Abstract:
In a first aspect, an apparatus for cleaning a thin disk is provided. The apparatus includes a support roller for supporting a rotating wafer within a wafer cleaner. The support roller comprises a guide portion, for receiving an edge of a wafer, having an inclined surface comprising a low-friction material and adapted to allow the wafer edge to slide thereagainst; and an edge-trap portion for retaining the edge of the wafer and having a transverse surface comprising a high-friction material and adapted, when in communication with the edge of the wafer, to resist sliding thereagainst. Numerous other aspects are provided.

Description:
This application is a division of, and claims priority to, U.S. Non-Provisional patent application Ser. No. 10/976,011, filed Oct. 28, 2004, now abandoned, and titled “WAFER EDGE CLEANING”, which claims priority to U.S. Provisional Application Ser. No. 60/514,938, filed Oct. 28, 2003, and titled “WAFER EDGE CLEANING”. Both of these patent applications are hereby incorporated by reference herein in their entirety for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to cleaning thin disks, such as semiconductor wafers, compact disks, glass substrates and the like. More particularly, the invention relates to scrubbing devices for simultaneously scrubbing the entire surface of a thin disk, including the edges thereof. 
     BACKGROUND OF THE INVENTION 
     To manufacture a thin disk such as a semiconductor wafer, an elongated billet of semiconductor material is cut into very thin slices or disks, about ½ mm in thickness. The slices or wafers of semiconductor material are then lapped and polished by a process that applies an abrasive slurry to the wafer&#39;s surfaces. After polishing, slurry residue conventionally is cleaned or scrubbed from wafer surfaces via a mechanical scrubbing device, such as a device which employs polyvinyl acetate (PVA) brushes, brushes made from other porous or sponge-like material, or brushes having bristles made from nylon or similar materials. Although these conventional cleaning devices remove a substantial portion of the slurry residue which adheres to wafer edges, slurry particles nonetheless may remain and produce defects during subsequent processing. 
     A conventional PVA brush scrubber is shown in the side elevational view of  FIG. 1 . The conventional scrubber  11 , shown in  FIG. 1 , comprises a pair of PVA brushes  13   a ,  13   b , a platform  15  for supporting a wafer W, and a mechanism (not shown) for rotating the pair of PVA brushes  13   a ,  13   b . The platform  15  comprises a plurality of rollers  17   a - c  for both supporting and rotating the wafer W. 
     Preferably, the pair of PVA brushes  13   a ,  13   b  are positioned to extend beyond the edge of the wafer W, so as to facilitate cleaning the wafer&#39;s edge. However, research shows that slurry induced defects still occur, and are caused by slurry residue remaining along the edges of the wafer despite cleaning with apparatuses such as that described above. Specifically, subsequent processing has been found to redistribute slurry residue from the wafer edges to the front of the wafer, causing defects. 
     A number of devices have been developed to improve wafer edge cleaning. One such device is shown in the side elevational view of  FIG. 2 . The edge-cleaning scrubber  19 , shown in  FIG. 2 , includes a pair of rollers  17   b ,  17   c  adapted to support and rotate the wafer W, and further includes an edge-cleaning roller  21  that fits over the edge of the wafer W for cleaning the edge as the wafer rotates. Although the edge-cleaning roller  21  addresses the need to clean slurry residue from wafer edges, it can be subject to quick wear, such wear typically being concentrated at locations where it contacts the wafer W. 
       FIGS. 3A-3C  illustrate details related to how the edge-cleaning roller  21  of the edge-cleaning scrubber  19  of  FIG. 2  cleans the edge of the wafer W. Referring to the side elevational view of  FIG. 3A , which shows the wafer W above the edge-cleaning roller  21 , the edge-cleaning roller  21  of  FIG. 2  is shown in contact with the wafer W. Specifically, opposing first and second inclined surfaces  23 ,  25  of the edge-cleaning roller  21  are in contact with respective opposite first and second edge corners  27 ,  29  of the edge of the wafer W. For example, either or both of the first and second edge corners  27 ,  29  may comprise a bevel so as to form, e.g., a truncated frustoconical edge surface (not separately shown) which may be placed in surface-to-surface contact with the first and second inclined surfaces  23 ,  25  of the edge cleaning roller  21 . 
