The effects of electron beam damage on the degradations of n-MOSFETs due to the creation of interface traps were investigated using charge-pumping and subthreshold slope measurement methods. The in situ device characteristics such as threshold voltage, drain current were not changed much by the electron beam damage as compared with those of unirradiated ones if the devices were annealed at $450\,^\circ\!C$ in $N_2/H_2$ environment for 30 min. That is, the electron beam damage effects were severe when the devices were irradiated by the electron beam, while almost all of the damage effects were removed if the devices were annealed. The subthreshold slope and the interface trap density, however, were significantly degraded even with a small dose of electron beam irradiation when they were measured after annealing. As a result, the long-term reliability characteristics were changed for the large amount. Especially device lifetimes were shown to decrease at a fast rate as the electron beam irradiation dose was increased even after annealing. This indicates that proper annealing processes are required after electron beam lithography, in order that the electron beam lithography could be robust enough for the direct writing applications such as metal layer delineation in application specific IC (ASIC) fabrications which are not accompanied by subsequent high-temperature annealing processes. It was also observed that the interface trap density dependency on electron beam irradiation dose investigated by the charge-pumping method was highly consistent with that by the subthreshold slope measurement technique.
