Development and characterization of a secondary RF plasma-assisted closed-field dual magnetron sputtering system for optical coatings on large-area substrates

Abstract

An RF-assisted closed-field dual magnetron sputtering system was developed to characterize the plasma and the ionization fraction of sputtered material to provide a suitable system for depositing optical thin films on large-area substrates at low temperatures (<130 °C). The ‘prototype’ system consists of dual 76 mm dc magnetrons operated at both balanced and unbalanced (closed-field) configurations with an RF coil to initiate a secondary plasma. The RF plasma assistance enhanced the electron density to one order of magnitude higher, increased the deposition rate and effectively enhanced the ionization fraction of the sputtered flux to above 80% as measured from the quartz crystal microbalance combined with electrostatic filters. Based on the prototype system, a large-scale RF-assisted system using two 9 × 46 cm linear magnetron cathodes was also developed and evaluated. Both systems were also tested for reactive deposition of indium tin oxide on both small-scale and large-area polyethylene terephthalate substrates with the actual substrate surface temperature monitored to be <130 °C. From both the evaluation results of the plasma characterization and deposition performance, the prototype and the large linear magnetron system were found to be suitable for reactive thin film deposition of compound targets that can be extended to various types of optical coatings.