Atomic Layer Etching - Energy
Our first results on approaching atomic scale precision by energy control are shown here.
The key feature of the energy control is that one tries to limit the interaction potential of the plasma species to ranges that are also on the atomic scale. As such, conventional low energy systems like an inductively coupled plasma (ICP) only have limited success, as their intrinsic ion energy is typically 20eV or higher (due to their plasma potential). Low electron temperature plasma solutions however may offer additional benefits, as their plasma potential is much lower and with that of course also their intrinsic ion energy.
One approach to low electron temperature plasmas are electron beam generated plasmas. Such a system, called LAAPS was designed and tested at the Naval Research Labs (NRL). Our first result on their effect on atomic scale materials such as carbon nanotubes (CNTs) and/or graphene are shown below:
The I-V curves of the CNTs before plasma exposure are shown in a), whereas the same CNTs measured after exposure are shown in b). A clear damage to the electrical characteristics was noted, however the general semiconducting behavior was preserved. An exposure under similar conditions to a conventional ICP plasma resulted in complete destruction of the functionalities.
A similar result was found for etching off a silicon nitride film from graphene. While little damage was observed in case of exposure to e-beam generated plasmas (a), a severe transformation of the material properties was noted for exposures to ICP discharges (b).
A more detailled review can be found here:
Initial evaluation and comparison of plasma damage to atomic layer carbon materials using conventional and low Te plasma sourcesAshish V Jagtiani, Hiroyuki Miyazoe, Josephine Chang, Damon B Farmer, Michael Engel, Deborah Neumayer, Shu-Jen Han, Sebastian U Engelmann, David R Boris, Sandra C Hernandez and others
Journal of Vacuum Science & Technology A 34(1), 01B103, AVS: Science & Technology of Materials, Interfaces, and Processing, 2016