Phase stepping microscopy for rapid control of laser crystallization of Si for flat panel display applications

Low-temperature polycrystalline silicon (poly-Si) is today a promising material allowing the production of large-area thin-film transistor (TFT's) displays. High-performance poly-Si TFT's are currently obtained using a pulsed excimer laser beam to crystallize the amorphous deposited silicon (a-Si) film on a glass substrate. The final quality of the poly-Si devices depends on several key parameters such as the laser energy density, the beam homogeneity and the number of laser shots. However, rapid quality control is needed to optimize and stabilize the crystallization process. In this work, the micro-structural evolution of the crystallized area with the laser annealing conditions and the formation in the Super Lateral Growth (SLG) region of large grain poly-Si have been investigated by interference microscopy. Phase Stepping Microscopy (PSM), which allows nanometric measurement of surface morphology, has been used to follow the annealing process in Si thin films on glass irradiated using a large area (∼ 40 cm 2 ) and long pulse duration (200 ns) excimer (XeCl) laser. The results of the surface morphology obtained by interference microscopy and confirmed by Atomic Force Microscopy (AFM) attest to the PSM technique being one of the most interesting alternative ways that could be used for the calibration of the laser annealing process in an industrial environment.