Electrical and Structural Properties of Co-Sputtered Tantalum–Aluminum Films

Abstract

Tantalum-aluminum alloy films have been prepared by dc diode sputtering in argon from composite cathodes of tantalum sheet, with either inlaid strips of aluminum or aluminum strips attached to the tantalum. The aluminum coverage of the tantalum cathode has been varied between 0 and 85%. The coverages produced films ranging from 0% to about 85% aluminum, which are homogeneous in composition as determined by electron microprobe analysis. The as-deposited films of pure tantalum have either the bcc or β-Ta structure. Both structures form metastable solid solutions with up to 20 at.% aluminum. At 30% aluminum a new phase very similar to β-Ta appears. Between 30 at.% and 85 at.% aluminum a number of phases have been observed in the sputtered films but of the known bulk phases of the tantalum-aluminum system, Ta2Al, Ta17Al12, Ta12Al17, and TaAl3, only TaAl3 is observed in the sputtered films at 85% aluminum. The dependence of the electrical properties of tantalum-aluminum films on aluminum concentration has been determined. These properties include resistivity, dρ/dT, Hall coefficient, carrier concentration and type, and Hall mobility. Results on alloy films are compared to those reported for the bulk aluminides Ta2Al and TaAl3.