The microstructure and optical properties of alumina and titania multilayer coatings prepared using atomic layer deposition (ALD) has been investigated. The titania layers were prepared using TiCl4+H2O as the precursors while two different precursors, Al(CH3)3+H2O and AlCl3+H2O, were used to deposit the alumina layers. The results show that ALD can be used to produce amorphous, stoichiometric alumina and titania thin films with uniform thicknesses at low temperatures (120 °C). An antireflective coating design based on 4 alternating layers of titania and alumina was prepared and the resulting reflectance compared to theoretical calculations. The results demonstrate that ALD is a suitable technique for the deposition of optical thin films at temperatures compatible with thermally sensitive substrates.
A Filtered Cathodic Vacuum Arc (FCVA) thin film deposition system has been used to create Al2O3/Al/Al2O3 trilayer
antireflection coatings on silicon. X-ray photoelectron spectroscopy was used to verify the stoichiometry of the
deposited alumina. The optical properties of the deposited Al2O3 and Al have been examined using variable angle
spectroscopic ellipsometry. The complex refractive index functions of the antireflection coating components were
determined. Optical thin film software was used to optimise the required thicknesses of each of the layers in order to
achieve minimum perpendicular reflection on silicon across the optical spectrum. The simulations showed that the
thickness of the Al layer was critical and the required layer thickness was less than 10 nm. Antireflection coatings with
various Al layer thicknesses were deposited and characterised. The microstructure of the coatings was examined, in
detail, using cross sectional transmission electron microscopy. Reflectance measurements on the deposited coatings
were also performed, with the optimised antireflection coating (with an Al layer thickness of 6 nm) achieving an average
reflectance of 4% on silicon over the optical spectrum. The FCVA deposited trilayers are mechanically robust, easy to
fabricate and exhibit high performance.