Insights into Tungsten Chemical Mechanical Planarization: Part III. Mini-Marathons and Associated Numerical Simulations

Abstract

The effects of different types of conditioners (i.e. conventional vs. CVD-coated) on the evolution of frictional, thermal, and kinetic aspects of the tungsten chemical mechanical planarization (CMP) was investigated. Two types of conditioning discs were used to conduct mini-marathons. Due to its more aggressive nature, the conventional disc was able to result in steady values of coefficient of friction (0.438) and blanket tungsten removal rate (253 nm/min) throughout the mini-marathon. In contrast, the CVD-coated disc resulted in a significant decay in coefficient of friction (from 0.440 to 0.373) as the mini-marathon progressed. At the same time, removal rates also dropped from 286 to 246 nm/min. The decays observed with CVD-coated disc were likely due to its gentle nature and thus in its inability to remove reaction by-products as they got generated during repeated polishing. This hypothesis was confirmed by performing a mini-marathon with a much less chemically active slurry which did not cause any decays in polish metrics. Since mechanical effects were previously found to be rate-limiting, Preston's equation was able to adequately simulate the removal rates and their trends for each and every wafer polished during the mini-marathons.