Co60 Radiation Effects on Laser Annealed Silicon on Sapphire

Radiation-hard, short channel length (1.8¿M) NMOS transistors with improved electron mobility have been fabricated by laser annealing silicon islands on sapphire. Conditions which give maximum mobility improvement without radiation induced degradation, compared with samples processed identically but without laser annealing, are: pulsed excimer laser (0.6 J/cm2; three exposures) and pulsed ruby laser (1.1-1.3 J/ cm2; three exposures). At these energy densities, nominal mobility improvements are 35% and 25% for excimer and ruby lasers; threshold voltage shifts on 680°A gate oxide NMOS transistors due to Co60 gamma radiation exposure at a dosage of 1×106 rad (Si) under + 10V gate bias is approximately -3.0 volts. Although cw Argon laser annealing improves mobility by 23% at a power of 5 watts, radiation induced back-channel leakages are higher than with no laser annealing.