Analysis of thin thermal silicon nitride films on silicon

We have investigated the chemical and electrical properties of very thin (<32 Å thick) silicon nitride films grown by rapid thermal nitridation of silicon. These films were of interest as a possible means of tailoring the barrier heights of silicon Schottky barrier diodes. Auger and XPS analysis showed that the level of oxygen contamination in the films was very low ([N]/[N]+[O]) =0.85 to 0.95). The oxygen is located primarily at the surface and interface of the films. Metal-nitride-silicon devices were characterized by I-V and C-V techniques. These measurements indicated an increase in barrier heights to p-type substrates and a decrease in barrier heights to n-type substrates compared to values measured in the absence of the nitride layers. The magnitude of the change in barrier height increases with increasing nitride thickness. The barrier height can be varied reproducibly over a wide range. For molybdenum on p-type, this range is greater than half the bandgap. For titanium and molybdenum on p-type diodes, barrier heights higher than 1.0 V can be achieved. These measurements could be explained by a reduction in the density of silicon interface states with increasing nitride thickness or by the presence of positive fixed charge in the nitride layer.