Optical thin films of silica and titania deposited by plasma polymerisation process: System design and fabrication

Abstract

Plasma polymerization provides a very versatile and cost-effective technique for the deposition of a wide variety of dielectric films, in particular optical thin films of silica (silicon dioxide) and titania (titanium dioxide) that are widely used as low and high index films in optical multilayer coatings for a variety of applications. The deposition of these films is often carried out using toxic and corrosive precursors–silane gas for silica and titanium tetrachloride liquid for titania – that are expensive and difficult to handle. The use of non-toxic organic liquid precursors, that are cheaper and safer and easier to handle, has been reported for the deposition of these films. In order to develop indigenous expertise in such deposition processes, a plasma polymerization deposition system that uses non-toxic and safe organic liquid precursors for the deposition of optical quality silica and titania films has been designed and fabricated in-house and successfully made operational. The problems that arise in this deposition process, the methods adopted to overcome them, the precautions that must be taken, have been studied in detail. Optical quality silica and titania films with satisfactory refractive indices and extinction coefficients have been deposited using this home-made deposition system.