Dielectric properties of RF-sputtered silicon nitride thin films with gold electrodes

Earlier DC conduction measurements on RF-sputtered silicon nitride thin films have been extended to include the AC conductivity and dielectric properties. Sandwich structure films were sputtered from a silicon nitride target at a power of 100 W The AC conductivity sigma, was observed to follow an expression sigma=Aomega(s), where A is a constant, omega is the angular frequency and s is an index. The values of s were found to lie in the range 0.83-1.31, showing a systematic increase with increasing frequency in the range 100 Hz-20 kHz and a decrease with increasing temperature in the range 173-373 K. This type of behaviour was associated with a carrier hopping process, having a value of the density of localised states Nsimilar to10(24) m(-3). Carrier activation energies were in the range 0.006-0.1 eV and increased with increasing temperature, further indicating the presence of hopping rather than free-band conductivity. The capacitance followed a geometric relationship, with relative permittivity approximately 6.8, and showed a moderate decrease with increasing frequency and an increase with increasing temperature, tending towards a constant value at higher frequencies and lower temperatures. Measurements of loss tangent as functions of frequency and temperature showed evidence of a minimum value, which appeared to shift to higher frequencies with increasing temperature. Such measurements were in accordance with an existing model of dielectric behaviour in sandwich samples. (C) 2003 Elsevier Science B.V. All rights reserved.