Leakage currents induced in ultrathin oxides on (100)Si by deep-UV photons

Degradation of ultrathin (dox=3–6 nm) oxides on (100)Si under irradiation with deep-UV (hν=10 eV) photons was studied in order to evaluate the possible oxide damage by deep-UV lithography. The irradiation was found to lead to a significant enhancement in electrical conduction of the ultrathin oxides. The leakage current observed after irradiation correlates with the concentration of radiolytic atomic hydrogen in the oxide and includes two components. A first transient one is related to thermally unstable defects similar to the H-related donor interface states observed after irradiation of thicker oxides. The second, stable component correlates with the enhanced density of Si dangling bond defects in the oxide (E′ center) which points to the H-assisted rupture of SiO bonds. It is also found that the leakage currents observed after electrical stress and after deep-UV irradiation exhibit similar annealing behavior. The two revealed sources of the degradation-induced leakage current may account for the enhanced electron transport across ultrathin Si oxides under various circumstances.