Anti-reflective coatings deposited by HWCVD process on glass and plastics

Using a large scale HWCVD in-line deposition system with maximum deposition areas of 500 x 600 mm² SiOx and SiNx films were deposited from gas mixtures of SiH4 and O2 as well as SiH4 and NH3 respectively. At first the SiO2 and Si3N4 films were optimized on glass substrates. The SiOx-films were deposited at pressures between 0.5 and 5 Pa at substrate temperatures from 100 up to 400 °C. Keeping the silane gas flow at constant levels between 50 and 150 sccm the ratio of oxygen gas flow to silane was varied from 0 to about 170% in order to vary the stoichiometry of the deposited films. The SiNx-films were deposited at pressures between 0.5 and 10 Pa at substrate temperatures from 140 up to 600 °C. The total gas flow was varied between 100 and 600 sccm. The ratio of ammonia gas flow to silane was varied in order to reach the optimum stoichiometry of the Si3N4. The activation of the gas atmosphere was achieved via tungsten wires with diameters of 0.25 and 0.53 mm at temperatures from 1900 up to 2100 °C for SiOx and 2100 up to 2400 °C for SiNx. EPMA measurements were done for optimization of stoichiometry. Further on optical transmission and reflection was measured on silica glass substrates. Further characterizations of the film properties were done by spectroscopic ellipsometry, AFM with nano indentation for determination of hardness and measurement of film stresses. After optimization of the process parameters, highly transparent stoichiometric SiO2 and Si3N4 films with residual low compressive stresses were deposited. With this development antireflective coatings based on Si3N4-SiO2 layer on 10 x 10 cm² were deposited on glass and polycarbonate to show the potential for optical applications.