     Referring to the side elevational view of  FIG. 3B , in which the wafer W is shown in phantom across the edge-cleaning roller  21 , the wafer W rotates in a nominal rotation plane  31 , as does the edge-cleaning roller  21 . By “nominal rotation plane” is meant that plane within which the wafer W is expected to rotate based on the specific arrangement of rollers (e.g., the rollers  17   b ,  17   c ) used to support, drive and guide the wafer W within the edge-cleaning scrubber  19  of  FIG. 2 . Further, it may be seen that contact between inclined surfaces  23 ,  25  of the edge-cleaning roller  21  and the first and second edge corners  27 ,  29  of the wafer W takes place along respective first and second contact areas  33 ,  35  on the inclined surfaces  23 ,  25 . 
     Referring to the cross-sectional view of the edge-cleaning roller  21  shown in  FIG. 3C , corresponding to section  3 C- 3 C as shown on  FIG. 3B , the first contact area  33  on the first inclined surface  23  translates to a ring-shaped wear sector  37  on the first inclined surface  23 , typically relatively narrow, which performs the edge-cleaning function and is subject to friction-induced wear over time. Conversely, the remaining portions of the first inclined surface  23  may not typically contact the wafer W during edge cleaning, and therefore may not be subject to such friction-induced wear. 
     Other rollers that may rotate in a common plane with a wafer W while contacting a portion of the wafer edge, but that perform additional or separate functions such as rotating the wafer W (e.g., drive rollers, such as the spinning mechanism  17   a - c  of  FIG. 1 ) or guiding the rotating wafer W so as to limit or prevent tilting of the same (e.g., idling guide rollers (not separately shown)), are typically also subject to rapid wear where contact is made with the wafer W. The cost of maintaining proper operation of such parts and/or conducting frequent replacement of the same can mount quickly. 
     Accordingly the field of wafer cleaning requires methods and apparatus for effectively performing one or more of the functions of cleaning, supporting, driving and guiding both the flat surfaces and the edge surfaces of a semiconductor wafer, preferably so as to reduce the cost and/or frequency of replacement due to frictional wear from wafer contact. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the need for a more effective edge cleaner by providing a number of different roller embodiments that are adapted for wafer edge cleaning. Specifically:
         (1) for cleaning the edge bevel of a wafer, an edge cleaning roller is adapted to rotate within a plane that is at an angle to a first plane in which the wafer is supported and rotated;   (2) for cleaning the circumferential edge of a wafer, an edge cleaning roller is provided with a flat-bottomed channel having a frictional surface along the channel&#39;s bottom; and/or   (3) for cleaning an edge region of a major surface of a wafer, an edge cleaning roller is provided with a straight-walled channel having a frictional surface along at least one of the straight walls thereof.       

     In a first aspect of the invention, an apparatus for cleaning a thin disk is provided. The apparatus includes (1) a plurality of support rollers adapted to support an edge of the thin disk as the thin disk rotates within a first plane; and (2) an edge-cleaning roller adapted to rotate within a second plane oriented at a first non-zero angle to the first plane, so as to contact an edge bevel of the thin disk while so rotating. 
     In a second aspect of the invention, a support roller is provided for supporting a vertically rotating wafer. The support roller includes (1) a guide portion, for receiving an edge of a wafer, having an inclined surface comprising a low-friction material and adapted to allow the wafer edge to slide thereagainst; and (2) an edge-trap portion for retaining the edge of the wafer and having a transverse surface comprising a high-friction material and adapted, when in communication with the edge of the wafer, to resist sliding thereagainst. 
     In a third aspect of the invention, a side-contact roller is provided for contacting one or more major surfaces of a rotating wafer. The side-contacting roller includes (1) a guide portion, for receiving an edge of a wafer, having an inclined surface comprising a low-friction material and adapted to allow the wafer edge to slide thereagainst; and (2) an edge-trap portion for retaining the edge of the wafer and having a planar surface comprising a high-friction material and adapted, when in communication with a major surface of the wafer, to resist sliding thereagainst. Numerous other aspects, as are methods in accordance with these and other aspects of the invention. 
     Other features and aspects of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a side elevational view of a conventional PVA brush scrubber. 
         FIG. 2  is a side elevational view of a conventional scrubber comprising a conventional edge-cleaning roller for improving wafer edge cleaning. 
         FIG. 3A  is a side elevational view of the edge-cleaning roller of  FIG. 2 , shown cleaning the edge corners of the wafer W. 
         FIG. 3B  is another side elevational view of the edge-cleaning roller of  FIG. 2 , shown contacting the wafer W along contact areas on respective inclined surfaces of the edge-cleaning roller. 
         FIG. 3C  is a cross-sectional view, corresponding to view  3 C- 3 C of  FIG. 2 , of the edge-cleaning roller of  FIG. 2  showing a relatively narrow wear sector on an inclined surface of the edge-cleaning roller where contact is made with an edge corner of the wafer W. 
