In one embodiment, a method for depositing a cobalt-containing capping layer on a metal layer is provided which includes rinsing the metal layer with a deionized water wetting step, depositing a palladium layer on the metal layer by exposing the metal layer to an electroless activation solution comprising a palladium precursor and an acid, and depositing the cobalt-containing capping layer on the palladium layer by exposing the palladium layer to an electroless cobalt-containing solution comprising a cobalt source, a tungsten source, an oxygen scavenger and a surfactant. Ascorbic acid may be used as the oxygen scavenger. In another embodiment, a composition of an electroless plating solution is provided which includes a cobalt source at a concentration in a range from about 50 mM to about 250 mM, a tungsten source at a concentration in a range from about 10 mM to about 100 mM, a complexing agent at a concentration in a range from about 10 mM to about 200 mM, at least one reductant at a concentration in a range from about 1 mM to about 100 mM, a surfactant at a concentration in a range from about 1 mg / L to about 100 mg / L, and ascorbic acid at a concentration in a range from about 30 mg / L to about 300 mg / L.