The effect of pre-Co-deposition Ni ion implantation on the stress level of CoSi2 film formed by deposition of Co films on Si(100) substrates and subsequent ex situ rapid thermal annealing was investigated. X-ray diffraction was employed to measure the tensile stress in the CoSi2 films. It was found that the pre-Co-deposition Ni ion implantation was effective in reducing the stress level of CoSi2 films and the stress decreased linearly with the increase of reserved Ni ion implantation dose. In the present study, reduced lattice mismatch was proposed to explain the reduction of internal stress in CoSi2 films. (C) 2004 Elsevier B.V. All rights reserved.