Abrading – Precision device or process - or with condition responsive... – By optical sensor
Reexamination Certificate
1998-03-30
2001-09-25
Ostrager, Allen (Department: 3725)
Abrading
Precision device or process - or with condition responsive...
By optical sensor
C451S005000
Reexamination Certificate
active
06293846
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polishing apparatus for polishing a workpiece such as a semiconductor wafer, and more particularly to a polishing apparatus having a workpiece dislodgment detector for detecting a workpiece which is dislodged from a top ring while the workpiece is being polished.
2. Description of the Prior Art
Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One of the processes available for forming such interconnection is photolithography. Though the photolithographic process can form interconnections that are at most 0.5 &mgr;m wide, it requires that surfaces on which pattern images are to be focused by a stepper be as flat as possible because the depth of focus of the optical system is relatively small. Conventionally, as apparatuses for planarizing semiconductor wafers, there have been used a self-planarizing CVD apparatus, an etching apparatus or the like, however, these apparatuses fail to fully planarize semiconductor wafers. Recently, attempts have been made to use polishing apparatus for planarizing semiconductor wafers to a flatter finish with more ease than those conventional planarizing apparatus.
Conventionally, a polishing apparatus has a turntable and a top ring which rotate at respective individual speeds. A polishing cloth is attached to the upper surface of the turntable. A semiconductor wafer to be polished is placed on the polishing cloth and clamped between the top ring and the turntable. An abrasive liquid containing abrasive grains is supplied onto the polishing cloth and retained on the polishing cloth. During operation, the top ring exerts a certain pressure on the turntable, and the surface of the semiconductor wafer held against the polishing cloth is therefore polished by a combination of chemical polishing and mechanical polishing to a flat mirror finish while the top ring and the turntable are rotated. This process is called Chemical Mechanical polishing.
If a semiconductor wafer is transferred normally to the top ring, then the semiconductor wafer will not be dislodged or disengage from the top ring while the semiconductor wafer is being polished. However, if a semiconductor wafer is not transferred normally to the top ring, but is partially placed on a retainer ring of the top ring, the semiconductor wafer will tend to be dislodged from the top ring while the semiconductor wafer is being polished.
When the semiconductor wafer is dislodged, i.e., slipped out from the top ring, the semiconductor wafer is rotated with the turntable and collides with the top ring, with the result that the semiconductor wafer is liable to be damaged and/or to damage components of the polishing apparatus including the retainer ring for retaining the wafer therein, the polishing cloth on the turntable, a backing pad mounted on the lower surface of the top ring and supporting the semiconductor wafer, and a dressing tool mounted on a dressing apparatus. It has heretofore been customary to detect whether there is foreign matter on the polishing cloth by direct visual observation of the surface of the polishing cloth or image processing of the surface of the polishing cloth obtained by a television camera installed over the polishing cloth or the like.
The visual observation of the surface of the polishing cloth with the naked eye or the television camera fails to accurately detect foreign matter or a semiconductor wafer on the polishing cloth depending on the property of the semiconductor wafer, e.g., whether the detected surface thereof is polished to a mirror finish or a rough finish or carries an oxide layer, and also depending on whether there is water or an abrasive liquid on the polishing cloth, or the type of an abrasive liquid present on the polishing cloth.
If the surface of the polishing cloth is monitored with a monitoring device such as a television camera, then an output signal from the monitoring device is processed by a complex process such as an image processing to detect whether or not there is foreign matter on the polishing cloth, or whether or not the polishing cloth is defective. Because the complex process is time-consuming, it takes too much time after a semiconductor wafer is dislodged until the trouble is actually detected. Even if the polishing apparatus is shut down when the malfunction is actually detected, the semiconductor wafer will be damaged or broken, and damage to components of the polishing apparatus including th polishing cloth, the backing pad and the dressing tool can occur by the time the rotations of the turntable and the top ring are stopped.
Another problem with the image processing system is that since it needs a microcomputer capable of effecting high-speed computation for processing image information from the monitoring device at a high speed, the entire polishing apparatus is complex in structure and expensive to manufacture.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a polishing apparatus having a workpiece dislodgment detector which can immediately detect a semiconductor wafer which is dislodged from a top ring while the semiconductor wafer is being polished, has a relatively simple arrangement in which an adjustment for detection can be effected only by establishing a threshold with respect to an output signal from a sensor, and is relatively inexpensive to manufacture.
According to one aspect of the present invention, there is provided a polishing apparatus for polishing a workpiece, comprising: a turntable having a polishing surface; a top ring for holding a workpiece and pressing the workpiece against the polishing surface of the turntable; and a workpiece dislodgment detector for detecting the workpiece which is dislodged from the top ring, the workpiece dislodgment detector including a sensor positioned adjacent to the top ring.
The workpiece dislodgment detector may comprise a photoelectric sensor for emitting light, receiving a reflected light and detecting the workpiece which is dislodged from the top ring based on a change in a quantity of the reflected light.
The photoelectric sensor may comprise a gloss sensor, and the gloss sensor may comprise a red light-emitting diode for emitting red light, a polarizing filter for allowing only S wave of the light from the red light-emitting dioxide to pass therethrough, and a beam splitter for separating the reflected light into S wave and P wave, and detecting the workpiece which is dislodged from the top ring based on a difference in glossiness.
The sensor of the workpiece dislodgment detector may be mounted directly or through an attachment on the top ring head.
The rotations of the turntable and the top ring may be stopped immediately when the workpiece dislodgment detector detects the workpiece which is dislodged from the top ring.
The top ring may be lifted immediately when the workpiece dislodgment detector detects the workpiece which is dislodged from the top ring.
The polishing apparatus may further have a bumper disposed around the turntable for dampening or cushioning movement of the workpiece dislodged from the top ring.
According to another aspect of the present invention, there is provided a method for polishing a workpiece by pressing the workpiece held by a top ring against a polishing surface on a turntable; detecting a dislodgment of the workpiece from the top ring during polishing; and stopping rotations of the turntable and the top ring when the dislodgment of the workpiece is detected.
According to still another aspect of the present invention, there is provided a method for polishing a workpiece by pressing the workpiece held by a top ring against a polishing surface on a turntable; detecting a dislodgment of the workpiece from the top ring during polishing; and lifting the top ring when the dislodgment of the workpiece is detected.
The above and other objects, features, and advantages o
Ebara Corporation
Hong William
Ostrager Allen
Wenderoth , Lind & Ponack, L.L.P.
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