Abrading – Abrading process – With tool treating or forming
Reexamination Certificate
2000-06-29
2002-01-22
Banks, Derris H. (Department: 3723)
Abrading
Abrading process
With tool treating or forming
C451S527000
Reexamination Certificate
active
06340325
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of making polishing pads, and more specifically to providing macrotextured surfaces on polishing pads used in the chemical-mechanical planarization (CMP) of semiconductor substrates.
BACKGROUND OF THE INVENTION
Chemical-mechanical polishing has been used for many years as a technique for polishing optical lenses and semiconductor wafers. More recently, chemical-mechanical polishing has been developed as a means for planarizing intermetal dielectric layers of silicon dioxide and for removing portions of conductive layers within integrated circuit devices as they are fabricated on various substrates. For example, a silicon dioxide layer may cover a metal interconnect conformably such that the upper surface of the silicon dioxide layer is characterized by a series of non-planar steps corresponding in height and width to the underlying metal interconnects.
The step height variations in the upper surface of the intermetal dielectric layer have several undesirable characteristics. Such non-planar dielectric surfaces may interfere with the optical resolution of subsequent photolithographic processing steps, making it extremely difficult to print high resolution lines. Another problem involves the step created in the coverage of a second metal layer over the intermetal dielectric layer. If the step height is relatively large, the metal coverage may be incomplete such that open circuits may be formed in the second metal layer.
To combat these problems, various techniques have been developed to planarize the upper surface of the intermetal dielectric layer. One such approach is to employ abrasive polishing to remove the protruding steps along the upper surface of the dielectric layer. According to this method, a silicon substrate wafer is mounted face down beneath a carrier and pressed between the carrier and a table or platen covered with a polishing pad that is continuously coated with a slurried abrasive material.
Means are also provided for depositing the abrasive slurry on the upper surface of the pad and for forcibly pressing the substrate wafer against the polishing pad, such that movement of the platen and the substrate wafer relative to each other in the presence of the slurry results in planarization of the contacted face of the wafer. Both the wafer and the table may be rotated relative to each other to rub away the protruding steps. This abrasive polishing process is continued until the upper surface of the dielectric layer is substantially flat.
Polishing pads may be made of a uniform material such as polyurethane or nonwoven fibers impregnated with a synthetic resin binder, or may be formed from multilayer laminations having non-uniform physical properties throughout the thickness of the pad. Polyurethane polishing pads are typically formed by placing a reactive composition in a mold, curing the composition to form the pad material, and then die cutting the pad material into the desired size and shape. The reagents that form the polyurethane or the resin binder also may be reacted within a cylindrical container. After forming, a cylindrically shaped piece of pad material is cut into slices that are subsequently used as the polishing pad. A typical laminated pad may have a plurality of layers, such as a spongy and resilient microporous polyurethane layer laminated onto a firm but resilient supporting layer comprising a porous polyester felt with a polyurethane binder. Polishing pads typically may have a thickness in the range of 50-80 mils, preferably about 55 mils, and a diameter in the range of 10 to 36 inches, such as about 22.5 inches.
Polishing pads also may have macrotextured work surfaces made by surface machining using various techniques, many of which are expensive and produce undesirable surface features of widely varying depths. Surface features include waves, holes, creases, ridges, slits, depressions, protrusions, gaps, and recesses. Some other factors which influence the macroscopic surface texture of a polishing pad are the size, shape, and distribution frequency or spacing of the surface features. Polishing pads typically may also have microtextured surfaces cause by a microscopic bulk texture of the pad resulting from factors intrinsic to the manufacturing process. Since polishing does not normally occur across the entire pad surface, any microtexture of the pad and the macrotextures made by surface machining, may only be formed into the portion of the pad over which polishing is to take place.
During the polishing process, the material removed from the wafer surface and the abrasive, such as silica, in the slurry tend to become compacted and embedded in the recesses, pores, and other free spaces within the microscopic and macroscopic bulk texture of the polishing pad at and near its surface. One factor in achieving and maintaining a high and stable polishing rate is providing and maintaining the pad surface in a clean condition. Another factor is reducing or preventing a hydroplaning effect caused by the buildup of a layer of water between the abutting surfaces of the pad and the wafer. It has also been determined that increasing the flexibility of the pad in a controlled manner will increase polishing uniformity, i.e., the uniformity of the polished wafer surface.
Thus, consistently achieving uniform and high quality polishing of wafer surfaces by conventional pads has presented three problems. The first of these is the buildup of abrasive particles and debris between the pad and the wafer causing uneven polishing and damage to both the pad and the wafer. Secondly, uneven polishing due to hydroplaning between the wafer and the pad during conventional processes has resulted in the relatively high loss of product yield due to the resulting wafer damage. Thirdly, uneven polishing and wafer damage has also resulted from overly rigid pads produced by prior art manufacturing techniques. Therefore, there is a need for a method and apparatus for providing polishing pads capable of consistently producing high quality wafers with uniformly polished surfaces.
SUMMARY OF THE INVENTION
The present invention, therefore, provides a pad grooving method and apparatus for producing a polishing pad that is capable of consistently forming uniformly polished surfaces on high quality wafers. The apparatus comprises a platen with positioning post for holding a polishing pad in position for engagement by a router to machine grooves in the working surface of the pad. In order to precisely control the depth of the grooves as they are routed in the pad, a spacing mechanism provides a constant and precise separation between the working surface of the pad and the chuck for holding and rotating the router.
The pad is placed on the supporting surface of the platen with its working surface in spaced relation opposite to the router bit. The router chuck and drive motor are supported opposite to the pad by a frame. The spacing mechanism comprises at least one, preferably two or more, stop members mounted on the frame adjacent to an aperture through which passes the router bit. An outer end portion of the bit projects beyond the stop member(s), which preferably are pins threaded within the frame so as to be axially adjustable. A vacuum system is provided for applying a vacuum to the working surface of the pad to pull the pad first against the outer end of the router bit and then against the stop member(s).
Rotation of the router bit by the motor while the vacuum is applied to the pad causes the outer end portion of the bit to cut an initial recess (hole) into the pad to a depth below its working surface. The recess depth is precisely limited by the stop member(s), which comes into contact with the working surface of the pad as the rotating bit cuts into the pad to form the initial recess. After formation of the initial recess, a lateral motion mechanism causes relative lateral movement between the rotating router bit and the pad while the vacuum maintains the pad in contact with the stop member(s).
This lateral movement cau
Chen Shyng-Tsong
Chi Hsu Oscar Kai
Chung Alex Siu Keung
Davis Kenneth M.
Rodbell Kenneth P.
Banks Derris H.
Connolly Bove Lodge & Hutz
International Business Machines - Corporation
Trepp, Esq. Robert
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