Würzburg / 06/11/2018 - 06/15/2018
International Conference on Coatings on Glass and Plastics ICCG12
The Fraunhofer IST participates with one contribution in the 12th International Conference on Coatings on Glass and Plastics ICCG. The conference offers experts from science and industry an important platform to exchange views on future trends, new technologies and current developments and applications in the field of coating on glass and plastics.
In his lecture on ”Anti-reflective coatings deposited by HWCVD process on glass and plastics” Dr. Volker Sittinger, head of the department ”Chemical Vapour Deposition” at the Fraunhofer IST, gives a lecture about the hot-wire CVD process as a method for antireflection coatings on large glass and plastic surfaces.
”Anti-reflective coatings deposited by HWCVD process on glass and plastics”
Volker Sittinger, Markus Höfer, Tino Harig, Madeleine Justianto, Hendrik Thiem
Using a large scale HWCVD in-line deposition system with maximum deposition areas of 500 x 600 mm2 SiOx films and SiNx were deposited from gas mixtures of SiH4 and O2 as well as SiH4 and NH3 respectively. At first the SiO2 and Si3N4 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 percent in order to vary the stoichiometry of the deposited films. 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.
Optical transmission was measured on quartz glass substrates and polycarbonate. Further characterizations of the film properties were done by spectroscopic ellipsometry, SEM, AFM, X-ray microanalysis, grazing incidence X-ray reflectometry, measurement of film stresses, etc.
Starting at oxygen fractions O2/SiH4 < 100 % increase of oxygen gas flow at first leads to an increase of transparency. After passing through maxima at O2/SiH4 ratios of about 110 - 140 % further increase of oxygen gas flow leads to a decrease of transparency due to incorporation of partly vaporized tungsten wires. Location of the optima and properties of the most transparent films were investigated in detail as a function of the deposition parameters by using design of experiments. After optimization of the process parameters highly transparent stoichiometric SiO2 films with residual compressive stresses of about ‑150 MPa were deposited.
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.