engleski

WHISKER FORMATIN DURING Al-W AMORPHOUS THIN FILM DEPOSITION ONTO HEATED SUBSTRATES

Whisker formation during amorphous Al-W thin films deposition onto substrates at elevated temperatures is reported. The films with nominal composition Al75W25 were prepared by codeposition onto sapphire substrates, held at selected (well below crystallization) temperatures, ranging from LN2 to 400°C. The structure of the films was examined by X-ray diffraction analysis: films deposited at substrates heated up to 200°C were completely amorphous, while films deposited onto substrates held at 250-400°C exhibited additional sharp lines. Three sharp diffraction lines, corresponding to the 0,383 nm interplanar distance, were superimposed upon diffraction pattern of the amorphous/nanocrystalline film. HREM investigation confirmed a phase with 0,383 nm interplanar distance in such samples. The SEM examination revealed a dense population of whiskers at the surface of samples with most pronounced two-phase XRD pattern. A reduction of film thickness (by decrease of deposition time) resulted in decrease and ultimate extinction of sharp lines. A sharp peaks in the XRD pattern seem to be related to the whiskers atop the amorphous film. The observed interplanar distance does not, however, match any of the three stable Al-W intermetallic compounds, aluminum, a- or b-tungsten, which leaves three metastable intermetallics Al3W, Al7W3, Al2W as possible whisker composition. No whisker-related XRD pattern appeared upon (even prolonged) heating up to 700-800°C of the corresponding amorphous films deposited at room temperatures. Therefore, the formation of whiskers atop the amorphous Al75W25 films was determined by a particular conditions at the film surface during deposition.

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