Etching of SiO2 in C4F8∕Ar plasmas. I. Numeric kinetics modeling and Monte Carlo simulation in a three-dimensional profile simulator

Abstract

In this article, the etching kinetics of SiO2 in C4F8∕Ar plasmas was modeled and calculated in a three-dimensional (3D) Monte Carlo profile simulator. The kinetics models were developed using the numerical integration of the rate equations with mass balance constraints for a planar surface and iteratively solved to determine the rate coefficients by least squares regression. The assumptions including the well mixed surface layer and equal reactivity of similar species were used to simplify the reaction scheme. Initially, etching yields of SiO2 in multiple CFx+ beam scattering experiments were fitted to determine the rate coefficients associated with ion-induced etching and sticking coefficients of the neutrals. The reaction set and the initially fitted rate coefficients were then adjusted using numerical integration of the set of rate equations to steady state and least squares regression of the model coefficients to fit SiO2 etching in C4F8∕Ar gas plasma. The etching yield was modeled over a wide range of neutral-to-ion flux ratios, ion energies, and ion bombardment angles with good agreement with the experimental results. The surface composition was modeled to evaluate the fundamental reaction set and the parameters such as the sticking probability. The kinetics was then incorporated into the 3D cell-based profile simulator with Monte Carlo flux calculation. Similar etching yields were obtained for SiO2 planar surfaces using either the profile simulator or the numerical integration of the set of rate equations over a wide range of plasma conditions and for off-normal ion bombardment, thereby verifying the Monte Carlo solution of the set of rate equations within the 3D profile simulator.