Electroless-deposited Ag-W films for microelectronics applications

Thin Ag-W films, with a tungsten concentration of up to 3.2 at.% and a thickness in the range 20-300 nm, were directly deposited on Si(100) substrate by the electroless (auto-catalytic) method. The deposition characteristics and the thin film electrical and physical properties were studied as a function of the bath composition. The role of tungsten in the silver matrix was studied via measurements of the film microhardness and thermal stability as a function of the thin film composition. Ag-W films thicker than 200 nm had a shiny appearance with good reflectivity and their specific electrical resistivity was 2 μΩ cm. The specific resistivity of films increased with decreasing thickness. Exposure of electroless silver films to air at 200°C for a few h causes them to tarnish severely and their sheet resistance to significantly increase, while similar Ag-W films were not affected under the same conditions. Therefore, we assume that silver-tungsten films can be used for applications that require reliable conducting thin films, such as packaging and interconnects for microelectronics.