Application of Ion Doping and Excimer Laser Annealing to Fabrication of Low-Temperature Polycrystalline Si Thin-Film Transistors

Feasibility of the non-mass-separated ion implantation (ion doping) technique followed by excimer laser annealing for fabrication of low-temperature polycrystalline Si thin-film transistors (TFTs) is studied. High-speed doping, less than 10 s for formation of the source and drain of TFT, can be achieved by using a bucket-type ion source. Hydrogen ions incorporated in a non-mass-separated ion beam induce undesirable etching of Si films during implantation. To avoid this, He-diluted gas is used. The fabricated TFTs exhibit excellent characteristics comparable to those of TFTs fabricated conventionally. There is no instability due to contamination which may be introduced from a non-mass-separated ion beam. OFF-state characteristics of TFTs can be improved by increasing laser energy for impurity activation. However, also the avalanche-induced short channel effect is enhanced by increasing laser energy. Adjustment of laser energy is required to optimize the device characteristics. It is concluded that ion doping and excimer laser annealing techniques are promising solutions to problems plaguing poly-Si TFTs.