Fabrication of Polycrystalline Si Films by Silicide-Enhanced Rapid Thermal Annealing and Their Application to Thin Film Transistors

Abstract

Amorphous (a-Si) films were epitaxially crystallized on a very thin large-grained poly-Si seed layer by a silicideenhanced rapid thermal annealing (SERTA) process. The poly-Si seed layer contained a small amount of nickel silicide which can enhance crystallization of the upper layer of the a-Si film at lower temperature. A 5-nm thick poly-Si seed layer was then prepared by the crystallization of an a-Si film using the vapor-induced crystallization process in a NiCl2 environment. After removing surface oxide on the seed layer, a 45-nm thick a-Si film was deposited on the poly-Si seed layer by hot-wire chemical vapor deposition at 200 °C. The epitaxial crystallization of the top a-Si layer was performed by the rapid thermal annealing (RTA) process at 730 °C for 5 min in Ar as an ambient atmosphere. Considering the needle-like grains as well as the crystallization temperature of the top layer as produced by the SERTA process, it was thought that the top a-Si layer was epitaxially crystallized with the help of NiSi2 precipitates that originated from the poly-Si seed layer. The crystallinity of the SERTA processed poly-Si thin films was better than the other crystallization process, due to the high-temperature RTA process. The Ni concentration in the poly-Si film fabricated by the SERTA process was reduced to 1 × 1018 cm-3. The maximum fieldeffect mobility and substrate swing of the p-channel poly-Si thin-film transistors (TFTs) using the poly-Si film prepared by the SERTA process were 85 cm2/V·s and 1.23 V/decade at Vds = -3 V, respectively. The off current was little increased under reverse bias from 1.0 × 10-11 A. Our results showed that the SERTA process is a promising technology for high quality poly- Si film, which enables the fabrication of high mobility TFTs. In addition, it is expected that poly-Si TFTs with low leakage current can be fabricated with more precise experiments.