Some aspects of atom probe specimen preparation and analysis of thin film materials

Abstract

Some of the factors in the preparation of atom probe specimens of metallic multilayer thin films have been investigated. A series of Ti/Nb multilayer films were sputtered deposited on n-doped Si [0 0 1] substrates with either 5 or 0.05 Ω cm resistivity. Each wafer was pre-fabricated into a series of 5 μm×5 μm× ≈80 μm island posts by photolithography and reactive ion etching. Once the film was grown on the wafer, a Si post was mounted to either a tungsten or stainless steel fine tip needle that was mechanically crimped to a Cu tube for handling. The specimen was then loaded into a Focus Ion Beam instrument where a sacrificial Pt cap was in situ deposited onto the surface of the film and subsequently annularly ion milled into the appropriate geometry. The Pt cap was found to be an effective method in reducing Ga ion damage and implantation into the film during milling. The multilayers deposited on the high resistivity Si exhibited uncontrolled field evaporation which lead to high mass tails in the mass spectra, a reduction in the mass resolution, high background noise, propensity for “flash-failure”, and a variation in the apparent layer thickness as the experiment elapsed in time. The multilayers deposited on lower resistivity Si did not suffer from these artifacts.