Periodic density fluctuations in sputtered aluminum-doped silicon oxynitride layers

Official URL: http://dx.doi.org/10.1111/ijag.13616

Magnetron sputtering of silicon oxynitride (SiOxNy) coatings on glass is widely used for large-area applications. Because repeated deposition simulates factory-scale in-line processing, around 250 nm-thick amorphous aluminum doped SiOxNy layers were deposited by reactive pulsed DC sputtering in a multi-pass process with repeated linear movement of a glass substrate under an Al-alloyed Si target. Using specular X-ray reflectivity, we show periodic fluctuations in material density through the entire thickness of the resulting coating. The number of periods corresponds to the number of passes of the substrate through the plasma formed inside the magnetron. Fitting results suggest a model consistent with a periodic alternation in O/N ratio. These subtle stoichiometric fluctuations in SiOxNy layer composition were confirmed with nanoscale resolution by scanning transmission electron microscopy analysis, with detailed elemental maps of characteristic X-rays of the layered cross-section. Our study demonstrates the superior sensitivity of the relatively simple, nondestructive X-ray reflectivity method for industrial line-process inspection, compared to ellipsometry.