A kinetic model of stress evolution in thin films
Eric Chason (Brown University)
Mechanics of Thin Films and Multilayered Structures
Tue 2:40 - 4:00
Salomon 203
Thin films often go through a series of stress states as they grow. The layers can start out with compressive stress, change to tensile stress and then back to compressive. The evolution is found to depend on multiple factors, including the film microstructure, the atomic mobility and the processing conditions (temperature, deposition rate, etc.). We have developed a model that explains the stress evolution in terms of a kinetic competition between different mechanisms that operate as the boundary forms between adjacent grains. The stress changes with the microstructure because the balance between these mechanisms shifts as the film changes from isolated islands, through coalescence and finally into a steady state uniform film. The model also predicts that the steady state stress scales with the dimensionless parameter D/LR where D is the diffusivity, R is the growth rate and L is the grain size. The model calculations are compared with wafer curvature measurements that enable the stress evolution to be measured in real-time. The dependence of the stress on the film thickness, growth rate, temperature and grain size are considered.