The embedding effect of physical vapour deposited and electrochemical deposited copper films due to a high-pressure annealing process at 400 ℃ and 150 MPa was investigated in order to apply this high-pressure annealing process to dual-damascene fabrication technology for copper interconnections. The experimental results support a thermal elasticity and plasticity analysis using a finite-element method which predicts that additional external pressure acts to push copper films to the via holes. This analytical result agrees well with the hole filling performance under the high-pressure annealing of test element group specimens on which via holes of 0.28 μm in diameter and 1.2 μm in depth were previously formed. The residual stress left after lowering the temperature and pressure has no dependence on the additional external pressure and therefore does not reduce the reliability of the copper interconnections. However, the additional external pressure reduces the incremental creep strain of copper during the heating and holding step and reduces the stress transition point during the cooling step. This indicates that the additional external pressure on annealing at approximately 400 ℃ is effective for the perfect filling of copper into via holes without minute voids and in suppressing the siphoning phenomenon in copper from via holes.