Abstract
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.
Highlights
Most ion reactive machining, including focused ion beam (FIB) milling, is applied to device fabrication, as well as mask repair and modifications, where controlled material ablation needs to be achieved, while preserving the quality of structures and patterns
FIB technology has relied on liquid metal ion sources (LMISs), of which the most developed and widely used is the gallium source
ionic liquid ion sources (ILISs) beams share some of the characteristics of LMIS that are required for FIB applications
Summary
Most ion reactive machining, including focused ion beam (FIB) milling, is applied to device fabrication, as well as mask repair and modifications, where controlled material ablation needs to be achieved, while preserving the quality of structures and patterns. Several new types of sources have emerged, such as ionic liquid ion sources (ILISs), gas field emission ion source, and liquid metal alloy ion sources, expanding the application field of FIB.. ILIS beams share some of the characteristics of LMIS that are required for FIB applications. There are noticeable advantages such as the presence of chemically reactive species and the ability to produce pure ion emission with no intervening droplets, making target contamination less of a concern.. The variety of available ionic liquids is immense, generating a collection of new ions and clusters that could be extracted in a beam. Most of the ions in ILIS beams include chemically active species, making them ideal for reactive ion etching (RIE) without introducing process gases. It has been found that ILIS can etch silicon at higher rates than LMIS.
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