Molecular dynamics simulations of oxygen-containing polymer sputtering and the Ohnishi parameter

Abstract

The effects of ion bombardment on polymer surfaces can be profound, with implications for all plasma-based pattern transfer processes that involve the use of polymer etch masks in lithography and etching. We report results from molecular dynamics (MD) simulations of Ar+ (100 eV) sputtering of oxygen-containing polymers. The MD data are compared with available experimental results, with special focus on the so-called Ohnishi parameter, which has been shown to correlate with sputtering yields for many O-containing polymers. The MD simulations match the measured data as well as the published correlations. We present a quantitative model of sputtering for these polymers that shows why the Ohnishi parameter (a function of the polymer composition) is proportional to the steady-state sputtering yield. However, we also show that the Ohnishi parameter does not correlate with yields for other polymers, including polyfluoroethylene and polyethylene. The MD simulations show that the validity of this parametrization is dependent on whether or not the sputtering of the polymer transitions between ion-induced scissioning and cross-linking at steady state.

Plasma-polymer interactions: A review of progress in understanding polymer resist mask durability during plasma etching for nanoscale fabrication

“…188 In Fig. We also would like to point out that this relationship has been reproduced in MD simulations on Ar sputtering of different oxygen-containing polymer structures.…”

28 nm pitch of line/space pattern transfer into silicon substrates with chemo-epitaxy Directed Self-Assembly (DSA) process flow

“…the number of atoms in the polymer repeat unit (N), divided by the number of carbons (N c ) minus the number of oxygen atoms (N o ). This rule has been demonstrated to be valid for pure sputtering case at ion energy >100 eV, and the physical explanation comes from the formation of a C-rich damaged layer at the film surface [11]. From this damaged layer, C removal is the limiting step and is mainly dictated by the fraction of C not leaving as CO, i.e.…”

“…the necessary condition for the Ohnishi rule to hold is not met. In this case, Molecular Dynamics (MD) simulations from [11] suggest that C is then leaving as CO or bound to H as large entities, i.e. in the form of the monomer unit or hydrocarbon fragments C x H y which might be more difficult to desorb from the surface at low ion energy -therefore making also the re-deposition process more likely (condensation of non-volatile species).…”

Microplasma Drug Delivery

“…This process is not valid for all polymers. If polymers compose of many H or O atoms, amorphous layer of carbon is not formed because released H and O atom can etch carbon atoms [48]. …”