Properties of plasma-enhanced chemical-vapor-deposited a-SiNx:H by various dilution gases

Abstract

The effects of dilution gases on hydrogenated amorphous silicon nitride (a‐SiN_x:H) films were investigated. Silane and ammonia were used as the reactive species, while nitrogen, helium, hydrogen, and argon were used as the dilution gases in a plasma‐enhanced chemical vapor‐deposition system at a substrate temperature of 300 °C. The electrical, physical, and chemical properties of the a‐SiN_x:H films were found to be highly sensitive to the various kinds and flow rates of the carrier gases in the deposition. Additionally, the physical properties of growth rate, refractive index, and etching rate were also investigated. The hydrogen bonding configuration was explored by infrared spectroscopy. The total hydrogen concentrations for all a‐SiN_x:H films were observed to be smaller than 3.0×10²² cm⁻³. The electrical properties were characterized by I‐V and C‐V measurements in metal‐insulator‐semiconductor structures. The breakdown strength was determined at the current density of 3 mA/cm²; in addition, the dominant mode of electronic conduction would appear to be the Poole–Frenkel emission. The interface trap state density D_it which ranged from 3.4×10¹¹ to 1.3×10¹² cm⁻² eV⁻¹ was evaluated by the C‐V characteristics. Finally, the influences of the gas dilution in the a‐SiN_x:H films, as applied to the devices, were investigated by using the hydrogenated amorphous silicon thin‐film transistors (a‐Si:H TFTs). Analyses of the transfer characteristics of the TFT devices revealed that the density of deep gap states is 4×10¹² cm⁻² eV⁻¹ and the field‐effect mobility μ_FE is changing from 0.37 to 1.45 cm²/V s.