CF4-plasma-induced fluorine passivation effects on poly-Si TFTs with high-kappa Pr2O3 gate dielectric

Abstract

High-performance polycrystalline silicon thin-film transistors (poly-Si TFTs) integrating high-kappa Pr2O3 gate dielectric and fluorine-passivated poly-Si film are demonstrated. High gate capacitance density and thin equivalent-oxide thickness provided by the high-kappa Pr2O3 gate dielectric have the advantage of increasing the driving current capability of the TFT device, but an undesirable off-state leakage current could be introduced from the high electric field near the drain side. Introducing fluorine atoms into poly-Si films by employing a low-temperature CF4 plasma treatment can effectively passivate the trap states. With 10 W CF4 plasma treatment on poly-Si film, the electrical characteristics of poly-Si Pr2O3 TFTs can be significantly improved, including a steeper subthreshold swing, smaller threshold voltage, higher field-effect mobility, and better on/off current ratio compared with that without CF4 plasma treatment. The maximum off-state leakage current of the fluorine-passivated TFT is more than one order of magnitude lower than that of the control TFT. Furthermore, the incorporation of fluorine atoms by CF4 plasma treatment also improves the reliability of poly-Si Pr2O3 TFTs against hot carrier stressing, which is due to the formation of stronger Si-F bonds in place of weak Si-H bonds in the poly-Si channel and at the Pr2O3 gate dielectric/poly-Si interface. Therefore, high-performance and high-reliability poly-Si TFTs with Pr2O3 gate dielectric and CF4 plasma treatment on poly-Si film are suitable for active-matrix liquid crystal display application. (c) 2007 The Electrochemical Society.