Study On The Time Dependent Dielectric Breakdown And Reliability Simulation Of Ultra-thin Gate Oxides

This dissertation investigates the breakdown theory and reliability characterization methods of the time dependent dielectric breakdown (TDDB) for the ultra-thin gate oxide, and the hot-carrier effect (HCE) in deep sub-micron MOSFET's. The author's main contributions are outlined as following:First, the roles of hot electron and hole in dielectric breakdown of ultra-thin gate oxides have been quantitatively investigated by separately controlling the amounts of hot electron and hot hole injection using substrate hot hole (SHH) injection method. The changes of threshold voltage have been discussed under different stress conditions. This dissertation is the first report that points out the cooperation of hot electron and hole is essential for the TDDB of ultra-thin gate oxides. A detailed theory analysis is made and a two-step breakdown model of ultra-thin gate oxide is presented. The first step is the creation of trap centers in ultra-thin gate oxides by hot electron injection, and the second step is oxides breakdown induced by hole trapping. A new physical model of TDDB of ultra-thin gate oxides is presented on the bases of above analysis.TDDB and HCE always take place simultaneously under device operation conditions. Hot-carrier enhanced TDDB effect of ultra-thin gate oxide is investigated by using substrate hot-carrier injection technique. Hot-carrier induced oxide breakdown shows different characteristics compared with that induced by conventional FN stress. The correlation between the calculated electron energy in the oxide and the electric field in the silicon substrate indicates that the difference between hot electron injection and the FN tunneling can be explained in terms of the average electron energy in the oxide. Hot hole injection experiments reveal that the lifetime of ultra-thin gate oxide is not simply determined by the total number of injected hole. A new hot-carrier-induced TDDB model of ultra-thin gate oxide is reported in this dissertation.Secondly, the transient characteristics of FN tunneling and hot hole (HH) stress induced leakage current (SILC) in ultra-thin gate oxide are investigated respectively in this dissertation. Under both stress conditions, stress induced leakage current follows a power law against stress time with different power factors. For HH SILC, the exponential factor significantly deviates from -1. HH SILC is found to have a more pronounced transient effect. The results show that HH SILC is attributed to oxide holedetrapping and the annihilation of positive charge-assisted tunneling centers. The positive charge assisted tunneling current can be greatly reduced by using appropriate substrate hot electron injection technique.Moreover, the breakdown characteristics of ultra-thin gate oxides are measured under constant voltage and constant current stresses in the dissertation, and the reliability characterization methods of TDDB are studied. Charge to breakdown Qbd is measured and analyzed. The results show that charge to breakdown Qbd depends not only on the gate oxide quality but also on the voltage stress, current density and the gate oxide area. Relative coefficients are fitted and analytical express of Qbd is deduced. Extrapolating results obtained from above model are in good agreement with the experiment data. This dissertation presents a new characterization method of ultra-thin gate dielectric TDDB.Important results are derived in measuring and calculating trap density in this dissertation. TDDB evaluation experiments are carried out with constant current stress on MOS capacitors with ultra-thin gate oxides, and a method of precise measurement and characterization of the trap density and accumulative failure is presented. This method is based on dynamic equilibrium equation of charge trapping. We can obtain the trap density by measuring the change of gate voltage of MOS capacitance under constant current stress and the change of high frequency C-V curve before and after the stress. The dynamic parameters of characterization the trap density can be e...