Effect of abrasive nanoparticle concentration on the tribological, thermal and kinetic attributes of tungsten chemical mechanical planarization

The effect of slurry abrasive nanoparticle (NP) concentration on the tribological, thermal and kinetic attributes of tungsten chemical mechanical planarization (CMP) was investigated. Three tungsten slurries with different amounts of colloidal silica NPs, without any detectable changes in formulation chemistry, yielded three different polishing outcomes. As slurry nanoparticle concentration [NP] increased, the coefficient of friction (COF), temperature, tungsten removal rate (RR) and tungsten to silicon dioxide RR selectivity decreased. For tungsten, trends in COF, temperature and RR were successfully simulated using a two-step modified Langmuir-Hinshelwood model which also yielded values for the chemical and mechanical rate constants. Simulation results indicated that the process was chemically-limited for most polishing conditions, and that the process became even more chemically limited as P × v increased. Moreover, the process became more chemically-limited as [NP] increased. During the extraction of an important parameter for simulation purposes (apparent activation energy), a unique change in curvature of the Arrhenius plot was observed and attributed to the fact that chemical vapor deposited (CVD) tungsten films differ in their density, chemical composition and film morphology as a function of their thickness. The same explanation also accounted for the observed changes in instantaneous shear force vs polish time.