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 betw een room temperature and 600 degrees C. Stresses were measured using a subs trate curvature method and simulated using standard strain-rate equations w hich describe creep deformation. Simulations based on the mechanisms and da ta for bulk Cu could not reproduce the measured thin film data. Both the va lues 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 diffusiona l creep was neglected. The behavior could be simulated over a wide range us ing the rate equation for power-law creep with a stress exponent of 7 (dete rmined from relaxation experiments), a thickness-dependent activation energ y, and the temperature-dependent dislocation density (determined from X-ray peak widths). Mechanistic implications and the principal limitations of su ch a simulation approach are discussed. (C) 1999 Acta Metallurgica Inc. Pub lished by Elsevier Science Ltd. All rights reserved.