Improved Electrical Performance of MILC Poly-Si TFTs Using $\hbox{CF}_{4}$ Plasma by Etching Surface of Channel

In this letter, a new manufacturing method for metal-induced lateral crystallization (MILC) polycrystalline silicon thin-film transistors (poly-Si TFTs) using CF₄ plasma was proposed. It was found that CF₄ plasma effectively minimizes the trap-state density by etching away the top surface of MILC and passivating the trap states, leading to superior electrical characteristics such as high field-effect mobility, low threshold voltage, low subthreshold slope, low leakage current, and high ON-/ OFF-current ratio. CF₄-plasma MILC TFTs also possess high immunity against the hot-carrier stress and thereby exhibit better reliability than that of conventional MILC TFTs. Moreover, the manufacturing processes are simple (without any additional thermal annealing step) and compatible with MILC TFT processes.

I. Introduction

Metal-Induced Lateral Crystallization (MILC) thin-film transistors (TFTs) exhibit good electrical properties and can be used in systems on panel. In MILC, Ni islands are selectively deposited on top of an amorphous silicon (-Si) film and allowed to crystallize at a temperature below 600 °C [1], [2]. Unfortunately, poly-Si/oxide interfaces and poly-Si grain boundaries trap Ni and precipitates, thus increasing leakage current and shifting the threshold voltage [3]–[7]. This problem can be solved using a Ni-gettering method [8]. However, the crystal quality of Ni-gettering poly-Si films was poorer than that of conventional MILC poly-Si films.