THE EFFECTS OF X-RAY IRRADIATION-INDUCED DAMAGE ON RELIABILITY IN MOSSTRUCTURES

The effects of X-ray irradiation induced damage on long-term reliabili ty of MOS structures have been investigated. The gate leakage currents at low electric field during a measurement of Fowler-Nordheim tunneli ng were increased after X-ray exposure, it was explained by the interf ace trap-assisted tunneling mechanism. This leakage component was comp letely eliminated by forming gas annealing at 450 degrees C. The long- term reliability of MOS gate oxide is significantly affected by the re sidual damages in the oxide even after forming gas annealing. In X-ray damaged MOS structures, the average values of cumulative charge-to-br eakdown (Q(bd)) were reduced about 15% as compared with the unexposed devices. The major mechanism responsible for reduction of Q(bd) in irr adiated devices is enhanced electron trapping into the neutral traps.