Abstract:
A wafer bevel processing apparatus comprises a plurality of rollers for rotatably supporting a wafer, first process roller, a second process roller, and a process tape extending between the first process roller and the second process roller. The first and second process rollers are positioned to cause the process tape to contact an edge of the wafer when the wafer is loaded into the processing apparatus. The process tape is configured to frictionally prepare the edge where contact occurs with the process tape.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to semiconductor wafer cleaning and preparation, and more particularly, to a method and apparatus for cleaning or preparing wafer edges after various fabrication operations. 
   2. Description of the Related Art 
   In the field of semiconductor chip fabrication processing, it is well known that there is a need to clean a semiconductor substrate wafer where a fabrication operation has been performed that leaves unwanted residuals on the surface of the wafer. Examples of such fabrication operations include plasma etching, material depositions and chemical mechanical planarization (CMP). CMP is commonly performed on both dielectric materials and conductive materials such as oxide and copper. If particles or films are left on the surface of the wafer without removing them, the unwanted residual particles or material may cause defects on the wafer surface and inappropriate interactions between metallization features or with subsequent lithography operations. Such defects may cause devices on the wafer to become inoperable. It is therefore necessary to clean the wafer after fabrication operations that leave unwanted residuals on the surface of the wafer. 
   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 generate 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 material, debris, and contaminants are removed from the wafer before engaging in further processing. 
   Standard brush scrubbing techniques often fail to clean and remove the metal edge beading and loose particles from wafer edge surfaces including the bevel edge and exclusion zone which extends from about 1 to 3 millimeters from the bevel. Although sufficient center cleaning is performed using roller brushes, not enough mechanical scrubbing is performed at the edge. Consequently, unwanted material may remain even after repeated conventional brush cleaning. 
     FIG. 1  shows an exemplary prior art wafer brush-box  50 . The brush-box  50  includes a drive roller  61  that rotates in a direction  62  that drives the wafer  12  in a direction  63 , and a stator roller  68  that forces the wafer into engagement with the circumferential groove  70  of drive roller  61 . Edge cleaner  65  cleans the bevel  74  of the wafer  12 . Edge cleaner  65  may rotate in the direction  67  at a different speed than the drive roller  61  to provide some scrubbing action between edge cleaner  65  and wafer bevel  74 . Edge cleaner  65  comprises a grooved roller having a soft compliant material lining the groove for conforming to the edge profile and removing debris. An exemplary edge cleaner of this type is shown in U.S. Pat. No. 6,334,229, which issued to Moinpour et al. on Jan. 1, 2002. Stationary, U-shaped scrub brush edge cleaners are also known. 
   Unfortunately, prior art wafer edge cleaners must be replaced periodically, increasing operating costs. Furthermore, the prior art devices have a small area of contact between the cleaning implement and the wafer. The small area of contact results in reduced efficiency in cleaning, requiring longer cleaning times. 
   In view of the foregoing, there exists an unmet need for a substrate edge cleaning system and method that provides a less costly, more effective and efficient alternative to current technologies. 
   SUMMARY OF THE INVENTION 
   Broadly speaking, the present invention fills these needs by providing an improved substrate bevel and exclusion zone cleaning mechanism. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, computer readable media, or a device. Several inventive embodiments of the present invention are described below. 
   One embodiment includes a wafer bevel processing apparatus comprises a first process roller, a second process roller, and a process tape extending between the first process roller and the second process roller. The first and second process rollers are positioned so as to engage a wafer edge. The process tape comprises a material suitable for one of cleaning, scrubbing, or abrading at and around the wafer edge. 
   In another embodiment, a method for processing a bevel of a semiconductor wafer is provided. In the method, a process tape is extended between a first process roller and a second process roller so that the bevel of the wafer contacts the process tape. The wafer is rotated on its axis so that the entire circumference of the wafer is processed. 
   Other aspects and advantages of the 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 invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, and like reference numerals designate like structural elements. 
       FIG. 1  shows a prior art wafer bevel and exclusion zone cleaning apparatus. 
       FIG. 2A  shows one embodiment of a wafer bevel and exclusion zone cleaning apparatus. 
       FIG. 2B  shows a detail view of process rollers and process tape of the embodiment shown in  FIG. 2A . 
       FIG. 3  shows an embodiment with the circumferential grooves of the process rollers moved out of engagement with the wafer edge. 
       FIG. 4  shows an embodiment having a cleaning apparatus that uses a continuous process tape. 
       FIGS. 5A and 5B  show detail views of process tape wrapping around a wafer bevel. 
       FIG. 6  shows an alternate embodiment of a bevel and exclusion zone cleaning system using a strong process tape. 
