Abrading – Abrading process – With tool treating or forming
Reexamination Certificate
2000-12-05
2002-05-14
Banks, Derris H. (Department: 3723)
Abrading
Abrading process
With tool treating or forming
C451S398000, C451S287000, C451S041000
Reexamination Certificate
active
06386955
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a carrier head for a chemical mechanical polishing system.
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, the layer 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 non-planar. This non-planar outer surface presents a problem for the integrated circuit manufacturer. If the outer surface of the substrate is non-planar, then a photoresist layer placed thereon is also non-planar. A photoresist layer is typically patterned by a photolithographic apparatus that focuses a light image onto the photoresist. If the outer surface of the substrate is sufficiently non-planar, then the maximum height difference between the peaks and valleys of the outer surface may exceed the depth of focus of the imaging apparatus, and it will be impossible to properly focus the light image onto the outer substrate surface.
It may be prohibitively expensive to design new photolithographic devices having an improved depth of focus. In addition, as the feature size used in integrated circuits becomes smaller, shorter wavelengths of light must be used, resulting in a further reduction of the available depth of focus. Therefore, there is a need to periodically planarize the substrate surface to provide a substantially planar layer surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted to a carrier or polishing head. The exposed surface of the substrate is then placed against a rotating polishing pad. The carrier provides a controllable load, i.e., pressure, on the substrate to press it against the polishing pad. In addition, the carrier may rotate to provide additional motion between the substrate and polishing pad. A polishing slurry, including an abrasive and at least one chemically-reactive agent, may be distributed over the polishing pad to provide an abrasive chemical solution at the interface between the pad and substrate.
A CMP process is fairly complex, and differs from simple wet sanding. In a CMP process, the reactive agent in the slurry reacts with the outer surface of the substrate to form reactive sites. The interaction of the polishing pad and abrasive particles with the reactive sites results in polishing.
An effective CMP process has a high polishing rate and generates a substrate surface which is finished (lacks small-scale roughness) and flat (lacks large-scale topography). 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. Because inadequate flatness and finish can create defective substrates, the selection of a polishing pad and slurry combination is usually dictated by the required finish and flatness. Given these constraints, the polishing rate sets the maximum throughput of the polishing apparatus.
The polishing rate depends upon the force pressing the substrate against the pad. Specifically, the greater this force, the higher the polishing rate. If the carrier head applies a non-uniform load, i.e., if the carrier head applies more force to one region of the substrate than to another, then the high pressure regions will be polished faster than the low pressure regions. Therefore, a non-uniform load may result in non-uniform polishing of the substrate.
An additional consideration in the production of integrated circuits is process and product stability. To achieve a high yield, i.e., a low defect rate, each successive substrate should be polished under substantially similar conditions. Each substrate should be polished by approximately the same amount so that each integrated circuit is substantially identical.
In view of the foregoing, there is a need for a chemical mechanical polishing apparatus which optimizes polishing throughput while providing the desired flatness and finish. Specifically, the chemical mechanical polishing apparatus should have a carrier head which applies a substantially uniform load across the substrate.
SUMMARY OF THE INVENTION
In one aspect, the present invention is directed to a carrier head for a chemical mechanical polishing apparatus. The carrier head comprises a base, a support structure connected to the base by a flexure, and a flexible membrane connected to the support structure. The flexible membrane has a mounting surface for a substrate and extends beneath the support structure to define a chamber.
Implementations of the invention include the following. The flexure may be secured between an upper clamp and a lower clamp, and the membrane may be secured between the lower clamp and the support structure. The flexure may be substantially horizontal and annular, with an outer circumferential portion attached to the base and an inner circumferential portion attached to the support structure. The support structure may include an annular ring or a circular plate. A portion of the chamber above the plate may be connected by an aperture through the plate to a portion below. An outer edge of the support structure may have a downwardly projecting lip.
The carrier head may include one or more of the following: a housing connectable to a drive shaft to rotate therewith, a gimbal mechanism pivotally connecting the housing to the base to permit the base to pivot with respect to the housing, a retaining ring connected to the base and surrounding the flexible membrane, and a loading mechanism connecting the housing to the base to apply a downward pressure to the base. The housing may have a substantially vertical passage, and the gimbal mechanism may include a rod with its upper end slidable disposed in the passage. The gimbal mechanism may include a bearing base with a spherical outer surface connected to a lower end of the rod and a gimbal race with a spherical inner surface engaging the bearing base.
The support structure, flexure and membrane may be configured such that a downward pressure on the flexure is substantially balanced by an upward pressure on the support structure so that a downward pressure at the edge of the membrane is substantially the same as a downward pressure at other portions of the membrane. A surface area of the lower surface the support structure may be approximately equal to a surface area of the upper surface of the flexure. An outer diameter of the clamp may be less than an outer diameter of the support structure.
There may be a gap between the support structure and the flexure, and there may be a passage through the support structure to carrying a fluid into the gap to force a slurry out of the gap.
In another aspect, to a carrier head includes a housing, a base, a loading mechanism, and a gimbal mechanism. The gimbal mechanism includes a rod having an upper end slidably disposed in the passage in the housing, and a slightly flexible member connecting a lower end of the rod to the base.
Implementations of the invention include the following. The member may be a ring with an inner circumferential portion connected to the rod and an outer circumferential portion connected to the base. The member may be bendable vertically but is rigid radially. A stop may be connected to the upper end of the rod to limit downward travel of the base.
In another aspect, a carrier head includes a housing, a base, a loading mechanism connecting the housing to the base to control the vertical position of the base relative to the housing, and a cushion attached to a lower surface of the housing to stop an upward motion of the base.
In another aspect, the carrier head includes a base, a first flexible membrane, and a second flexible membrane. The first membrane has a mo
Chen Hung
Ko Sen-Hou
Zuniga Steven M.
Banks Derris H.
Fish & Richardson
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