engleski

NANOCRYSTALLINE ALLOYS OF HIGHLY IMMISCIBLE Ag-W SYSTEM

Metastable Ag-W alloys have recently attracted interest as a promising material in advanced sub-100 nm metallization. However, such alloys need to be produced by nonequilibrium processing due to a complete immiscibility of its constituents. Here we present the study of the structure of Ag-W thin films prepared by magnetron sputtering in a wide range of alloy composition. Thin films of Ag-W alloys have been prepared by codeposition of pure silver and pure tungsten sputtered by two independently controlled magnetron sources, respectively. Deposition rate onto the substrates (glass, alumina, sapphire, mono-Si) at room temperature has been about 0, 33 nm/s, and the final film thickness was about 0, 5 &#61549; m. The effects of working gas pressure, and of oxygen or aluminum incorporation, upon the film structure have been examined. The chemical composition of the prepared films has been determined by the RBS technique: It was found that true composition (which will be referred to in what follows) departs from nominal one in favour of tungsten, and more so with the increase of tungsten content. The structure of prepared films was examined by the XRD. No completely amorphous films have been obtained in a composition range Ag94W6-Ag12W88. A supersaturated solid solution Al(W) with the fcc structure is formed with <30 at.% W, while a bcc solid solution is formed for higher tungsten content. It is noted that the observed "switching" composition is at considerably lower tungsten content than that calculated by recent atomistic modeling (57 at.% W). As regards the grain size - a nanocrystalline bcc phase (grain size of about 5 nm) has been obtained in the Ag-W alloys with 30-50 at.% W content. The incorporation of oxygen into the film somewhat decreases the average grain size, producing no completely amorphous phase, however .

Nanocrystalline; alloys; silver; tungsten

nije evidentirano