layer of copper applied by a physical vapor deposition (PVD) process, followed by a thicker layer of copper using electroplating. However, poor quality at the edge of the wafer may result in the thin layer of copper flaking off causing contamination in subsequent steps of the etching process, or diffusing into the silicon or substrate material due to problems with the barrier layer of the substrate. Thus, the need exists for a process and apparatus to enable excess copper, and other undesirable deposits on the surface of the wafer, to be removed during the etching process. 
       SUMMARY OF THE INVENTION 
       [0006]    This problem may be solved by etching away the copper layer, or other undesirable contaminants, at the edge of the wafer to a distance where all the layers being deposited on the surface of the wafer are applied to the wafer properly without adversely impacting the performance of the device produced by the etching process. 
         [0007]    Layers that often need to be removed from the edge or other areas of the wafer are: copper, aluminum, silicon-oxide and silicon-nitrite, although it may be desirable to remove other materials from the wafer. The distance from the edge should be precisely controlled to insure that the defective areas are substantially completely removed and that there is no substantial undesired etching in the active areas of the device produced from the wafer being etched. 
         [0008]    In one embodiment of this invention, a bevel etch spin chuck, for use in a device for removing unwanted material from an edge and bevel area of a wafer, comprises means for providing a cushion of continuously flowing gas sufficient to support a wafer placed on the chuck; a plurality of retaining pins disposed in a substantially circular pattern to center the wafer on the chuck; a substantially circular fluid channel that is substantially concentric to the pattern of the retaining pins; a substantially circular gas channel that is substantially concentric to the fluid channel; and a substantially circular separation barrier that is substantially concentric to the fluid channel and disposed between the fluid channel and the gas channel, wherein a fluid provided to the fluid channel contacts one or more areas at the edge and bevel area of the wafer, and a stream of continuously flowing gas provided to the gas channel purges an active side of the wafer. 
         [0009]    In another embodiment, the bevel edge spin chuck of further comprises: first supply means for supplying the fluid; and a first lower channel connected to the fluid channel adapted to direct the fluid from the first supply means to the fluid channel by centrifugal force when the wafer is spinning on the chuck. 
         [0010]    In another embodiment, the means for supplying the fluid includes a nozzle pointed toward the first lower channel. 
         [0011]    In another embodiment of the invention, a method for removing unwanted material from edge and bevel areas of a wafer having a feature and non-feature surfaces, comprises: placing the wafer, feature-side down, on a cushion of continuously flowing gas sufficient to support the wafer on a bevel edge spin chuck, wherein the chuck comprises a plurality of retaining pins disposed in a substantially circular pattern to center the wafer on the chuck a substantially circular fluid channel that is substantially concentric to the pattern of the retaining pins, a substantially circular gas channel that is substantially concentric to the fluid channel, and a substantially circular separation barrier that is substantially concentric to the fluid channel and disposed between the fluid channel and the gas channel; rotating the chuck and supported wafer at a rate that creates a centrifugal force that carries a fluid to the fluid channel; and providing a stream of continuously flowing gas to the gas channel, wherein the fluid contacts one or more areas at the edge and bevel area of the wafer, and the stream of continuously flowing gas purges the feature side of the wafer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Understanding of the present invention will be facilitated by consideration of the following detailed description of the embodiments of the present invention taken in conjunction with the accompanying drawings, in which like numerals refer to like parts, and wherein: 
           [0013]      FIG. 1  shows a plan view of the active side of a wafer produced by this invention. 
           [0014]      FIG. 2  is a perspective view of one embodiment of a bevel etch spin chuck of this invention. 
           [0015]      FIG. 3A  is a cross section of the bevel etch spin chuck of  FIG. 2 , taken through the fluid path. 
           [0016]      FIG. 3B  is a cross section of the bevel etch spin chuck of  FIG. 2 , taken through the gas path. 
           [0017]      FIG. 4  depicts a cross sectional view of the wafer of  FIG. 1 , and an exploded view of the edge of the wafer of  FIG. 4 . 
