This work investigates the thermal stability of Al/W/p(+)-n junction diodes, in which the W contact was filled using selective chemical vapor deposition to a thickness of about 450 nm and served as diffusion barrier between the Al and the Si substrate. The effects of in situ N-2 plasma treatment on the barrier effectiveness were also investigated. The Al/W(450 nm)/p(+)-n junction diodes can sustain a 30 min furnace annealing up to 575 degrees C. With an in situ N-2 plasma treatment on the W surface caused a thin layer of WNx to form on the W surface, and the nitrified layer of WNx/W acting as barrier between the AZ and the Si substrate effectively suppressed WAl12 formation at elevated temperatures, resulting in a significant barrier improvement. N2 plasma treatment at 100 W for 300 s enabled the Al/WNx/W(450 nm)lp(+)-n junction diodes to sustain thermal annealing at temperatures up to 625 degrees C without degradation of electrical characteristics.