         FIG. 4  is a side elevational view of an inventive edge-cleaning roller, shown contacting edge corners of the wafer W and in an inventive angled orientation to a plane of rotation of the wafer W. 
         FIG. 5A  is a view, corresponding to view  5 A- 5 A of  FIG. 4 , of a major surface of the wafer W showing separate radial locations at which the inventive edge-cleaning roller of  FIG. 4  contacts respective edge corners of the wafer W. 
         FIG. 5B  is a cross-sectional view, corresponding to view  5 B- 5 B of  FIG. 4 , of the inventive edge-cleaning roller of  FIG. 4  showing a relatively wide wear sector on an inclined surface of the edge-cleaning roller where contact is made with an edge corner of the wafer W. 
         FIG. 6A  is a side elevational view of an inventive edge-cleaning support roller, shown in contact with a cylindrical edge surface of the wafer W. 
         FIG. 6B  is an exploded assembly perspective view of an edge-cleaning support roller that is a particular embodiment of the inventive edge-cleaning support roller of  FIG. 6A . 
         FIG. 7A  is a side elevational view of an inventive edge-cleaning side-contact roller, shown engaging the edge of the wafer W. 
         FIG. 7B  is a cross-sectional view of an edge-cleaning side-contact roller that is a particular embodiment of the inventive edge-cleaning side-contact roller of  FIG. 7A . 
         FIG. 8  is a side elevational view of an inventive edge-cleaning roller, shown contacting edge corners of the wafer W and in another inventive angled orientation to a plane of rotation of the wafer W. 
         FIG. 9  is a side elevational view of two inventive edge-cleaning rollers of  FIG. 8 , shown contacting edge corners of the wafer W and in opposite inventive angled orientations to a plane of rotation of the wafer W. 
     
    
    
     DETAILED DESCRIPTION 
     Edge Cleaning Roller 
       FIG. 4  is an side elevational view of an inventive edge-cleaning roller  101  in which the wafer W is shown in phantom across the edge-cleaning roller  101 , the edge-cleaning roller  101  being adapted to contact edge surfaces (e.g., edge bevels as described above with reference to  FIG. 3A ) of the wafer W for cleaning. Where, as described above, the wafer W is supported and driven so as to rotate and remain within the nominal rotation plane  31  of the wafer W (rotation and support means for the same not being shown), the edge-cleaning roller  101  may be inventively oriented relative to the wafer W so as to form a first angle  103 , the first angle  103  being that angle which is described between the nominal rotation plane  31  of the wafer W and a rotation plane  105  within which the edge-cleaning roller  101  is disposed and is adapted to rotate. 
     As shown in  FIG. 4 , the rotation plane  105  of the edge-cleaning roller  101  may be oriented relative to the nominal rotation plane  31  of the wafer W such that, in forming the first angle  103 , the rotation planes intersect along a line (not separately shown) generally extending radially outward from the center of rotation of the wafer W. Other relative orientations are possible, such as a relative orientation between the rotation planes whereby the planes intersect along a line generally extending tangentially to the wafer W, as is illustrated in  FIGS. 8 and 9  and as will be described later. 
     Referring again to  FIG. 4 , the edge-cleaning roller  101  may comprise opposing first and second inclined surfaces  107 ,  109  which contact the respective opposite first and second edge corners  27 ,  29  ( FIG. 3A ) of the edge of the wafer W. By contrast to the pattern of contact between the wafer W and the edge-cleaning roller  21  as shown above in  FIGS. 3A and 3B , e.g., in which both the first and the second edge corners  27 ,  29  of the wafer W are contacted by the edge-cleaning roller  21  at substantially the same radial location along the perimeter of the wafer W, the inventive angled orientation of the edge-cleaning roller  101  relative to the wafer W shown in  FIG. 4  may result in divergent radial contact locations along the perimeter of the wafer W. For example, as shown in the planar view of a major surface of the wafer W shown in  FIG. 5A  (corresponding to the view  5 A- 5 A of  FIG. 4 ), contact between the first inclined surface  107  ( FIG. 4 ) of the edge-cleaning roller  101  and the first edge corner  27  of the wafer W may occur at a first radial location  111  along the perimeter of the wafer W, contact between the second inclined surface  109  ( FIG. 4 ) of the edge-cleaning roller  101  and the second edge corner  29  of the wafer W may occur at a second radial location  113  along the perimeter of the wafer W, and a second angle  115  separates the first radial location  111  and the second radial location  113 . 
