The structure and composition of contacts made of AL(2% Cu)TiW films on amorphized (100) silicon

Abstract

The effect of amorphizing the surface of (100) silicon substrate on the stability of the microstructure and the composition of Al(2% Cu)Ti/WSi contacts under heat treatments, in N 2 gas ambient, at temperatures between 450 and 520 °C was studied and compared with such contacts made on unamorphized (100) single-crystal silicon. The amorphization of the silicon surface was obtained by argon ion implantation at energies between 60 and 180 keV and a dose of 1 × 10 16 ions cm -2. The intermediate Ti/W layer was 150 nm thick and the Al(2% Cu) film was 1 μm thick. The microstructure and the composition of the samples were studied by means of transmission electron microscopy, X-ray diffraction and Auger electron spectroscopy. It was found that the amorphization of the (100) silicon surface and the subsequent heat treatment at the lower temperature (450 °C) induced diffusion of silicon atoms through the grain boundaries of the Ti/W layer into the aluminum film and aluminum atoms into the amorphized silicon surface layer. As a result, TiSi, TiSi 2 and (Ti 6W 4)Si 2 silicides were formed at the interface between the aluminum film and the Ti/W layer. Heat treatments of these samples at higher temperatures (between 500 and 520 °C) led to the formation of an additional silicide of WSi 2 and an intermetallic compound of AlTi 3 at the AlTi/W interface. However, no such diffusion and silicide formation processes could be detected in the contacts made on silicon that was not amorphized and underwent identical heat treatments. The results are explained on the basis of thermodynamics and kinetic considerations.