The two-step rapid thermal annealing effect of the prepatterned a-Si films

Hydrogenated amorphous silicon (a-Si:H) films which were deposited by plasma enhanced chemical vapor deposition (PECVD) have been recrystallized by the two-step rapid thermal annealing (RTA) employing the halogen lamp. The a-Si:H films evolve hydrogen explosively during the high temperature crystallization step. In result, the recrystallized polycrystalline silicon (poly-Si) films have poor surface morphology. In order to avoid the hydrogen evolution, the films have undergone the dehydrogenation step prior to the crystallization step. Before the RTA process, the active area of thin film transistors (TFT's) was patterned. The prepatterning of the a-Si:H active islands may reduce the thermal damage to the glass substrate during the recrystallization. The computer generated simulation shows the heat propagation from the a-Si:H islands into the glass substrate. We have fabricated the poly-Si TFT's on silicon wafers. The maximum ON/OFF current ratio of the devices was over 10(5).