Optical modeling and XRR/AFM characterization of highly conductive thin Ag layers

Thin silver layers ( 12 nm) are widely used in low-E architectural glass coatings. For these and other applications thin Ag films with high conductivity are desired. We prepared Glass/ZnO:Al/Ag layer stacks with Ag thicknesses in the range of 7 - 40 nm by means of magnetron sputtering. The ZnO:Al Layer was RF/DC sputtered from a ceramic target and serves as seed layer for growth of strongly (111) oriented silver with high conductivity (M. Arbab, Thin Solid Films 381, 15 (2001) [1]). Layer thicknesses, top surface and interface roughnesses were determined by XRR and compared with AFM rough ness for the top layer. We present a dielectric function model for thin silver films with which the optical measurements are excellently described. The hereby determined layer thicknesses correspond precisely to those determined by XRR. The best agreement was found when only reflectance and transmittance measurements were used. The model for the dielectric function assumes a constant charge density and uses the electron mobility as free parameter. For the Ag resistivity we found a strong decrease with increasing Ag thickness. A value of -Ag = 3.83 µ cm was interpolated for an Ag thickness of 12 nm for pure DC plasma excitation during ZnO:Al seed layer deposition.