Nano-pillar evolution by FIB irradiation with heavy ions

The European H2020 project “ion4SET” is directed to the development of advanced computation and communication devices with significantly lower power consumption. The general objective is to demonstrate the manufacturability of single electron transistors (SETs) using CMOS compatible technology. The basic idea of this SET is a nano-pillar (NP) transistor having a single Si nanodot (ND) in the oxide layer separating source and drain. The ND is formed by ion beam mixing and post annealing from a Si top layer. The ion irradiation under normal incidence is a crucial process for the small nano-pillars which are only 10 to 30 nm in width and about 80 nm in height.
In this work the evolution nano-pillars shape is investigated under heavy ion irradiation from a mass separated focused ion beam (FIB) for different ion energies at RT and 400°C target temperature. In particular Si (60 keV), Pb (30 and 60 keV), Au (30 and 60 keV) ions as well as polyatomic projectiles Au2 and Au3 (Uacc = 30 kV) with a fluence of 5 x 1015 cm-2 were applied.
Whereas the Si ion irradiation of Si pillars at elevated temperatures only deforms the pillar tip, the heavy ion irradiation leads depending on the fluence up to a total removing of the pillar. The fluence variation was obtained on the slope of the beam profile. The irradiation at RT with Pb ions at 30 keV showed a more pronounced bending of the pillar due to the high energy deposition caused stress and viscous flow than that at 60 keV. The influence of the irradiation is also depending on the thickness and the distance of the pillars in different lithographic prepared fields. For a better comprehension of the irradiation results the experiments were simulated using the TRI3DYN code.