OPTICAL CHARACTERIZATION OF SILICON-NITRIDE FILMS DEPOSITED BY ECR-CVD

Optical properties (refractive index and band gap) and atomic bonding structure of silicon nitride films deposited at room temperature by the ECR-CVD method are analysed as a function of two main production parameters: microwave power (50-200W) and N-2/SiH4 ratio (1.6-9). Transmission and reflection measurements in the UV-VIS-NIR region show that optical properties of the films are strongly dependent on the deposition conditions: refractive index values from 2.8 to 1.7 and band gap values in the 2.1-5.3 eV range are obtained depending on deposition conditions. The FTIR spectra analysis show that silicon-rich films are obtained at low microwave powers and low N-2/SiH4 ratios, whereas films with oxygen contamination are deposited at high powers for every flow ratios. Close to stoichiometric silicon nitride films are obtained at 100 W with N-2/SiH4 ratios higher than 5.