Energetic ion bombardment of SiO₂ surfaces: Molecular dynamics simulations

Numerous profile evolution simulation studies strongly suggest that ions reflecting with glancing angles from etched feature sidewalls are responsible for microtrench formation at the feature bottom. Within these studies such reflections are traditionally assumed specular, where the ion retains all of its incident energy. In this study, we gauge the validity of that assumption by describing the distributions of reflected ion energies, E_r, reflected ion angles (polar, θ_r; azimuthal, ø_r; and total scatter, α_r), obtained via MD simulations of Ar⁺ bombardment of model SiO₂ surfaces. We modeled the physics of the surface atom interactions using an empirical interatomic potential energy function developed by Feuston and Garofalini [J. Chem Phys. 89, 5818 (1988)]. We considered Ar⁺ ion energies, E_i, of 100 and 200 eV, and incident polar angles, θ_i, of 0 °, 30 °, 45 °, 60 °, 75 °, and 85 °, measured from the macroscopic surface normal. Each (E_i, θ_i) combination was used to generate a unique roughened model oxide surface by repeated ion bombardment of an initially crystalline configuration. We observed that the degree to which a surface is roughened (as measured by the fractal dimension of the surface height distribution function, Δ_bc[h]) is a weak function of bombarding ion incident angle for angles less than 85 °. We discuss the sensitivity of the (E_r, θ_r, ø_r) distributions to incident ion energy and angle, and to roughness characteristics of the target surface. We compare the reflection data to the predictions of the binary collision model. We report sputter yields as functions of incident angle and energy, and discuss the distributions in energy of the sputtered products. We discuss the implications of the reflection distributions and surface character for feature scale simulation.