Two-piece clamp ring for holding semiconductor wafer or other workpiece

A clamp ring assembly for securing a generally circular workpiece to a supporting surface comprises an annular base ring having a radial inner surface of a predetermined diameter and at least one locking member. The base ring further includes at least one opening extending axially therethrough for securing the base ring to the supporting surface. An annular securing ring having a radial outer surface and a radial inner surface is provided. The diameter of the outer surface of the securing ring is the same as or slightly smaller than the diameter of the inner surface of the base ring and the securing ring includes at least one locking member for engaging the locking member of the base ring when the securing ring is assembled with the base ring. The securing ring also includes at least one workpiece engaging member for engaging and holding the workpiece against the supporting surface.

BACKGROUND OF THE INVENTION
 The present invention relates generally to clamping or clamp rings and,
 more particularly, to a two-piece clamp ring assembly which is
 particularly well suited for holding a workpiece, such as a semiconductor
 wafer, firmly in place against a supporting surface particularly, during
 the performance of processing steps.
 One-piece clamp rings are used extensively within semiconductor wafer
 processing chambers and elsewhere for the purpose of holding a round
 semiconductor wafer or other such workpiece in place on a supporting
 surface during the performance of various processing steps. Such one-piece
 clamp rings generally comprise a single generally annular structure having
 a series of engaging lugs on the inner circumferential portion and a
 series of circumferentially spaced openings extending therethrough
 proximate the outer circumference. Typically, eight to twelve such spaced
 openings are employed in the one-piece clamp ring and each such opening is
 adapted to receive a screw, bolt or other fastener for securing the
 one-piece clamp ring and thus, the semiconductor wafer or other workpiece
 to a supporting surface with the workpiece being held in place by the
 lugs.
 While such one-piece clamp rings are highly effective in performing the
 requisite holding function, such one-piece clamp rings, particularly the
 portion proximate to the inner circumferential surface and the lugs which
 engage the semiconductor wafer or other workpiece tend to erode over time
 due to exposure to the materials employed in performing the various
 semiconductor wafer processing steps. When a one-piece clamp ring has so
 eroded to the point where it is no longer able to provide the proper
 clamping force to hold the semiconductor wafers in place, it becomes
 necessary to replace the entire clamp ring, which involves removing all of
 the securing fasteners and then installing a new clamp ring which then
 requires torquing all of the securing fasteners, a time consuming task
 which increases the semiconductor wafer processing time. The replaced
 one-piece clamp ring is then discarded, resulting in the loss of a
 substantial amount of the specialized material used in forming the one
 piece clamp ring.
 The present invention comprises a two-piece clamp ring, including a radial
 outer ring section or base ring which is normally secured directly to the
 supporting surface and a removable, radial inner ring section or securing
 ring which is employed for engaging and holding the semiconductor wafer or
 other workpiece when removably secured or assembled to the base ring. In
 this manner, as the securing ring, through normal use, is eroded, the
 securing ring, by itself, can be quickly removed and replaced without the
 need for replacing the entire two ring assembly, thereby saving cost and
 time and more effectively utilizing the specialized material used to form
 the rings.
 BRIEF SUMMARY OF THE INVENTION
 Briefly stated, the present invention comprises a clamp ring assembly for
 securing a generally circular workpiece to a supporting surface. The clamp
 ring assembly comprises an annular base ring having a radial inner surface
 of a predetermined diameter and at least one locking member. The base ring
 further includes at least one opening extending axially therethrough for
 securing the base ring to the supporting surface. The clamp ring assembly
 further comprises an annular securing ring having a radial outer surface
 and a radial inner surface. The diameter of the outer surface of the
 securing ring is the same as, or slightly smaller than the diameter of the
 inner surface of the base ring. The securing ring includes at least one
 locking member for engaging the locking member of the base ring when the
 securing ring is assembled with the base ring. The securing ring further
 includes at least one workpiece engaging member for engaging and holding
 the workpiece against the supporting surface.
 In another embodiment, the present invention comprises a clamp ring
 assembly for securing a generally circular semiconductor wafer to a
 supporting surface. The clamp ring assembly comprises an annular base ring
 having a radial inner surface of a predetermined diameter with the inner
 surface including a plurality of generally arcuate, radially inwardly
 extending circumferentially spaced locking members. The base ring further
 includes a plurality of circumferentially spaced openings extending
 axially therethrough for receiving fasteners for securing the base ring to
 the supporting surface. The clamp ring assembly further comprises an
 annular securing ring having a radial outer surface and a radial inner
 surface. The diameter of the outer surface of the securing ring is the
 same as, or slightly smaller than the diameter of the inner surface of the
 base ring. The outer surface of the securing ring includes a plurality of
 generally arcuate radially inwardly extending grooves so that when the
 securing ring is assembled with the base ring, each of the locking members
 is located within one of the grooves. The securing ring further includes a
 plurality of generally circumferentially spaced engaging members extending
 radially inwardly from the inner surface for engaging and holding the
 semiconductor wafer against the supporting surface.