     Referring again to  FIG. 4 , the inventive angled orientation of the edge-cleaning roller  101  relative to the wafer W may result in a longer useful life for the edge-cleaning roller  101 . For example, where in  FIGS. 3A and 3C  it is shown that coplanar orientation between the respective rotation planes of the edge-cleaning roller  21  and the wafer W may result, as mentioned above, in a relatively narrow ring-shaped wear sector  37  on the first inclined surface  23  of the edge-cleaning roller  21 , the inventive angled orientation of  FIG. 4  may increase wear sector width, thus distributing the edge-cleaning function over larger contact areas (see  121 ,  FIG. 5B ) on the inclined surfaces of the edge-cleaning roller  101 . The inventive angled orientation of  FIG. 4  therefore may increase the wafer&#39;s edge cleaning duty cycle and may extend the useful life of the roller  101 . 
       FIG. 5B , which is a cross-sectional view of the edge-cleaning roller  101  taken along a section  5 B- 5 B of  FIG. 4 , illustrates the above-described feature. Referring to  FIG. 5B , contact between the first inclined surface  107  of the edge-cleaning roller  101  and the edge of the wafer W (shown in phantom) at the first edge corner  27  ( FIG. 3A ) of the wafer W takes place along a first contact area  117  on the first inclined surface  107 , and a ring-shaped wear sector  119  on the second inclined surface  109  may be produced thereby (e.g., by virtue of the rotation of the edge-cleaning roller  101 ) having a characteristic width  121 . 
     As shown in  FIG. 5B , the first contact area  117  tends to extend not only laterally across the slope of the first inclined surface  107 , e.g., similarly to the first contact area  33  of  FIG. 3C , but also up the slope of the first inclined surface  107 , e.g., in contrast to the first contact area  33  of  FIG. 3C . It may readily be seen, therefore, that the width  121  of the ring-shaped wear sector  119  on the first inclined surface  109  of the edge-cleaning roller  101  may be proportionately greater than a corresponding dimension (not separately shown) of the wear sector  37  on the first inclined surface  23  of the edge-cleaning roller  21  of  FIGS. 3A-3C . Given a greater wear sector width, it follows that the area of the first inclined surface  107  subjected to friction-induced wear during wafer edge cleaning (i.e., the wear sector area) will be proportionately greater. 
     Assuming the degree of edge cleanliness required by the process remains the same, providing a greater area for the ring-shaped wear sector  119  as described above can reduce the edge-cleaning burden per unit area of the wear sector, which may result in a longer useful life for the edge-cleaning roller  101 . For example, given a larger portion of the first inclined surface  107  of the edge-cleaning roller  101  is being used to clean the first edge corner  27  of the wafer W, edge cleaning may be more efficient, thus allowing, e.g., the length of time that the first inclined surface  107  is applied to the first edge corner  27  of the wafer W to be decreased, or the contact pressure between the same to be reduced, while still producing the required degree of wafer edge cleanliness. Those possessing skill in the art will recognize that the same dynamic exists between the second edge corner  29  (FIG.  3 A) of the wafer W and the second inclined surface  109  ( FIG. 4 ) of the edge-cleaning roller  101 , resulting in a similar beneficial broadening of a corresponding wear sector (not separately shown), and the same benefits as to part life. 
     Those possessing skill in the art will also recognize that additional flexibilities may be obtained by dividing edge-cleaning contact between the edge-cleaning roller  101  and the wafer W between radially spaced-apart locations on the edge of the wafer W, e.g., as shown in  FIG. 5A . For example, in some embodiments of the edge-cleaning roller  101 , a third angle  123  (see  FIG. 4 ) described between the first inclined surface  107  and the second inclined surface  109  may be provided that is wider than is typical for edge-cleaning rollers, e.g., so as to more readily facilitate rotation of the rotation plane  105  of the edge-cleaning roller  101  relative to the nominal rotation plane  31  of the wafer W. Nevertheless, despite the wider third angle  123 , the respective effective angles of contact (not shown) between the first inclined surface  107  and the second inclined surface  109  relative to the nominal rotation plane  31  of the wafer (e.g., as measured along the slope of the first inclined surface  107  normal to the direction along which the scrubber  117  extends, and along the slope of the second inclined surface  109  in a corresponding direction) may be controlled so as to be equivalent to those of typical edge-cleaning rollers. 
