Sputter yield of heavy monatomic and polyatomic ions: dependence on impact angle and substrate temperature

Focussed ion beam irradiation can be used to pattern surfaces at a scale of tens of nm by direct writing as well as by self-organization. Both patterning modes are controlled by ion beam erosion, where the sputter yield depends on the ion species, i.e. their mass, energy and angle of incidence. It depends also on the composition, temperature and surface roughness of the substrate.
Here, peculiarities of sputtering with heavy monatomic and very heavy polyatomic ions will be presented. Ion erosion of Si, SiO2, Ge and GaAs with Au_n and Bi_n ions from a liquid metal ion source has been investigated for different irradiation conditions.
The sputter yield per incoming atom is, compared with monatomic ions, considerably higher for polyatomic ions, even if the kinetic energy per atom is chosen to be equal. A newly developed sample holder allows irradiation at substrates temperatures up to 500°C and angles of ion incidence in the range from 0° to almost 90°, which will be used to elaborate sputter yield data of polyatomic ions in a range not yet explored so far. Due to the extremely high energy density deposition into the collision cascade volume by a very heavy polyatomic ion impact, an almost classical but tiny, transient melt pool can form, which adds to the collisional sputtering a loss of atoms by evaporation [1]. The latter contribution can be increased by substrate heating. Besides of the increased sputter yield, the repeated melting and resolidification of tiny pools leads to well-ordered surface pattern [2], which in turn influence the sputter yield.
[1] C. Anders, K.-H. Heinig and H. Urbassek, Phys. Rev. B 87 (2012) 198.
[2] L. Bischoff, K.-H. Heinig, B. Schmidt, S. Facsko and W. Pilz, Nucl. Instr. Meth. Phys. Res.
B 272 (2012) 198.