Mechanism of oxide thickness and temperature dependent current conduction in n+-polySi/SiO_2/p-Si structures - a new analysis

摘要

The conduction mechanism of gate leakage current through thermally grown silicon dioxide (SiO_2) 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 SiO_2 films between 25 and 300 °C. The leakage current measured up to 300 °C 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 SiO_2 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 SiO_2 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.