Optical, electrical, and structural properties of sputtered aluminum alloy thin films with copper, titanium and chromium additions

Abstract

Aluminum alloys containing copper, chromium, and titanium were sputter deposited with the goal of maintaining the high bulk reflectance of aluminum while providing surface topography more suited for optical applications. Films were deposited at room temperature with no additional thermal processing. Results show that copper solute addition generates films that maintain much of the bulk reflectance of pure aluminum while refining surface morphology to create a more specular surface consisting of smaller, more uniform grains. X-ray diffraction studies revealed that copper addition into the aluminum lattice caused both a reduction in the preferred orientation of the film and change in the lattice parameter. Copper concentrations of 1.0% at. and above led to spatial variation in copper content within the films. The addition of titanium and chromium to Al-1.0%Cu films caused further microstructure refinement. Al-2.0%Ti-1.0%Cu and Al-2.0%Cr-1.0%Cu exhibited reflectivity spectra that differ significantly in both inter- and intraband absorption from that of pure aluminum. A dielectric function model combining a surface effective medium and a bulk Lorentz–Drude layer was applied to all alloy films to understand the observed reflectivity. Excellent agreement has been shown between the measured resistivity values and those obtained from the Drude model.