DETAILED DESCRIPTION OF THE INVENTION
 Referring to the drawings, wherein like numerals are used to indicate like
 elements throughout the several figures, there is shown in FIGS. 1-2 a
 preferred embodiment of a two-piece clamp ring assembly 10 for securing a
 semiconductor wafer or other generally circular workpiece (not shown) to
 an underlying supporting surface (not shown) in accordance with the
 present invention. In the present embodiment, the two-piece clamp ring
 assembly 10 is comprised of a first generally annular, radially outer ring
 or base ring 12 and a second, generally annular, radially inner ring or
 securing ring 14. The base ring 12 is generally irregularly shaped in
 cross section as shown in FIGS. 3a and 3b includes a generally continuous
 generally circumferential radial inner surface 12A of a first
 predetermined diameter. The securing ring 14 is also generally irregularly
 shaped and includes a generally circumferentially extending radial inner
 surface 14A and a generally circumferentially extending radial outer
 surface 14B, which has a second predetermined diameter. Preferably, the
 second predetermined diameter, the diameter of the radial outer surface
 14B of the securing ring 14 is generally the same as or slightly smaller
 than, the first predetermined diameter, the diameter of the radial inner
 surface 12A of the base ring, so that the securing ring 14 and the base
 ring 12 may be assembled together in the manner which will hereinafter be
 described to form the clamp ring assembly 10 as shown in FIG. 1. Forming
 the base ring 12 and the securing ring 14 in this manner permits quick and
 convenient assembly and disassembly of the securing ring 14 to the base
 ring 12 for reasons which will hereinafter become apparent.
 The base ring 12, although irregularly shaped in cross-section, includes an
 upper surface 12C and an under surface, or lower surface 12D, which
 includes two outwardly extending annular flanges. The lower surface 12D in
 combination with the annular flanges firmly engages an underline
 supporting surface (not shown) when the clamp ring assembly 10 is employed
 for securing a semiconductor wafer or other workpiece to such a supporting
 surface. At least one generally circular opening and preferably a
 plurality of such openings 16 extend through the base ring 12 from the
 upper surface 12C to the lower surface 12D. Preferably, there are twelve
 such openings 16 which are generally equally circumferentially spaced
 around the base ring 12 as best shown in FIG. 1. Preferably, each of the
 openings 16 includes a suitable countersink on the upper surface 12C of
 the base ring 12. Each of the openings 16 is adapted to receive a screw,
 bolt or other such elongated fastener (not shown) for the purpose of
 securing the base ring 12 to an underlying supporting surface (not shown)
 in a manner which will be appreciated by those of ordinary skill in the
 art. Preferably, the head end of each such fastener is suitably sized and
 shaped to fit within the countersink of the applicable opening 16, so that
 when the base ring 12 is secured to the underlying supporting surface, the
 fasteners and the upper surface 12C of the base ring provide a generally
 continuous, smooth appearance. It will be appreciated by those of ordinary
 skill in the art that a greater number or lesser number of openings 16 may
 be provided in the base ring 12. It will also be appreciated by those of
 ordinary skill in the art that the size, location and spacing of the
 openings 16 may vary from what is shown and described. Further, it will be
 appreciated by those of ordinary skill in the art that while in the
 present embodiment, the openings 16 are provided for receiving fasteners
 for securing the base ring 12 to an underlying supporting surface, some
 other type of structure, such as a removable clamp, a latch mechanism, a
 clip, an adhesive, or the like may alternatively be employed for securing
 the base ring 12 to the underlying supporting surface. Hence, the present
 invention is not limited to the use of fasteners extending through
 openings 16 as employed in connection with the present embodiment.
 The base ring 12 further includes at least one locking member and
 preferably, a plurality of locking members 18 each of which preferably
 extends generally radially inwardly a predetermined distance from the
 radial inner surface 12A of the base ring 12. As best shown in FIGS. 2, 3a
 and 3b, in the present embodiment, the base ring 12 includes six generally
 identical locking members 18, with each locking member 18 being generally
 arcuate and of a predetermined arcuate length and with each locking member
 being spaced from the adjacent locking member by a predetermined arcuate
 distance. As best shown in FIGS. 3a and 3b, each of the locking members 18
 also has a predetermined radial width and a predetermined axial thickness,
 which is less than the overall axial thickness of the base ring 12. For
 reasons which will hereinafter become apparent, the arcuate length of each
 of the locking members 18 is less than the arcuate length of the spacing
 between adjacent locking members 18. It will be appreciated by those of
 ordinary skill in the art that, if desired, a greater or lesser number of
 locking members 18 could be provided on the base ring 12 and that the
 arcuate length, spacing, radial width and/or axial thickness of the
 locking members 18 could vary from what is shown and described. The
 purpose of the locking members 18 is to facilitate the assembly and
 locking together of the base ring 12 and the securing ring 14 in a manner
 which will hereinafter be described. It should be understood by those of
 ordinary skill in the art that some other type of structural arrangement
 may be employed for attaching together the base ring 12 and the securing
 ring 14. Thus, the present invention is not limited to the particular
 locking members 18, as shown and described.
