Enhanced optical performance of aluminum films by copper inclusion

The aluminum film is a standard coating material for optics. It yields a hi gh reflectance over a broad wavelength region, and films can be made suffic iently smooth for high quality optical applications. However, it suffers fr om a high sensitivity to hillock formation and severe degradation of its lo w light scattering properties, already at temperatures of 70-80 degrees C. In order to raise the temperature for onset of hillock formation we have co -evaporated a slight amount (3 at.%) of Cu into the Al film. The anti-hillo cking performance was indeed confirmed by raising this temperature to simil ar to 130 degrees C. But, we also greatly reduced the surface roughness of the as-deposited 3600 Angstrom films to the outstanding values of 1-3 Angst rom rms as measured by the ASTM F 1048-87 total integrated scattering (TIS) method. This yields very low light scattering films despite their thicknes s. Also, the specular reflectance was coming out just as high as for a pure Al film over a wide wavelength range. The enhanced optical performance is attributed to less light scattering of the co-evaporated him and to the str engthening effect in the film. (C) 1999 Elsevier Science S.A. All rights re served.