Practical Aspects of Focused Ion Beam Time-of-Flight Secondary Ion Mass Spectrometry Analysis Enhanced by Fluorine Gas Coinjection

The interest in using high vacuum-compatible time-of-flight secondary ion mass spectrometry (TOF-SIMS) detectors integrated within focused ion beam instruments (FIB) has increased due to the possibility of conducting correlative and/or complementary studies with other techniques such as scanning electron microscopy, energy dispersive spectroscopy (EDS), wavelength dispersive spectroscopy, electron backscatter diffraction, atomic force microscopy, and Raman spectroscopy without breaking vacuum conditions. This work discusses the practical aspects of FIB-TOF-SIMS analysis enhanced by fluorine gas. A series of systematic experiments with high-purity Al and Cu single crystals was conducted. We demonstrate that fluorine-assisted FIB-TOF-SIMS analysis yields up to several orders of magnitude higher SIMS signals due to chemically improved ionization probability of elements. The potential of fluorine gas-assisted FIB-TOF-SIMS analysis and the correlated benefits are demonstrated on a real-life sample based on comparing the results to EDS and TOF-SIMS experiments conducted without any gas. Our studies indicate that the presence of fluorine gas reduces the negative effect of preferential reoxidation of the sample surface. This enables high lateral resolution FIB-TOF-SIMS mapping because the secondary ion signals are not dominated by elements with strongly oxygen-enhanced ionization probability.