Thermo-mechanical stresses in copper interconnects – A modeling analysis

This study focuses on numerical modeling of thermo-mechanical stresses in copper interconnects. The three-dimensional analyses utilize a two-level metal structure connected by a via. Attention is devoted to the effects of the incorporation of polymer-based low-k dielectric material. Deformation is generated by thermal strain mismatches during cooling from an elevated temperature, as well as from cyclic thermal excursions. The thin barrier layers encasing the copper are also included in the models. Plastic deformation in the metal is taken into consideration in the analysis. The stress and deformation fields are examined in detail. It is found that the incorporation of low-k dielectric in place of traditional oxide-based dielectric significantly reduces the triaxial tensile stresses in copper but enhances plastic deformation, particularly in the via and its vicinity. The generation of shear stresses at the interface regions is also assessed. A parametric analysis is conducted to elucidate the individual influences of the thermal expansion and elastic properties of the dielectric material. Salient features having direct implications in device reliability are highlighted and discussed.