The effect of the microstructure and the surface topography on the electrical properties of thin Ag films deposited by high power pulsed magnetron sputtering

In this work thin silver (Ag) films are grown employing high power pulsed magnetron sputtering (HPPMS) for various pulse on/off time configurations, as well as by dc magnetron sputtering (dcMS), for reference. It is shown that the increase of the pulse off-time from 450 μs to 3450 μs, while the pulse on-time is kept constant at 50 μs, results in an increase of the peak target current (ITp) from 3 A to 22 A. The increase of ITp is accompanied by an increase of the ion flux towards the growing film. This is particularly pronounced for ITp > 11 A. The microstructure, the surface topography and the electrical properties of Ag films grown at ITp = 11 A, ITp = 22 A and by dcMS are investigated, as a function of the film thickness d. It is shown that for d > 20 nm the electrical resistivity of films sputtered at ITp = 22 A is similar to that of films grown by dcMS. Slightly higher values are measured for films grown at ITp = 11 A. It is found that in this thickness range the film conductivity is strongly affected by the vertical grain size and the scattering of the charged carriers at the film interfaces. For d < 15 nm the resistivity of films deposited at ITp = 22 A is substantially lower as compared to that of films grown by dcMS. Films deposited at ITp = 11 A exhibit also in this case a higher conductivity. In this thickness regime the electronic transport and, thus the conductivity are profoundly determined by the surface topography and the film density.