Molecular dynamic simulation of glancing-angle scatterings on different materials in a high aspect ratio etching process*

Forming high aspect ratio (HAR) hole structures is a common objective in plasma etching. Energetic ions interacting with side walls plays a key factor in HAR process, particularly with regard to profile shape, and can lead to faceting and bowing issues.  Understanding how etching ions interact at near glancing angles with side walls helps in optimizing etching processes.

These ions are accelerated in the plasma sheath and are mostly energetic and directional; the interaction between those ions and side walls are mainly glancing-angle events. These events depend on incident energies and angles. In this work, the effect of glancing-angle scatterings on different parts of a substrate (photoresist, hard mask and SiO₂) in an HAR etching process using molecular dynamics (MD) simulations is presented.

LAMMPS has been used for MD simulations in this work. For the interatomic potentials, REBO potential is used to model polystyrene as a photoresist surrogate, Tersoff potential is used to model the deposition and formation of amorphous carbon layer hard mask material, and ZBL potential is used to model the interaction of Ar ions with other atoms.  Angle and energy dependent scattering matrices for these process relevant materials and possible implications for HAR processes will be presented.