Charge trapping properties of ultra-thin TiO_2 films on strained-Si

摘要

Ultra-thin high-k titanium oxide (equivalent oxide thickness ～2.2 nm) films have been deposited on strained-Si/relaxed-SiGe heterolayers using microwave plasma at < 200℃. The dielectric breakdown and reliability of the dielectric films have been studied using constant voltage stressing. An improvement in the leakage current characteristics is observed after post-deposition annealing. During constant voltage stressing of MIS capacitors, a time-dependent gate current increase and an anomalous current variation have been observed. The amplitude of the anomalous current is found to decrease with increase in annealing temperature. A time-dependent defect density variation in the dielectric layers for different annealing temperature has been observed. The effect of transient response and dielectric relaxation on annealing conditions has been investigated under high voltage pulse stressing. The stress-induced trap charge density and its spatial distribution have been studied. A high time-dependent dielectric breakdown (TDDB, t_(bd) > 1000 s) is observed for as-deposited TiO_2 under high constant voltage stress.