     Alternatively, if it is desired to increase the wafer&#39;s edge cleaning “duty cycle”, e.g., that angular fraction of the wafer&#39;s perimeter which is in contact with the inclined surfaces  107 ,  109  of the edge-cleaning roller  101  at any given time, or if it is desired to increase the size of an area of edge-cleaning contact on one or more edge surfaces of the wafer W, the same angles of contact may be reduced below that which is typical, in effect narrowing the angular gap between the inclined surfaces  107 ,  109  of the edge-cleaning roller  101  and the major surfaces of the wafer W. This may be accomplished without undue risk of causing the edge of the wafer to become wedged between the inclined surfaces of the edge-cleaning roller  101  and the rotation of the wafer W to become impeded thereby, e.g., since an angular space exists in the form of the second angle  115  between the first and second radial locations  111 ,  113  ( FIG. 5A ) along the perimeter of the wafer W at which contact with the inclined surfaces  107 ,  109  of the edge-cleaning roller  101  takes place. 
     Many different angles may be specified for the third angle  123 . For example, applicants observe that an angle of 70 degrees, ±10 degrees, produces a good result. 
     The edge-cleaning roller  101  may further include a normal surface  125  ( FIG. 4 ), e.g., cylindrical in shape, and occupying a space between the inclined surfaces of the edge-cleaning roller  101 . Such a space may be introduced so as to facilitate the rotation of the edge-cleaning roller  101  relative to the nominal rotation plane  31  of the wafer W. Although many different widths may be specified for such a space, including widths of up to 10 mm or more, applicants observe that a dimension of 2 mm, ±1 mm produces a good result. In addition, the normal surface  125  in that space may or may not be disposed directly adjacent to the inclined surfaces. For example, the normal surface  125  may comprise a bottom surface of a channel disposed in a space between the inclined surfaces (see, e.g.,  FIG. 4 ). 
     In some modes of use of the edge-cleaning roller  101 , the normal surface  125  is spaced apart from a cylindrical edge surface  39  ( FIG. 3A ) of the wafer W while the first inclined surface  107  and the second inclined surface  109  of the edge-cleaning roller  101  clean the edge corners  27 ,  29  of the wafer W. In other modes of use of the edge-cleaning roller  101 , the normal surface  125  may be caused to contact and/or support and/or clean the cylindrical edge surface  39  of the wafer W. 
     In addition, applicants observe that beneficial edge cleaning may be provided where the first angle  103  described between the rotation plane  105 , within which the edge-cleaning roller  101  is disposed, and the nominal rotation plane  31  ( FIG. 3B ) of the wafer W, ranges from 10-30 degrees. Optionally, therefore, the first angle  103  may be set at 15 degrees, which applicants observe produces a good result. 
     Values of (1) a width of the space between the first inclined surface  107  and the second inclined surface  109 , (2) the third angle  123 , and (3) the first angle  103  may be established/selected via an iterative, coordinated design process, so as to produce the desired interaction between the edge-cleaning roller  101  and the wafer W. Alternatively, selection of such values may be performed automatically based on the desired result. Respective values of 3 mm, 50 degrees, and 20 degrees for those three values provide a good result. 
     Furthermore, if desired, a slight torque may be introduced, e.g., to increase a frictional cleaning pressure between the inclined surfaces  107 ,  109  of the edge-cleaning roller  101  and the edge corners  27 ,  29  ( FIG. 3A ) of the wafer W. In some embodiments, such a torque serves to increase an area of the edge of the wafer W to be cleaned by the edge-cleaning roller  101 , without undue risk of the wafer&#39;s edge being pinched between the inclined surfaces of the edge-cleaning roller  101  and thus without wafer rotation tending to be inhibited thereby. 
     In operation, the wafer W may be inserted between the first inclined surface  107  and the second inclined surface  109  of the edge-cleaning roller  101 , placed in contact with same, e.g., according to the pattern of  FIG. 5A , and rotated in the nominal rotation plane  31  ( FIG. 3B ). For example, the wafer may be inserted between the first inclined surface  107  and the second inclined surface  109  of the edge-cleaning roller  101  with the rotation plane  105  of the edge-cleaning roller  101  preliminarily in a coplanar relationship with the nominal rotation plane  31  of the wafer W, and the edge-cleaning roller  101  may thereafter be rotated to achieve the desired first angle  103 . Alternatively, the first angle  103  may be established prior to the wafer W being introduced to the edge-cleaning roller  101 . 
     As mentioned above, the edge-cleaning roller  101  may be utilized in a mode in which contact with the wafer W is restricted to the first inclined surface  107  and the second inclined surface  109 . Alternatively, and as also mentioned above, the cylindrical edge surface  39  of the wafer W may also be made to contact a normal surface  125  ( FIG. 4 ) of the edge-cleaning roller  101  at one or more times, e.g., either before or during wafer edge cleaning, or before or during rotation of the edge-cleaning roller  101 . 
