Effect of NH3 plasma treatment of gate nitride on the performance of amorphous silicon thin-film transistors

Abstract

The effect of NH3 plasma treatment of the hydrogenated amorphous silicon nitride (a-SiNx:H) gate insulator on the performance of hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) has been studied for different deposition conditions of the gate nitride. The TFT subthreshold slope and threshold voltage decrease with increasing rf power of gate nitride deposition. When increasing the rf power from 25 to 100 W, an increase in field-effect mobility, from 0.29 to 0.37 cm2/V s, is obtained. The NH3 plasma treatment causes a general increase in subthreshold slope and threshold voltage. It also degrades the field-effect mobility as large as 40%. However, the desirable effect of the plasma treatment is that the resulting devices have a higher stability exhibited by a 25% reduction of hysteresis width of transfer characteristics and by their higher resistance to prolonged positive gate field application. Based only on the electrical measurements, an exact model of the plasma interaction with the a-SiNx:H could not be developed. However, it is postulated that both radiation damage and nitridation/amination can occur.