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R. Ritter, R.A. Wilhelm, R. Ginzel, R. Heller, W. Rupp, J.R. Crespo López-Urrutia, S. Facsko, F. Aumayr:
"Ion beam lithography with slow highly charged ions";
Poster: 16th International Conference on the Physics of Highly Charged Ions (HCI 2012), Heidelberg/Germany; 03.09.2012; in: "Book of Abstracts, 16th International Conference on the Physics of Highly Charged Ions (HCI 2012)", (2012), S. 144.

Poly(methyl metacrylate) (PMMA) is commonly used as a photoresist in the electron beam
lithography process in semiconductor industry and research. In a recent systematic study [1] we have
investigated the formation of nano-sized pits (craters) on PMMA after exposure to slow highly
charged Xeq+ ions in charge states q = 12 - 48 and impact energies ranging from 5 eV/amu to
4 keV/amu. The pits are formed on the polymer surface as a direct result of individual ion impacts.
Intermittent contact mode atomic force microscopy (AFM) was employed to study the size evolution
of the pits in dependence of potential and kinetic energies of the incident ions. A potential energy
threshold value of approximately 7 keV (Xe24+) was found for pit formation [1]. Above this value an
increase in potential energy results in an increasing pit volume, while the pit shape can be tuned by
varying the ions kinetic energy [1].
Figure 1: Intermittent contact mode AFM images of pits induced by individual impacts of Xe36+ (Ekin
= 360 keV, left) and Xe48+ (Ekin = 480 keV, right) ions on PMMA. The insets show one individual pit
for both cases at triple magnification.
Conventional lithography processes on PMMA require the removal of the latent damage zone by
exposure to an etchant or chemical developer. Following the same principle, we have etched the
irradiated samples with 2-Isopropanol and found that the threshold for pit-formation due to
individual ion impact can be lowered from Xe24+ to Xe20+. At higher charge states, where pits are
already formed without the aid of a developer, the pit volume is increased by etching. Our results
show, that this volume increase is mainly caused by an increase in pit depth and, to a much lesser
extent, in pit diameter.