The Nonlinearity of Stress Evolution in Polymer-Metal Composite Thin Films During Thermal Treatment

Composite thin films consisting of multi-layered polymers and metals are widely used in integrated circuits(IC) and its packaging, and it arises intricate wafer warpage problems due to complex inner stress distribution and evolution. The wafer warpage origination and mechanism of a multi-layered polymer-metal composite thin film is identified and analyzed in this paper. Different PI/Cu composite structures are employed to characterize the composite film's thermal mechanism. The wafer warpage evolution during thermal process is measured in-situ by a Multi-beam Laser Optical Sensor system. It's found that the cure shrinkage process of PI at evaluated temperature has little effect on wafer warpage in this work, however, the coefficient of thermal expansion (CTE) mismatch between the deposited materials contributes to major warpage during cooling to room temperature (RT). Despite the fact that PI cushions impact stress, it exacerbates overall warpage at RT in proportion to thickness. The ECD Cu embedded in PI also accounts for a substantial proportion to overall wafer warpage and leads to a hysteresis loop during the thermal processes, indicating plastic deformation such as grain growth or surficial diffusion or grain boundary diffusion, and the hysteresis can be largely inhibited by PI layers.