Multilayer optical coating fabrication by dc magnetron reactive sputtering

A conventional box coating chamber has been equipped with three dc magnetron sputtering cathodes, reactive gas (O2, N2, H2) pressure and flow control, planetary substrate holder, and optical monitoring to produce a low-temperature batch coating system for multilayer optical coating fabrication using oxides, nitrides, semiconductors and semitransparent metals. The system realizes the benefits traditionally derived from this geometry: maximum area of uniform coating thickness, spatially-averaged coating flux impingement angles, and precise thickness monitoring. The use of sputtering cathodes adds the benefits of increased flexibility in choice of materials deposited, increased adatom energy at the substrate, and increased chemical reactivity in a gas discharge. Dense, durable, fully-reacted dielectric coatings are achieved at low processing temperatures. Metal targets (sources) are used for ease of fabrication, and dc power avoids radio-frequency impedance matching requirements. The chamber and components are described and operation of the cathodes explained. Thickness uniformity profiles, deposition rates, and substrate temperature data are related. A list of materials investigated to date is presented with pertinent optical properties and intrinsic mechanical stress values. Illustrative performance examples for multilayer coatings on glasses and plastics are included