New excimer laser crystallization in the lattice shape to improve the uniformity of electrical characteristics of poly-Si TFT

The new laser annealing technique to control the surface morphology and microstructure of poly-Si film is proposed. Compared with the conventional laser annealing technique where the laser beam is irradiated on the whole area of active layer, our new method make the laser beam transmitted locally onto the active amorphous silicon (a-Si) layer. Using the masking window in grid shape, the active layer is recrystallized in the lattice shape during the laser irradiation. By the optical microscope and scanning electron microscopy (SEM), we observed the orderly pattern, which consists of amorphous and poly-Si regions. In our new poly-Si film, the rough surface morphology, which is shown in conventional sample, could not be found. Furthermore we fabricated a poly-Si TFT utilizing the active poly-Si film recrystallized by our new method. The new poly-Si TFT showed much higher ON current than the conventional poly-Si TFT, although the leakage current is relatively high. The excellent ON characteristics may be attributed to the uniform surface morphology. After hydrogenation, the electrical characteristics of our new poly-Si TFT was improved considerably and this device may be applied successfully to the active matrix liquid crystal displays (AMLCD's).