Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – By mechanically introducing gas into material
Reexamination Certificate
1999-08-31
2001-09-18
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
By mechanically introducing gas into material
C264S158000
Reexamination Certificate
active
06290883
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to semiconductor processing, and, more particularly, to articles for planarizing or polishing semiconductor wafers during the manufacture of integrated circuits, and methods and apparatus for making the articles.
BACKGROUND OF THE INVENTION
Integrated circuits are used in many electronic devices. A typical integrated circuit includes a semiconductor substrate, such as formed of silicon. A number of active regions may be formed in the substrate, and a plurality of interconnect layers are formed on the substrate to interconnect the active regions and/or facilitate external connections to the active regions. Typically a plurality of integrated circuits are collectively formed on a semiconductor wafer.
It is also typically important to planarize the wafer after various process steps to remove unwanted portions or to ensure a planar upper surface for forming a next layer thereon. One common technique to planarize a wafer is known as chemical mechanical polishing (CMP). CMP is very widely used technique which delivers a slurry of material to the wafer surface and while a polishing pad or belt is passed over the wafer surface. For example, U.S. Pat. No. 4,972,432 entitled “Pad Material for Grinding, Lapping and Polishing” discloses a polishing pad including a porous thermoplastic resin matrix, such as comprising polyurethane, reinforced with a fibrous network provided by a felted mat of polyester fibers. The polishing material is modified by coalescing the resin among the fibers, preferably by heat treatment, to increase the porosity and hardness of the material as well as increasing the surface activity of the resin. The two different resins have different melting temperatures so that one is coalesced first. The polishing material may also incorporate polishing aids, such as particulate abrasives.
Another polishing pad is disclosed in U.S. Pat. No. 5,578,362 to Reinhardt et al. This patent discloses in its background a number of different pad constructions including a so-called “minitexturized” pad which includes intermediately sized textured artifacts on the pad, which may be produced by use of lasers or the incorporation of air or gas within the pad material. Conventional pads are described as including “microtexture” which is the intrinsic microscopic bulk texture of the pad after manufacture which is largely random. “Macrotextures” are artifacts or features generally greater than about 5 mm, and spacing and sizes are typically very regular and repetitive. The patent further discloses a pad including a plurality of microelements impregnated into a polymeric matrix. The polymeric microelements at the work surface are less rigid than those embedded. Accordingly, the less rigid microelements at the work surface cause the surface of the pad to be continuously regenerated.
U.S. Pat. No. 5,584,146 to Shamouillan et al. discloses a polishing pad including a plurality of conduits passing through the entire thickness of the pad. The conduits are to hold the slurry uniformly across the surface of the polishing pad, and to permit the addition of slurry or other materials therethrough.
Rodel, Inc. of Newark, Del. makes a line of CMP pads formed from filled and/or blown urethanes such as IC-series, MH-series and LP-series polishing pads. These have a surface structure made up of semicircular depressions derived from the cross-section of exposed hollow spherical elements or incorporated gas bubbles.
Despite continuing advances in the area of pads for CMP, there still exists a need for pads having more uniform surfaces, especially as the pad wears. In addition, the purity of such pads is desirably controlled to produce more consistent polishing results.
SUMMARY OF THE INVENTION
In view of the foregoing background, it is therefore an object of the present invention to provide a method and apparatus for producing CMP pads and/or belts, which have greater uniformity, and which are readily manufactured.
These and other objects, features and advantages in accordance with the present invention are provided by a method for making a chemical mechanical polishing (CMP) article comprising a matrix with voids therein. In particular, the method preferably comprises the steps of: dissolving gas into solidifiable material, and reducing pressure on the solidifiable material to form gas bubbles therein while solidifying the solidifiable material to make the matrix with voids therein. The step of dissolving preferably comprises subjecting the solidifiable material to gas at an elevated pressure. The gas bubbles are preferably formed to define voids interconnected with adjacent voids to thereby define a porous matrix.
The porous matrix ensures uniform distribution of the CMP slurry for greater polishing uniformity. The method produces a CMP pad, for example, with very uniform porosity throughout its working thickness so that polishing remains uniform as the pad is consumed in use. Moreover, the method of using the bubbles to define the voids allows the pad to have a high purity which is also important for polishing uniformity. In other words, the matrix material is the only constituent material of the pad, unlike pads which use microcapsules of different material to form voids.
The gas and the solidifiable material may preferably be non-reactive with one another. The gas may comprise at least one inert gas, such as nitrogen or argon, for example.
In one particularly advantageous embodiment, the solidifiable material comprises a polymer-forming liquid and at least one of a curing and cross-linking agent mixed therein. The polymer-forming liquid may comprise urethane, for example, so that the resulting matrix is polyurethane. Polyurethane is a widely used material for CMP pads with excellent wear, hardness, and other characteristics. The polymer-forming liquid and the curing or cross-linking agent can be combined just prior to the step of dissolving the gas.
The solidifiable material may be retained in a mold during the processing steps explained above. The method may also include the step of shaping the solidified material to have at least one planar major surface. The solidified material is typically formed into at least one generally-disk shaped body for use as a CMP pad. An elongate version can be shaped for a CMP belt.
Another aspect of the invention is directed to an apparatus for making the CMP article comprising the matrix with voids therein. The apparatus preferably includes a mold containing solidifiable material, a gas source, and a pressure chamber receiving the mold therein and connected to the gas source. In addition, the apparatus also preferably includes a pressure controller associated with the pressure chamber for controlling a pressure therein for dissolving gas into the solidifiable material, and reducing pressure on the solidifiable material to form gas bubbles therein while the solidifiable material solidifies to make the matrix with voids therein.
The pressure controller preferably subjects the solidifiable material to gas at an elevated pressure to dissolve the gas. In addition, the pressure controller preferably causes the gas bubbles to form to define voids interconnected with adjacent voids to define a porous matrix. The gas and the solidifiable material are preferably non-reactive with one another in one embodiment, again to ensure the purity of the finished CMP article. The solidifiable material may comprise a polymer-forming liquid and at least one of a curing and cross-linking agent mixed therein.
The apparatus may also comprise respective dispensers for the polymer-forming liquid and the at least one of a curing and cross-linking agent. The dispensers may dispense the materials into the mold prior to positioning into the chamber. The apparatus may also include a heater associated with the chamber, and a heater controller connected to the heater.
The apparatus may also include a shaping station downstream from the chamber for shaping the solidified material to have at least one planar major surface. The shaping station preferably
Crevasse Annette Margaret
Easter William Graham
Maze John Albert
Miceli, III Frank
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Kuhns Allan R.
Lucent Technologies - Inc.
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