     Where sliding contact is intended between the edge-cleaning roller  101  and the wafer W, the surfaces of the edge-cleaning roller  101  involved may be adapted so as to further improve cleaning through greater friction. For example, such surfaces may comprise polyurethane, or some other suitable frictional material. 
     Additionally, edge surfaces of the wafer W and frictional surfaces of the edge-cleaning roller  101  may be caused to rotate at different velocities so as to enhance sliding contact. For example, the speed of rotation of the edge-cleaning roller  101  may be controlled via a separate motor, e.g., so as to cause the normal surface  125  to rotate at a different velocity than the cylindrical edge surface of the wafer W it contacts. Also for example, the speed of the edge-cleaning roller  101  may be selectively retarded (e.g., with a brake) if the wafer W itself is used to drive the edge-cleaning roller  101 . 
     Where the edge corners  27 ,  29  ( FIG. 3A ) of the wafer W comprise edge bevels, the first and second inclined surfaces  107 ,  109  of the edge-cleaning roller  101  may be angled and disposed so as to increase an area of the edge bevels of the wafer W contacted/cleaned by the inclined surfaces. For example, the effective angles described between the inclined surfaces along the areas of contact described above and the nominal rotation plane  31  of the wafer W can be controlled so as to maximize contact with the edge bevels. 
     Additional Edge-Cleaning Rollers 
       FIGS. 6A ,  6 B,  7 A and  7 B illustrate additional rollers adapted to achieve frictional contact with the edge of the wafer W, e.g., for purposes of driving or supporting the wafer W, and/or for preventing tilting thereof during rotation. It will be understood, also, that where the rollers of  FIGS. 6A-B  and  7 A-B achieve frictional contact with the edge of the wafer W, edge cleaning of the wafer may also take place, such that the rollers may also be denominated edge-cleaning rollers, e.g., either by design, or by virtue of how they are used in conjunction with a wafer edge. 
     Unlike the edge-cleaning roller  101  of FIGS.  4  and  5 A-B, which is adapted to achieve frictional contact with edge corners (or edge bevels)  27 ,  29  ( FIG. 3A ) of the wafer W, the rollers of  FIGS. 6A-B  and  7 B are adapted to achieve frictional contact with edge surfaces of the wafer W that may be adjacent to the edge corners  27 ,  29 . For example, the roller of  FIGS. 6A-B  is adapted to achieve frictional contact with the cylindrical edge surface  39  ( FIG. 3A ) between the edge corners  27 ,  29 , and the roller of  FIGS. 7A-B  is adapted to achieve frictional contact with one or both of a first edge-adjacent region  41  ( FIG. 3A ) of a first major surface  43  ( FIG. 3A ) of the wafer W, and a second edge-adjacent region  45  ( FIG. 3A ) of a second major surface  47  of the wafer W ( FIG. 3A ). Additionally, the rollers of  FIGS. 6A-B  and  7 A-B may comprise easily replaceable frictional components adapted to bear the greater portion of friction-induced wear where such frictional contact between the rollers and the wafer W is intended to occur. Such frictional components may be of low cost relative to other components of the rollers, and may assist in reducing and/or minimizing the cost of maintaining the rollers at a proper performance level, given that a certain level of wear may be anticipated and planned for. 
     Edge-Cleaning Support Roller 
       FIG. 6A  is a side elevational view of an inventive support roller  601 , shown adjacent to a wafer W and in contact with the cylindrical edge surface  39  of the wafer W. The support roller  601  comprises a cylindrical frictional surface  603 , e.g., comprising polyurethane or some other suitable frictional material, adapted to achieve frictional contact with the cylindrical edge surface  39  ( FIG. 3A ) of the wafer W, as shown in  FIG. 6A . The support roller  601  is adapted, via such frictional contact, to support and/or rotate the wafer W. 
     In operation, the edge of the wafer W may be introduced between first and second guide surfaces  605 ,  607  of the support roller  601 , which may comprise low-friction, low-wear material such as virgin PTFE to encourage sliding communication with the edge of the wafer W down the slopes of the guide surfaces  605 ,  607  toward the cylindrical frictional surface  603 . Once frictional contact is established between the cylindrical frictional surface  603  of the support roller  601  and the cylindrical edge surface  39  of the wafer W, the support roller  601  may be used to rotatably support and/or drive the wafer W. As described above, the cylindrical frictional surface  603  of the support roller  601  may also be used to clean the wafer W&#39;s cylindrical edge surface  39 , e.g., via rubbing contact caused by unmatched speeds of rotation. 
