Stress-temperature behavior of unpassivated thin copper films

The stress-temperature behavior of unpassivated thin (0.6-1.0 mu m) copper films on silicon substrates with Si3N4 diffusion barriers was examined between room temperature and 600 degrees C. Stresses were measured using a substrate curvature method and simulated using standard strain-rate equations which describe creep deformation. Simulations based on the mechanisms and data for bulk Cu could not reproduce the measured thin film data. Both the values which enter the rate equations and the rate equations themselves were modified in an attempt to obtain optimum correspondence between experiment and simulation. The best agreement was found when grain-boundary diffusional creep was neglected. The behavior could be simulated over a wide range using the rate equation for power-law creep with a stress exponent of 7 (determined from relaxation experiments), a thickness-dependent activation energy, and the temperature-dependent dislocation density (determined from X-ray peak widths). Mechanistic implications and the principal limitations of such a simulation approach are discussed. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.