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 nanosecond pulsed laser crystallization of unhydrogenated amorphous Si thin films has been investigated. Two types of lasers have been used: a large area (almost-equal-to 1 cm2) single ArF excimer laser pulse and a small diameter (almost-equal-to 100 mum) frequency-doubled Nd:YAG laser beam, working in the scanning regime. Processed films have been characterized in detail by different optical and microscopic techniques. Device 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 quartz substrates by low-temperature thermal (630-degrees-C) crystallization of amorphous Si films (mu(fe) almost-equal-to 55 cm2/Vs).