Electron Beam Induced Damage in Poly‐Si Gate MOS Structures and Its Effect on Long‐Term Stability

Abstract

Repeated electron beam irradiation and annealing processes are shown to enhance radiation damage in the gate , compared to only one irradiation and annealing cycle. Repeated irradiation with 20 keV electrons causes an introduction of more positive charge, neutral traps, and interface traps. Neutral trap density gradually increases with increasing repeated cycles, even after 700°C annealing in dry , though these traps are removed completely by only one cycle. Positively charged and neutral traps are determined by avalanche hot‐electron injection, and interface traps at the interface are determined by quasistatic C‐V measurements. Long‐term stability for electron beam irradiated MOS capacitors has been examined through positive and negative bias‐temperature (BT) stress aging. Devices annealed at 450° and 700°C result in faster and larger shifts and interface trap generation under BT stress than those for devices annealed at 1000°C. Around 1000°C annealing is found necessary to completely remove structural defects in the oxides induced by ionizing radiation and to assure good long‐term stability for MOS devices fabricated by electron beam lithography.