Abrading – Precision device or process - or with condition responsive... – With indicating
Reexamination Certificate
1998-02-19
2001-12-11
Hail, III, Joseph J. (Department: 3725)
Abrading
Precision device or process - or with condition responsive...
With indicating
C451S287000, C451S288000, C451S388000, C451S398000
Reexamination Certificate
active
06328629
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for polishing a workpiece, and more particularly to a method and apparatus for polishing a planar workpiece such as a semiconductor wafer to a flat mirror finish.
2. Description of the Related 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 a 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.
After the semiconductor wafer is polished, it is detached from the top ring, and transferred to a next process such as a cleaning process.
While a workpiece such as a semiconductor wafer is being polished, it occasionally is broken into pieces which are scattered on the polishing cloth. Each time the workpiece being polished is broken, the polishing cloth has to be replaced with a new one because fragments of the workpiece on the polishing cloth would otherwise cause damage to the surface of another workpiece to be polished. Another problem is that a workpiece such as a semiconductor wafer which is being polished is sometimes disengaged from the top ring due to lack of secure attachment of the workpiece to the top ring. If the workpiece is a fragile object such as a semiconductor silicon wafer, then an outer circumferential edge of the workpiece may suffer same damage such as chipping upon collision with a wall surface that covers the turntable. When the damaged workpiece is polished again, it can easily be broken apart under small forces which are applied to the damaged area or thereabouts of the workpiece.
There have been made various efforts to prevent a workpiece from being broken and also from being disengaged from the top ring. For example, a cushioning member such as an elastic mat is interposed between the top ring and the workpiece to reduce cracking or chipping of the workpiece while the workpiece is being polished. A retainer ring is provided on the outer periphery of the top ring to retain the outer circumferential edge of the workpiece and to firmly hold the workpiece on the top ring for thereby preventing the workpiece from being disengaged from the top ring while the workpiece is being polished.
However, the above attempts fail to completely prevent the workpiece from being broken or being disengaged from the top ring while the work piece is being polished. Since the polishing process is continued even when the workpiece is broken or disengaged from the top ring, various resultant problems have not been eliminated.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method and apparatus for polishing a workpiece while monitoring the workpiece continuously when it is being polished, for thereby minimizing damage that would otherwise be caused when the workpiece is broken or disengaged from a top ring.
According to one aspect of the present invention, there is provided a method for polishing a lower surface of a workpiece, the method comprising: holding a workpiece by a top ring; polishing the lower surface of the workpiece by pressing the workpiece against a polishing surface of a turntable; detecting at least one of a pressure and a flow rate of a fluid which is supplied to an upper surface of the workpiece while the workpiece is being polished; and stopping polishing of the workpiece when at least one of the detected pressure and the detected flow rate changes.
According to another aspect of the present invention, there is provided a method for polishing a lower surface of a workpiece, the method comprising: attracting a workpiece to a top ring under vacuum from a vacuum source; detecting at least on of a pressure and a flow rate of a gas in a vacuum line interconnecting the top ring and the vacuum source to judge whether the workpiece is properly attracted to the top ring; polishing the lower surface of the workpiece by pressing the workpiece against a polishing surface of a turntable; and detecting at least one of a pressure and a flow rate of a fluid which is supplied to an upper surface of the workpiece while the workpiece is being polished to judge whether the workpiece is damaged.
According to still another aspect of the present invention, there is provided an apparatus for polishing a lower surface of a workpiece, the apparatus comprising: a turntable having a polishing surface on an upper surface thereof; a top ring disposed above the turntable and holding a workpiece to be polished and pressing the workpiece against the polishing surface, the top ring having a plurality of openings; a pressurized fluid source for supplying a fluid under pressure through the openings to an upper surface of the workpiece; a detector disposed between the openings and the pressurized fluid source for detecting at least one of a pressure and a flow rate of the fluid supplied from the pressurized fluid source; and a controller for stopping polishing of the workpiece when at least one of the detected pressure and the detected flow rate changes.
According to the present invention, while the workpiece is attached to the top ring, polished and removed from the top ring, the workpiece is always monitored for occurrence of damage. Therefore, the workpiece is prevented from being broken in a sequence of process including attachment of the workpiece to the top ring, polishing, and detachment of the workpiece from the top ring. Any damage which would otherwise be caused when the workpiece is broken is reduced to a minimum.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.
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patent: 59577
Kimura Norio
Ono Koji
Togawa Tetsuji
Ebara Corporation
Hail III Joseph J.
Hong William
Wenderoth , Lind & Ponack, L.L.P.
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