CROSS-SECTIONAL TRANSMISSION ELECTRON-MICROSCOPE STUDIES ON INTRINSICBREAKDOWN SPOTS OF THIN GATE OXIDES

Cross-sectional transmission electron microscopy was used to study the intrinsic breakdown spots of 10-nm-thick gate oxides thermally grown on (001) Si substrates. At a breakdown spot with a breakdown field of 15 MV/cm, (111) twin planes are confirmed by electron diffraction to e xist in the surface region of the Si substrate. High resolution observ ation also reveals Si lattice fringes in the gate oxide, penetrating f rom the Si substrate and gate electrode of polycrystalline Si, and sig nificant roughening of the anode interface between oxides and Si subst rates. Also, similar growth twins and anode interface roughening are o bserved for a lower Geld breakdown spot with a breakdown field of 7 MV /cm. The presence of growth twins indicates that a Si substrate is loc ally molten during dielectric breakdown. These results are well explai ned by the local thermal breakdown model of intrinsic oxides. The inte rface roughening, presumably caused by deoxidization at the SiO2/Si in terface in a local hot spot, is indicative of an initial stage of intr insic dielectric breakdown of thin oxide.