Electron Beam-Induced Deposition for Atom Probe Tomography Specimen Capping Layers

摘要

Six precursors were evaluated for use as in situ electron beam-induced deposition capping layers in the preparation of atom probe tomography specimens with a focus on near-surface features where some of the deposition is retained at the specimen apex. Specimens were prepared by deposition of each precursor onto silicon posts and shaped into sub-70-nm radii needles using a focused ion beam. The utility of the depositions was assessed using several criteria including composition and uniformity, evaporation behavior and evaporation fields, and depth of Ga+ ion penetration. Atom probe analyses through depositions of methyl cyclopentadienyl platinum trimethyl, palladium hexafluoroacetylacetonate, and dimethyl-gold-acetylacetonate [Me2Au(acac)] were all found to result in tip fracture at voltages exceeding 3 kV. Examination of the deposition using Me2Au(acac) plus flowing O-2 was inconclusive due to evaporation of surface silicon from below the deposition under all analysis conditions. Dicobalt octacarbonyl [Co-2(CO)(8)] and diiron nonacarbonyl [Fe-2(CO)(9)] depositions were found to be effective as in situ capping materials for the silicon specimens. Their very different evaporation fields [36 V/nm for Co-2(CO)(8) and 21 V/nm for Fe-2(CO)(9)] provide options for achieving reasonably close matching of the evaporation field between the capping material and many materials of interest.