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A critical step in the fabrication of polycrystalline silicon thin-film transistors (TFT's) is to crystallize the amorphous silicon layer deposited on glass. This paper describes a complete rapid thermal annealing (RTA) process applied to the crystallization of the amorphous layer. The RTA heating and cooling rates have been optimized to minimize thermal gradients and to improve glass substrate stability. Numerical simulations taking into account the lamp characteristics, the annealing chamber configuration and the sample properties have been developed and allow elucidation of thermal nonuniformities in the sample during the RTA process. Although the transition point of a glass (T g) is often considered as an upper limit in usual polysilicon TFT's processes, this paper shows that if the cooling rate is accurately controlled, annealing temperatures can be above T g without thermal damage to the glass.

This letter describes a new process for realization of polysilicon thin-film transitors (TFT) on glass substrates. The process is based on crystallization by rapid thermal annealing of amorphous silicon films deposited by low-pressure chemical vapor deposition (LPCVD). With this technique, the time of crystallization of the silicon films is reduced to a few seconds. Thin-film transistors have been realized using this process, and the field-effect mobility is in the range of 20 cm2·V-1·s-1.