Dielectric function of Ni-Pt alloys from 0.6 to 6.6 eV by spectroscopic ellipsometry

The complex dielectric function $\varepsilon $ of metals is difficult to determine, because it depends on crystallinity, purity, native oxide, surface roughness, thickness, deposition method, etc. Nevertheless, a precise knowledge of $\varepsilon $ is useful for process control in semiconductor manufacturing. In this work, we have determined $\varepsilon $ of thin Ni-Pt alloy films (10{\%} to 25{\%} Pt, 10 nm thickness) from 0.6 to 6.6 eV using spectroscopic ellipsometry. The films were sputtered on thick SiO$_{2}$ layers to avoid reaction with the Si substrate. The ellipsometric angles (determined at three angles of incidence) were fitted using previously determined optical constants for Si and SiO$_{2}$. The optical constants for the metal were described with a Drude (free carrier) term, a pole due to lattice absorption (outside of our spectral range), and three weak interband transitions modeled with Lorentz oscillators. Variations with composition (from 10{\%} to 25{\%} Pt) and annealing at 500\r{ }C for 30s were insignificant.