Pulsed laser deposition of aluminum and zirconium for extreme UV optical coatings applications.*

We used pulsed laser deposition technique with 248 nm KrF excimer to deposit Al/Zr multilayer thin films, analyze their structure and surface morphology for extreme-ultraviolet (EUV) optical and protective coating applications. Al and Zr layers were deposited on Si substrates in high vacuum, with nanoscale thickness control verified using spectroscopic ellipsometry. X-ray diffraction revealed that substrate heating to 400 °C enhanced crystallinity with strong Zr(100) texture. SEM and AFM were used to study the change in the surface morphology with temperature. To further interpret the experimental findings, computational modeling was employed to analyze the transition from 2D layer-by-layer growth to 3D island formation at elevated temperatures. Using a multi-parameter model based on free energy minimization, the critical film thickness for this transition was determined to be ~1–2 nm, aligning well with experimental observations. These results demonstrate that PLD can be routinely used to produce high-quality Al/Zr multilayers for EUV mirror systems and advanced optical coatings.