The effect of substrate bias on the degradation during applying a negative bias temperature(NBT) stress is studied in this paper.With a smaller gate voltage stress applied,the degradation of negative bias temperature instability(NBTI) is enhanced,and there comes forth an inflexion point.The degradation pace turns larger when the substrate bias is higher than the inflexion point.The substrate hot holes can be injected into oxide and generate additional oxide traps,inducing an inflexion phenomenon.When a constant substrate bias stress is applied,as the gate voltage stress increases,an inflexion comes into being also.The higher gate voltage causes the electrons to tunnel into the substrate from the poly,thereby generating the electron-hole pairs by impact ionization.The holes generated by impact ionization and the holes from the substrate all can be accelerated to high energies by the substrate bias.More additional oxide traps can be produced,and correspondingly,the degradation is strengthened by the substrate bias.The results of the alternate stress experiment show that the interface traps generated by the hot holes cannot be annealed,which is different from those generated by common holes.
This paper studies the degradation of device parameters and that of stress induced leakage current (SILC) of thin tunnel gate oxide under channel hot electron (CHE) stress at high temperature by using n-channel metal oxide semiconductor field effect transistors (NMOSFETs) with 1.4-nm gate oxides.The degradation of device parameters under CHE stress exhibits saturating time dependence at high temperature.The emphasis of this paper is on SILC of an ultra-thin-gate-oxide under CHE stress at high temperature.Based on the experimental results,it is found that there is a linear correlation between SILC degradation and V h degradation in NMOSFETs during CHE stress.A model of the combined effect of oxide trapped negative charges and interface traps is developed to explain the origin of SILC during CHE stress.
The degradation of device under GIDL (gate-induced drain leakage current) stress has been studied using LDD NMOSFETs with 1.4 nm gate oxides. Experimental result shows that the degradation of device parameters depends more strongly on Vd than on Vg. The characteristics of the GIDL current are used to analyze the damage generated during the stress. It is clearly found that the change of GIDL current before and after stress can be divided into two stages. The trapping of holes in the oxide is dominant in the first stage, but that of electrons in the oxide is dominant in the second stage. It is due to the common effects of edge direct tunneling and band-to-band tunneling. SILC(stress induced leakage current)in the NMOSFET decreases with increasing stress time under GIDL stress. The degradation characteristic of SILC also shows saturating time dependence. SILC is strongly dependent on the measured gate voltage. The higher the measured gate voltage, the less serious the degradation of the gate current. A likely mechanism is presented to explain the origin of SILC during GIDL stress.
