Effect of thermal processing on silver contacts for zinc oxide and indium tin oxide

Silver thin film contacts of varying thickness (25, 45, and 60 nm) were deposited on indium tin oxide (ITO) on silicon and zinc oxide (ZnO) on silicon. The films were annealed in vacuum for 1 hour at different temperatures (300-650°C). The resistivity of the films was determined using four-point-probe measurements. The films underwent an abrupt change in resistivity beyond an onset temperature that varied with thickness. Rutherford backscattering spectrometry measurements suggest agglomeration of the Ag films upon annealing caused the resistivity breakdown. X-ray pole figure analysis reveals that the annealed films took on a preferential 〈111〉 texturing; however, the degree of texturing was significantly higher in Ag on ZnO than on ITO. This observation was accounted for by interface energy minimization. Atomic force microscopy (AFM) measurements revealed an increasing surface roughness of the annealed films with temperature. The resistivity behavior is accounted for by the increasing crystallinity countered by an increasing surface roughness. Average surface roughness obtained from AFM measurements were also used to model the agglomeration of Ag based on Ostwald ripening theory.