Composite coating materials for the moulding of diffractive and refractive optical components of inorganic glasses

The application of glass moulding processes to the fabrication of microoptical components is up to now limited by the problem of sticking between the aggressive glass melts and the moulding tools. In order to prevent this problem, the moulding tools must be coated with anti-sticking, high temperature and oxidation resistant coatings. In the present investigation TiAlN/ZrN composite coatings with superlattice structures were deposited onto fused silica and silicon substrates by r.f.-magnetron sputtering. The influence of deposition parameters and of the superlattice period on residual film stress, oxidation behaviour and the behaviour in contact with hot inorganic glasses was investigated. Fused silica and silicon tool-substrates having optically functional structures generated by lithographic techniques were coated and deployed in moulding experiments performed at temperatures of 600 °C and higher. From the experimental investigations it was found that the oxidation resistance and also the behaviour in contact with hot melts of inorganic glasses were dependent on the superlattice period Λ. It could be observed in thermogravimetric analyses, which have been performed in pure oxygen atmosphere, that for a special superlattice period Λopt no oxidation takes place up to 700 °C. Such coatings could be applied in moulding experiments without reduction of the tools performance by sticking or corrosion in contact with the glass melts. Examples for first applications of the coatings in the moulding of components like micro lens arrays and phase grids from high quality optical glasses are presented.