Improvement in Characteristics of Thin Film Transistors upon High-Pressure Steam Annealing

概要

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Low-temperature (350 °C) and high-pressure (1 MPa) steam annealing is effective for improving the characteristics of low-temperature-processed polycrystalline silicon thin film transistors (LTPS-TFTs) and their uniformity. We developed high-pressure annealing systems for $600\times 720$ and $400\times 500$ mm2 glass substrates, and investigated the annealing effects on the electrical properties of n-channel TFTs. The TFTs fabricated without high-pressure annealing have a low saturation mobility caused by the large amount of fixed oxide charge in SiO2, and a high threshold voltage ($V_{\text{th}}$) caused by the high trap density at the SiO2/Si interface. High-pressure steam annealing effectively reduces the amount of fixed oxide charge and the number of interface traps, resulting in the improvement of TFT properties. The crystal orientation of poly-Si strongly affects the interface trap density, which causes the nonuniformity of the TFT characteristics. High-pressure annealing also decreases the deviation of the trap density caused by the crystal orientation, and uniform electrical properties are achieved.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2007-11-15