Comparison of glancing-angle scatterings on different materials in a high aspect ratio plasma etching process using molecular dynamics simulation

In plasma etching for microelectronics fabrication, one of the objectives is to produce a high aspect ratio (HAR) via and trench structures. A principal contributor to the HAR feature shape is the manner in which energetic ions interact with sidewalls inside the feature. The scattering angle and energy loss of ions reflecting from sidewalls determine the sidewall slope and can lead to defects such as microtrenching and bowing. Understanding how ions interact with sidewalls can improve our control of the critical dimensions of HAR features. Ions accelerated in the plasma sheath arrive in the feature with energies as large as a few keV and initially strike the sidewalls at glancing angles. These scattering events extend to the photolithographic mask. Scattering from the mask at glancing angles can produce ions incident into the underlying feature with a broader angular distribution, leading to less desirable feature properties. In this work, results are discussed from Molecular Dynamics (MD) simulations of glancing-angle scattering of argon ions from three materials common to HAR etch: polystyrene (as a photoresist surrogate), amorphous carbon (a hard mask material), and $SiO2$ (a common insulating material used in microelectronics devices). Results from simulations reveal a transition from specular scattering to diffuse scattering as the angle of the incident ion decreases (90$°$ being glancing incidence) and incident energy increases. Scattering from polystyrene is more diffuse compared to amorphous carbon and $SiO2$ for identical incident ion conditions.