COMPOSITIONAL DEPENDENCE OF GRAIN-SIZE IN SILVER COPPER-ALLOYS PREPARED BY DIRECT-CURRENT MAGNETRON SPUTTERING

Cosputtering provides a simple, direct method of preparing alloy films across the entire compositional range, as an alternative to sputtering from diphasic targets of single compositions. Metal thin films were prepared by dc magnetron sputtering in an argon plasma at a pressure of 2.5 mTorr and ambient temperatures. Alloy films of Ag-Cu were deposited by simultaneous sputtering of the two elemental targets, as well as metal films of Ag and Cu by sputtering from the appropriate pure target. The low sputtering pressure utilized in this study insured the preparation of dense, smooth, highly reflective films, indicative of energetic ion bombardment. X-ray diffraction (XRD) was performed to identify the alloy phases present and estimate their crystallite size. Transmission electron microscopy (TEM) was utilized to observe the microstructure and estimate grain size. Electrical resistivity measurements were carried out at room temperature on 1500 angstrom thick, pure and alloy metal films to complement XRD and TEM results. A dramatic reduction in grain size from that of pure metal was detected when the second element was simultaneously sputtered. Electrical resistivity of the alloys increased from that of the pure films. A region of greatest resistivity was noted and found to correspond to the smallest grain size, which occurred between 40 and 70 at. % Cu.