Minimal Glass Deformations with Rapid Thermal Annealing Control

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.