Abrading – Machine – Rotary tool
Reexamination Certificate
1999-07-08
2001-06-12
Rose, Robert A. (Department: 3723)
Abrading
Machine
Rotary tool
C451S398000
Reexamination Certificate
active
06244942
ABSTRACT:
BACKGROUND
The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a carrier head with a flexible membrane.
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 can results in either overpolishing (the removal of too much material from the substrate) or underpolishing (the removal of too little material) at the substrate perimeter, e.g., the outermost five to ten millimeters of a 200 millimeter (mm) wafer.
SUMMARY
In general, in one aspect, the invention is directed a carrier head for a chemical mechanical polishing apparatus. The carrier head has a base, a retaining ring secured to the base, an annular spacer positioned beneath the base, a first flexible membrane portion extending beneath the base and the spacer to define a pressurizable chamber, and a second flexible membrane portion extending over the spacer. The first membrane portion has a lower surface that provides a mounting surface for a substrate, and an edge portion secured between the base and the retaining ring. At least one of the retaining ring and the spacer includes a projection or an indentation positioned adjacent the second membrane portion to adjust the pressure applied at a perimeter of the first membrane portion.
Implementations of the invention may include one or more of the following features. The first and second membrane portions may be portions of a single flexible membrane. The flexible membrane may extend inwardly beneath a lower surface of the spacer, upwardly around an inner surface of the spacer, and outwardly above an upper surface of the spacer. A volume between the first membrane portion and the portion of the flexible membrane that extends inwardly beneath the lower surface of the spacer may define a pressurizable pocket. A support structure may be positioned inside the chamber. The spacer may include a flange that extends over the support structure.
In another aspect, the invention is directed to a method of polishing a substrate. In the method, a substrate is positioned against a first flexible membrane portion of a carrier head. The first flexible membrane portion extends beneath a base and a spacer in the carrier head to define a pressurizable chamber. The chamber is pressurized so that a second flexible membrane portion extending over the spacer and having an edge portion secured between the base and a retaining ring applies a downward pressure to the spacer. At least one of the retaining ring and the spacer includes a projection or an indentation positioned adjacent the second membrane portion, so that the pressure applied at a perimeter of the first membrane portion differs from the pressure applied in center of the first membrane portion.
Advantages of the invention may include the following. Non-uniform polishing of the substrate can be reduced, and the resulting flatness and finish of the substrate are improved. A single pressure control can be used to adjust the polishing rates at the center and edge of the substrate.
Other advantages and features of the invention will be apparent from the following description, including the drawings and claims.
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Applied Materials Inc.
Fish & Richardson
Rose Robert A.
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