Where does the FIB sputtered matter accumulate in the SEM chamber ?

Abstract

Scanning electron microscopes (SEM) equipped with focused ion beam (FIB) column are nowadays dual platform instruments commonly used in various micro sample preparation processes. While the mainstream of FIB usage remains within the semiconductor industry, it has expanded to a wide range of materials in metallurgical research. In particular, FIB milling capabilities are today used in the area of advanced materials for nuclear applications, involving in most cases the manipulation of activated samples. Sputtering of radioactive materials is far from trivial and numerous questions remain still open to guarantee the user safety even if small volumes of matter are generated by FIB milling [1]. For instance, where does the FIB sputtered matter accumulate in the SEM chamber? Angular distributions of FIB sputtered atoms have been investigated for 0°, 30° and 54° ion beam incidence. FIB patterns have been milled on a nanocrystalline Nickel alloy using a 30 keV Ga + ion bombardment in a scanning electron microscope (Fig 1a). Sputtered matter is collected on a silicon planar collector. The thickness of the deposit on the collector is measured by means of Z‐contrast imaging and two dimensional spatially resolved thickness maps are drawn (Fig 1b and Fig 1c). Angular distributions of sputtered atoms, in a plane containing the primary ion beam, are deduced from the maps (Fig 3). Our experimental data show that, at oblique incidence, sputtering matter is emitted in two main emission directions, normal to the target surface and towards the FIB column. For normal incidence, all the sputtered matter is projected towards the FIB column. The microstructure of the deposit, at normal incidence, has been studied by Transmission Electron Microscopy and Atom Probe Tomography (Fig 2).