       FIG. 6B  illustrates a particular embodiment of the support roller  601  of  FIG. 6A  (support roller  601   a ), shown in an exploded assembly perspective view. As shown in  FIG. 6B , the cylindrical frictional surface  603  of the support roller  601   a  may comprise a portion of a friction disk  609 , which may be of a simple, low-cost design adapted to minimize cost of replacement. 
     The support roller  601   a  may further comprise a main body  611 , of which the second guide surface  607  may comprise a part, and an end portion  613 , of which the first guide surface  605  may comprise a part. The friction disk  609  may be adapted to fit between the main body  611  and the end portion  613 , and the assembly may be adapted to be secured such that the friction disk  609  rotates along with the main body  611  and the end portion  613 . 
     The support roller  601   a  may still further comprise a channel  615  ( FIG. 6A ) comprising first and second sides  617 ,  619  ( FIG. 6A ) for retaining the edge of the wafer during rotational support thereof (e.g., by forming an “edge-trap” for retaining the edge of the wafer that includes the frictional surface  603  ( FIG. 6B )). In the embodiment of  FIG. 6A , the frictional surface  603  may form a transverse frictional surface that is adapted to contact the edge of the wafer and resist sliding thereagainst. The channel  615  may be straight, i.e., the first side  617  and the second side  619  of the channel  615  may be arranged so as not to form a V, unlike the first inclined surface  23  and the second inclined surface  25  of the edge-cleaning roller  21  of  FIG. 3A . Additionally, an offset may be established between the first side  617  and the second side  619  of the channel  615  that is sufficiently large to permit insertion of the edge of the wafer W, which may have, for example, a nominal thickness of 0.030 inches, and yet is sufficiently small so as to prevent tilt in the wafer W during rotation of the same, e.g., via low-friction contact between the first side  617  of the channel  615  and the first edge-adjacent region  41  ( FIG. 3A ) of the wafer W and/or between the second side  619  of the channel  615  and the second edge-adjacent region  45  ( FIG. 3A ) of the wafer W. 
     Edge-Cleaning Side-Contact Roller 
       FIG. 7A  is a side elevational view of an inventive side-contact roller  701 , shown adjacent to a wafer W. The side-contact roller  701  comprises a first frictional planar surface  703 , e.g., comprising polyurethane or some other suitable frictional material, adapted to achieve frictional contact with the first edge-adjacent region  41  ( FIG. 3A ) of the wafer W. The side-contact roller  701  may additionally comprise a second frictional planar surface  705 , similar to the first frictional planar surface  703 , and adapted to achieve frictional contact with the second edge-adjacent region  45  ( FIG. 3A ) of the wafer W. The first frictional planar surface  703  and the second frictional planar surface  705  may comprise sides of a straight channel  707 , e.g., similar to that described above with reference to  FIG. 6B , such that the edge of the wafer W may be accommodated between the channel sides, and tilt in the wafer W may be prevented. The side-contact roller  701  is adapted to rotate the wafer W via frictional contact between the frictional planar surfaces of the side-contact roller  701  and the edge-adjacent regions of the major surfaces of the wafers. 
     In operation, the edge of the wafer W may be introduced between first and second guide surfaces  709 ,  711  of the side-contact roller  701 , which may comprise a low-friction, low-wear material such as virgin PTFE to encourage sliding communication with the edge of the wafer W down the slopes of the guide surfaces  709 ,  711  toward the channel  707  of the side-contact roller  701 . Once the edge of the wafer W has been inserted into the channel  707 , e.g., between the first frictional planar surface  703  and the second frictional planar surface  705 , a vertical gap  713  may be maintained between the cylindrical edge surface  39  ( FIG. 3A ) of the wafer W and a corresponding portion of the side-contact roller  701  to restrict contact between the side-contact roller  701  and the wafer W to the frictional “side” contact described above (i.e., at the edge-adjacent regions of the wafer&#39;s major surfaces), which frictional contact may be employed to drive the wafer W. Specifically, the wafer W may be vertically supported by other rollers (not shown) that prevent the wafer W from fully descending into the channel  707 . As described above, the first frictional planar surface  703  and the second frictional planar surface  705  of the side-contact roller  701  may also be used to clean the edge-adjacent regions of the wafer&#39;s major surfaces, e.g., via rubbing contact. 
