Investigating Optical Properties of SiON Thin Film Produced by Plasma Enhanced Chemical Vapor Deposition Method

The optical properties of silicon oxynitride thin films (SiON) have been investigated. SiON films were grown on glass and silicon substrates by plasma enhanced chemical vapor deposition. A radio frequency power source with a capacitor coupler is used to produce plasma. Moreover, tetraethyl-orthosilicate (TEOS), oxygen, and nitrogen have been used as silicon source, oxidizing gas, and nitrogen source, respectively. Growth mechanism and the variation of the refractive index as well as the variation of the optical absorption of the films have been studied. From the results, it can be understood that the atomic and ionic active nitrogen species produced in the plasma volume act similar to oxygen species in the oxidation mechanism and cause the decomposition of TEOS molecules. Therefore, the increase of nitrogen flux in the plasma gas mixture results in the reduction of organic impurities caused by TEOS monomers. The roughness of the films was measured below 0.2 nm. The results also showed that by adding nitrogen gas in the plasma gas mixture, it is possible to increase the refractive index of the silicon oxide films without significant change in their transparency. Finally, with the increase of nitrogen flux from 0 to 80 sccm, the refractive index of the films increased from 1.446 to 1.464, while the optical absorption was measured to be less than 1 in all cases.