Fundamental Tribological and Removal Rate Studies of Inter-Layer Dielectric Chemical Mechanical Planarization

In this work, real-time coefficient of friction (COF) analysis, in conjunction with a new method for approximating the Sommerfeld Number, is used to determine the extent of normal and shear forces during chemical mechanical planarization (CMP) and to help identify the tribology of the system. A new parameter termed the 'tribological mechanism indicator' is defined and extracted from the resulting Stribeck curves. The information on COF, 'tribological mechanism indicator' and inter-layer dielectric (ILD) removal rate results in a series of 'universal' correlations to help identify polishing conditions for optimized pad life and removal rate. Results further show that abrasive concentration, surface texture and pad grooving dramatically shift the tribology of the system from boundary lubrication to partial lubrication. Trends are explained using several models based on area of contact between wafer and abrasive particles, the extent of lubricity of the system and the compliance of the pad in micro- and macro-scales.