A thorough study of quasi-breakdown phenomenon of thin gate oxide in dual-gate CMOSFET's

The conduction mechanism of quasibreakdomn (QB) mode for thin gate oxide ha s been studied in dual-gate CMOSFET with a 3.7-nm thick gate oxide. Systema tic carrier separation experiments were conducted to investigate the evolut ions of gate, source/drain, and substrate currents before and after gate ox ide quasibreakdown (QB), Our experimental results clearly show that QB is d ue to the formation of a local physically-damaged-region (LPDR) at Si/SiO2 interface [1], tit this region, the effective oxide thickness is reduced to the direct tunneling (DT) regime. The observed high gate leakage current i s due to DT electron or hole currents [14] through the region where the LPD R is generated. Twelve V-g, I-sub, I-s/d versus time curves and forty eight I-V I curves of carrier separation measurements have been demonstrated. Al l curl-es can be explained in a unified wag by the LPDR QB model and the pr oper interpretation of the carrier separation measurements. Particularly, u nder substrate injection stress condition, there is several orders of magni tude increase of I-sub(I-s/d) at the onset point of QB for n(p) - MOSFET, w hich mainly corresponds to valence electrons DT from the substrate to the g ate. Consequently, cold holes are Left in the substrate and measured as sub strate current. These cold holes have no contribution to the oxide breakdow n and thus the Lifetime of oxide after QB is very long. Under gate injectio n stress condition, there is sudden drop and even change of sign of I-sub(I -s/d) at the onset point of QB for n(p)-MOSFET, which corresponds to the di sappearance of impact ionization and the appearance of hole DT current from the substrate to the gate.