Characterization of leakage current in thin gate oxide subjected to 10 KeV X-ray irradiation

Abstract

Two components of the low-field current have been identified in thin oxides, following 10 KeV X-ray irradiation. The first component, observed in the direct tunneling region, can be removed by a 100 °C anneal, and is also greatly suppressed if the irradiation is done in vacuum or in a nitrogen ambient, or if the oxide is preannealed before irradiation. The origin of this current is speculated to be related to adsorbed water molecules on the gate surface. The second component is observed to begin in the pre-Fowler-Nordheim tunneling (FNT) region and extends into the FNT region, only in oxides less than approximately 8 nm thick, and persists even after several days of anneal at 300 °C. This current exhibits a power law dependence on radiation dose. The origin of this second component is believed to be due to the trap-assisted tunneling via neutral electron traps, similar to the leakage current observed in the oxide after high-voltage stress.