Optimization of the reflectivity of magnetron sputter deposited silver films

Silver films were deposited using direct current (dc) and midfrequency (MF) magnetron sputter deposition processes on floatglass in order to achieve m aximum reflectivity over the entire visual and infrared spectral range. The films were investigated by means of ex situ and in situ spectroscopic elli psometry, spectral photometry, electrical conductivity measurements, and at omic force microscopy. The following deposition parameters were varied: mid frequency and de technique, power density, sputtering pressure, substrate t emperature, sputtering gas (Ar, Kr, Ne), oxygen residual gas, and film thic kness. With the aid of in situ spectroscopic ellipsometry, it can be shown that for certain process parameters an optimum layer thickness exists for a chieving a maximum reflectivity in the visual spectral range. With increasi ng thickness, optical losses which are due to the formation of larger grain s come into play. This optimum layer thickness is smaller for the films dep osited by MF sputtering, indicating a smoother surface and smaller grain si zes compared to that of the de mode. As a maximum value, a reflectivity of R = 99.3% is achieved, which is close to the theoretical value, which was d etermined from the Drude fit parameters with respect to the resistivity. Th e resistivity of this film was found to be rho = 2.4 mu Omega cm. The measu red reflectivity of the sputter deposited films is comparable to e-beam eva porated silver films. (C) 2000 American Vacuum Society. [S0734-2101(00)1070 4-3].