           [0018]      FIG. 5  is a cross section of another embodiment of the bevel etch spin chuck of this invention. 
           [0019]      FIG. 6  shows a cross sectional detail of the spin chuck of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0020]    It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for the purposes of clarity, many other elements which may be found in the present invention. Those of ordinary skill in the pertinent art will recognize that other elements are desirable and/or required in order to implement the present invention. However, because such elements are well known in the art, and because such elements do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein. 
         [0021]    Turning now to  FIGS. 1 and 4 ,  FIG. 1  shows a plan view of active side  401  of wafer  10 , which during at least one embodiment of the bevel etching process of this invention is facing downward. Numeral  401  depicts active protected area of wafer  10  which is not etched. Referring now to  FIG. 4 , areas  402 ,  403  (comprising areas  403   a ,  403   b , and  403   c ), and  404  are the areas where etching takes place, while area  401  is the active feature area of wafer  10  which is not etched. 
         [0022]      FIG. 2  depicts a bevel edge spin chuck  20  in accordance with one embodiment of the invention, showing retaining pins  202 , fluid channel  204 , gas channel  206 , and separation barrier  208 . In preferred embodiments, a fluid such as an etching solution is provided to fluid channel  204  and an inert gas such as nitrogen is provided to gas channel  206 . 
         [0023]      FIG. 3A  is a cross section of chuck  20  taken along a path leading to fluid channel  204 . A wafer  10  is placed on the chuck with the active surface facing down onto a cushion of inert gas  304 . Preferably, inert gas  304  is nitrogen, provided in a conventional manner from a source (not shown) at a relatively low flow rate. Retaining pins  202  are used to center the wafer and prevent it from floating sideways off the chuck. 
         [0024]    In a preferred embodiment, stream nozzle  302  delivers an etching solution below the wafer into lower channel  303  in chuck  20  while the chuck is rotating. Preferably, stream nozzle  302  is stationary and pointed toward lower channel  303 . Centrifugal force carries the etching solution to fluid channel  204 , where the solution contacts the edge of the wafer. Excess fluid flows out radially away from the wafer. 
         [0025]    Preferably, fluid channel  204  delivers etching solution so that a portion of area  402  (up to separation barrier  208 ) and areas  403   a  and  403   b  are affected, while areas  403   c  and  404  are not. The placement and size of separation barrier  208  determine the portion of area  402  that is affected by the etching solution in fluid channel  204 . Those skilled in the art will recognize that other embodiments of the invention may be used so that the etching solution affects either or both of area  403   c  and a portion of area  404 . 
         [0026]    In this embodiment, an inert gas  305  is provided to lower channel  306  in chuck  10  while the chuck is rotating. Preferably, inert gas  305  is also nitrogen, provided in a conventional manner at a relatively high flow rate and in relatively high volume so that it flows through lower channel  306  to gas channel  206 . In this way, inert gas  305  is used to purge the active side  401  of wafer  10  to ensure that vapors from the etching solution do not affect active side  401 . 
         [0027]      FIG. 3B  is a cross section of chuck  20 , slightly rotated from the cross section of  FIG. 3A , taken along a path leading to gas channel  206 . A high volume of inert gas  304  is introduced at the edge of wafer  10 , inward from the area to be etched by the etching solution in fluid channel  206 . Inert gas  304  is allowed to escape toward the bottom of chuck  20  through gas openings  308 . (Although only one gas opening  308  is depicted in  FIG. 3B , preferably a number of gas openings  308  are provided at intervals around chuck  20 .) By maintaining, in a conventional manner, a slightly positive pressure in air channel  310  next to separation barrier  208 , fumes from the etching solution flowing to fluid channel  204  are prevented from migrating to active side  401  of wafer  10 . 
