Paper PS-WeA8
INVITED TALK: A Brief Overview on Molecular Dynamics Simulations of Plasma-surface Interaction in Reactive Ion Etching

Wednesday, October 23, 2019, 4:40 pm, Room B130

In the mid-70s, John Coburn and his colleague Harold Winter started to study plasma etching and reactive ion etching (RIE) processes which, at that time, were starting to be considered for pattern transfer and stripping processes in the semiconductor industry. Their research work focused on the physico-chemical mechanisms involved in this process, emphasizing surface science aspects, and continued for almost 20 years until they both retired from IBM in 1993. By designing insightful experiments, they highlighted in particular the role of energetic ion bombardment in RIE or the mechanisms responsible for a good Si/SiO₂ selectivity. 25 years later, reactive ion etching is a key process which has played a crucial role in the progress made in micro- and nano-electronics, a field which has affected every aspect of our modern lives.

Nowadays, advanced transistors feature ultrathin layered materials and must be etched with a nanometric precision and a nearly infinite selectivity to preserve the electronic properties of active layers. This challenge can no longer be addressed by conventional CW plasma processes, in which the ion-neutral synergy tends to create thick reactive layers which can compromise the etch precision. Alternative plasma technologies are thus needed and various approaches are investigated, to reduce the ion energy by decreasing the electron temperature (e.g. pulsed or low-Te plasmas), to avoid thick reactive layers using sequential and limited reaction steps (e.g. plasma-enhanced ALE), or to decouple the action of ions and radicals using sequential ion modification and chemical removal steps.

As shown by John Coburn during his entire career, the development of advanced etch processes requires a fundamental understanding of the surface reaction mechanisms involved in plasma-material interaction. Coupled with plasma diagnostics and surface characterization tools, Molecular Dynamics (MD) simulations can provide information about the reactions processes involved at the atomic scale and help to understand the phenomena governing the etch process. Since the pioneering work of Harrison et al. in the late 60s [1], atomistic simulations have been routinely used to study RIE and were shown to be a powerful tool to understand how the flux and energy of plasma species affect the structural and chemical modification of substrates. This talk will provide a brief overview of the basics of molecular dynamics for RIE simulations (principles, accessible time and length scales, suitable force fields, etc.) as well as a review of various works performed on this topic from the 70s until very recently.

[1] D. E. Harrison et al, J. Appl. Phys. 39, 3742 (1968)