Study of Si/SiO2 interface passivation and SiO2 reliability on deuterium implanted silicon
Department of Electrical and Computer Engineering
Doctor of Philosophy
Levy, Roland A.
One of the major defects that contribute to the interface states in the silicon band gap is the dangling bond, which degrades performance of MOS devices. Passivation of these bonds with hydrogen had been found to diminish their effect but the improvement degrades the operation due to hot electron effect. Passivation with deuterium annealing has proven to improve the lifetime of the metal oxide semiconductor devices but this technique is not very effective for a multi-level metal-dielectric structure. This work investigates and optimizes incorporation of deuterium by ion implantation into the silicon substrate before the growth of 6.5 nm thin oxides. Different implantation conditions were used for optimization of passivation in the silicon dangling bonds effectively. The interface states density and reliability of deutenum-implanted capacitors was investigated by extensive electrical characterization. Deuterium and hydrogen implanted capacitors showed identical interface passivation effect. Secondary Ion Mass Spectroscopy (SIMS) study supported the electrically measured data and showed the presence of deuterium both at the interface and in the oxide. The optimum passivation was obtained for deuterium implantation at 20keV with dose of lx1014atoms/cm2. For higher dose of implantation, 1x1015/cm2, the reduced passivation and oxide quality has been observed and attributed to implantation induced damage not being completely annealed during oxidation.
Deuterium distribution in silicon/silicon oxide systems was further investigated by subjecting the MOS capacitors to annealing conditions at 600°C and 700°C. Interface quality and oxide reliability degraded in annealed devices with lower dose of implantation, lxl014/cm2 while improved for higher dose of implantation at 1x1015/cm2. The out diffusion of deuterium ions during annealing governed the interface and oxide degradation for lower dose. The improvement in case of higher dose is due to the partial recovery of the damage, which is not completely removed during oxidation. Also, diffusion of deuterium during annealing from damage sites lead to the incorporation of deuterium ions at the interface and in the oxide.
For comparison, hydrogen implantation was carried out at similar conditions. Hydrogen-implanted devices exhibited more charge trapping (increased Stress Induced Leakage Current and Flat Band voltage shift), larger generation of interface states, and a smaller charge to breakdown under electrical stress, compared to the deuterium devices confirming the isotope effect.
njit-etd2005-129 (135 pages ~ 7,093 KB pdf)
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Created September 8, 2008