   

   DETAILED DESCRIPTION 
   Several exemplary embodiments for wafer bevel and exclusion zone cleaning system are described below. It will be apparent to those skilled in the art that the present invention may be practiced without some or all of the specific details set forth herein. 
     FIG. 2A  shows one embodiment of an edge cleaning apparatus  100 . Cleaning apparatus  100  comprises a plurality of rollers to support and rotate wafer  12 . Any number of rollers may be used. In one embodiment, driver roller  102  and stator roller  104  engages wafer bevel  74  to support wafer  12 . As used herein, the wafer bevel  74  is defined to include the wafer edge surface. As the edge of the wafer has a surface that is sometimes somewhat rounded or curved, the edge can extend up to or past the curved portions and onto the flat surface of either or both of the top and bottom of the wafer. The flatter surfaces near the edge are referred to as the edge region  66  and include what is commonly referred to as the exclusion zone. The term “wafer” should also be interpreted broadly, as other substrates such as magnetic media for hard drives can be similarly processed. 
   As shown, a cleaning mechanism  110  engages wafer bevel  74 . In one embodiment, cleaning mechanism  110  comprises a process tape supply reel  112  on a first spindle  114  and a process tape take-up reel  116  on a second spindle  118 . Process tape  120  passes from tape supply reel  112 , around first drive loop roller  122 , first process roller  124 , second process roller  126  and second drive loop roller  128 , and returns to process tape take-up reel  116 . 
   A drive belt  130  is a continuous belt that extends around first and second drive loop rollers  122 ,  128  and first and second process rollers  124 ,  126 . Drive belt  130  is formed from a strong flexible material that frictionally engages process tape  120 . Drive belt  130  may include friction enhancing features (not shown) such as protruding spikes, nubs, ridges, etc, to increase friction between belt drive  130  and process tape  120 . One or both drive loop rollers  122 ,  128  may be spring biased in direction  132  away from wafer  12  to place drive belt  130  in tension. The tension of drive belt  130  will cause it to exert pressure on process tape  120  which in turn increases the pressure against wafer bevel  74 , which improves the performance of cleaning mechanism  110 . 
   Drive belt  130  is driven in direction  134  by belt drive motor  136 , which, for example, may be a stepping motor. In other embodiments, it is contemplated that only one drive loop roller is required, the single drive loop roller being connected to the belt drive motor. It is also contemplated that belt drive motor may be connected to one of the first and second process rollers, and therefore no drive loop rollers would be required. In this case, drive belt  130  would extend only around the two process rollers. 
   A take-up drive mechanism  117  drives process tape take-up reel  116 . In one embodiment, take-up drive mechanism  117  comprises an electric motor. If take-up drive mechanism  117  is an electric motor, it can be operated using a tensioning pulley (not shown) or rod, connected to a microswitch to advance take up reel  116  when too much slack is present as detected by the tensioning pulley. Alternatively, it can be controlled by control unit  142  to be activated along with belt drive motor  136 . In an alternate embodiment, take-up drive mechanism  117  may comprise some mechanical linkage (not shown) to belt drive motor  136 . Note that there may be some friction device allowing take up wheel  116  to slip with respect to spindle  118  to maintain appropriate tension of process tape  120 . 
   Process tape  120  may comprise different materials depending upon the application. For example, when used for removing particulates, process tape  120  may comprise a soft compliant polyurethane pad material as known in the art for cleaning, polishing, and abrading (when used with an abrasive slurry) semiconductor wafers. Typical polyurethane pads, such as the either perforated or grooved IC 1000/SubaIV, include of pores or voids having an average diameter of about 30 μm, the voids accounting for approximately 30% of the volume of the pad. It is also known to use other materials for cleaning, polishing and abrading, including felt and mohair. When removing polymer buildup or metallization, a harder material may be used. A fluid or slurry dispenser or applicator (not shown) may be provided to wet process tape  120  to improve its cleaning or abrasive qualities. Drive belt  130  frictionally engages, backs, and supports process tape  120  thereby protecting process tape  120  from shearing and other stresses caused by the scrubbing action. 
   Process rollers  124 ,  126  are mounted to spindles  138 ,  139 , respectively, which can be moved closer together or farther apart using an actuating mechanism (represented by slots  140 ). The distance between process rollers  124 ,  126  causes a contact distance x to vary. Depending on the application of the device and other considerations, the distance can be varied to accommodate various goals. For example, a larger contact area may be required for abrading or scrubbing, while a smaller contact area may be necessary when simply brushing away particulates. 
   The axes of process rollers  124 ,  126  form an angle φ with the wafer axis  106 . The curvature of bevel  74  and tension of process tape  120  around angle φ causes process tape  120  and drive belt  130  to curl or form around bevel  74  and contact edge region  66 , which includes the exclusion zone.  FIG. 2B  shows a detail view of process rollers  124 ,  126  with process tape  120  and drive belt  130  engaging a wafer  12 . In one embodiment, each process roller  124 ,  126  has a circumferential groove  125  in the outer perimeter that can engage wafer bevel  74 . However, circumferential groove  25  is not necessarily required as the process tape  120  will curl or form around bevel  74  in response to edge perimeter curvature even in the absence of circumferential groove  125 . Process tape  120  and drive belt  130  pass between process rollers  124 ,  126  and wafer bevel  74 . As process tape  120  and drive belt  130  traverses the angle φ around wafer bevel  74 , the upper and lower edges wrap around bevel  74  and contact edge region  66  of wafer  12 , as shown by cross-section view  150  in  FIG. 5A . Because process tape  120  is flexible, it wraps around bevel  74  and easily conforms to any geometry of the bevel. 
   Referring to  FIG. 2A , cleaning mechanism  110  includes a controller  142  which may be located locally or remotely from cleaning mechanism  110 . Controller  142  operates belt drive motor  136  to advance process tape  120  by advancing drive belt  130 . The operation of cleaning system  100  may vary depending on the application. In one exemplary application, in what may be referred to as an indexing operation, belt drive motor  136  and drive belt  130  advances process tape  120  until a clean unused portion thereof is extending between process rollers  124 ,  126 . A wafer is then positioned between stator roller  104 , drive roller  102 , and process rollers  124 ,  126 , and the wafer is rotated against the stationary process tape  120  causing a scrubbing action between contact area of process tape  120  and wafer bevel  74  and edge regions  66  of wafer  12 . In another exemplary operation, process tape  120  is slowly advanced during the cleaning process. In this case, a mechanical linkage such as a belt, gear or other device (not shown) may be provided between drive motor  105  and one of drive loop rollers  122 ,  128  and/or process rollers  124 ,  126 . In yet another exemplary operation, process tape  120  may be reciprocated using belt drive motor  136  to provide enhanced scrubbing action. When reciprocating, supply reel  112  can take up slack using a friction-slip spring return (not shown) which may comprise a coiled spring connected to supply reel  112  at one end and frictionally engaging a spindle  114 , which may be fixed, at the other end. 
   Note that other cleaning processes may take place simultaneously with the bevel and exclusion zone cleaning process. For example, top and bottom brush rollers (not shown) may engage and scrub the top and bottom surfaces of wafer  12  while bevel and exclusion zone cleaning is taking place. During the cleaning process, cleaning and/or rinsing chemicals as known to those skilled in the art such as deionized water may be sprayed on wafer  12  to aid in carrying away debris loosened by brush rollers (not shown) and process tape  120 . 
     FIG. 3  shows an operational variation wherein process rollers  124 ,  126  are moved far apart and are not in engagement with wafer  12 . To support wafer  12 , a second stator roller  107  cooperates with stator roller  104  and drive roller  102 . In this case, process tape is permitted to uncurl slightly so that it does not contact the edge region  66  of wafer  12 , as shown in cross-section view of  FIG. 5B . 
     FIG. 4  shows another embodiment comprising a cleaning apparatus  160  using a continuous process tape  165 . Process tape  165  may comprise a soft flexible material requiring a stronger backing belt to stabilize it, or it may comprise a stronger material or multi-layer material as described below with reference to  FIG. 6 . Continuous process tape  165  is positioned around process rollers  124 ,  126  and drive loop rollers  122 ,  128 . Process tape  165  may be reusable and, in one embodiment, is rinsed by spray nozzle  168  to remove debris from previous cleaning operations. Note that a continuous process tape  165  can be used without changing the configuration of cleaning apparatus  100  shown in  FIG. 2A  thereby providing multiple modes of operation of the cleaning apparatus  100 . It is anticipated that continuous process tape  165  would cost less and last longer than prior art cleaning rollers or stationary brushes. 
     FIG. 6  shows an alternate embodiment of a bevel and exclusion zone cleaning system  170  using a process tape  175  that is strong enough to withstand the tension of take-up drive mechanism  117  and sheer stresses resulting from the scrubbing action with wafer  12 . Process tape  175  may comprise a layered structure comprising a layer of process material such as a scrubbing pad bonded to a backing material such as a fabric formed from a polyamide or like material, vinyl, polyester, or other strong, flexible material. The scrubbing pad layer may be bonded to the backing material by use of an adhesive, by welding, e.g., using ultrasonic welding, or by mechanically engaging the scrubbing pad to the backing layer, or by other known means. In another embodiment, process tape  175  comprises a scrubbing pad material that is sufficiently strong so as not to need a backing material to support and stabilize it. In other aspects, cleaning apparatus  160  operates similarly to the embodiment shown in  FIG. 2A . 
   Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.