Electroless CoWPB barriers can be deposited on Cu without Pd catalysis, thus they are suitable for sub 45 nm interconnect capping applications. CoWP and CoWBP films are investigated as thin capping layers for copper metallization. The films were made by electroless deposition methods from a plating bath containing two reducing agents: aminoborane and hypophosphite. Thin films were deposited on silicon oxide using a ultra thin sputtered copper seed layer. The barrier properties of the films were tested by XPS and SIMS profiling. In this paper we expand the surface adsorption model presented in an earlier work to include the effect of the tungsten in the case of boron containing reducing agent only and also in the case when all three components, i.e. DMAB, hyphosphite and tungstate ions, co-exit in the solution.