Tailoring the Composition of B ₄ C Layer by H ₂ /Ar Sputtering for High‐Reflectance La/B ₄ C‐Base

High‐reflectance multilayer mirrors represent key components for next‐generation lithography applications. In this work, La/LaN/B ₄ C multilayers were deposited with different flow ratios of H ₂ /Ar mixed gas using magnetron sputtering. The interface properties and composition of multilayers were characterized by X‐ray reflectivity, atomic force microscopy, transmission electron microscopy, X‐ray photoelectron spectroscopy, time‐of‐flight secondary ion mass spectroscopy, and EUV reflectivity. The results reveal that La/LaN/B ₄ C multilayers via H ₂ /Ar sputtering, the density and composition of the B ₄ C layer are significantly influenced, while the interface properties remain largely unaffected. Specifically, the O and C atomic content in the B ₄ C layers was precisely tailored through H ₂ /Ar sputtering to improve the reflectance of La/LaN/B ₄ C multilayers. Finally, the highest reflectance of 67.9% at 6.65 nm for the La/LaN/B ₄ C multilayer was achieved at 6% flow ratio of H ₂ /Ar mixed gas.