Shallow n + junction formation using ion mixing of tungsten at elevated temperatures

Abstract

Shallow n + junctions with WSi 2 contacts were fabricated using ion mixing with arsenic and antimony at elevated temperatures. The silicide formation was found to be a function of dopant dose and temperature during implantation. The silicide formed with arsenic mixing was hexagonal WSi 2, which was transformed to the tetragonal phase after annealing. The diffusion depth values determined by secondary ion mass spectroscopy and spreading resistance measurements were in reasonable agreement whereas the SUPREM III simulation gave lower values; this is attributed to enhanced dopant diffusion during the ion mixing not being included in the simulation. The diffusion depths for both arsenic- and antimony-mixed contacts (350 and 190 nm respectively at 1 × 10 18 cm − were caused by high energy-high dose implantations. Functional diodes with ion-mixed WSi 2 contacts were fabricated showing a sheet resistivity of 17.5Ω/□ and relatively good current-voltage characteristics. There was a slight improvement for diodes after two-step anneals compared with single-step annealings. The current transport is believed to be a combined generation-recombination and diffusion process, since the average activation energy of the reverse current is between E E g0 2 and E g0 . The annealing of defects caused by the ion implantation may be incomplete for the ion-mixed diodes.