Finite Element Predictions of the Effect of Diffusion-Accommodated Interfacial Sliding on Thermal Stresses in Cu/Polymer Dielectric and Cu/Oxide Dielectric Single Level Damascene Interconnect Structures

The finite element method was used to estimate the stresses in single level, 1 μm thick Cu-dielectric interconnect line arrays with Ta liners resulting from heating from 20°C to 400°C assuming that the structure was stress free at 20°C. Benzocyclobutene (BCB) and $SiO2$ were chosen to represent typical polymer and ceramic dielectric materials being evaluated for Cu damascene interconnect structures. Experimentally observed Cu-Ta and Cu-Cu interfacial sliding was incorporated into the model using a 1 nm thick creep element that was calibrated to match the predictions of a classical diffusion-accommodated sliding model. The effect of Cu-Ta and Cu-Cu interfacial sliding was evaluated by comparing the relaxed and unrelaxed stresses. The effect of line width-to-thickness (w/t) ratio and Ta liner thickness on the shear, normal, and Ta liner-plane stresses at the Cu-Ta-dielectric interface was investigated because this interface is a likely failure site.