X-ray photoelectron spectroscopy depth profiling of oxidized aluminum thin films

Pure aluminum films have the highest reflectance among all metals in the far-ultraviolet (FUV) wavelength range extending from 120-230 nm. Unfortunately, aluminum is a highly reactive material and is only free of oxidation when deposited in an ultra-high vacuum chamber (p -10 torr). Aluminum films prepared in high-vacuum (conventional) chambers (p approximately equals 10 -6 torr) always oxidize regardless of deposition technique, deposition rate, and substrate temperature. Therefore, if a conventional chamber is sued for fabrication of aluminum multilayer devices based on theoretical designs, each aluminum film in the theoretical model should be considered as at least a two-layer structure of aluminum and aluminum oxide film.s Spectral performance optimization of an aluminum mirror is possible if the thickness and optical constant of the oxidized part of the aluminum film are known. Experimental results where XPS depth profiling was used to determine oxide thicknesses are reported.