Optical Characteristics of Amorphous Silicon Nitride Thin Films Prepared by Electron Cyclotron Resonance Plasma Chemical Vapor Deposition

Amorphous silicon nitride thin films were prepared by electron cyclotron resonance (ECR) plasma chemical vapor deposition (CVD) at low substrate temperatures of 65–400°C, and their optical attenuation, refractive index and optical band gap were examined. The typical attenuation is as low as 0.1–0.3 dB/cm in the 0.63–1.35 µm wavelength range, but the attenuation becomes much higher in the 1.4–1.6 µm range with a peak value of 7.5 dB/cm at 1.52 µm. The attenuation values and the refractive index largely depend on the amount of hydrogen included in the films, although this does not affect the optical band gap. The peak attenuation decreases to about 0.6 dB/cm after annealing. It is thought that the peak is due to the second overtone absorption of the N–H stretching vibration.