Thermal stability of W-contacted junction diodes

Abstract

This work investigates the thermal stability of W-contacted p(+)n junction diodes, in which the tungsten contact was formed by selective chemical vapor deposition (CVD) or sputtering process. Reaction of Al and CVD-W at elevated temperature leads to the formation of WAl12, and the barrier capability of CVD-W film was dependent on the consumption of W. The sputter-W film has a columnar structure and contains a higher content of oxygen. The presence of oxygen retarded the formation of WAl12 and thus enhanced the thermal stability of the Al/W/Si structure. However, degradation of the Al/sputter-W (100 nm)/p(+)n diodes occurred after 30 min annealing at 550 degrees C, presumably due to Al diffusion along the grain boundary of sputter-W film. For the CVD-W contacted junction diodes, insertion of a thin TiN barrier layer between the Al and W film was effective in suppressing the formation of WAl12 and thus improved the device's thermal stability.