STRESS INDUCED MIGRATION IN POLYCRYSTALLINE FILMS: A TIME-SCALE ANALYSIS

摘要

We discuss studies of stress induced grain boundary motion in polycrystalline Cu films, using 3D grain-continuum modeling; i.e., we represent a polycrystalline material as a system of distinct but interacting continua. Field variables are computed as functions of position in each grain; e.g., internal stresses and concentrations. To highlight the importance of anisotropy, we consider thermally induced stresses in an idealized thin Cu film, with hexagonal 3D grains, on a SiO_2 film on a Si substrate. Stresses computed in a < 111 > textured film using the anisotropic elastic constants of single crystal Cu (rotated appropriately for each grain) are higher than the stresses computed using isotropic (bulk) properties. When one grain is < 100 > oriented in the midst of < 111 > oriented grains, strain energy gradients will lead to the growth of the < 100 > oriented grain. Grain boundary velocities and the time scales for significant evolution are calculated for both strain energy induced and vacancy transport induced grain boundary motion, and strain energy-driven motion is shown to dominate.