Improved lifetime of poly-Si TFTs with a self-aligned gate-overlapped LDD structure

We investigated the lifetimes for various poly-Si thin film transistor (TFT) structures. A gate-overlapped lightly doped drain (GOLDD) structure was self-aligned by the side etching of Al-Nd in an Al-Nd/Mo gate electrode. The dopant activation process in the LDD regions of GOLDD TFTs was performed by using a H-2 ion-doping technique. We also observed the effect of lifetime on the source/drain activation process. The thermal annealing of the source/drain region was found to extend the lifetime. The predicted lifetime of our GOLDD poly-Si TFT is superior to those of nonlightly doped drain (non-LDD) and lightly doped drain (LDD) poly-Si TFTs. The trapped-electron density at the drain junction after bias-stressing was also investigated using a two-dimensional (2-D) simulation.