Effect of out-of-plane properties of a polyimide film on the stress fields in microelectronic structures

The detailed modeling of microelectronic structures involving thin polyimide films is difficult due to the limited amount of information available on the out-of-plane polyimide properties. In the present analysis, we treat the out-of-plane mechanical properties of the polyimide as design variables and investigate their effect on the thermal stresses that develop in a one layer copper-polyimide interconnection structure using a combined finite element-design of experiment method. The interconnection structure is modeled by a three-dimensional representative cell composed of a square copper via in a thin polyimide film mounted on top of a silicon substrate. The cell is assumed to be stress free at an elevated temperature, and it is subsequently cooled uniformly. In the analysis, we obtain the initial elastic response of the cell for each combination of the out-of-plane polyimide properties called for in the experimental design, and generate response functions for the stress components at key bimaterial interfaces. Additional finite element trials are then performed over a broad temperature range, allowing for copper plasticity, to investigate the role of the out-of-plane polyimide properties when a material nonlinearity is present in the structure.