Irradiation effects of filtered beams of ionic liquid ion sources on semiconductor materials

Ionic liquid ion sources (ILIS) provide access to alternative ion chemistries for focused ion beam processing and surface modification. Previous literature has reported on the irradiation effects of full ILIS beams, but there is limited data on the effects of individual species from these polydisperse beams. In this work, irradiation on Si, SiC, and GaAs target substrates has been conducted with the liquids 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate (EMI-FAP) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4). Full and Wien-filter selected beams of both operation polarities of the source have been used, and the sputtering yields at 15 keV landing energy are reported. Sputtering yields reaching tens to hundreds of atoms per incident ion are observed with the FAP− ion and the full beams, consistent with overlapping cascade mechanisms similar to those observed with cluster ions such as C60+. While ion mass appears to correlate with sputtering yield, fluorine-assisted chemical etching is also likely to contribute. X-ray photoelectron spectroscopy (XPS) analysis of the surfaces post-irradiation with beams containing FAP− reveals F bonding in the surface of Si and SiC, confirming chemical activity of the ions with the surface.