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This paper discusses time-dependent dielectric breakdown (TDDB) in n-FETs with HfSiON gate stacks under various stress conditions. It was found that the slope of Weibull distribution of Tbd, Weibull β, changes with stress conditions, namely, DC stress, unipolar AC stress and bipolar AC stresses. On the other hand, the time evolution component of stress-induced leakage current (SILC) was not changed by these stresses. These experimental results indicate that the modulation of electron trapping/de-trapping and hole trapping/de-trapping by stress condition changes the defect size in high-k gate dielectrics. Therefore, the control of injected carrier and the characteristics of trapping can provide the steep Weibull distribution of Tbd, leading to long-term reliability in scaled CMOS devices with high-k gate stacks.

We have studied depth profiling of the chemical composition, bonding features and defect states in 2 nm-thick HfSiO"xN"y (Hf/(Hf+Si)=~43%) films with N content of ~13 at.% before and after post-deposition annealing (PDA) at 1050 ^oC in O"2 and N"2 ambience by using high-resolution x-ray photoelectron spectroscopy (XPS) and total photoelectron yield spectroscopy (PYS) in combination with oxide thinning by a dilute HF solution. NO"x and Hf-N"x (x=2, 3) bonding units existing in the sample before PDA were effectively eliminated or reduced by PDA and Si-N and Hf-N bonds were the main N bonding features after PDA. We found the formation of a region with a low Si content and a residue of Hf-N"2 bonding units in the HfSiO"xN"y film by O"2-PDA in comparison to N"2-PDA. The PYS measurements revealed a high density of filled defect states in such a Si-deficient region with a large number of Hf-N"2 bonds.

We have investigated the reaction mechanism of the nitridation process based on first principles calculations and experimental results. We found that oxidation-resistant Si3N4 film can be formed by uniformly arranging 3-fold coordinated N atoms into Si sub-surface layer, and we successfully incorporated O atoms into the SiN/Si interface with minimum disruption of SiN structures. We have realized a high-quality ultra-thin gate SiON film with an equivalent oxide thickness of 0.7 nm and a leakage current of 95 A/cm2, 1/10 or less than that of traditional SiON films. Mobility is not reduced to less than 89% of an ideal SiO2 film.