Characterization of niobium, tantalum and chromium sputtered coatings on steel using eddy currents

A method that uses induced eddy current for characterization of niobium, tantalum and chromium sputtered coating on steel is presented in this paper. The objective of this work is to find the correlation between the sputtering conditions and resistivity of coatings and to develop a system for fast inspection of coatings as a coating quality control tool during production as well as in the field for determining coating degradation levels. A two-probe differential system having higher sensitivity and less noise than a one-probe system with 2D scanning ability was developed. A computer program that controls an XY table and performs fast data acquisition was written. Resistivity maps of the niobium, tantalum and chromium coated samples were constructed and are shown in the paper. For niobium coatings, the relationship between sputtering pressure and resistivity of coatings is examined, as well as the relationship between impurity level of process gas and resistivity of coatings. For tantalum coatings, the relationship between beta-Ta fraction and resistivity is analyzed. For chromium coatings, the relationship between micro-crack density and resistivity of coatings is analyzed. The topographic picture and destructive analysis of the samples show very good correlation with eddy currents measurements.