Performance and reliability improvements in poly-Si TFT's by fluorine implantation into gate poly-Si

High-performance and high-reliability TFT's have been obtained using a fluorine ion implantation technique. The fluorine implantation into the gate poly-Si of TFT caused a positive Vth shift, increased the ON current, and decreased the leakage current significantly. Our investigation indicates that the Vth shift originates from negative charges generated in the gate oxide by the fluorine implantation. The improvement of drain current is attributed to fluorine passivation of trap states in the poly-Si and to a modulation of offset potential due to the same negative charges under the offset region. Furthermore, high immunity against the -BT stress and TDDB of the gate oxide was achieved by the fluorine implantation. It is considered that the strong Si-F bonds created by the fluorine implantation raise the stress immunity. >