Classical molecular dynamics and ab initio simulations of chemical-mechanical polishing of amorphous silica

Chemical-mechanical polishing (CMP) is a widely accepted process in the semiconductor industry. Despite intense theoretical and experimental research on CMP, there is a serious lack of fundamental understanding of the physical-chemical processes of polishing. The present work is intended to investigate these fundamental processes on an atomistic level.; To model CMP on the atomic scale, a model of the amorphous silica is prepared by applying Design of Experiments (DOE) techniques to systematically investigate molecular dynamics preparation. These simulations yield high-quality models of amorphous silica, which are in excellent agreement with experimental results and are defect-free.; Molecular dynamics simulations are performed to investigate the mechanical deformation during CMP of silica for different geometries and relative velocities. The simulations clarify asperity shape evolution during the process of shear and reveal temperature distributions as a function of time. It is found that the ratio of radii of a particle and asperity strongly affects the amount of the material removed whereas the relative velocity has a weaker affect on it. During shear, a significant local temperature increase occurs. This temperature increase lasts for a short time (picoseconds), but it can have a major impact on the amount of material removed. It is found that there could be significant deposition of the material from the particle to the slab, which can fill surface trenches and thereby make the surface smoother. An analytic model is developed for describing the amount of material removed as a function of asperity and particle radii and relative velocity.; Density-functional calculations of different surfaces of two silica polymorphs, α-quartz and β-cristobalite, are performed. The surface energies are calculated as a function of oxygen partial pressure for several different surface reconstructions and terminations. The case of hydrogen passivation is investigated to determine the most stable surface as a function of hydrogen partial pressure/chemical potential. The results allow prediction of the structural stability of different kinds of surface terminations for various oxygen and hydrogen concentrations. A detailed analysis of the surface electronic structure is carried out.