Minimization of dangling bond defects in hydrogenated silicon nitride dielectrics for thin film transistors (TFTs)

Plasma deposited hydrogenated amorphous silicon nitride alloys are the preferred gate dielectric for amorphous silicon thin film transistors (TFTs). This paper identifies for the first time a correlation between the relative concentrations of silicon, [Si], nitrogen, [N] and hydrogen, [H], in these alloys, and optimization of TFT performance. The TFT electron channel mobility, mu(e), has been shown to be a function of the NH(3) to SiH(4) source gas ratios which determine [Si], [N] and [H] in plasma deposited dielectrics. Optimized performance with mu(e) similar to 1.5 cm(2) V(-1) s, has been demonstrated for remote plasma deposited nitrides with [Si] similar to 0.28, [N] similar to 0.42 and [H] similar to 0.3. This alloy composition has approximately the same average number of (i) bonds per atom, [N], and (ii) bonding constraints per atom, [C], as thin film SiO(2), and also forms a continuous random network with a low density of defect states accounting for optimized TFT performance. (C) 1998 Elsevier Science B.V. All rights reserved.