       FIG. 7B  illustrates a particular embodiment of the side-contact roller  701  of  FIG. 7A  (side-contact roller  701   a ), shown in a cross-sectional view. As shown in  FIG. 7B , the first frictional planar surface  703  of the side-contact roller  701   a  may comprise a portion of a first friction ring  715 , which may be of a simple low-cost design adapted to minimize cost of replacement. Also, as shown in  FIG. 7B , if the side-contact roller  701   a  includes a second frictional planar surface  705 , the second frictional planar surface  705  may comprise a portion of a similar second friction ring  717 . 
     The side-contact roller  701   a  may further comprise a hub  719 , a first guide ring  721  mounted on the hub  719  of which the first guide surface  709  may comprise a part, and a second guide ring  723  mounted on the hub  719  of which the second guide surface  711  may comprise a part. The first friction ring  715  and the second friction ring  717  may also be mounted on the hub  719 , e.g., between the first guide ring  721  and the second guide ring  723  as shown. An assembly may be formed thereby in which all components rotate in unison. 
     Wafer Cleaning Apparatus Including the Above Inventive Rollers 
     One or more edge-cleaning rollers of FIGS.  4  and  5 A-B, and one or more of the frictional rollers of  FIGS. 6A-B  and  7 A-B may be incorporated within a wafer cleaning apparatus (not separately shown) utilizing scrubber brushes to clean major surfaces of a wafer in a manner similar to that of the scrubber mechanism of  FIG. 2 . Such a mechanism can take many forms and/or perform many functions, including:
         (1) comprising separate drive motors for the edge cleaning roller and the other frictional rollers, e.g., so as to facilitate an angled plane of rotation for the edge-cleaning roller;   (2) comprising a toggle enabling the edge-cleaning roller to switch between a mode in which it either lags behind or exceeds the speed of rotation of the wafer edge so as to slide against the wafer edge when in contact with it, and a mode in which it matches the wafer edge speed and therefore does not slide thereagainst when contacting the same;   (3) allowing the angle between the plane of rotation of the edge-cleaning roller and the plane of rotation of the wafer to be selectively varied;   (4) permitting the edge cleaning roller to toggle between speed-matching and speed-lagging or speed-exceeding modes while other frictional rollers remain in a speed-matching mode;   (5) the toggle of (2) above comprising a clutch that engages for speed-exceeding or speed-lagging and disengages for speed matching; and/or   (6) the toggle of (2) above comprising a friction brake that engages for speed-lagging and disengages for speed matching.
 
Other configurations are also permissible.
       

     The foregoing description discloses only exemplary embodiments of the invention. Modifications of the above disclosed apparatus and methods which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. For instance, according to one or more embodiments, such as shown in  FIG. 8 , an edge cleaning roller  801  may be provided having a plane of rotation  803  at an inventive angled orientation to the plane of rotation  805  of the wafer W, e.g., as described by an angle  807 , such that the plane of rotation  803  of the roller  801  intersects the plane of rotation  805  of the wafer W along a line (not separately shown) extending generally tangentially to the wafer W (e.g., as opposed to extending generally radially from the center of the wafer W as in the embodiment of  FIG. 4 ). Such an arrangement permits the creation of multiple wear sectors on a single inclined surface of the roller  801  by permitting removal, inversion, and reinstallation of the same roller  801  midway through a useful life that may be twice that of a conventionally oriented roller. This may be possible, for example and as is apparent from  FIG. 8 , since each edge corner tends to produce a wear sector at a unique location along the slope of a given inclined surface of the roller  801 , such that inversion and reinstallation of the roller exposes unworn or “fresh” friction surfaces to each of the edge corners. In other embodiments, such as shown in  FIG. 9 , multiple edge-cleaning rollers  801  may be inventively oriented at one of two preferably equal and opposite angles to the plane of rotation of the wafer W, e.g., for balancing of out-of-plane forces imparted to the wafer W by the angled rollers. 
     Finally, it should be understood that the inventive edge cleaning rollers described herein are each independently inventive, and may be employed in apparatuses other than those adapted to scrub a wafer&#39;s major surface. Further, as will be apparent to those of ordinary skill in the art, the inventive rollers may be employed to clean the edge of a wafer supported in any orientation (e.g., horizontal, vertical, etc.). Thus the inventive edge cleaning rollers may be advantageously employed in a vertically-oriented scrubber such as that disclosed in U.S. Pat. No. 6,575,177, the entire disclosure of which is incorporated herein by this reference. 
     Accordingly, while the present invention has been disclosed in connection with exemplary embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims.