Controlling the plasmonic properties of titanium nitride thin films by radiofrequency substrate biasing in magnetron sputtering

Titanium nitride (TiN) is a promising plasmonic material alternative to gold and silver thanks to its refractory character, low resistivity (<100 μΩ cm) and compatibility with microelectronic industry processes. Extensive research is currently focusing on the development of magnetron sputtering as a large-scale technique to produce TiN thin films with low resistivity and optimized plasmonic performance. As such, more knowledge on the correlation between process parameters and the functional properties of TiN is needed. Here we report the effect of radiofrequency (RF) substrate biasing during the sputtering process on the structural, optical and electrical properties of TiN films. We employ spectroscopic ellipsometry as a sensible characterization method and we show that a moderate RF power, despite reducing the grain size, allows to achieve optimal plasmonic quality factors and a low resistivity (<100 μΩ cm). This is attributed to the introduction of a slight under-stoichiometry in the material (i.e., TiN0.85), as opposite to the films synthesized without bias or under intense bombardment conditions. RF substrate biasing during magnetron sputtering appears thus as a viable tool to prepare TiN thin films at room temperature with desired plasmonic properties.