Development and characterization of an iodine field emission ion source for FIB applications

Abstract

Emission of positive and negative ions is possible when a room temperature molten salt, or ionic liquid, is exposed to a sufficiently high electric field. Ionic liquid ion sources (ILIS) have shown potential to be used in various focused ion beam (FIB) applications, since their operation and characteristics are similar to those of liquid metal ion sources, with the advantage that ILIS work at low temperatures in comparison and a large number of ionic liquids with many different compositions are available. In this paper we present results on the emission characteristics of negative ions extracted from an iodine-based ionic liquid using a time-of-flight mass spectrometer and a retarding potential analyzer. The ionic liquid BMI-I is used as source media, producing a droplet free beam with multiple solvated ion species. Attention is given to BMI-I in particular due to the potential of creating a beam of pure and clustered I- ions, which are expected to improve the performance in applications based on secondary emission and reactive species. Properties important to the focusing of the ion beam such as mass and energy distributions are obtained. Effects on the ion emission are studied through a comparison of the source using temperature as a parameter to modify the liquid viscosity and electrical conductivity.