Periodic density fluctuations in sputtered aluminum‐doped silicon oxynitride layers

Magnetron sputtering is widely used for deposition of silicon oxynitride (SiOxNy) coatings on glass in large‐area applications. Since repeated deposition simulates the factory‐scale in‐line processing, amorphous aluminum‐doped SiOxNy layers with thickness of about 250 nm 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 of the material density throughout the entire thickness of the resulting coating. The number of periods corresponds to the number of passes of the substrate through the plasma of the magnetron. Fitting results suggest a model consistent with a periodic alternation of the O/N ratio. These subtle stoichiometric fluctuations in the SiOxNy layer composition were confirmed by scanning transmission electron microscopy analysis with nanoscale resolution, and 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.