Abrading – Machine – Rotary tool
Reexamination Certificate
2000-03-02
2001-04-24
Morgan, Eileen P. (Department: 3723)
Abrading
Machine
Rotary tool
C451S288000, C451S398000
Reexamination Certificate
active
06220944
ABSTRACT:
BACKGROUND
The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a carrier head for chemical mechanical polishing.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, it is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly nonplanar. This nonplanar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Therefore, there is a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a polishing surface, e.g., a rotating polishing pad. The polishing pad may be either a “standard” or a fixed-abrasive pad. A standard polishing pad has a durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles, if a standard pad is used, is supplied to the surface of the polishing pad. The carrier head provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. Some carrier heads include a flexible membrane that provides a mounting surface for the substrate, and a retaining ring to hold the substrate beneath the mounting surface. Pressurization or evacuation of a chamber behind the flexible membrane controls the load on the substrate.
The effectiveness of a CMP process may be measured by its polishing rate, and by the resulting finish (absence of small-scale roughness) and flatness (absence of large-scale topography) of the substrate surface. The polishing rate, finish and flatness are determined by the pad and slurry combination, the relative speed between the substrate and pad, and the force pressing the substrate against the pad.
SUMMARY
In one aspect, the invention is directed to a carrier head. The carrier head has a housing, a plurality of substantially independently movable rods, and a first chamber located between the rods and the housing. The chamber is pressurizable to force the rods into contact with a substrate and to surround the substrate to retain the substrate beneath the housing.
Implementations of the invention may include the following features. A lower boundary of the first chamber may be defined by a flexible membrane attached to the housing, and the rods may be attached to the flexible membrane. Alternately, the first chamber may apply pressure directly to the rods. The rods may have a circular or hexagonal cross-section, a longitudinal dimension of about 0.06 to 0.5 inches, and a cross-sectional dimension of about 0.03 to 0.25 inches. The longitudinal dimension of the rods may be about twice their cross-sectional dimension. The rods may be spaced apart by about 0.0005 to 0.005 inches. The rods may be positioned around a perimeter portion of the substrate during polishing, and the carrier head further may include a flexible membrane having a mounting surface to contact a central region of the substrate. A second chamber that is pressurizable to apply a load to the central region of the substrate may be located between the flexible membrane and the housing. The rods may be positioned substantially parallel to each other.
In another aspect, the invention is directed to a carrier head to hold a substrate on a polishing surface. The carrier head has a housing defining a chamber, a flexible membrane defining a lower boundary of said chamber, and a bundle of independently movable rods secured to the flexible membrane. When a pressure within the chamber is increased, the rods and move into contact with the substrate and the polishing surface to apply a force to the substrate and retain the substrate substantially beneath the housing.
In another aspect, the invention is directed to a method of polishing a substrate. In the method, a substrate is positioned between a polishing surface and a plurality of independently movable rods of a carrier head, and a pressure is applied to the plurality of rods. One group of rods contacts a back surface of the substrate, and a second group of rods contacts the polishing surface to surround the substrate to retain the substrate beneath the carrier head.
Advantages of the invention may include the following. The spacing between the retainer and the substrate can be reduced, thereby improving polishing uniformity near the edge of the substrate. The carrier head has a large tolerance for misalignment of the substrate at a loading station. The carrier head is also usable with substrates of different sizes and geometries.
Other advantages and features of the invention will be apparent from the following description, including the drawings and claims.
REFERENCES:
patent: 5662518 (1997-09-01), James et al.
patent: 5730642 (1998-03-01), Sandhu et al.
patent: 5733182 (1998-03-01), Muramatsu et al.
patent: 5888120 (1999-03-01), Doran
patent: 6050882 (2000-04-01), Chen
Applied Materials Inc.
Fish & Richardson
Morgan Eileen P.
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