Etching of glass, silicon, and silicon dioxide using negative ionic liquid ion sources

Ionic liquid ion sources have been proposed as a new type of ion source for focused ion beam and broad ion beam applications. In this paper, the ionic liquid EMI-BF₄ (1-ethyl-3-methylimidazolium tetrafluoroborate) was used as an ion source to generate negatively charged ions and irradiate glass (Pyrex 7740), silicon, and silicon dioxide targets. The results indicate that negative EMI-BF₄ ion beams can prevent issues related to surface charge accumulation on dielectric substrates, achieving etching selectivities of SiO₂:Si of at least 1.55. The etching rate increases on glass, silicon, and silicon dioxide at higher ion landing energies. It is shown that the negative EMI-BF₄ beam has a higher yield than traditional metal gallium ion beams, likely due to the chemical reactivity of fluorine radicals. This effect is also noticeable when compared to results using positive EMI-BF₄ beams.