PULSED LASER CRYSTALLIZATION OF HYDROGEN-FREE A-SI THIN-FILMS FOR HIGH-MOBILITY POLY-SI TFT FABRICATION

The possibility to fabricate high-mobility polysilicon TFTs by nanosec ond pulsed laser crystallization of unhydrogenated amorphous Si thin f ilms has been investigated. Two types of lasers have been used: a larg e area (almost-equal-to 1 cm2) single ArF excimer laser pulse and a sm all diameter (almost-equal-to 100 mum) frequency-doubled Nd:YAG laser beam, working in the scanning regime. Processed films have been charac terized in detail by different optical and microscopic techniques. Dev ice performances indicate that the best results are achieved with the excimer laser leading to high mobility values (up to 140 cm2/Vs) which are much larger than in polysilicon TFTs fabricated onto the same qua rtz substrates by low-temperature thermal (630-degrees-C) crystallizat ion of amorphous Si films (mu(fe) almost-equal-to 55 cm2/Vs).