Growth of very large grains in polycrystalline silicon thin films by the sequential combination of vapor induced crystallization using AlCl3 and pulsed rapid thermal annealing

Metal-induced crystallization method is one of the favorable non-laser crystallization methods for thin-film transistors in large-area displays. However, it is necessary to reduce metal contamination in the film to lower leakage current for the device applications. A new two-step crystallization method, consisting of a nucleation step by AlCl3 vapor-induced crystallization and a grain growth step by a pulsed rapid thermal annealing, has been proposed to increase the grain size and reduce the residual metal contamination in crystallized poly-Si films. The grain size of the poly-Si film crystallized by the VIC + PRTA two-step crystallization process was as large as 70 μm. Furthermore, the Al concentration in the poly-Si film was reduced by two orders of magnitude from 1 × 1020 cm−3 by VIC only process to 1.4 × 1018 cm−3 by the two-step process. As a result, the minimum leakage current of poly-Si TFTs using the poly-Si film prepared by the two-step process was reduced from 1.9 × 10−10 A/μm to 2.8 × 10−11 A/μm at a drain voltage of 5 V, without carrier mobility degradation.

► We have proposed a novel two-step crystallization process.
► The process consists of initial crystallization by VIC and grain growth by PRTA.
► The grain size of the poly-Si film crystallized by the VIC + PRTA was increased.
► The Al concentration in the poly-Si film was reduced by the two-step process.
► The leakage current was decreased by reducing the Al concentration.