Optical characteristic of ion beam sputter deposited aluminum thin films

Aluminum is a typical active metal very easy to oxidize. An oxide surface layer of about 2~6nm quickly formed in air which adds difficulty to the optical constants determination. An ex-situ method is used to determine the optical constants of aluminum thin films. First, alumina (Al2O3) thin film is deposited by ion beam sputter deposition. The optical constants and thickness are determined by spectral ellipsoemtry (SE). The thickness is verified by grazing x-ray reflection (GXRR) fitting method; Second, Al thin film with an Al2O3 cap layer on top is deposited. This cap layer is of the same deposition condition with the first step. By fitting the GXRR spectra, the structure information (the thickness of the aluminum and the cap layer, surface roughness and the diffusion between Al-Al2O3) is obtained; Third, based on the acquired structure information, the ellipsometric spectra are fitted. The optical constants of the aluminum layer are extracted with the aid of the Drude model. Finally, an induced transmission filter (ITF) is designed and deposited.

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