Numerical Simulation and Experimental Analysis on the Crystal Growth of Excimer-Laser Crystallization of a-Si Film

In this work, the excimer-laser-induced crystallization of amorphous silicon (a-Si) films was investigated numerically and experimentally. The basic structure is an a-Si film on a glass substrate. This study had investigated the effects of irradiating energy density on the grain size and structure by scanning electron microscopy (SEM). In the surface microstructure analysis of the laser-irradiated area, the critical fluences (full-melt threshold, FMT) between the partial melting and complete melting regimes can be found by applying scanning electron microscopy. An efficient two-dimensional numerical model is carried out to predict the critical fluences (FMT) and the transient temperature distribution during the laser processing. Numerical analysis of the temperature profile showed that a temperature drop occurred at the center of melted zone immediately after laser irradiation. From the analysis of temperature responses, the FMT obtained from the simulation results of the proposed model agree fairly well with those from the experimental data reported in the literature and acquired in this research. Furthermore, the grain growth of the poly-Si was studied by the grain observation of the cross section and its corresponding numerical simulation. The cross-sectional grain structure of the resulting poly-Si film was observed with different laser intensities. The grain sizes decreased with increasing irradiating energy intensity in the partial melting regime. From the surface observation, the grain distribution was uniform and most of the grain has a single crystallographic direction. The average grain size had the biggest value at FMT. But some super large grains occurred and combined with more than one crystallographic direction when the film obtained sufficiently high energy intensities that was closed or over the FMT. The grain distribution was not uniform. The super large gain was around the small grain size. The modified cellular automation method (MCA) was used to simulate the grain growth two-dimensionally and explain the grain development during the solidification process. The grain morphology of the numerical simulation was satisfied with the experimental observation. From the analysis of the grain growth, this model was able to simulate the undercooling effect and grain growth phenomenon and fitted for the experimental grain observation in the excimer-laser-induced crystallization.