Abstract:
The present invention generally provides a workpiece handling device and, more particularly, a vacuum operated chuck for securing a substrate to a substrate handling device. In one embodiment, the invention provides a chuck having three vacuum chuck rings projecting from a chuck base and having no resilient materials such as o-rings or the like exposed to the operating environment within which the wafer is being handled. In another embodiment, the present invention provides a substrate handling chuck having removable vacuum chuck rings for permitting interchangeable chuck ring elements for a particular application.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to workpiece handling devices and, more particularly, to a vacuum operated chuck for securing a substrate to a substrate handling device in processing systems. 
     2. Background of the Related Art 
     Modern semiconductor processing systems include workpiece handling devices such as wafer indexing devices, wafer pre-alignment devices, wafer transfer robots, and the like to handle and manipulate various workpieces such as processed and/or unprocessed silicon wafers during the fabrication of semiconductor devices. The various workpiece handling devices may be employed within a variety of operating environments having different environmental characteristics. Certain processing steps may require, for example, that the wafer be handled within process chambers such as degas chambers, substrate preconditioning chambers, cooldown chambers, transfer chambers, chemical vapor deposition chambers, physical vapor deposition chambers and etch chambers. The operating environments within these process chambers are typically high-vacuum environments and may include various combinations of high temperature operating conditions, energized gas plasma fields, and/or damaging chemical agents introduced therein while the wafer is being handled within the process chambers. 
     It is generally desirable that the wafer or other workpiece being handled be securely held to the workpiece handling device within the various operating environments. FIG. 1 shows a prior workpiece handling chuck  1  previously utilized to secure a wafer to a wafer pre-aligner. The pre-aligner chuck  1  includes a large vacuum chuck area  2  having a series of intersecting radial and circular grooves  3 ,  4 . The chuck  1  shown in FIG. 1 contacts a wafer over substantially the entire surface of the chuck. Because of its large vacuum chuck area  2 , this type of chuck can exert high stress forces on the wafer, particularly if the wafer is warped and the chucking forces acting on the wafer force the wafer into a into a planar orientation. In addition, the large vacuum chuck area  2  between the chuck and the wafer can produce an undesirable number of particles within the particular operating environment due to sliding contact between the back-side of the wafer and the chuck. Further, this type of chuck is typically constructed of aluminum. The undesirable metallic contact with the back-side of the wafer being handled can damage the wafer during handling. 
     To partially address the problems created by prior workpiece handling devices such as the chuck  1  shown in FIG. 1, other prior workpiece handling devices such as the chuck  5  shown in FIG. 2 utilize resilient members  6  disposed in one or more grooves  7  within the chuck  5  for reducing initial surface contact between the metallic chuck body  8  and the wafer  9 . However, it has been found that such chuck designs do not sufficiently reduce the surface contact between the wafer and the chuck body during and after vacuum sealing has been effected. It has also been found that such chuck designs do not sufficiently reduce the high stress forces exerted against the surface of even marginally non-planar substrates by the vacuum pressure sealing forces which are still exerted against substantially the entire back-side surface of the wafer being handled. In addition, the inclusion of resilient members into the often harsh operating environments may present process complications as the resilient materials are exposed to processing conditions within the operating environments that may be incompatible with resilient materials. Such incompatibility may create undesired particles within the operating environment due to decomposition or other destructive effects acting on the resilient member. 
     Other prior systems have attempted to solve the aforementioned problems associated with chuck designs. FIG. 3 shows a third type of prior workpiece handling device  11 , which attempts to reduce the surface area of the chuck in contact with the wafer by providing one or more vacuum chuck projections  12  mounted to the sealing surface of the chuck body  13  to minimize the contacting surface area between the chuck  11  and the wafer  9  or other workpiece being handled. However, these prior chucks still utilize resilient sealing members associated with each of the projections, which as described above, may not be desirable in certain operating environments. Over time, these resilient members must be replaced and may cause contamination during use. 
