Confocal sputtering of (111) orientated smooth gold films for surface plasmon resonance approaches

We report on the influence of sputtering parameters on the microstructural growth of 200 nm thick Au layers and, moreover, on their crystalline, electrical, and optical properties using a confocal sputtering arrangement. The confocal sputtering arrangement allows the production of highly homogeneous layer thicknesses that depend on pressure, power, and target-substrate distance. Layers deposited at low Ar pressure show extremely smooth and densely-packed films, as well as a preferred {111}-texture contrary to films deposited at higher Ar pressure. Furthermore, an increase in electrical resistivity combined with a decrease in grain size is observed for these layers. A subsequent annealing process up to a temperature of 600 °C reduces the resistivity, increases the grain size, improves the fraction of {111}-texture, and significantly changes the surface morphology for all initial states. Investigations at 4.2 K showed that the decrease in resistivity is caused by a structural change that takes the number of grain boundaries into consideration. The dielectric function investigated by ellipsometric measurements is dependent on the deposition process parameters, especially on Ar pressure. Surface plasmon resonance calculations based on the layers produced using the Otto configuration show the best performance using a specific setup for layers deposited at low Ar pressure.