2 MeV electron irradiation effects on bulk and interface of atomic layer deposited high-k gate dielectrics on silicon

摘要

2 MeV electron irradiation effects on the electrical properties of A1_2O_3 and HfO_2-based metal-insulator-semiconductor capacitors have been studied. High-k dielectrics were directly grown on silicon by atomic layer deposition. Capacitors were exposed to three different electron irradiation doses of 0.025, 0.25 and 2.5 MGy. Capacitance-voltage, deep-level transient spectroscopy, conductance transients, flat-band voltage transients and current-voltage techniques were used to characterize the defects induced or activated by irradiation on the dielectric bulk and on the interface with silicon substrate. In all cases, positive charge is trapped in the dielectric bulk after irradiation indicating the existence of hole traps in the dielectric. When the samples are exposed to 2 MeV electron beam (e-beam) irradiation, electron-hole pairs are created and holes are then captured by the hole traps. Insulator/semiconductor interface quality slightly improves for low irradiation doses, but it is degraded for high doses. Irradiation always degrades the dielectric layers in terms of gate leakage current: the trapped holes are mobile charge which can contribute to leakage current by hopping from trap to trap.