High Performance Bottom Gate TFTs by Excimer Laser Crystallization and Post Hydrogenation

Abstract

Small grain poly-Si has defects of the order of 1018 to 1019 spins/cm3. Hydrogen is generally used to terminate these defects, which is introduced from a hydrogen plasma. Damage caused by UV emitted from the plasma glow discharge was identified as one of the causes limiting the quality of the bottom gate thin film transistor (TFT) devices. The effect of UV on the TFT transfer characteristics was studied. ESR was used to measure the change in the poly-Si dangling bond density as a result of UV irradiation. It was confirmed that plasma UV creates damage in the poly-Si. A combination of plasma hydrogenation and SiNx : H passivation and thermal annealing was found to be particularly effective in reducing the defect density by reconstruction of dangling bonds and redistribution of hydrogen without hydrogen loss. The excellent characteristics obtained using this hydrogenation method are presented.