Ultra Large-Grain Poly-Si Thin-Film Transistor Using NiSi2 Seeding Si-Amplified Layer

A novel technique for enlarging grains of poly-Si thin-film has been successfully demonstrated, using a 1-μm thick Si-amplified layer (SAL) and NiSi₂ seeds on the top. It was applied to top-gated thin-film transistors (TFTs) and showed high electrical performance. The NiSi₂ seeds induce vertical crystallization in the SAL and migrate toward the bottom, forming columnar grains. The grain size of the poly-Si thin-film increases when the NiSi₂ seeds diffuse deeply into the SAL and eventually an ultralarge-grain (ULG) poly-Si thin film is formed. The SAL was removed for use in the fabrication of a top-gated TFT. The performance of the ULG poly-Si TFT was compared with that of a NiSi₂ seed-induced crystallized poly-Si TFT which was fabricated without an SAL.

I. Introduction

Rcently, polycrystalline-Si (poly-Si) thin-film transistors (TFTs) are of great interest due to their application in flat-panel displays (FPDs) and static random access memories (SRAMs) [1]. Although the poly-Si TFT shows high mobility and high current density compared to the amorphous-Si (a-Si) TFT, its grain boundaries are mainly responsible for the limitations in its performance, such as high threshold voltage, poor sub-threshold slope and poor reliability. In all these areas it is inferior to the crystalline-Si (c-Si) TFT [2], [3].