 It will be appreciated by those of ordinary skill in the art that the size
 of the base ring 12 could vary depending upon the particular application
 and that the overall structure of the base ring could vary from that
 described above and shown in the drawings. For example, the base ring 12
 could be thicker, could be more elongated or the like.
 As best shown in FIGS. 2, 3a and 3b, the securing ring 14, although
 irregularly shaped, includes an upper surface 14C and an under surface or
 lower surface 14D. As best shown in FIGS. 1 and 3a, when the securing ring
 14 is assembled to the base ring 12, the upper surface 14C of the securing
 ring is in substantially the same plane as the upper surface 12C of the
 base ring 12 to provide a smooth, generally continuous appearance. As
 previously mentioned, the radial outer surface 14B of the securing ring 14
 is generally of the same diameter or of a slightly smaller diameter than
 inner radial surface 12A of the base ring 12, so that when the securing
 ring 14 is assembled to the base ring 12 as shown in FIGS. 1 and 3a, the
 radial spacing between the two rings 12, 14 is minimal, again, to provide
 a generally continuous smooth appearance.
 As best shown in FIGS. 2 and 3a, the radial outer surface 14B of the
 securing ring 14 includes at least one locking member and preferably, a
 plurality of locking members which are adapted to cooperate with the
 locking members 18 on the radial inner surface 12A of the base ring 12 for
 assembling the securing ring 14 to the base ring 12. In the presently
 preferred embodiment as illustrated, the securing ring locking members
 comprise a plurality of generally arcuate grooves 14F which extend
 radially inwardly from the outer surface 14B of the securing ring 14. More
 particularly, each of the arcuate grooves 14F is formed by a generally
 arcuate flange 14E extending radially outwardly along the lower surface
 14D of the securing ring 14. The radial width of each groove 14F is the
 same as or slightly wider than the radial width of each of the locking
 members 18 of the base ring 12. The axial thickness of each groove 14F is
 the same as, or slightly greater than the axial thickness of each of the
 locking members 18 of the base ring 12. In this manner, when the securing
 ring 14 is assembled with the base ring 12 as hereinafter described, each
 of the locking members 18 of the base ring 12 is effectively captured
 within one of the grooves 14F of the securing ring 14 as shown in FIG. 3a
 to thereby prevent relative axial movement therebetween. Preferably, the
 arcuate length of each of the flanges 14E and therefore, the arcuate
 length of each of the grooves 14F of the securing ring 14 generally
 corresponds to or is greater than the arcuate length of each of the
 locking members 18.
 In the illustrated embodiment, the securing ring 14 includes six generally
 identical, equally spaced grooves 14F with the arcuate spacing between
 adjacent grooves being greater than the arcuate length of each of the
 grooves 14F. It will be appreciated by those of ordinary skill in the art
 that the location and number of grooves 14F, the arcuate length, radial
 width and axial thickness of the grooves 14F, as well as the spacing
 between adjacent grooves 14F may vary in different applications. It will
 also appreciated by those of ordinary skill in the art that a mechanical
 structure, other than one or more grooves 14F may alternatively be
 employed for cooperating with the locking members 18 or some other
 structure of the base ring 12 for attaching the securing ring 14 to the
 base ring 12 when the two rings 12, 14 are assembled together as shown in
 FIG. 1. Accordingly, the foregoing description of the locking members 18
 and the grooves 14F is provided only for purposes of illustrating a
 preferred, but not the only, way to interconnect the base ring 12 and the
 securing ring 14 in accordance with the present invention.
 It will be appreciated by those of ordinary skill in the art that the size
 and/or shape of the securing ring 14 may vary from what has been shown and
 described. For example, the securing ring 14 could be thicker or more
 elongated for a particular application. Thus, the present invention should
 not be considered to be limited to a securing ring having the
 above-described characteristics.
 The securing ring 14 includes at least one, but preferably, a plurality of
 workpiece engaging members 26 for engaging and holding a semiconductor
 wafer or other workpiece (not shown) against an underlying supporting
 surface (not shown). In the present embodiment, the engaging members 26
 are generally circumferentially spaced and extend radially inwardly from
 the inner surface 14A of the securing ring 14. In the present embodiment,
 there are twelve such engaging members 26 with each of the engaging
 members 26 being generally equally spaced from each adjacent engaging
 member 26 around the circumference of the securing ring 14. As best shown
 in FIGS. 1, 2 and 3a, each engaging member 26 is generally triangular
 shaped in plan view with a tapered or beveled upper surface and a
 generally flat lower surface.
