Reaction processes for low temperature (<150°C) plasma enhanced deposition of hydrogenated amorphous silicon thin film transistors on transparent plastic substrates

This article presents mechanisms for low temperature (<150 degrees C) rf plasma enhanced chemical vapor deposition of silicon and silicon nitride thin films that lead to sufficient electronic quality for thin film transistor (TFT) fabrication and operation. For silicon deposition, hydrogen abstraction and etching, and silicon disproportionation reactions are identified that can lead to optimized hydrogen concentration and bonding environments at <150 degrees C. Nitrogen dilution of SiH4/NH3 mixtures during silicon nitride deposition at low temperatures helps promote N-H bonding, leading to reduced charge trapping. Good quality amorphous silicon TFT's fabricated with a maximum processing temperature of 110 degrees C are demonstrated on flexible transparent plastic substrates. Transistors formed with the same process on glass and plastic show linear mobilities of 0.33 and 0.12 cm(2)/Vs, respectively with I-ON/I-OFF ratios > 10(6).