Polysilicon transistors fabricated on plasma-deposited amorphous silicon

P-channel MOS transistors were fabricated on plasma-enhanced chemical-vapor deposited (PECVD) amorphous silicon films. The films were deposited at temperatures of 425, 450, and 475 degrees C and crystallized at 600 degrees C. Film thicknesses were between 50 and 250 nm. Transistors were also fabricated on 150-nm-thick low-pressure chemical-vapor-deposited (LPCVD) amorphous silicon films deposited at 560 degrees C. A comparison of device characteristics using 150-nm-thick PECVD and LPCVD films shows that the PECVD films deposited at 425 degrees C produced devices with a factor-of-two-higher hole mobility, a factor-of-1.5-lower subthreshold slope, and a factor-of-3.5-higher on-off current ratio. For all film thicknesses tested there was an increase in the hole mobility and on-off current ratio as the PECVD film temperature was decreased.<
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