We have developed a new process, cyclic deposition with O-2 plasma treatment (C-DOP), to obtain a high-quality interfacial layer (IL) that can be applied to low-temperature poly-Si thin-film transistors (TFTs). The C-DOP process uses sequential deposition followed by O-2 plasma treatment. By increasing radio frequency power during O-2 plasma treatment, the SiO2 film becomes denser, and the density of the C-DOP-formed SiO2 becomes close to that of thermal oxide. The amounts of residual impurities, such as OH, H, and C, are decreased by the C-DOP process. We applied the C-DOP process to form a thin IL. It is effective in suppressing the flatband voltage shift (Delta V-FB) due to Fowler-Nordheim negative stress when the IL thickness is more than 5 nm. By applying the C-DOP-formed IL to poly-Si TFTs, drain-current degradation due to drain-avalanche hot-carrier stress is successfully suppressed, and the time to 10% reduction of the drain current is prolonged by 1 order of magnitude. (c) 2006 The Electrochemical Society.