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VUV reflectance

The optical parameters (index of refraction and extinction coefficients—n and k) of various dielectrics in the VUV range (50 – 150 nm) were determined via Kramers-Kronig analysis of reflectance data. The reflectance data was obtained by measuring the photoemission current produced in a biased 90% transmission nickel mesh placed at the output of a synchrotron at two conditions. First, the beam was allowed to travel directly through the mesh to a beam disperser. Then, a dielectric wafer was moved to intercept the beam normally so that photons were reflected back to the mesh. A comparison between the two measured photoemission currents was made to find the reflectance. To obtain the index of refraction and the extinction coefficient, the Kramers-Kronig algorithm was used. To increase the accuracy, the data was supplemented with values of n and k obtained from spectroscopic ellipsometry from adjacent spectral regions (155 – 800 nm). These were converted to an equivalent reflectance and the combined data was then used to obtain n and k.

VUV reflectometer