Reactive dual magnetron sputtering of Ta2O5 and Al2O3: optical and structural properties and thin film applications

In this paper we perform a systematic investigation and optimization of lambda controlled, reactive ion beam sputter deposition process conditions for a range of optical materials. The deposited films are compared for suitability for applications such as planar waveguides for optical interconnect, laser device manufacture, multi-layer interference filters, and precision optical mirrors. Thin films of tantalum pentoxide and aluminum oxide were deposited using a reactive dual-magnetron sputtering system (Leybold Optics Helios Pro). Deposited film quality was optimized as a function of plasma power and gas flow, and an optimum oxygen working point was determined for each material. Lambda control methods were used for the purpose of optimizing optical quality of the layer. Deposited layers were characterized by variable angle spectroscopic ellipsometry (VASE), X-ray diffraction (XRD) and SEM imaging. Waveguide losses were measured for each sample using a prism coupling arrangement. Tantalum pentoxide slab waveguides with loss as low as 1dB/cm were produced ideal for waveguide applications. Interference filters/mirrors consisting of alternating SiO2, and Ta2O5 or Al2O3 material layers were deposited and characterized. Reflectivity and transmission of the deposited mirrors was compared to the theoretical design. Good agreement between the theory and the practical filter/mirror designs was achieved confirming the material film quality.