Oxygen redistribution during sintering of Ti/Si structures

Abstract

We have used helium backscattering spectroscopy (RBS) to trace the evolution of oxygen depth profiles after UHV sintering, in 1430 Å titanium films, sputter deposited onto single crystal silicon substrates. The as-deposited films exhibit a roughly exponential oxygen distribution, decreasing from the titanium film surface. After sintering at 350 °C, 30 min the oxygen has moved into the film and after 450 °C, 20 min the oxygen is uniformly distributed in the titanium. At higher temperatures, as silicide formation progresses, the oxygen is snowplowed back toward the surface and is completely driven from the TiSi2 film after sintering at 800 °C, 30 min. The low temperature oxygen redistribution in titanium correlates well with increases in the sheet resistance of the unreacted films, as has been suggested earlier from x-ray diffraction results which revealed an increase in the titanium c axis after sintering at 500 °C [S. P. Murarka and D. B. Fraser, J. Appl. Phys. 51, 342 (1980)]. The sheet resistance reaches a maximum near the onset of silicide formation and continues to decrease as the silicide reaction goes to completion. We do not detect any oxygen at the silicide/silicon interface, within the detection limits of RBS (1.5×1020 oxygen/cm3).