         [0028]    In another embodiment, this invention generally comprises a method and apparatus for removing unwanted material from the edge and bevel areas of a wafer, by: placing the wafer (having a feature side and non-feature side), feature-side down on a cushion of gas above a spin chuck, wherein the chuck has a bevel flow ring; vertically setting the size of the flow ring; rotating the spin chuck and supported wafer at a rate in order to create a centrifugal force affecting any fluid applied to the wafer; and applying a chemical etching fluid to the non-feature-side of the wafer, in amount sufficient to fill a gap between the wafer and the flow ring as the etching fluid flows over the edge of the wafer onto the flow ring, and into a space between the wafer and the flow ring, wherein the feature side of the wafer is substantially protected from exposure to the etching fluid and the areas etched are determined by an overlap between the wafer and the ring. 
         [0029]      FIG. 5  depicts the cross section of a bevel etch spin chuck  30  in accordance with another embodiment of this invention. Chemical etching fluid is dispensed above wafer  10  and as spin chuck  30  rotates, the etching fluid flows to the outside periphery or edge of wafer  10 . 
         [0030]      FIG. 6  shows a detail of the cross section of spin chuck  30  of  FIG. 2 . Wafer  10  is placed on chuck  30  with the active area  401  facing down and protected by a continuous flow of nitrogen or other gas  603  which creates a cushion between wafer  10  and the chuck  30 . The gas is fed through channel  604  to create gas cushion  603 . An outside ring  607  can be adjusted in the vertical orientation by adjusting screw  601 . The adjustment is made so there is a gap  605  between ring  607  and active area  401  of wafer  10 . The fluid dispensed above wafer  10  fills gap  605 , with the excess overflowing into area  606 . 
         [0031]    Wafer  10  is processed feature side  401  down on a rotating chuck  30 . Wafer  10  floats on nitrogen or other gas cushion  603  that prevents contact with chuck  30  and prevents chemical etching fluid or other chemistry from reaching active area  401  of wafer  10 . Chuck  30  contains bevel flow ring  607  that can be set to a fixed gap  605  between flow ring  607  and wafer  10 . Chemical etching fluid or other chemistry is dispensed from above on the backside or non-active area  404  of wafer  10 . Due to the centrifugal force, the chemistry flows to the outer edge of wafer  10 . The chemistry then flows off wafer  10  edge and down onto flow ring  607 . The chemistry fills bevel flow ring  607  and contacts the outer edge (typically by about several millimeters) on feature side  401  of wafer  10 . With a relatively slow rotational velocity (typically between about 50 rpm and about 1200 rpm), chemistry is held by surface tension in gap  605  between wafer  10  and flow ring  607 . The etch distance from the edge of wafer  10  is determined by the distance that flow ring  607  overlaps with wafer  10 . The fluid in gap  605  also acts as a seal and prevents fluid from splashing onto active area  401  of wafer  10 . 
         [0032]    Once the etching process is complete, the rotational velocity is increased (typically from between about 500 rpm to about 2000 rpm) to force the chemistry out of gap  605 . 
         [0033]    If multiple layers are present, several chemistries may be required to etch down to the desired surfaces of wafer  10 . When the etching process is complete, wafer  10  may be rinsed and spun dry. 
         [0034]    In the instant embodiment, gap  605  varies between about 0.001″ and about 0.015″ depending on the viscosity and surface tension of the etching fluid. Also in this embodiment, wafer  10  and flow ring  607  may overlap by about 0.5 to about 5 mm which determines the distance from the edge of the etched area of wafer  10 . 
         [0035]    Another embodiment of the invention concerns backside and bevel edge cleaning. Bevel etch control for 300 mm wafers allows oxide, nitride, poly silicon, and copper removal from backside and bevel exclusion zone. Proprietary spindle tooling enables specific bevel and side edge etching, independent of the wafer backside using a simple, mechanically determined etching area. This capability includes programmable flow rate for the bevel etch and the ability for DI rinse of the bevel area. The process can be used for all wafer sizes, including notched and flat wafers, with bevel 0.8-5 mm. 
         [0036]    The disclosure herein is directed to certain features of the elements and methods of the invention disclosed as well as others that will be apparent to those skilled in the art in light of the disclosure herein. Thus, it is intended that the present invention covers all such modifications and variations of this invention, provided that those modifications come within the scope of the claims granted herein and the equivalents thereof.