Silicide formation with codeposited titanium-tantalum alloys on silicon

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Abstract
The formation of disilicides of titanium and tantalum from Ti‐Ta alloys codeposited on silicon and polycrystalline silicon have been investigated using x‐ray diffraction techniques, resistance measurements, and Auger electron spectroscopy. Titanium and tantalum in the Ti‐Ta alloy interacted independently with silicon. There was no titanium/tantalum compound formation and no ternary was detected. The growth of each metal silicide was sustained by continuous out‐diffusion of silicon into the Ti‐Ta alloy film until the metals were consumed in the silicide transformation. This behavior may account for the absence of phase separation and component accumulation. An initial reaction was observed after the 600 °C, 30 min anneal. The stable end phases formed at temperatures ≥800 °C are TiSi2 and TaSi2. High molecular weight intermetallics such as Ta5Si3 and Ti5Si3 that are normally not detected in Ta‐Si and Ti‐Si interaction studies were detected, suggesting a stabilizing effect of the impurities. The sheet resistance of the heat‐treated samples is: (a) a strong function of the titanium content of the Ti‐Ta alloy (low for Ti‐rich alloys); (b) lower on silicon substrates; (c) invariant at temperatures >900 °C. The etch rate of the heat‐treated samples in buffered hydrofluoric acid increased with increasing titanium content in the film.