RANDOM TELEGRAPH SIGNALS IN SMALL MOSFETS AFTER X-RAY-IRRADIATION

The Random Telegraph Signals (RTS's) in small MOSFET's before and after x-ray irradiation and after annealing have been studied. It is believed that the RTS's arise from the trapping/detrapping of individual defect(s) near the SiO2/Si interface, and they are expected to be altered by ionizing radiation and annealing processes. The key results from this study are: (i) RTS's existed prior to x-ray irradiation in both weak inversion and strong inversion due to process-induced defects, (2) x-ray irradiation causes the disappearance of the original RTS and the appearance of new RTS with different emission time constants, (3) x-ray irradiation also causes high frequency current fluctuations with much more irregular amplitude distribution than the slower RTS's (4) annealing at 200-300-degrees-C in nitrogen removes most of the high frequency component and reveals more clearly some of the radiation-induced RTS's, and (5) annealing at 400-degrees-C essentially removes all of the radiation-induced RTS's, but causes the reappearance of one set of the original RTS traces in strong inversion. Several possibilities are discussed to account for the observations.