Abstract:
A substrate cleaning system incorporating an edge scrubbing roller is disclosed. The system includes a cleaning station having a first brush and a second brush. The second brush is oriented relative to the first brush so as to receive a flat circular substrate therebetween. The first brush and the second brush are configured to simultaneously scrub a first and second surface of the flat circular substrate. The cleaning station also includes a scrubbing roller that is configured to receive an edge of the flat circular substrate. The scrubbing roller has a scrubbing pad for scrubbing a first surface edge of the first surface, a second surface edge of the second surface, and an edge that is not part of either the first or second surface. The edge scrubbing provided by the scrubbing roller advantageously assists in removing edge beading, metal debris, and other particulates that form during fabrication operations, such as metal deposition. In one example, a spray nozzle or multiple nozzles can be directed at the scrubbing roller so as to deliver targeted cleaning fluids that further assist in removing the desired materials from the wafer periphery, whether it be on the top surface edge, the actual edge, or the bottom surface edge.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to semiconductor wafer cleaning and, more particularly, to apparatuses and methods for cleaning wafer edges before, during and after fabrication operations. 
     2. Description of the Related Art 
     In the semiconductor chip fabrication process, it is well-known that there is a need to clean a wafer where a fabrication operation has been performed that leaves unwanted residuals on the surface of the wafer. Examples of such a fabrication operation include plasma etching, material depositions and chemical mechanical planarization (CMP). CMP is commonly performed on both dielectric materials and conductive materials, e.g., such as oxide and copper. If particles or films are left on the surface of the wafer for subsequent fabrication operations, the unwanted residual particles or material may cause, among other things, defects such as scratches on the wafer surface and inappropriate interactions between metallization features. In some cases, such defects may cause devices on the wafer to become inoperable. In order to avoid the undue costs of discarding wafers having inoperable devices, it is therefore necessary to clean the wafer adequately yet efficiently after fabrication operations that leave unwanted residue on the surface of the wafer. 
     FIG. 1A shows a high level schematic diagram of a wafer cleaning system  50 . The cleaning system  50  typically includes a load station  10  where a plurality of wafers in a cassette  14  may be inserted for cleaning through the system. Once the wafers are inserted into the load station  10 , a wafer  12  may be taken from the cassette  14  and moved into a brush box one  16   a , where the wafer  12  is scrubbed with selected chemicals and water (e.g., de-ionized (DI) water). The wafer  12  is then moved to a brush box two  16   b . After the wafer has been scrubbed in the brush boxes  16 , the wafer is moved into a spin, rinse, and dry (SRD) station  20  where DI water is sprayed onto the surface of the wafer and spun to dry. During the rinsing operation in the SRD station. After the wafer has been placed through the SRD station  20 , the wafer is moved to an unload station  22 . 
     FIG. 1B shows a simplified view of a cleaning process performed in brush box one  16   a . In brush box one  16   a , the wafer  12  having a top surface  12   a  (i.e., the active side) is inserted between a top brush  30   a  and a bottom brush  30   b . The wafer  12  is capable of being rotated by holding and driving rollers (not shown) and the rotating brushes  30   a  and  30   b  to adequately clean the entire top and bottom surfaces of the wafer. After typical CMP operations, a wafer is placed into the cleaning station  50 . In brush box one  16   a , the top brush  30   a  and the bottom brush  30   b  are preferably concentrated with a cleaning chemical, which is received from a source  32  or other sources controlled by a chemical/DI water dispensing system (not shown). 
     A common fabrication operation includes the deposition of metals over previously formed dielectric features, which is commonly done in damascene and dual-damascene processes. As is generally defined, damascene and dual-damascene processes include the formation of features, such as interconnect lines and vias into dielectric materials, filling the dielectric features with conductive material, e.g., such as copper, and then performing CMP operations to remove the excess metallization material. The metal material can be formed over the wafer using various techniques, such as, for example, deposition, electroplating, sputtering, and the like. 
     In either case, the formation of metal material may form excess beading around the periphery of the wafer. It is also a common operation to perform standard cleaning operations after such metal deposition operations, to ensure that the excess metal and lose particles and contaminants are removed from the wafer before engaging in further processing. 
