Polyurethane Pad Degradation and Wear Due to Tungsten and Oxide CMP
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Polyurethane Pad Degradation and Wear Due to Tungsten and Oxide CMP Amy L. Moy*, Joseph L. Cecchi*, Dale L. Hetherington|, and David J. Stein| *University of New Mexico, Department of Chemical and Nuclear Engineering, 209 Farris Engineering Center, Albuquerque, NM 87131, U.S.A. | Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87123, U.S.A.
ABSTRACT Polyurethane polishing pads are commonly used for chemical-mechanical polishing (CMP) of semiconductor wafers. Structural, chemical, and mechanical property changes of the polishing pads due to CMP are examined. Tungsten and oxide film layers are polished from the wafer surface using the polishing pad and abrasive slurry system. The polishing pad surface is flattened with polishing, and hence, reducing the effective area for slurry transport. The abrasive is used for abrading off the film from the surface. W, Al, I, and K accumulate in the polishing pad after tungsten CMP and Si accumulates after oxide CMP. Material accumulates in the pad pores and grooves. Electron Microprobe X-ray Analysis and Wavelength Dispersive Spectrometry (WDS) were used to examine the changes across the thickness of the pad. Fourier Transform Infrared Spectroscopy (FTIR) was used to determine the changes to the polyurethane isocyanate group. The reduction in the isocyanate group and increase in the hydroxyl group after tungsten CMP indicates that a hydrolysis reaction of the isocyanate to form carboxylic acid occurs.
INTRODUCTION Glass polishing has been in practice for many years throughout history. Polishing has been used for preparing glass surface of telescopes and according to Sir Isaac Newton in 1721, “nothing is wanting to perfect these telescopes but good workmen who can grind and polish glasses truly spherical.” [1]. The softening of the glass by chemicals and the removal of the glass by abrasives occurs during glass polishing [2]. Similar to the polishing of glass, chemicalmechanical polishing is the polishing of film layers on wafers. The purpose of this research study is to examine the structural, chemical, and mechanical property changes of the polyurethane polishing pad due to tungsten and oxide CMP. CMP is the removal of mass by chemical reactions and mechanical abrasion. It is a combination of direct slurry particle contact and local contact reactions [3].
CONSUMABLES AND EQUIPMENT The planarization of the wafer surface and the removal of the tungsten film layer from the wafer surface are done using chemical-mechanical polishing. There are many consumables used for the tungsten CMP, including an oxidizer and an abrasive. The oxidizer, potassium iodate, reacts with the tungsten film to form a passivation layer [3]. The oxidizer is present in the Rodel M1.7.1
MSW2000B slurry. The abrasive is alumina (aluminum oxide), present in the Rodel MSW2000A slurry. The polishing pad used for the tungsten CMP is as follows: 22.5” diameter Rodel IC1400 k-groove polyurethane pad. The consumables used for oxide CMP are as follows: 22.5” diameter Rodel IC1400 k-groove polyurethan
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