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The Effect of Wafer Shape on Slurry Film Thickness and Friction Coefficients in Chemical Mechanical Planarization

Published online by Cambridge University Press:  14 March 2011

Joseph Lu
Affiliation:
Tufts University, Dept. Mechanical Engineering, Medford, MA 02155, USA
Jonathan Coppeta
Affiliation:
Tufts University, Dept. Mechanical Engineering, Medford, MA 02155, USA
Chris Rogers
Affiliation:
Tufts University, Dept. Mechanical Engineering, Medford, MA 02155, USA
Vincent P. Manno
Affiliation:
Tufts University, Dept. Mechanical Engineering, Medford, MA 02155, USA
Livia Racz
Affiliation:
Tufts University, Dept. Mechanical Engineering, Medford, MA 02155, USA
Ara Philipossian
Affiliation:
Intel Corporation, Santa Clara, CA 95052, USA
Mansour Moinpour
Affiliation:
Intel Corporation, Santa Clara, CA 95052, USA
Frank Kaufmanc
Affiliation:
Cabot Corporation, Aurora, IL 60504, USA
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Abstract

The fluid film thickness and drag during chemical-mechanical polishing are largely dependent on the shape of the wafer polished. In this study we use dual emission laser induced fluorescence to measure the film thickness and a strain gage, mounted on the polishing table, to measure the friction force between the wafer and the pad. All measurements are taken during real polishing processes. The trends indicate that with a convex wafer in contact with the polishing pad, the slurry layer increases with increasing platen speed and decreases with increasing downforce. The drag force decreases with increasing platen speed and increases with increasing downforce. These similarities are observed for both in-situ and ex-situ conditioning. However, these trends are significantly different for the case of a concave wafer in contact with the polishing pad. During ex-situ conditioning the trends are similar as with a convex wafer. However, in-situ conditioning decreases the slurry film layer with increasing platen speed, and increases it with increasing downforce in the case of the concave wafer. The drag force increases with increasing platen speed as well as increasing downforce. Since we are continually polishing, the wafer shape does change over the course of each experiment causing a larger error in repeatability than the measurement error itself. Different wafers are used throughout the experiment and the results are consistent with the variance of the wafer shape. Local pressure measurements on the rotating wafer help explain the variances in fluid film thickness and friction during polishing.

Type
Research Article
Copyright
Copyright © Materials Research Society 2000

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