Phase formation between codeposited Co-Ta thin film and single crystal silicon substrate

A combination of near-noble and refractory metal silicides was considered for shallow contacts to silicon in VLSI circuits [1]. The objective of the present work is to investigate formation of phases between codeposited Co-Ta film, of 150 nm thickness, and n-type silicon substrates of (100) or (111) orientation. Characterization of the specimens annealed in the temperature range of 600-1100°C was done by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that in addition to the silicide phases of Co and Ta, the intermetallic compound Co₂Ta was also formed. Co₂Ta appears only in the lower temperature range of about 600-800°C. At temperatures of 900-1100°C only the silicon rich phases were present. These are the low resistivity phases useful for devices. No ternary phases have been observed. Silicide formation occurs at a faster rate on (111) oriented silicon substrates.