Cosputtered Aluminum-Rich AlTa Alloy Films

An R F sputtering system was employed with a target consisting of a 20cm diameter aluminum disk, about 1/4 of which was covered by a segment of tantalum. This target construction makes it possible to obtain on a single substrate a broad range of film compositions in one sputtering run. The result, concluded from X-ray analysis, is that only three phases are observed on a 10 cm by 10 cm Coming glass substrate. 1 ) On the aluminum side there is the fcc AI lattice with about 7 at% Ta dissolved in it-93 at% AI 7 at% Ta. 2) On the tantalum side there is a -Ta lattice with about 20 at% AI dissolved in it--80 at% Ta 20 at% AI. 3)Between these two phases exists an amorphous phase--85 at% AI 15 at% Ta. The thickness profile over the substrate shows a deep well between the 80 at% Ta and the 15 at% Ta-phase. This profile indicates that there is a condensation gap for the composition from 15 to 80 at% tantalum. Resistivity and measurements of temperature coefficient of resistivity (TCR) yield values from 30 to 240 -cm and from +500 to --125 ppm/deg K, respectively, depending on the position on the substrate, that is, depending on the phase present, The two aluminum-rich phases have, as far as we know, not previously been reported, neither in bulk nor in thin film form. We have observed most attractive features of these phases in their annealing and anodizing behavior.