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) te chnique followed by excimer laser annealing for fabrication of low-tem perature polycrystalline Si thin-film transistors (TFTs) is studied. H igh-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 i ons incorporated in a non-mass-separated ion beam induce undesirable e tching of Si films during implantation. To avoid this, He-diluted gas is used. The fabricated TFTs exhibit excellent characteristics compara ble to those of TFTs fabricated conventionally. There is no instabilit y due to contamination which may be introduced from a non-mass-separat ed ion beam. OFF-state characteristics of TFTs can be improved by incr easing laser energy for impurity activation. However, also the avalanc he-induced short channel effect is enhanced by increasing laser energy . Adjustment of laser energy is required to optimize the device charac teristics. It is concluded that ion doping and excimer laser annealing techniques are promising solutions to problems plaguing poly-Si TFTs.