High rate deposition of mixed oxides by controlled reactive magnetron-sputtering from metallic targets

Mixed optical materials open new possibilities for the design and optimization of thin film properties. For example the refractive index may be tuned between the refractive indices of the pure materials. Low film stress of mixed optical materials can lead to high mechanical and optical capability. Therefore such materials are of great interest for optical applications, especially if the dielectric properties can be tailored during film deposition. A reactive pulsed magnetron deposition using two different pure metallic targets is proposed to alleviate the unfavorable performance of existing mixed optical film deposition methods. Co-sputtering of different materials in such a dual magnetron setup leads to separate hysteresis for each target. Each target is individually controlled using an optical emission spectroscopy system with separated optical fibers integrated in a closed-loop control. Embedded proportional-integral controllers modify a digital pulse pattern used for pulsed discharge power control to stabilize the emission intensity at the set point for pre-selected wavelengths. In this way the composition of the resulting films can be adjusted while the process is controlled in the high-rate transition mode. It was shown that the proposed deposition method is capable to provide continuous tuning of the refractive index of the mixed optical materials throughout the whole range defined by the single-material films. After discussing the process control system, deposition results of hafnium-aluminum-oxide and zirconium-aluminum-oxide films prepared with this technique are presented. Optical and mechanical film properties of the mixtures are compared to the properties of single homogeneous films. (C) 2011 Elsevier B.V. All rights reserved.