A Material Removal Rate Model for Tungsten Chemical Mechanical Planarization

Abstract

A tungsten removal rate model is proposed in the chemical mechanical planarization (CMP) process to investigate the removal mechanism with consideration of the synergistic effect of chemical reaction and mechanical abrasion. Based on the fundamentals of steady-state chemical reaction and mechanical abrasion, a chemical reaction kinetics CMP model is first built up to relate the removal rate to the chemical reagent and mechanical rate parameters. Then the Greenwood-Williamson contact theory is introduced into the chemical reaction kinetics model to construct a closed-form equation of removal rate, which captures the synergistic coupling effect of chemical and mechanical interactions. Furthermore, the present model is verified by the collected experimental data and utilized to investigate the impact of the design pattern effects on the removal rate. The consistency of the model prediction and the experimental data as well as the removal characteristics of design pattern structures indicate that the new proposed tungsten CMP model can be adopted to elucidate the synergistic effect of chemical and mechanical interactions and perform the sensitivity analysis of the design pattern dependency on removal rate of tungsten films.

A Physics-Based Chip-Scale Surface Profile Model for Tungsten Chemical Mechanical Planarization

“…The tungsten film surface is composed of the unreacted fresh surface [W] and the reacted materials of initial oxide W L and mature oxide W H in consideration of the major chemical reactions in the W CMP process. 43 Furthermore, the chemically modified wafer surface is then mechanically abraded into the flowing slurry by the abrasives and polishing pad. As the chemical and mechanical equilibrium of polishing is reached, the material removal rate can be derived through solving some algebraic equations of chemical reaction kinetics.…”

“…As the chemical and mechanical equilibrium of polishing is reached, the material removal rate can be derived through solving some algebraic equations of chemical reaction kinetics. Therefore, the final MRR can be represented as: 43…”

“…In the tungsten CMP process, two-step polishing process is introduced to first remove the tungsten overburden and then eliminate the residual W, TiN barrier, and SiO 2 . 43,44 Tungsten dishing and oxide erosion generally occur as a result of the design pattern effects in the over-polishing phase. Precisely predicting these pattern dependent defects is quite important in chip surface topography simulation and design parameter control in chip-scale CMP modeling.…”