CMP (chemical mechanical polishing) is a vital IC (integrated circuit) manufacturing process. CMP is performed by rubbing the IC surface with a roughened polyurethane polishing pad in the presence of a chemically active, abrasive containing slurry. Friction is a natural consequence of CMP, and this friction can damage next generation, mechanically weak, porous dielectric materials on the IC surface. Earlier research has been done to characterize this friction, but the data is confounded with hydrodynamic effects. More recent experiments have measured the coefficient of friction with varying slurry characteristics but at low speeds and constant normal load which could decouple hydrodynamic effects. This new research measures the coefficient of friction with varying low speeds and varying loads. The coefficient of friction had a very small, statistically significant decrease with increasing normal load. This effect was attributed to elastic Hertzian pad asperity deflection with friction force being proportional to the asperity contact area. At lower normal loads, there was not statistically significant change in the coefficient as a function of speed. At the highest normal load, there was a very small increase in the coefficient of friction as the speed increased. It is proposed that counter-intuitive trend was a result of the following mechanism. Time dependent surface hydration film reduces the coefficient of friction. This surface film is damaged by rubbing, and the lower speed permitted more time for the film to regenerate.
- Tribology Division
The Variation of CMP Pad Asperity Friction as a Function of Speed and Normal Load
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Levert, JA, Haas, D, Korach, CS, Lakomcik, N, & Peters, E. "The Variation of CMP Pad Asperity Friction as a Function of Speed and Normal Load." Proceedings of the STLE/ASME 2008 International Joint Tribology Conference. STLE/ASME 2008 International Joint Tribology Conference. Miami, Florida, USA. October 20–22, 2008. pp. 731-733. ASME. https://doi.org/10.1115/IJTC2008-71217
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