Laser crystallization has been the most promising technology to manufacture low temperature poly-silicon (LTPS) thin film transistors (TFTs), since LTPS technology can make LCD panels with integrated drivers. Higher mobility and lower leakage current than the solid-phase crystallization (SPC) counterparts can be obtained by laser crystallization.[1] Excimer laser emit in the UV region with a short pulse duration (10-30ns), and high temperature can be developed in the Si-surface region, causing melting, without appreciate heating (400°C) with the glass substrate.[2] Laser processes should provide uniform and stable laser beam profiles to obtain uniform distribution of electrical characteristics of TFTs.In this study, the effects of laser beam profiles were investigated on the crystallization of poly-Si films. "One Pulse" laser crystallized poly-Si was analyzed by SEM and alpha-step to distinguish the effects of non-uniform laser beam profiles. Surface smoothness of poly-Si films with various laser-overlapping ratios was also measured to investigate the effects of laser beam profiles. Then the relationships of TFT characteristics and laser overlapping ratios will be discussed.
We have investigated the laser crystallized LT poly-Si TFT characteristics in the overlapped area of excimer laser scans in the long axis direction. Continuous TFTs located at the edges of single scan and overlaps of two scans were used. Different laser energy densities were dual-scanned to study the characteristics of the TFTs in overlapped area. It was found that the laser with higher energy density dominates the TFT characteristics, and their characteristics in the overlapped area can be as good as those in the non-overlapped area. Based on these results, large uniform LT poly-Si panel can be fabricated by overlapping the laser scans in the long axis direction.
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