Fluorine Gas Coinjection as a Solution for Enhancing Spatial Resolution of Time-of-Flight Secondary Ion Mass Spectrometry and Separating Mass Interference

Abstract

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) detectors have been intensively developed in recent decades due to their unprecedented capability of representing a sample elemental composition in a three-dimensional space from nano- to submilliscale with high spatial resolution and mass resolution. A compact high-vacuum-compatible version of these detectors can be integrated into a focused ion beam (FIB) system which, assembled with scanning electron microscopy (SEM), is the most popular tool used in nanotechnology and material science. This gives a new opportunity for combining TOF-SIMS analysis with other instruments within the same analytical chamber. In this work we present the results of conducting elemental characterization of a dedicated model multilayer sample composed of 100 nm thick thin films of Cu, Zr, and ZrCuAg alloy in a fluorine gas atmosphere provided by an in situ gas injection system (GIS). In general, the secondary ion signals were significantly enhanced by up to 3 orders of magnitude, leading to much higher spatial resolution. The quality of elemental images and depth profiles was improved during a single measurement (which usually cannot be obtained at standard vacuum conditions) at a high beam energy of 20 keV. Moreover, fluorine assistance has enabled a mass interference between ¹⁰⁷Ag⁺ and ⁹¹Zr¹⁶O⁺ ions to be separated. This remarkable finding has never been reported before and is expected to play an important role in the future evolution of TOF-SIMS analytical protocols, as currently the mass interference between ions remains one of the main drawbacks of the technique.