Mechanism of oxide thickness and temperature dependent current conduction in n+-polySi/SiO2/p-Si structures — a new analysis

The conduction mechanism of gate leakage current through thermally grown silicon dioxide (SiO2) films on (100) p-type silicon has been investigated in detail under negative bias on the degenerately doped n-type polysilicon (n+-polySi) gate.The analysis utilizes the measured gate current density JG at high oxide fields Eox in 5.4 to 12 nm thick SiO2 films between 25 and 300 ℃.The leakage current measured up to 300 ℃ was due to Fowler-Nordheim (FN) tunneling of electrons from the accumulated n+-polySi gate in conjunction with Poole Frenkel (PF) emission of trapped-electrons from the electron traps located at energy levels ranging from 0.6 to 1.12 eV (depending on the oxide thickness) below the SiO2 conduction band (CB).It was observed that PF emission current IpF dominates FN electron tunneling current IFN at oxide electric fields Eox between 6 and 10 MV/cm and throughout the temperature range studied here.Understanding of the mechanism of leakage current conduction through SiO2 films plays a crucial role in simulation of time-dependent dielectric breakdown (TDDB) of metaloxide-semiconductor (MOS) devices and to precisely predict the normal operating field or applied gate voltage for lifetime projection of the MOS integrated circuits.