 Once the base ring 12 has been secured to the supporting surface, the
 securing ring 14 is assembled to the base ring 12 by first supporting the
 securing ring 14 above the base ring 12 as shown in FIG. 2 with the
 locking members 18 of the base ring 12 generally aligned with the arcuate
 spaced portions of the securing ring 14 located between adjacent grooves
 14F. The securing ring 14 is then lowered onto the base ring 12 and is
 then rotated with respect to the base ring 12, in either direction, so
 that the locking members 18 of the base ring 12 are contained within the
 grooves 14F of the securing ring as shown in FIG. 3a. Removal of the
 securing ring 14 from the base ring 12 is accomplished by reversing the
 foregoing steps.
 As best shown in FIGS. 1 and 2, the base ring 12 includes a first generally
 rectangular keyway 20 formed by a groove extending into the upper surface
 12C of the base ring 12. A second generally triangular keyway 24 is
 provided in the form of a groove on the upper surface 14C of the securing
 ring 14. The first and second keyways 20, 24 may be aligned with each
 other when the securing ring 14 is assembled with the base ring 12. A
 separate key 22 is provided for being installed into the first and second
 keyways 20, 24 to effectively lock together the securing ring 14 and the
 base ring 12 by preventing rotational movement of the securing ring 14
 with respect to the base ring 12. The key 22 includes a generally circular
 opening 22A extending completely therethrough. A similar opening 20A is
 provided in the first keyway 20 so that when the key 22 is positioned
 within the first and second keyways 20, 24 as shown in FIG. 1, the key
 opening 22A is in registry with the keyway opening 20A so that a screw,
 bolt or other fastener may be installed within the openings to effectively
 lock the key 22 in place within the two keyways 20, 24. It will be
 appreciated by those of ordinary skill in the art that while in the
 present embodiment, two keyways 20, 24 are provided on the base ring 12
 and clamping ring 14 and a suitably sized and shaped key 22 is provided
 for locking together the two rings 12, 14, the rings may be secured
 together in some other manner utilizing some other structure. For example,
 a small opening may extend through one or more of the grooves 14F and one
 or more locking members 18 for receiving a pin, screw or other fastener
 device for locking together the clamping ring 14 and the base ring 12.
 Preferably, both the base ring 12 and the securing ring 14 are made of the
 same material. Materials which are typical for use in making such a clamp
 ring assembly 10, includes polyamide, ceramic, polyetheretherkeytone,
 polyetherimide and polybenzimidazole. However, it will be appreciated by
 those of ordinary skill in the art that other materials including other
 polymeric materials, certain metals or the like may alternatively be
 employed for making either or both of the rings. It will also be
 appreciated that while in the preferred embodiment, both rings 12, 14 are
 made of the same material, the rings 12, 14 could be made of different
 materials, if desired. Preferably, the key 22 is also made of the same
 material as the rings 12, 14, but could be made of some other suitable
 material.
 The two-piece clamp ring assembly 10 was developed to provide a simple,
 cost effective method to address the problem of ring replacement once
 material erosion has occurred to a point that negatively impacts the
 performance of a one-piece clamp ring. With the one-piece clamp ring, the
 entire ring had to be replaced, resulting in a waste of a substantial
 amount of material, as well as a substantial time loss to remove all of
 the fasteners holding down the one-piece ring. With the present invention,
 only the securing ring 14 must be replaced do to wear. The securing ring
 14 can be conveniently replaced by simply removing the fastener in the key
 22 (if used), removing the key 22, and rotating the securing ring 14 with
 respect to the base ring 12 so that the locking members 18 of the base
 ring are aligned with the spacing between the grooves 14F of the securing
 ring. The securing ring 14 may then be lifted away from the base ring 12
 and a new securing ring 14 can be installed following the steps discussed
 above. Replacing only the securing ring 14 reduces overall material
 consumption by up to 85%. The use of a single, easily removable key 22 to
 lock the securing ring 14 to the base ring 12 substantially reduces the
 time both for removal and replacement of the securing ring 14.
 From the foregoing description, it can be seen that the present invention
 comprises a two-piece clamp ring assembly for holding a semiconductor
 wafer or other workpiece on a supporting surface. It will be appreciated
 by those of ordinary skill in the art that changes could be made to the
 embodiment described above, without departing from the broad inventive
 concepts thereof. It is understood, therefore, that this invention is not
 limited to the particular embodiment disclosed, but is intended to cover
 all modifications within the spirit and scope of the invention as set
 forth in the claims.