Molecular dynamics simulations of plasma etching processes for microelectronics processing applications

Abstract

Energetic ion bombardments on inorganic thin films and resultant sputtering processes were investigated with molecular dynamics simulations. By tracing the trajectories of incident ions, we could find the amount of the incident ions either be implanted or reflected. For the reflected ions, the reflection angles and energies after the collision with a substrate could be calculated and their distributions were obtained for various incident angles and incident energies. And surface atom removal rate due to energetic ion bombardments was also determined in terms of the sputtering yield from the results of our atomic scale simulations. Dynamics among substrate atoms was described by suitable empirical potential energy functions, Vashishta``s potential for $Si_3N_4$ and Feuston-Garofalini potential for $SiO_2$, and the interactions of an impacting Ar+ ion with the substrate atoms were modeled with a fully repulsive Moli$\grave{e}$re potential. For sputtering of each substrate, an amorphous surface configuration was prepared by simulating the surface evolution due to successive ion impacts and structure relaxation at high temperature. We considered Ar+ ion bombardment on the amorphous surfaces, for various incident angles ($\theta_i$ = 0˚, 30˚, 45˚, 60˚, 75˚, and 85˚) and incident energies ($E_i$ = 100 eV and 200 eV). Sputtering yields had its maximum around the incident angle of 60˚ ~ 75˚ and the preferential sputtering of light atoms (N or O) in these multicomponent materials were observed. Comparing the sputtering yields of these two materials, we could find that silicon nitride substrate is more likely to be sputtered than oxide in physical sputtering process. It indicates that the chemical effect of plasma and surface interactions are essential to realize the selective etching of oxide layer over nitride layer in self-align contact process. Reflection characteristics and degree of energy deposition of several impacting ion species ($He^+$, $Ne^+$, $Ar^+$, $Kr...