Antireflective trilayer films fabricated using a filtered cathodic vacuum arc

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.