Excimer laser annealing system for AMLCDs: a long laser pulse for high-performance, uniform, and stable TFT

The excimer-laser-based machine developed by SOPRA for the Low Temperature Poly Silicon (LTPS) exhibit unique characteristics described in the present paper. The machine consists in a laser source, an optical set-up to homogenize the beam and a motion stage. The laser source is able to deliver up to 20 J per pulse. A shot to shot stability currently better than 4 percent ensures a high reproducibility of the annealing. The pulse duration of 200 ns is also known to improve the process in terms of resulting Si grain size. Due to the high energy per pulse, a large surface of typically 18 cm 2 is annealed at once. Recent studies pointed out the good reproducibility of the TFT made of Si annealed by mean of this system: a deviation of the mobility of only 7.6 percent has been obtained for several tens of TFT which average mobility is of 234 cm 2 /V.s. Performances of TFT can be improved by annealing the a-Si in controlled atmosphere. TFTs submitted to an electrical stress, exhibit a much better stability than that of TFTs obtained by Solid Phase Crystallization. The variation of the slope of the 'laser processed' TFTs is two to three times lower than that of 'SPC' TFTs.