Improvement on performance and reliability of TaN/HfO2 LTPS-TFTs with fluorine implantation

Abstract

In this paper, we demonstrate the low-temperature polycrystalline silicon thin-film transistors (LTPS-TFTs) with TaN metal-gate and HfO2 gate dielectric to achieve high performance characteristics. A high performance LTPS-TFT with low threshold voltage 0.9 V, excellent subthreshold swing 0.15 V/decade and high I-on/I-min current ratio 1.9 x 10(6) are derived without any hydrogen treatment. In addition, we also introduce the fluorine implantation prior to the Si thin-film crystallization to passivate the defects in grain-boundaries of the channel film and HfO2/polysilicon interface. Significant improvements on subthreshold swing and I-min are observed. In addition, the transconductance degradation and threshold voltage instability due to hot carrier stress is also investigated, respectively. Finally, we derive a high reliability and performance LTPS-TFT with low threshold voltage similar to 1.38 V, ultra-low subthreshold swing 0.132 V/decade and high I-on/I-min current ratio 1.21 x 10(7), which is suitable for the application of system-on panel (SOP). (c) 2007 Elsevier Ltd. All rights reserved.