The properties of electroless CoWP barrier films with different phosphorus contents in Cu/CoWP/Si stacked samples were explored. The Cu/CoWP/Si stacked samples with 30 nm CoWP films, contained about 5.7, 8.2 and 10.8 at.% P. were prepared by electroless deposition, and then annealed in a rapid thermal annealer at a temperature between 300 and 700 degrees C. The effect of phosphorus content in CoWP film on the barrier properties in preventing copper diffusion and the failure of the Cu/CoWP/Si stacked samples after thermal annealing were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDS). Auger electron spectroscopy (AES), and sheet resistance measurement. Increasing the phosphorus content in the electroless CoWP film markedly improves the barrier properties. The failure temperature of Cu/CoWP/Si increased from 500 to 600 degrees C with the phosphorus content in CoWP film increasing from 5.7 to 10.8 at.%, and the failure of the Cu/CoWP/Si has mainly arisen from the interdiffusion of copper and cobalt during thermal annealing. (C) 2011 Elsevier B.V. All rights reserved.