     A problem typically experienced is that standard brush scrubbing and edge cleaning techniques fail to clean and remove the metal edge beading and loose particles from wafer edge surfaces sufficiently well. One approach to edge cleaning was described in U.S. Pat. No. 5,861,066, entitled “Method and Apparatus for Cleaning Edges of Contaminated Substrate.” This U.S. Patent is incorporated herein by reference. Although this apparatus does well at cleaning the immediate edge of the wafer, other portions of the wafer edge in which beading and particulates adhere are most commonly not sufficiently addressed. That is, although sufficient center cleaning is performed using the brushes  30  of FIG. 1B, not enough mechanical scrubbing is performed directly on the top and bottom surface areas near the edge. Consequently, edge beading particle collection will remain even after repeated conventional brush cleaning. 
     In view of the foregoing, there is a need for an apparatus and method for enhancing wafer edge cleaning, especially in cases of post metal deposition operations. 
     SUMMARY OF THE INVENTION 
     Broadly speaking, the present invention fills these needs by providing an improved method for cleaning semiconductor wafer edge regions. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device or a method. Several inventive embodiments of the present invention are described below. 
     In one embodiment, a substrate cleaning system is disclosed. The system includes a cleaning station having a first brush and a second brush. The second brush is oriented relative to the first brush so as to receive a flat circular substrate therebetween. The first brush and the second brush are configured to simultaneously scrub a first and second surface of the flat circular substrate. The cleaning station also includes a scrubbing roller that is configured to receive an edge of the flat circular substrate. The scrubbing roller has a scrubbing pad for scrubbing a first surface edge of the first surface, a second surface edge of the second surface, and an edge that is not part of either the first or second surface. 
     In another embodiment, a substrate cleaning system is disclosed. The system includes a cleaning station having a first brush and a second brush. The second brush is oriented relative to the first brush so as to receive a flat circular substrate therebetween. The first brush and the second brush are configured to simultaneously scrub a first and second surface of the flat circular substrate. The cleaning station also includes a scrubbing clamp. The scrubbing clamp is configured to receive an edge of the flat circular substrate. The scrubbing clamp has a scrubbing pad for scrubbing a first surface edge of the first surface, a second surface edge of the second surface, and an edge that is not part of either the first or second surface. 
     In yet another embodiment, a scrubbing roller is disclosed. The roller includes a top roller core and a bottom roller core. The top roller core and the bottom roller core define a U-shaped circular pocket. The roller further includes a scrubbing pad that is configured to line the U-shaped circular pocket. The scrubbing pad is configured to receive an edge region of a semiconductor wafer. The edge region is configured to be inserted into the U-shaped circular pocket so as to scrub a top surface region, an edge surface region and a bottom surface region of the edge region of the semiconductor wafer. 
     The advantages of the present invention are numerous. Most notably, the wafer edge scrub roller and clamp each are configured to locally scrub the top surface, the edge surface, and the bottom surface of the wafer along the periphery. This localized scrubbing assists in removing post metal deposition beading, removal of metal debris, loosely held metallic deposition films, and particulates. The edge scrubbing is preferably assisted by the implementation of one or more nozzles that direct cleaning fluids, such as, DI water and other know cleaning fluids directly at the edge/pad material being used for scrubbing. This localized and concentrated mechanical/chemical scrubbing of the wafer edge thus assists in providing cleaner wafers throughout the entire surface (e.g., along the edge and non-edge regions), thus improving yield for wafer cleaner end users. 
     Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings. To facilitate this description, like reference numerals designate like structural elements. 
     FIG. 1A shows a high level schematic diagram of a wafer cleaning system. 
     FIG. 1B shows a detailed view of a wafer cleaning process performed in a brush. box. 
     FIG. 2A shows a side view of a wafer cleaning system, in accordance with one embodiment of the present invention. 
     FIG. 2B shows a top view of the cleaning system of FIG. 2A, in accordance with one embodiment of the present invention. 
     FIG. 3A shows a top view of a wafer cleaning apparatus having an edge scrub roller and a drive roller, in accordance with one embodiment of the present invention. 
     FIG. 3B shows a three dimensional view of a wafer incorporating an edge scrub roller and nozzle, in accordance with one embodiment of the present invention. 
     FIG. 4 illustrates a cross sectional view of a scrub roller receiving an edge region of a wafer, in accordance with one embodiment of the present invention. 
