Impact of structural strained layer near SiO₂/Si interface on activation energy of time-dependent dielectric breakdown

A structural transition region near the SiO₂/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 O₂ oxidation and N₂O oxynitridation. Furthermore, we investigate the properties of the structural transition region, such as the density of SiO₂ 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 (<15°) 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).