A SELF-ALIGNED, TRILAYER, A-SIH THIN-FILM TRANSISTOR PREPARED FROM 2 PHOTOMASKS

A new self-aligned TFT structure that requires two photomasks is described in this paper. Three process steps, i.e., the backlight lithography, the top dielectric etch, and the n+ etch, have been studied in detail. The finished TFT has transfer characteristics and I(d) - V(d) curves similar to those of a TFT prepared from a more complicated conventional process. TFT structure parameters, such as the channel length, the a-Si:H thickness, the source/drain via size, and the contact resistance, affect the field effect mobility and the I(on)/I(off) ratio. These relations were examined. Including a Ta2O5 thin layer in the gate dielectric structure changes the device characteristics. The relation between the Ta2O5 process and the device has been studied.