Electron traps and excess current induced by hot-hole injection into thin SiO2 films

Abstract

Electron capture and excess current after the substrate hot-hole injection into a 131 /spl Aring/ oxide have been studied. The gate current-gate voltage characteristics, drain current-gate voltage characteristics, and capacitance-voltage curves in p-channel MOSFETs were measured before and after the hole injection and after subsequent electron injection. Excess current obviously appeared under positive gate bias after the hole injection and disappeared after the electron injection from the substrate. For the oxide after the hole injection, the electron capture occurred even at low electric fields under positive gate bias. The trapping rate of the electrons injected from the substrate is much larger than that of the electrons injected from the gate. In order to explain the experimental results, we have proposed a model, including the tunneling of electrons from the substrate into the positive charge centers generated by the hole injection and into the neutral trap centers created during the electron injection. Dynamics of electron trapping in the oxide with the positive charge centers have been also studied. Analyzing the gate voltage shift under a constant gate current for the sample after the hole injection, the trapping parameters were obtained. The characteristic behavior of the excess current is explained sufficiently, taking into account the creation of the neutral trap centers-and filling of the positive charge and neutral trap centers. Finally, the effect of annealing on the positive charge centers and the electron capture is investigated. The annealing over 200/spl deg/C rapidly removes a large portion of the positive charges in the oxide. The density of electron trap centers is dependent on the density of the remaining positive charge centers.