Dependence of oxygen redistribution on titanium film thickness during titanium silicide formation by rapid thermal annealing

Abstract

Silicidation of titanium (Ti) thin films sputter-deposited onto (100) oriented single-crystal silicon (Si) was performed by rapid thermal annealing (RTA) at temperatures of 500–800 °C. Auger depth profiling shows that, when exposed to air, the Ti films take in oxygen atoms independently of Ti thickness. During RTA the oxygen tends to be redistributed uniformly throughout the Ti film near the onset of silicide formation. As silicide formation progresses, the redistributed oxygen is expelled by the advancing silicide front. For 50 nm Ti thickness, the oxygen driven from the TiSi2 is confined at the surface of Ti film and the silicide growth is almost stopped even though there remains unreacted Ti. For 100 and 200 nm Ti thicknesses, before the oxygen driven from the TiSi2 is confined at the surface a second silicide layer starts growing at the surface. The oxygen driven from the both silicides is buried where the two silicide fronts meet. The depth of the buried oxygen peak was found to be dependent on the annealing temperature and on the Ti thickness: The peak tends to penetrate deeper for higher temperatures and for thicker Ti films. Also, it was found that amorphous silicon (a-Si), which is sputter-deposited sequentially on Ti film without breaking the vacuum, is quite effective in forming oxygen free and homogeneous TiSi2 by preventing oxygen infiltration into Ti film.