Impact of Structural Strained Layer near SiO₂/Si Interface on Activation Energy of Time-Dependent Dielectric Breakdown

Abstract

A structural transition region near the SiO 2 /Si interface has been considered to play an important role with respect to gate oxide reliability. We clarify the effects of the structural transition region on the time-dependent dielectric breakdown (TDDB) characteristics, particularly the activation energy of the oxide breakdown for ultrathin gate oxides formed by different oxidation processes, i.e., pyrogenic oxidation, rapid thermal O 2 oxidation and N 2 O oxynitridation. Furthermore, we investigate the properties of the structural transition region, such as the density of SiO 2 as measured by the grazing incidence X-ray-scattering reflectivity (GIXR) method, the Si–O–Si bond angle by Fourier-transform infrared attenuated total reflection (FTIR-ATR), the etching rate by chemical etching and X-ray photoelectron spectroscopy (XPS). Through these investigations, it is clarified that the oxide breakdown tends to occur at the Si–O–Si network with a lower bond angle (<115°) and that the strain in the structural transition region reduces the barrier to the oxide breakdown. A 1-nm-thick strained layer is found to have a strong effect on the oxide reliability and to limit oxide scaling in future ultra-large-scale integrated circuits (ULSIs).