Origin of the substrate current after soft-breakdown in thin oxide n-MOSFETs

This paper presents an experimental investigation of the origin of the substrate current after soft-breakdown in n-MOSFETs with 4.5 nm-thick oxide. At lower voltages, this current shows a plateau that can be explained by the generation of hole-electron pairs in the space charge region and at the Si-SiO₂ interface, and by carrier diffusion between the channel and the substrate. At higher voltages, the substrate current steeply increases with voltage, due to trap-assisted tunneling from the substrate valence band to the gate conduction band, which becomes possible for gate voltages higher than the threshold voltage. Measurements on several devices at dark and in the presence of light, and in the case on substrate reverse bias, confirm the proposed interpretation