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

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 Ag and ZrO 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.