Grain growth in laser dehydrogenated and crystallized polycrystalline silicon for thin film transistors

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Abstract
Selective dehydrogenation and crystallization are realized by a three-step incremental increase in laser energy density. X-ray diffraction and transmission electron microscopy show that the polycrystalline grains formed with this three-step process are similar to those after a conventional one-step laser crystallization of unhydrogenated amorphous silicon. The grain size increases with increasing laser energy density up to a peak value of a few micrometers. The grain size decreases with further increases in laser energy density. The transistor field effect mobility is correlated to the material properties, increasing gradually with laser energy density until reaching its maximum value. Thereafter, the transistors suffer from leakage through the gate insulators. A dual dielectric gate insulator has been developed for these bottom-gate thin film transistors. Our structure simplifies fabrication of both high quality amorphous and polycrystalline thin film transistors on the same glass substrate. We discuss the application of this process for producing hybrid amorphous and polycrystalline silicon thin film transistors from hydrogenated amorphous silicon on glass substrates.