     Accordingly, there is a need for a workpiece handling device and, more particularly, a wafer handling chuck having a reduced contact surface area between the wafer and the chuck sealing surface, and having no resilient members associated therewith exposed to the operating environment in which the wafer is to be handled. 
     SUMMARY OF THE INVENTION 
     The present invention generally provides a vacuum operated chuck for holding a workpiece within an operating environment. The chuck generally comprises a chuck base having a plurality of chuck ring recesses formed in the chuck base and a chuck ring disposed in each of the chuck ring recesses. The chuck base may also include evacuation ports formed therein in fluid communication with each of the recesses and chuck rings disposed therein. Alternatively, the chuck rings may be formed integrally with the chuck base. A vacuum source is provided in fluid communication with the evacuation ports. 
     In one aspect, the chuck rings comprise a hollow cylinder having an inner wall defining an evacuation channel in fluid communication with the evacuation ports formed in the chuck base. The chuck rings may further include a substantially planar upper sealing surface adapted to receive the workpiece thereon, or the upper sealing surface may be canted, tapered, or rounded. In a particular embodiment, the chuck rings may be mounted to the chuck base by an adhesive, removably mounted to the chuck base, and/or threadably connected to the chuck base. The chuck rings may be constructed from polyetheretherketone (PEEK), polytetrafluoroethylene (TEFLON) or other polymeric materials. 
     In another aspect, the present invention provides a workpiece handling device having a chuck. The chuck preferably includes a chuck base having a plurality of chuck ring recesses formed therein with chuck rings disposed in each of the chuck ring recesses. Alternatively, the chuck rings may be formed integrally with the chuck. In one embodiment, the chuck may have evacuation ports formed therein in fluid communication with each of the recesses. In another embodiment where the chuck rings are integrally formed with the chuck, the chuck may have evacuation ports formed therein in fluid communication with each of the chuck rings. A vacuum source is provided in fluid communication with the evacuation ports in the base. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. 
     It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
     FIG. 1 is a top schematic view of a conventional type of vacuum chuck having a series of intersecting radial and circular grooves. 
     FIG. 2 is a cross-sectional view of a second conventional type of vacuum chuck having a series of intersecting radial and circular grooves with a resilient member disposed in at least one of the grooves. 
     FIG. 3 is a cross-sectional view of a third conventional type of vacuum chuck having a plurality of projections extending from the chuck body and also having resilient sealing members. 
     FIG. 4 is a substantially top exploded view of an improved vacuum chuck according to the present invention. 
     FIG. 5 is a cross-sectional view of the vacuum chuck of FIG.  4 . 
     FIG. 6 is a substantially bottom view of the vacuum chuck of FIGS. 4 and 5. 
     FIG. 7 is a cross-sectional view of an alternative chuck ring having a tapered sealing surface according to the present invention. 
     FIG. 8 is a cross-sectional view of an alternative chuck ring having a rounded sealing surface according to the present invention. 
     FIG. 9 is a plan view of a vacuum processing system with a robot having a vacuum chuck according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 4 is a substantially top exploded view of one embodiment of a vacuum chuck  100  of the present invention. Vacuum chuck  100  includes a plurality of workpiece holding members, preferably vacuum supports, such as chuck rings  102 , for supporting a wafer or other generally planar workpiece above the top surface  104  of the chuck base  106 . Preferably, the chuck  100  includes three vacuum chuck rings  102 , arranged symmetrically around the perimeter of the chuck  100 . The chuck rings  102  preferably have a lower annular base  108  which is received in a recess  110  formed in the chuck base  106 . An upper wafer support surface  112 , which is slightly larger in diameter than the lower base  108 , extends over the edge of the chuck ring recess  110  when disposed in the recess to provide a seal between the chuck ring  102  and the chuck base  106 . While the chuck rings  102  illustrated are annular, other embodiments such as square, rectangular, oval, c-shaped and the like may be used. 
