AVS 65th International Symposium & Exhibition
    Thin Films Division Thursday Sessions
       Session TF-ThP

Paper TF-ThP24
Using a Semitransparent Underlayer to Determine Optical Constants of a Mostly Opaque Layer by Thin Film Interference: Application to AlF3 on Al in the Extreme Ultraviolet

Thursday, October 25, 2018, 6:00 pm, Room Hall B

Session: Thin Film Poster Session
Presenter: Gabriel Richardson, Brigham Young University
Authors: J.G. Richardson, Brigham Young University
K.M. Wolfe, Brigham Young University
M.D. Barona, Brigham Young University
R.S. Turley, Brigham Young University
D.D. Allred, Brigham Young University
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The presence of interference fringes in thin-film reflectance and transmission are invaluable in obtaining thicknesses and optical constants of thin-film materials. When a material is highly absorbing, however, interference fringes may not be produced. One particularly noteworthy technique to deal with this complication in and near the visible range is to place a transparent layer beneath the semitransparent thin-film whose optical properties are to be determined. (Hilfiker, et al.) A portion of the light passing through the film, reflecting off the substrate and then, transmitting again through the film, interferes with the front-surface reflected light producing interference fringes whose position depends on the layers’ thicknesses and indices, and the light’s wavelength and angle of incidence. The damping of the fringes also highly constrains the optical constants of the overlayer. We have extended this approach into the extreme ultraviolet to obtain the optical constants of aluminum fluoride between 17.1 and 49.5 nm using evaporated aluminum as the “transparent” interference layer. The aluminum fluoride is evaporated within minutes after the aluminum and without breaking vacuum so as to minimize the presence of oxygen on the aluminum film. The AlF3 also acts as a barrier layer, drastically retarding the oxidation of the aluminum film after it is removed from the deposition system. Complications associated with obtaining the AlF3 EUV constants include: first, the fact that the aluminum layer is not perfectly transparent, and second that, in some cases, there is an ultrathin film of aluminum oxide on the Al which formed before the barrier is deposited or forms gradually with time afterwards. In fact, it is in probing the time evolution of such oxide layer thicknesses that the technique has the promise of becoming particularly useful for studying barrier layers for broadband Al mirrors. Hilfiker, James N.; Singh, Neha; Tiwald, Tom; et al., “Survey of methods to characterize thin absorbing films with Spectroscopic Ellipsometry,” THIN SOLID FILMS, 516(22), (2008) 7979-7989.