Proof of Principle Study of Thickness Measurements Using Characteristic X-Ray Line Ratio Techniques

Abstract

Abstract : Two characteristic x-ray line ratio techniques are experimentally investigated. One technique uses the ratio of the characteristic L x-ray line to the characteristic K alpha x-ray line of the substrate. The other technique uses the ratio between one characteristic x-ray line of the substrate and one characteristic x-ray line of the thin film overlay. Experimental measurements were taken for both techniques by bombarding a coated sample with electrons and measuring the ratio of the areas under the characteristic line peaks. The samples used in the experiment consisted of a copper substrate coated with aluminum and molybdenum substrate coated with aluminum. The data are presented by plotting the characteristic x-ray line ratios versus the thin film thickness from 400 to 7000 angstrom for 20, 25 and 30 keV electron bombardment. Based upon these experiments, it was found that the ratio of the characteristic x-ray lines from the substrate (L/K alpha ratio) is not suitable for thin film measurements. However, the ratio technique that uses one x-ray line from the substrate and one x-ray line from the thin film overlay produced large ratio changes (80%) over the thickness range of 5000 angstrom. This ratio was independent of accelerating electron energy and was an inverse function of the overlay thickness. (jhd)