Abrading – Work holder – Work rotating
Reexamination Certificate
1998-10-09
2001-08-21
Banks, Derris H. (Department: 3723)
Abrading
Work holder
Work rotating
C451S287000
Reexamination Certificate
active
06277014
ABSTRACT:
BACKGROUND
The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a carrier head with a flexible membrane 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 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. 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. 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 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.
A reoccurring problem in CMP is the so-called “edge-effect,” i.e., the tendency of the substrate edge to be polished at a different rate than the substrate center. The edge effect typically results in overpolishing (the removal of too much material from the substrate) at the substrate perimeter, e.g., the outermost five to ten millimeters of a 200 millimeter (mm) wafer.
Another problem, particularly in a carrier head with a flexible membrane, relates to the attachment of the flexible membrane to the carrier head. Typically, the flexible membrane is secured to the carrier head with a clamping ring. Unfortunately, there are a variety of potential problems with this arrangement, such as difficulty in securing the clamping ring, difficulty in ensuring that the seal between the flexible membrane and carrier head is fluid-tight, and danger that the flexible membrane will be torn or damaged.
SUMMARY
In one aspect, the invention is directed to a carrier head for a chemical mechanical polishing apparatus. The carrier head has a base, a flexible membrane extending beneath the base to define a pressurizable chamber, a support structure positioned in the chamber, and a spacer ring positioned outside the chamber. A lower surface of the flexible membrane provides a mounting surface for a substrate. The flexible membrane includes a perimeter portion that extends between a lower surface of the spacer ring and an upper surface of the support structure and around an inner surface of the spacer ring.
Implementations of the invention may include one or more of the following features. A retaining ring may surround the spacer ring to maintain the substrate beneath the mounting surface. A rim portion of the flexible membrane may be clamped between the retaining ring and the base. The spacer ring may include a flange portion that extends outwardly toward an inner surface of the retaining ring. The support structure may be a free-floating body. A ledge portion is formed in the base, and the support structure may include a rim portion that extends over the ledge portion to act as a stop to limit the downward motion of the support structure. The support structure may include a generally disk-shaped portion with a plurality of apertures therethrough, and a generally annular flange portion extending upwardly. The flexible membrane may extend between the inner surface of the spacer ring and the outer surface of the flange. The perimeter portion of the flexible membrane may extend above an upper surface of the spacer ring. The surface area of the lower surface of the spacer ring may be greater than the surface area of the upper surface of the spacer ring. The surface area of the upper surface of the spacer ring may be selected to adjust the pressure applied to an edge of a substrate. The perimeter portion of the flexible membrane may extend from the mounting surface upwardly around a first outer surface of the support structure, inwardly between a lower surface of the spacer ring and an upper surface of the support structure, upwardly around an inner surface of the spacer ring, and outwardly above an upper surface of the spacer ring. The perimeter portion may also extend between an inner surface of the spacer ring and a second outer surface of the support structure, and extend above an upper surface of the spacer ring to be attached to the base.
In another aspect, the invention is directed to a flexible membrane for a chemical mechanical polishing head. The flexible membrane has a central portion for contacting a substrate, and a perimeter portion that is molded in a serpentine path that extends from the mounting surface upwardly, inwardly, upwardly and outwardly.
Implementations of the invention may include the following. The flexible membrane may have a rim portion having a thickness greater than the perimeter portion.
Advantages of the invention may include the following. The flexible membrane may be secured to the carrier head in a quick, repeatable and reliable manner with little danger of damage. The single-piece flexible membrane reduces the number of parts in the carrier head and provides a reliable fluid-tight seal. Non-uniform polishing of the substrate is reduced, and the resulting flatness and finish of the substrate are improved.
Other advantages and features of the invention will be apparent from the following description, including the drawings and claims.
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Chen Hung
Zuniga Steven
Applied Materials Inc.
Banks Derris H.
Fish & Richardson
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