     FIG. 5 shows a more detailed diagram of FIG. 4 in which the wafer is inserted into the pad, in accordance with one embodiment of the present invention. 
     FIGS. 6A and 6B illustrate cross-sectional views of an alternative embodiment of the present invention, in which a clamp scrubber is implemented in place of a roller. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments for methods and apparatus for cleaning wafer edge regions are disclosed. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be understood, however, by one of ordinary skill in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention. 
     FIGS. 2A and 2B show a side view and a top view, respectively, of a cleaning system  120 . The cleaning system  120  typically includes an input station  100  where a plurality of wafers may be inserted for cleaning through the system. Once the wafers are inserted into the input station  100 , a wafer may be taken from the input station  100  and moved into a brush box one  102   a,  where the wafer is scrubbed with selected chemicals and water (e.g., de-ionized water) before being moved to a brush box two  102   b . As will be described below, each of the brush boxes  102  can include an edge brushing apparatus, such as a scrubbing roller. The edge brushing apparatus is configured to apply mechanical scrubbing to an edge region of the wafer as well as surface regions along the periphery of the wafer. The edge brush apparatus can be configured to apply different amounts of pressure and can be configured with accompanying spray nozzles, misters or fluid applicators to further assist in the scrubbing. 
     After the wafer has been scrubbed in the brush boxes  102 , the wafer is moved into a spin, rinse, and dry (SRD) station  104 , where de-ionized (DI) water is sprayed onto the surface of the wafer and spun to dry. After the wafer has been placed through the SRD station  104 , an unload handler  110  takes the wafer and moves it into an output station  106 . The cleaning system  120  is configured to be programmed and controlled from system electronics  108 . 
     FIGS. 3A shows a more detailed view of a cleaning apparatus inside one of the brush boxes  102 . A load handler may take the wafer  200  from the input station  100  and position the wafer inside the brush box  102   a . A top cleaning brush  30   a  and a bottom cleaning brush  30   b , are positioned on respective surfaces of the wafer surface  200  (as shown in FIG.  1 B). A cleaning brush  30  typically has a plurality of small surface mounds distributed in evenly spaced rows along the surface of a cleaning brush  30 . The brushes  30  can be made from polyvinyl alcohol (PVA), mohair, and other wrapped materials that are soft enough to prevent damage to circuit devices. The brushes  30  can also function as a conduit for fluids that are to be applied to the wafer surface. 
     For more information on wafer cleaning systems and techniques, reference may be made to commonly owned U.S. patent application having application numbers: (1) Ser. No. 08/792,093, filed Jan. 31, 1997, entitled “Method And Apparatus For Cleaning Of Semiconductor Substrates Using Standard Clean 1 (SC1),” U.S. Pat. No. 5,858,109 and (2) Ser. No. 08/542,531, filed Oct. 13, 1995, entitled “Method and Apparatus for Chemical Delivery Through the Brush”, abandoned. Both U.S. patent applications are hereby incorporated by reference. 
     During the cleaning process, the wafer  200  may be rotated between the cleaning brushes  30  and a set of rollers  202  and  204 . In a preferred embodiment, roller  202  is a scrub roller and roller  204  is a drive roller. Although, is should be understood that the rollers  202  and  204  can be interchanged with each other. In other embodiments, it is possible to have two or more scrub rollers  202  in addition to the drive roller  204 . Still further, drive roller  204  can also be omitted if at least two scrub rollers  202  are used. The wafer preferably rotates at about 20 rotations per minute or less. This is about ⅕ the rotational speed using in conventional SRD stations. 
     A chemical cleaning fluid is generally applied to the wafer  200  surfaces through the brush (TTB) as the cleaning brushes  30  scrub the wafer  200  surfaces. It should be appreciated by one of ordinary skill in the art that a chemical cleaning fluid may alternatively be applied by other means, such as an external drip applicator (not shown), as opposed to TTB. Where a chemical cleaning fluid has been applied to the wafer  200  surfaces via a TTB application technique, it is generally desired to clean the wafer  200  surfaces with water (preferably de-ionized “DI” water) after chemical scrubbing. If left on the wafer  200  surface, the chemicals may cause unwanted reactions in subsequent cleaning and post-cleaning operations. 
