A novel fabrication process for polysilicon Thin Film Transistors with source/drain contacts formed by deposition and lift-off of highly doped layers

A novel fabrication process for low-temperature (<500 C) polysilicon thin film transistors (TFTs) is proposed. The main features of such process are: (i) the source and drain contacts formation by deposition and lift-off of doped layers, allowing to eliminate ion-implantation; (ii) the use of a single excimer laser annealing step for active layer crystallization and doping activation. The gradual doping profile, resulting from the adopted contact formation process and further smeared by the laser annealing, enables a drain field reduction, if compared to doping profiles that can be achieved by conventional techniques. This allows a substantial reduction of the ''field enhanced'' mechanisms, affecting the electrical characteristics of polysilicon TFTs at high source/drain voltages, such as kink effect and leakage current. The present process, thanks to the above mentioned features, can be rather attractive for polysilicon TFTs applications.