Smart gas dosage by a peristaltic pump for reactive RF sputtering of composition spread combinatorial hafnium-oxy-nitride layers

Thin metal-oxy-nitride layers are widely used for wavelength selective optical coatings. We aimed to prepare composition spread metal-oxy-nitride combinatorial layers by reactive radiofrequency sputtering for a highly efficient characterization of their optical properties in a wide range of O/N ratios. Affinity of metals requires oxygen proportion, in the Ar-O-N plasma, be set orders of magnitude lower compared to nitrogen. The required low partial pressure range of oxygen was covered by a new concept self-regulating gas inlet assembly based on a peristaltic pump delivering gas from a finite volume vial. Accordingly, oxygen partial pressure was gradually decreasing from 8 x 10(-5) mbar towards the base pressure of the chamber. It effected a continuous oxygen depletion and a transition of the deposited film from oxide to nitride. The suitability of our combinatorial method was proved by both energy dispersive spectrometry mapping and ellipsometry of the correlated refractive indices along a composition-spread HfON sample.