     Still referring to FIG. 3A, the scrub roller  202  is implemented to perform a scrubbing operation at an edge of the wafer  200 , including surface regions of the wafer near the edge. As is well known, these regions are often referred to as the edge exclusion regions (EER)  210 . The EER in 200 mm and 300 mm wafers can extend from between about 1 mm and about 7 mm into the wafer from the peripheral edge. In another embodiment, the EER can extend from between about 2 mm and about 3 mm into the wafer from the peripheral edge. Preferably, the drive roller  204  is configured to assist in driving the wafer  200  in the wafer rotation direction  211 . The rotation of the brush  30  also assists in moving the wafer closer into and against the scrub roller  202  and the drive roller  204 . In a preferred embodiment, the scrub roller  202  is preferably configured to receive not only the edge of the wafer, but also a portion of both the top and bottom portions of the wafer  200  (e.g., the EER  210 ). The receiving by the scrub roller  202  is configured to be a tight enough fit (by adjustment or the like) such that the scrubbing material of the scrub roller  202  performs a sufficient degree of mechanical scrubbing against the surface of the wafer. This additional mechanical scrubbing will assist in removing, for example, edge beading, which commonly builds up during standard metal deposition and which is often not removed by simply using the brushes  30 . Edge beading is sometimes observed under fine microscopes and includes loosely held metallic particles, debris, and films. 
     FIG. 3B illustrates a three-dimensional diagram of FIG. 3A in which the scrub roller  202  is shown scrubbing the EER  210  of the wafer  200  as a spray nozzle  207  delivers cleaning fluids to the scrub roller  202 . Each roller is shown rotating in direction  203 . In a preferred embodiment, the spray nozzle  207  is configured to deliver just the right amount of cleaning solution, DI water, or chemicals (e.g., SC1, Ammonia, HF) to the scrub roller  202  and the wafer  200  during the cleaning operation. As shown, the drive roller  204  is also engaged with the wafer  200 , however, the wafer  200  is not fully engaged within the drive roller  204  as is the scrub roller  202 . The scrub roller  202  is shown having a pad  230  formed within a circular U-shaped pocket defined in the scrub roller  202 . The U-shaped pocket having the pad  230  lining thus provides an efficient way of scrubbing both the top, edge and bottom regions of the wafer along the periphery. Pad  230  can be made from polyvinyl alcohol (PVA), mohair, and Suba-IV™, Suba 1000™, IC1000™, IC14000™, Politex™, some of which are available from Rodel, Inc. of Phoenix, Ariz., and other materials that are strong enough to scrub unwanted particles from the wafer edge region yet prevent damage to delicate circuit devices. 
     The scrub roller  202  is driven by a shaft  216   a  that is connection to a belt  214   a  and a motor  212   a . The drive roller  204 , in a like manner, is connected to a shaft  216   b  which is driven by a belt  214   b  and the motor  212   b . In this illustration, both the scrub roller  202  and the drive roller  204  can be configured to rotate at different tangential velocities in direction  203  so as to promote a scrubbing operation that removes the desired materials, particulates, or edge beads commonly associated with metal deposition. Although not shown in FIG. 3B, the wafer  200  is also preferably scrubbed with brushes  30  at the same time the scrubbing of the edge and EER  210  of the wafer are scrubbed. 
     FIG. 4 illustrates a cross sectional view of the scrub roller  202  receiving an edge region of the wafer  200 . The scrub roller  202  includes a top roller core  202   a  and a lower roller core  202   b  which are clamped together by way of a clamping adjuster  232   a  and a screw  232 . Preferably, the top roller core  202   a  and lower roller core  202   b  are made of Teflon™ (or other chemically inert material). The scrub pad  230  is formed or inserted within a pocket formed by the top roller core  202   a  and the lower roller core  202   b . The scrub pad  230  can be taped on, glued on or attached in any manner that does not introduce contaminants or particulates during scrubbing. Preferably, the scrub pad  230  will have a thicker inner region near the center of the scrub roller  202  such that mechanical wear of the scrub pad  230  will provide a sufficient life span for the scrub roller  202  before the pad  230  will require replacement. 