     The chuck rings  102  define a vacuum channel  114  through the lower base which opens on one end into a vacuum port  116  in the upper surface of the chuck ring  102 . The vacuum channels  114  formed by the chuck rings  102  align with or are otherwise in fluid communication with evacuation ports  118  formed in the chuck base  106 . Preferably, the diameter of the evacuation ports  118  formed within the chuck base  106 , are smaller than the diameter of the evacuation channels  114  formed within the chuck rings  102  in order to minimize any reduction of vacuum pressure within the evacuation channel  114  from any misalignment of the chuck ring  102  within the chuck base recess  110 . While the chuck  100  preferably includes three chuck rings  102  to minimize wafer distortion due to defects in the planarity of the wafer which may exist and the particle generation, any number of chuck rings  102  may be used in which event an equal number of chuck ring recesses  110  would be formed within the chuck base  106  for receiving the chuck rings  102 . A vacuum is drawn by vacuum pressure provided by the vacuum source through the evacuation ports  118  of the chuck base and from within the evacuation channels  114  of each of the chuck rings  102  to secure a wafer to the chuck  100 . 
     FIG. 5 is a cross-sectional view of one embodiment of a chuck ring configuration of the invention. The top surface  104  of the chuck base  106  defines a plurality of chuck ring recesses  110  and counter bores  117  therein. Preferably, three chuck ring recesses  110  are sized and adapted to receive the chuck rings  102 . The chuck rings  102  may be fixedly attached to the chuck base  106  by use of an adhesive or other fasteners, which are preferably resistant to the conditions within the particular operating environment in which the chuck is to be used. Preferably, the chuck rings  102  are secured in the recesses using an adhesive such as Loctite Superbonder 422. Alternatively, the chuck rings  102  can be removably connected to the chuck base by threaded engagement or snap lock mechanisms. Vacuum channels  120  are formed in the lower surface of the chuck base  106  to provide vacuum conditions within each of chuck rings  102 . The chuck is mounted to a shaft or other mounting member by screws  119  which are disposed in counter bores  117 . 
     FIG. 6 is a substantially bottom perspective view of a chuck  100 . The chuck base  106  includes an outer annular flange  122  extending therefrom. A central recess  124  is disposed in the lower surface of the chuck. A plurality of channels  120  extend from the central recess  124  to each of the ports  118  disposed through the chuck. A second concentric recess  126  is provided around the central recess  124  and is adapted to receive a shaft or other mounting member to which the chuck is secured. The central recess  124  and the channels  120  provide fluid communication between the ports  118  (and the chuck rings  102 ) and the vacuum source which is preferably provided through the shaft  128  (shown in FIG. 5) to which the chuck is mounted. 
     The chuck base  106  can be made of aluminum, stainless steel, other metallic material or plastics such as PEEK, TEFLON or other materials having high physical and chemical resistance to the operating environments in which the chuck may be utilized. The chuck rings  102  can be made of a non-resilient material such as PEEK, TEFLON, or other materials having high physical and chemical resistance to the operating environments within which the chuck  100  may be utilized. In addition, aluminum or other metallic material could also be used to form the chuck rings. In a preferred embodiment, neither the chuck base  106  nor the chuck rings  102  include any resilient or thermoplastic materials in fluid communication with the operating environment. Accordingly, the sealing surface between the chuck rings  102  and the wafer or other workpiece being handled has no resilient sealing member associated therewith in order to prevent destructive elements or particles from being transferred within the operating environment, which may result from the potentially caustic or otherwise harmful operating characteristics within a particular operating environment. 
     While FIG. 5 shows chuck rings  102  which are connected to the chuck base using an adhesive, other methods of attachment could also be used. For example, the lower base of the chuck ring and the internal surface of the recesses can be threaded so that the chuck rings can be threadably connected to the chuck base. In addition, a rotation lock mechanism could be used to lock the chuck rings into the recess on partial rotation. 
