The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to an apparatus and method for supplying slurry to a polishing pad.
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 surface presents a photolithography problem for the integrated circuit manufacturer. Therefore, there is a need to periodically planarize the substrate surface to provide a flat 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 moving polishing pad. The polishing pad may be either a xe2x80x9cstandardxe2x80x9d pad or a fixed-abrasive pad. A standard 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. 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.
An effective CMP process not only provides a high polishing rate, but also provides 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 t.-ie substrate and pad, and the force pressing the substrate against the pad.
One problem in CMP is coagulation of the polishing slurry. Specifically, small abrasive particles in the slurry tend to conglomerate to form larger particulates. These large particulates create scratches, e.g., shallow grooves on the order of 300 angstroms (A) deep, in the substrate surface. These scratches render the substrate finish unsuitable for integrated circuit fabrication, decreasing process yield.
In one aspect, the invention is directed to an apparatus for supplying a slurry to a polishing surface. The apparatus has a slurry source, a slurry supply line, and a slurry return line. The slurry supply line extends from the slurry source and has an outlet that may be fluidly coupled to a dispensing port positionable over the polishing surface to deliver slurry thereto during a chemical mechanical polishing operation. The slurry return line extends between the dispensing port and the slurry source, and has an inlet that may be fluidly coupled to the outlet of the slurry supply line to direct slurry away from the dispensing port and to the slurry supply.
In another aspect, the slurry supply line extends from the slurry source and has an outlet located at or proximate to a slurry dispensing point. The slurry return line extends from the slurry source and has an inlet. The slurry supply line and slurry return line are configured so that slurry may be directed from the outlet of the slurry supply line onto the polishing surface during a chemical mechanical polishing operation, and from the outlet of the slurry supply line into the inlet of the slurry return line after the polishing operation is stopped to return slurry to the slurry supply. This substantially eliminates deadleg from the slurry supply line.
Implementations of the invention may include the following. A pump may provide a flow of slurry through the slurry supply line, e.g., during the polishing operation. The pump may also direct slurry through the slurry supply line and the slurry return line, e.g., after the polishing operation is stopped. Thus, the pump may operate to provide a substantially continuous flow of slurry through the slurry supply line. A filter may be located between the slurry source and the pump.
A valve, e.g., a ball valve or a plunger valve, at the outlet of the slurry supply line may be operable between a first position in which the outlet of the slurry supply line is fluidly coupled to the port to dispense slurry onto the polishing pad and a second position in which the outlet of the slurry supply line is fluidly coupled to the inlet of the slurry return line. A portion of the slurry supply line may be flexible and moveable between a first position in which the outlet of the slurry supply line dispenses slurry to the polishing surface and a second position in which the slurry supply line is fluidly coupled to the supply return line.
The inlet of the slurry return line may be located adjacent to the polishing surface to receive slurry from the slurry supply line. The outlet of the slurry supply line may be movable between a first position in which it is positioned over the polishing surface and a second position in which it positioned over the inlet of the slurry return line.
An arm may extend over the polishing surface and support at least a portion of the slurry supply line. The outlet of the slurry supply line may be located at the end of the arm. The slurry supply line can be a passage in the arm or tubing supported by the arm. A machine base may support the polishing surface, and the arm may be pivotally connected to the base.
A second slurry supply line may extend from the slurry source and have a second outlet proximate to a second slurry dispensing point. A second slurry return line may extend from the slurry source and have an inlet. The second slurry supply line and second slurry return line may be configured so that slurry may be directed from the outlet of the slurry supply line to a second polishing surface during a chemical mechanical polishing operation, and into the inlet of the slurry return line after the polishing operation is stopped to return slurry to the slurry supply. This substantially eliminates deadleg from the second slurry supply line.
In another aspect, the invention is directed to a method of chemical mechanical polishing. In the method, slurry is pumped from a slurry source to an outlet of a slurry supply line that is positionable over a polishing surface. The slurry is directed from the outlet to the polishing surface. The outlet of the slurry supply line is fluidly coupled to an inlet of a slurry return line after the polishing operation has stopped to return the slurry to the slurry source.
Implementations of the invention may include the following. The pumping may create a flow of slurry through the slurry supply line and the slurry return line after polishing operation has stopped. The pumping may create a substantially continuous flow of slurry through the slurry supply line.
Advantages of the invention may include the following. Coagulation of slurry is reduced or eliminated, thereby reducing scratch defects and increasing process yield.