Hot-electron-induced quasibreakdown of thin gate oxides

An oxide-breakdown mode induced by hot-electron injection into an oxide is reported for n-channel metal–oxide–semiconductor field-effect transistors with 6 nm thick gate oxides. The diameter of the current path formed after breakdown was estimated to be less than 10 nm based on spreading-resistance measurements. The measured charge to breakdown was 102–104 C/cm2 in an oxide field of 5–7 MV/cm. This value is much smaller than that extrapolated from the results of Fowler–Nordheim (FN) tunneling experiments. The charge to breakdown in the hot-electron injection method decreased as the electric field increased in a silicon substrate. This was quite different from the case with FN tunneling injection, where the oxide field plays a significant role in oxide breakdown. Good correlation between the calculated electron energy in the oxide and the electric field in the silicon substrate suggests that the difference between hot-electron injection and FN tunneling can be explained in terms of the average electron energy in the oxide.