CMP Friction as a Function of Slurry Silica Nanoparticle Concentration and Diameter

Abstract

Chemical mechanical polishing (CMP) is vital in the manufacturing of integrated circuits (IC). CMP removes unwanted material from an IC surface by rubbing it with numerous nanoscale abrasives that are brought into contact by polishing pad asperities. Friction is a consequence of this rubbing, and this friction may damage the next generation of porous IC dielectric materials with lower dielectric constants (low k). Fundamental experiments were done to understand the source of the friction to enable less damaging CMP. The coefficient of friction of an SiO 2 substrate on a polyurethane CMP pad was measured as a function of the slurry's SiO 2 abrasive particle concentration and size with a commercial pin on disk tribometer. Very low speeds (∼10− 3 m/s) were used to remove confounding hydrodynamic effects. The coefficient of friction increased by 10% with higher weight percentages of SiO 2 particles in the slurry, suggesting that a constant real area of contact is distributed between bare pad asperity contacts and higher friction SiO 2 particle contacts. The coefficient of friction also increased for the smallest slurry SiO 2 particle size. These results suggested possible routes for controlling CMP friction by controlling slurry particle size and concentration as well as the pad material.