     Alternatively, the chuck rings  102  could be formed integrally with the chuck base  106 . In this embodiment, the chuck rings  102  and the chuck base  106  would be made of the same material, such as PEEK, TEFLON, aluminum, or other materials having high physical and chemical resistance to the operating environments within which the chuck  100  may be utilized. 
     In each embodiment, three vacuum chuck rings  102  are provided on the chuck base  106  to minimize the vacuum chuck sealing area on the chuck  100  which contacts the wafer, but also provides a sealing area to hold a wafer during operation without unnecessary stresses being exerted on the wafer. Accordingly, the amount of contact between the vacuum chuck rings  102  and the wafer is minimized, which results in reduced wafer backside particle contamination as compared to conventional chucks having a sealing surface on substantially the entire back side surface of the wafer being handled. 
     It should be noted that the sealing surface  221 , as shown in FIGS. 7 and 8, may have different shapes depending on the contact characteristics desired between the substrate being handled and the chuck rings  102 . Referring to FIG. 7, an alternative chuck ring sealing surface configuration is shown. In this embodiment, the chuck ring sealing surface  221  is canted or tapered to provide a higher inner diameter  222  than outer diameter  224 , which provides a minimal contact surface, or contact point  223  between the chuck ring  102  and a substrate resting thereon. Such an embodiment provides a well defined edge contact between the chuck ring  102  and the wafer, which may be desirable in a particular application. 
     FIG. 8 illustrates a second alternative chuck ring  102  having a rounded chuck ring sealing surface  221  to provide a higher diameter at a desired contact point  223  between the inner and outer diameters  222 ,  224  and to eliminate the sharp, or well defined edge contact between the chuck ring  102  and a substrate which may exist in other embodiments. Still other configurations may also be employed depending on the particular application. 
     FIG. 9 is a plan view of a representative processing system in which a chuck of the invention can be used to advantage. In the embodiment shown, the chuck  100  of the invention is used in connection with a wafer aligner disposed in a front end staging area of a processing system. The processing system and the wafer aligner are connected to a controller which enables computer control of the operation of both the system and the wafer aligner. The chuck  100  is disposed on a rotatable shaft  128  (shown in FIG. 5) which is part of a wafer aligner  420 . One wafer aligner which could incorporate the chuck of the invention is available from Equippe Technology. The chuck is mounted on a shaft having a vacuum channel formed therein which connects to the channels formed on the underside of the chuck base  106 . The chuck base is sealably retained on the shaft of the wafer aligner by a plurality of screws, four shown in FIG.  4 . The wafer pre-aligner  420  aligns wafers for proper placement within the wafer cassettes  450 , load-lock chambers  455  or processing chambers  465  of the vacuum processing system  400  by rotating a wafer supported thereon by a chuck of the invention. Alignment notches or flat alignment edges of the wafer are determined using an optical inspection device which is also part of the wafer aligner. It should be noted, however, that other processes and other systems may benefit from the chuck  100  of the present invention. Accordingly, the improved wafer handling chuck  100  may be utilized in any appropriate system wherein wafer handling is desired such as on robot blades and on wafer supports disposed in process chambers. 
     The chuck will be described in operation with reference to FIG. 5. A wafer is placed upon the sealing surface  112  of each of the plurality of chuck rings  102  disposed on the chuck  100  by a robot. After the wafer is placed on the sealing surface  112  of each of the chuck rings  102 , vacuum pressure is provided to evacuate the air or other fluid contained within the evacuation channels  114  of the chuck rings  102 , thereby providing a sealing force between the wafer and the sealing surface  112  of the chuck rings  102 . Thereafter, the vacuum chuck is rotated or otherwise moved to enable wafer alignment prior to placement within a processing system. After the wafer has undergone alignment, the vacuum pressure is removed, thereby releasing the retaining force on the wafer. Thereafter, the wafer may be removed from the chuck  100  manually or by a wafer handling robot. 
     While the foregoing is directed to the preferred embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims which follow.