     As shown, the edge  200   a  of the wafer  200  is placed up against the edge surface scrub pad  230 ′ which serves to scrub the actual edge  200   a  of the wafer  200  while the edge exclusion region scrub pad  230   a  serve to scrub the top surface and the bottom surface respectively of the wafer in the edge exclusion region (EER)  210 . As shown, the shaft  216   a  is connected to the lower roller core  202   b  and the shaft  216   a  is connected to the belt  214   a  that then connects to the motor  212   a . The motor  212   a  can be adjusted to deliver the proper amount of torque and power to cause the roller to rotate at the desired speed to achieve a given cleaning operation. It should be noted that some cleaning operations require more vigorous scrubbing while others require slightly more gentle scrubbing to remove different types of materials and particulates. 
     For instance, the type of scrubbing performed after metal deposition operations which leave edge bead buildup require more vigorous scrubbing operations which then can be controlled by the rate at which the roller  202  rotates with respect to the drive roller  204 . In another embodiment, the scrub pad  230  can be adjusted in thickness so as to provide a tighter fit for the wafer  200  and thus, perform more vigorous scrubbing in the edge exclusion region  210 . 
     FIG. 5 shows a more detailed diagram of FIG. 4 in which the wafer  200  is inserted into the pad  230 , in accordance with one embodiment of the present invention. As shown, the pad  230  is designed to provide a tight fit for the wafer  200  so that as the wafer  200  enters the pocket formed by the pad  230 , the pad  230  will enlarge (pushed in) and thus, provide the desired amount of scrubbing over the surface regions of the wafer  200  and the edge regions  200   a . As shown, the pad  230  will compress at the edge exclusion region scrub pad portions  230   a  and over time, will wear at the edge surface scrub pad region  230 ′. As the pad  230  wears, the wafer  200  will progress from the edge surface scrub pad region  230 ′ out to the pad endpoint  230 ″. 
     In another embodiment, the top roller core  202   a  and the lower roller core  202   b  can be made to be adjustable and provide additional force upon the top and bottom portions of the wafer by way of the pad regions  230   a . In either case, as the pad  230  wears, a point will come where the pad  230  may have to be replaced to ensure that proper scrubbing is maintained for the particular process. 
     FIG. 6A illustrates a cross-sectional view of an alternative embodiment of the present invention. The alternative embodiment includes a scrub clamp  402  that can be brought up against the edge of the wafer  200  while the wafer is being scrubbed by rollers in one of the scrub brush boxes as described above. The scrub clamp  402  includes a clamp top  402   a  and a clamp bottom  402   b  which is adjustable by way of an adjustment screw  416  which allows size adjustment movements  420   a  against an adjustable joint  422 . 
     The scrub clamp  402  is also configured to be connected to a shaft  406  by way of an adjustable neck  404 . The adjustable neck  404  will allow angular movement  420   c  of the scrub clamp  402  so as to achieve the desired scrubbing on either the top portion of the wafer surface or the bottom portion of the wafer surface as may be needed. Although the adjustments to the scrub clamp  402  are shown by way of screw adjustments, other types of adjustment techniques may be used so long as the desired adjustment is made to the scrub clamp  402  to provide the desired scrubbing level over the wafer  200 , and in particular, at the edge exclusion region  210 . As shown, the scrub clamp  402  also includes a scrub pad  430  which is configured to receive the wafer  200  as shown in FIG.  6 B. Pad  430  is preferably the same as pad  230  described above. As the wafer rotates, the scrub clamp  402  will place a sufficient amount of pressure at the edge exclusion region such that the top surface and bottom surface in the edge exclusion region  210  of the wafer  200  is scrubbed to a sufficient level. 
     To ensure that the proper amount of edge exclusion region scrubbing is being performed, a nozzle  207  can also be provided in close proximity to the scrub clamp  402  such that the appropriate fluids that will facilitate the scrubbing can be delivered at the point of scrubbing by the scrub clamp  402 . As mentioned above, the fluids can include DI water, chemicals, hydrofluoric acid, and other chemicals that are well known in the art. 
     While this invention has been described in terms of several preferred embodiments, it will be appreciated that those skilled in the art upon reading the preceding specifications and studying the drawings will realize various alterations, additions, permutations and equivalents thereof. It is therefore intended that the present invention includes all such alterations, additions, permutations, and equivalents as fall within the true spirit and scope of the invention.