Experimental Investigation and Numerical Simulation of Pad Stain Formation during Copper CMP
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0991-C06-02
Experimental Investigation and Numerical Simulation of Pad Stain Formation during Copper CMP Hyosang Lee1, Yun Zhuang2, Leonard Borucki2, Fergal O'Moore3, Sooyun Joh3, and Ara Philipossian1,2 1 Department of Chemical and Environmental Engineering, University of Arizona, Tucson, AZ, 85721 2 Araca, Inc., Tucson, AZ, 85750 3 Novellus Systems, Inc., San Jose, CA, 95134 ABSTRACT Experiments and simulations were performed to investigate the characteristics of staining on pad surface. Experiments were performed on a table-top axisymmetric polishing system, consisting of a 12-inch non-rotating platen and a 4-inch rotating wafer carrier. Stain deposited on each land area was found to be darker in the direction of wafer rotation and in the radial direction, suggesting that the staining agent was produced by mechanical action during polishing and subsequently was advected downstream by slurry flow. While staining increased with polishing pressure, wafer rotation rate and polishing time, it did not seem to affect removal rate. Slurry velocity simulations showed shear flow on the land areas and wafer-driven circulation in the grooves. Temperature simulations showed a 12 °C rise in the reaction temperature on the surface of the copper wafer. Simulated stain images were in qualitative agreement with experimental results. INTRODUCTION During copper CMP, stain is often generated on the pad surface due to polishing byproduct buildup. The understanding of the mechanism of stain formation and its effect on removal rate are critical. Orbital polishers have a ‘through-the-pad’ slurry distribution and injection system. This approach can greatly reduce slurry use and enhance slurry utilization efficiency during polishing since all of the slurry is injected under the wafer. While orbital polishers have a potential benefit of up to 5 times reduction in slurry consumption compared with conventional rotary tools, various effects can reduce or offset this benefit in specific CMP processes. For example, non-uniform slurry distribution and sub-optimal pad grooving can lead to by-product build-up on the pad surface and cause low, non-uniform and unstable polish rates during the process. The objectives of this study are to experimentally investigate how process parameters affect by-product build-up and to simulate staining on pad surface by developing a staining model that incorporates models for slurry velocity and temperature simulation. EXPERIMENT A table-top polishing tool was constructed using a 12-inch diameter Struers rotating platen modified to allow injection through the center of the pad via a peristaltic pump. A 5-mm hole was drilled through the platen center and the pad for slurry delivery. All polishing was done with the pad being stationary. The rotating polishing head was aligned co-centrically with the pad. 100-mm blanket copper wafers were polished on IC1000 XY-groove pads. Copper wafers were mounted on a 4-inch optical flat attached to a gimbaled polishing head. Conditioning was performed ex situ using a 3M A165 4-inc
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