Material Sputtering with a Multi‐Ion Species Plasma Focused Ion Beam

Abstract

Focused ion beams are an essential tool for cross-sectional material analysis at the microscale, preparing TEM samples, and much more. New plasma ion sources allow for higher beam currents and options to use unconventional ion species, resulting in increased versatility over a broader range of substrate materials. In this paper, we present the results of a four-material study from five different ion species at varying beam energies. This, of course, is a small sampling of the enormous variety of potential specimen and ion species combinations. We show that milling rates and texturing artifacts are quite varied. Therefore, there is a need for a systematic exploration of how different ion species mill different materials. There is so much to be done that it should be a community effort. Here, we present a publicly available automation script used to both measure sputter rates and characterize texturing artifacts as well as a collaborative database to which anyone may contribute. We also put forth some ideas for new applications of focused ion beams with novel ion species.

Plasma FIB milling for the determination of structures in situ

“…This compares with a sputter rate of 7.7 µm 3 /nC for gallium in ice 24 . These sputter rates are ~20-100 times higher than those reported at 30kV in Silicon for these plasma beams 23 . This is of the same order as the factor of ten that is suggested within the community as a rule of thumb for the difference between milling in vitrified ice and silicon 25 .…”

“…The sputter rates for oxygen and nitrogen are the same within error. While there is an expectation that a greater MW should correlate with sputter rate from first logic, the sputter rate for different plasmas has been demonstrated previously to be material dependent 23 . In our case, the values are calculated for (vitreous) biological samples.…”

“…Determining the sputter rate of each plasma beam can inform the design of milling protocols. Others have already characterised the sputter rate for different materials 23 , but not on vitrified biological samples. We used a second microscope (Thermo Scientific Helios Hydra with gas-cooled cryogenic stage) with the same ion column as the first to determine sputter rates more accurately for xenon, nitrogen, oxygen, and argon, at normal incident angles.…”

Using Xe Plasma FIB for High-Quality TEM Sample Preparation

“…Argon has mostly been used for broad ion beam (BIB) applications (Unocic et al, 2010), but it is yet to be determined if Ar PFIB could be used exclusively for TEM sample preparation. Oxygen PFIB has shown to be useful for the fast removal of carbon-based materials, but is overall too reactive to work effectively with most materials (Brogden et al, 2021). Xe PFIB, on the other hand, thanks to its heavier ion mass (and thus high material sputter yield) and chemical inertness, has become the go-to instrument for large length scale (>100 μ m) cross-sectioning and FIB-SEM tomography (Burnett et al, 2016).…”

Low Energy 500 eV Focused Argon Ion Beam Provided by Multi-Ions Species Plasma FIB for Material Science Sample Preparations

“…Xe + ion beam has being greatly accepted by FIB microscopy community providing the advantages of not only for high sputtering yield, high current milling at 30 keV for a large 3D volume data acquisition and for correlated microscopy applications [2] , but also for a much less ion implantation and amorphization of gallium free TEM specimen preparation [3]. Reactive oxygen ion beam dramatically improves sample milling quality for carbon-carbon bonding hard or soft materials by smoothing the cut-face very effectively during sputtering [4]. Low energy broad Ar + ion beam for sample preparation have been widely used for material science sample preparation for decades but it is not integrated with FIB-SEM DualBeam microscope in general.…”