Retrograde-Mask Processed Polysilicon TFT for High Performance, Planar Structure, and Stable Operation

We fabricated polysilicon thin-film transistors (TFTs) using a retrograde-mask process (RMP) showing high electrical performance, planar geometry, and stable driving characteristics. The electrical performance of RMP polysilicon TFT was compared with conventional metal-induced laterally crystallized (MILC) polysilicon TFTs. The fabrication process changed the masking steps of the conventional pattern, but did not require an additional mask. It was found that the conventional MILC poly-Si TFT typically showed a hump current, and had a serious reliability problem due to the NiSi 2 contamination at the corner edges and geometry effect. One the other hand, an RMP poly-Si TFT improved the hump and the TFT's reliability due to the absent of NiSi 2 at the edges and the large effective channel length and width.