Abrading – Work holder – Work rotating
Reexamination Certificate
2001-08-07
2004-05-18
Eley, Timothy V. (Department: 3723)
Abrading
Work holder
Work rotating
C451S388000, C451S290000
Reexamination Certificate
active
06736713
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates, generally, to systems for polishing or planarizing workpieces such as semiconductor wafers. More particularly, the present invention relates to an apparatus for improving the uniform polishing of workpieces where the apparatus comprises a workpiece retaining element that engages a workpiece against a polishing surface during a polishing procedure.
BACKGROUND OF THE INVENTION
Many electronic and computer-related products such as semiconductors, CD-ROMs, and computer hard disks, require highly polished surfaces in order to achieve optimum operational characteristics. For example, high-quality and extremely precise wafer surfaces are often needed during the production of semiconductor-based integrated circuits. During the fabrication process, the wafers generally undergo multiple masking, etching and dielectric and conductor deposition processes. Because of the high-precision required in the production of these integrated circuits, an extremely flat surface is generally needed on at least one side of the semiconductor wafer to ensure proper accuracy and performance of the microelectronic structures created on the wafer surface. As the size of integrated circuits decreases and the density of microstructures on integrated circuits increases, the need for accurate and precise wafer surface polishing increases.
Chemical Mechanical Polishing (“CMP”) machines have been developed to. polish or planarize semiconductor wafer surfaces to the flat condition desired for integrated circuit components and the like. For examples of conventional CMP processes and machines, see U.S. Pat. No. 4,805,348, issued Feb. 21, 1989 to Arai et al.; U.S. Pat. No. 4,811,522, issued Mar. 14, 1989 to Gill; U.S. Pat. No. 05,099,614, issued Mar. 31, 1992 to Arai et al.; U.S. Pat. No. 5,329,732, issued Jul. 19, 1994 to Karlsrud et al.; U.S. Pat. No. 5,498,196, issued Mar. 12, 1996 to Karlsrud et al.; U.S. Pat. No. 5,498,199, issued Mar. 12, 1996 to Karisrud et al.; U.S. Pat. No. 5,558,568, issued Sep. 24, 1996 to Talieh et al.; and U.S. Pat. No. 5,584,751, issued Dec. 17, 1996 to Kobayashi et al.
Typically, a CMP machine includes a wafer carrier configured to hold, rotate, and transport a wafer during the process of polishing or planarizing the wafer. The wafer carrier is rotated to cause relative lateral motion between the polishing surface and the wafer to produce a substantially uniform thickness. In general, the polishing surface includes a horizontal polishing pad that has an exposed abrasive surface of cerium oxide, aluminum oxide, fumed/precipitated silica, or other particulate abrasives. Commercially available polishing pads may utilize various materials, as is known in the art. Typically, polishing pads may be formed from a blown polyurethane, such as the IC and GS series of polishing pads available from Rodel Products Corporation in Phoenix, Arizona. The hardness and density of the polishing pad depends on the material that is to be polished and the degree of precision required in the polishing process.
During a polishing operation, a pressure element (e.g., a rigid plate, a bladder assembly, or the like), which may be integral to the wafer carrier, applies pressure such that the wafer engages the polishing surface with a desired amount of force. The carrier and the polishing pad are rotated, typically at different rotational velocities, to cause relative lateral motion between the polishing pad and the wafer to promote uniform polishing. Most conventional carrier assemblies include some form of retaining structure that maintains the position of the wafer under the pressure element during polishing. Prior art carrier assemblies designed for compatibility with circular wafers employ round retaining structures such as retaining rings.
Retaining rings may either be fixed or “floating” within the wafer carrier. For example, U.S. Pat. No. 5,695,392, issued Dec. 9, 1997 to Kim, discloses the use of a fixed retaining ring collar that is bolted to the main carrier housing. U.S. Pat. No. 5584,751, issued Dec. 17, 1996 to Kobayashi et al., and U.S. Pat. No. 5,795,215, issued Aug. 18, 1998 to Guthrie et al., each teach the use of a floating retaining ring and a pressure regulating mechanism that controls the biasing pressure applied to the retaining ring.
Typically, retaining rings are made from engineering polymers such as, for example, acetal homopolymer, acetal copolymer, and polyphenylene sulfide. These materials are prone to wear due to the friction between the wafer, polishing pad and slurry abrasives that are used during polishing of the wafer. Wearing of the materials that comprise the retaining rings results in shortening the lives of the retaining rings which are functional and necessary components of the wafer carriers. Water absorption by the retaining rings can also distort dimensions of the acetal copolymers or homopolymers which comprise the retaining rings, thereby distorting the dimensions of the retaining rings themselves. Downtime associated with the repair or replacement of wafer retaining elements such as, for example, retaining rings, used in wafer carriers may be extremely undesirable, particularly if the workpiece throughput is critical.
An alternative to polymer retaining rings are retaining rings made of ceramic materials that are better able to withstand wear from friction created between the wafer and the retaining element, as well as abrasive slurries such as silicon dioxide and aluminum oxide. Because direct contact between the wafer and the retaining ring may result in damage to the wafer, prior art retaining rings may include a disposable liner positioned around the inside diameter of the retaining ring. The disposable liner is typically comprised of a material that is softer than the semiconductor wafer, for example, a polymer such as acetal copolymer or polybutyline terathalate (PBT) to prevent the retaining ring from damaging the wafer.
Despite their resistance to wear compared to retaining rings made from engineering polymers, ceramic retaining rings are still subject to chipping, cracking and other wear effects due to the friction between the wafer and the polishing pad, as well as from abrasive slurries. The surface of typical ceramic retaining rings may be relatively nonuniform, for example, having surface finishes of 6 to 8 microinches root mean square (“rms”). When subjected to the planarization process, ceramic particulates can be fractured from the nonuniform surface of the retaining ring. These ceramic particulates can cause scratches in the wafers that are being polished. Wafers that are scratched provide lower device yield and may be considered scrap, resulting in increased costs to the consumer. Further, the short lifetime of the retaining rings due to wear is significant in that the retaining rings are typically expensive consumable component parts of the CMP apparatus.
The inside diameter corners of the retaining ring at the anchor surface and polishing surface of the retaining ring are particularly susceptible to wearing and chipping.
FIGS. 1A and 1B
illustrate a conventional ceramic retaining ring
10
available in the prior art. Retaining ring
10
has a polishing surface
12
, which contacts a polishing pad, an anchor surface
20
, which contacts the wafer carrier, an inside diameter surface
16
, and an annular groove
18
which is positioned along the inside diameter surface
16
. Annular groove
18
has a depth “A” as measured from inside diameter surface
16
and is configured to receive a disposable liner (not shown). Retaining ring
10
also has at least one anchor bore
14
for receiving an anchor device, such as a screw or bolt, so that retaining ring
10
may be fixedly attached to a CMP wafer carrier. Although anchor bore
14
is shown in
FIG. 1B
as opening to anchor surface
20
to receive an anchor device previously inserted into a wafer carrier, anchor bore
14
may also be a through-hole which receives an anchor device for subsequent insertion into the wafer carrier to anchor the retaining
Key Robert
Lougher Wayne F.
McPeek Frank
Eley Timothy V.
Snell & Wilmer L.L.P.
SpeedFam-IPEC Corporation
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