Influence of deposition pressure on the output characteristics of low pressure chemical vapor deposited polycrystalline silicon thin-film transistors

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Abstract
The influence of the deposition pressure on the output characteristics of low pressure chemical vapor deposited polycrystalline silicon thin-film transistors is investigated. The polysilicon films are deposited at pressures 40, 10, and 0.5 mTorr. For channel lengths L greater than 10 μm, the device has the conventional output characteristics dominated by the grain boundaries. In short-channel devices (L<10 μm), the experimental results show the presence of the ‘‘kink’’ effect and a reduction of the threshold voltage at high drain biases. When the deposition pressure of the polysilicon layer decreases, despite the increase of the grain size, the kink effect becomes more pronounced due to the enhanced diffusion of dopants from the source and drain contacts along the grain boundaries. The enhanced dopant diffusion reduces the effective channel length resulting in higher channel electric fields and increased kink effect.