Super Smooth Metal Oxide Thin Films Using Closed Field Reactive Magnetron Sputtering

摘要

Magnetron sputtering has many advantages over conventional evaporation processes for the deposition of dielectric and electrically conducting thin films of metal oxides used in optical coatings. The sputtering process is "cold", making it suitable for use on the widest range of substrates, including polymers. The drum (or in-line) formats provide more efficient loading for high throughput production. The process is also easier to control and easier to maintain. In contrast to previous reactive dc sputtering strategies, the closed field process does not require a separate ion or plasma source for activation. Neither does it require the vacuum chamber to be separated by vacuum pumps or baffles into deposition and reaction zones. Oxidation occurs on the target and all the way round the substrate carrier, resulting in ultra low optical absorption. The use of the closed field and unbalanced magnetrons creates a magnetic confinement that extends the electron mean free path leading to high ion current densities. The combination of high current densities with ion energies in the range ～30eV creates optimum thin film growth conditions. As a result, the films are dense and spectrally stable. We have now discovered that the films are also exceptionally smooth as measured using non-contacting coherence correlation interferometry (CCI) and field emission SEM. Examples of the surface properties, optical properties and morphology of single layer electrically insulating (SiO_2, and Nb_2O_5) and conducting metal oxides (ITO) will be presented. Film smoothness is important in optical coatings to remove scatter, it is also important in display applications to minimize electrical noise.