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Influences of hydrogen in precursor Si films on excimer laser crystallization

The excimer laser crystallization (ELC) is a key technology of the low temperature polycrystalline silicon (LTP) thin film transistor (TFT) processes. The precursor Si for ELC is amorphous Si (a-Si) film, and hydrogen in the film has to be eliminated down to a certain concentration to prevent explosive evolution of hydrogen gas when excimer laser is irradiated. Hydrogen has been concerned only with respect to the effect for practical applications. This paper points out another aspect of hydrogen effect. There is correction between the bonding environments of precursor and polycrystalline Si (p-Si) structures produced through ELC process. The effect becomes explicit under 0.8 at percent of hydrogen conceits, and are clearly manifested in differences in lattice spacings of p-Si films. Variations of microscopic structure of the precursors are provided by three kinds of deposition methods, and dehydrogenation conditions. This paper also shows that transient boiling behaviors by the excimer laser discriminate prominently the differences among precursors. Although relationships between the behavior and microscopic structures are not clear, it gives an efficient measure for the bonding environment. It is also shown that the constants of p-Si is typically 1018/cm3 after multishot ELC process, and effusion of the hydrogen at one shot is rather small. This may lead to the inferences that hydrogen influence profoundly ELC process, and also contributes to preserve characteristic structure of the precursors.