Comprehensive study of lateral grain growth in poly-Si films by excimer laser annealing and its application to thin film transistors

Lateral grain growth in nondoped poly-Si films was studied by using Si thin films (500 Å) with different structures as a starting material for excimer laser crystallization. It was clarified that the lateral grain growth phenomenon (micron-size grains with strong (111) orientation) upon excimer laser annealing was strongly affected by both the microstructure and the orientation of the initial Si thin films. This result supports our previous speculation that the principal driving force of the lateral grain growth phenomenon is surface energy anisotropy. Poly-Si thin-film transistors using these films show a high field effect mobility of 440 cm 2 /V·s, achieved through a low-temperature process below 600° C. This excellent electrical characteristic is thought to be due to the large grain size of poly-Si thin film with controlled orientation, good crystallinity, and a smooth surface.