Temperature-Dependent Crystallinity and Growth Transition in Al/Zr Multilayer Thin Films Fabricated by Pulsed Laser Deposition

Al/Zr multilayer thin films were fabricated using pulsed laser deposition (PLD) with a 248 nm KrF excimer laser to study their structural and surface characteristics for potential use in extreme ultraviolet (EUV) optical and protective coatings. Alternating layers of aluminum and zirconium were deposited on silicon substrates under high vacuum conditions, with nanometer-scale thickness control verified by spectroscopic ellipsometry. X-ray diffraction analysis showed improved crystallinity at 400 °C, highlighted by a dominant Zr(002) orientation. Surface examinations by SEM and AFM indicated a transition from smooth, two-dimensional (2D) growth to a rough, three-dimensional (3D) morphology at 500 °C, likely due to increased adatom mobility and interfacial strain. SEM images of Al films deposited at 400 °C revealed a uniform nanocrystalline surface with compact grains and minimal porosity, characteristic of stable 2D growth. Computational modeling based on free-energy minimization further confirmed the 2D–3D transition, predicting a critical film thickness of around 1–2 nm, which aligns with experimental findings. Overall, this study highlights the effectiveness of PLD in producing high-quality Al/Zr multilayers suitable for EUV mirror and advanced coating applications.