Advanced excimer-laser crystallization techniques of Si thin-film for location control of large grain on glass

This paper reviews advanced excimer-laser crystallization techniques and its application to crystal-Si thin film transistors (TFTs). Combined microstructure and time-resolved optical reflectivity investigations during conventional excimer-laser crystallization showed that explosive crystallization occurs during excimer-laser irradiation. Two methods enabling location-control of large silicon islands will be reviewed. One of the methods uses local thermal relief by modifying locally the heat extraction rate towards the substrate. A small unmolten region remains at the center of high heat extraction part which then acts as a seed for radially grown Si grains with a diameter of 6 mum. One of the other methods uses geometric selection through a vertical narrow constriction. In this method, upon laser irradiation, a small unmolten Si region remains at the bottom of narrow holes etched in the underlying isolation layer. During vertical regrowth. a single grain is filtered out which subsequently seeds the lateral growth of large (6 mum) grains. We will also discuss the performance of crystal-silicon TFTs that are formed in the location-controlled Si grains. The field-effect mobility for electrons is 450 cm(2)/Vs, which is very close to that of TFTs made with silicon-on-insulator wafers.