Measurements of stress generation in Cu during low energy ion irradiation show that the induced stress depends on temperature and ion flux. A steady-state compressive stress is observed during irradiation, which turns into tensile stress after the irradiation is stopped. The results cannot be explained by the incorporation of gas ions alone, and point defects generated by the ions must be considered. In this work, the authors develop a continuum model that includes ion implantation, sputtering, and defect diffusion to explain the experimental data. The authors show that the experimental results can be reproduced primarily by considering a difference in diffusivity between interstitials and vacancies. (C) 2008 American Vacuum Society.