Compositional and structural studies of amorphous silicon-nitrogen alloys deposited at room temperature using a sputtering-type electron cyclotron resonance microwave plasma

High-quality amorphous silicon-nitrogen alloys (a-SiN_x) have been deposited at room temperature by a sputtering-type electron cyclotron resonance (ECR) plasma. A detailed analysis of the properties of a-SiN_x films in terms of their composition, microstructure and dielectric characteristics was performed using X-ray photoelectron spectroscopy, infrared (IR) spectroscopy and ramp current-voltage measurement techniques. Their characteristics were correlated with the N₂ gas flow rate (NGFR) in the ECR plasma formation. The dependence of solid-state [N]/[Si] ratios in the films on the NGFR indicated that the film composition changed from non-stoichiometry to stoichiometry as the NGFR increased from 0.5 to 1 seem. The dependence of the IR spectra on the NGFR indicated that silicon nitride network was well ordered for an NGFR of 1 seem, in which the dielectric breakdown-field was over 4 MVcm⁻¹. However, when the NGFR was over 1 seem, significant N≡N triple bonds (gaseous N₂ molecule) were formed and were trapped inside the films. These N₂ molecules formed many voids and defects; and enhanced disorder in the network. This is well correlated by chemical etch and IR results. The dependence of dielectric properties of a-SiN_x films on the NGFR demonstrated that these voids and defects lead to a decrease in average dielectric breakdown field and an obvious increase in the distribution of the low breakdown field.