Tailoring capping layers to reduce stress gradients in copper metallization

Capping layers for back-end-of-linemetallization, which primarily serve as diffusion barriers to prevent contamination, also play a role in mitigating electromigration in the underlying conductive material. Stress gradients can be generated incoppermetallization due to the conditions associated with the capping process. To study the effects ofdeposition and subsequent annealing on the mechanical response ofcopperfilms with various capping schemes, we employed a combination of conventional and glancing incidenceX-ray diffraction techniques to quantify the stress gradient maxima. TheCufilms withdielectric caps, such as silicon nitride, can exhibit large gradients that decrease slightly with thermal cycling. However, Co and TaN-based metallic capping layers create significantly lower stress gradient maxima incopper features both before and after annealing. The different evolution of stress gradients inCufilms withdielectric and metallic caps due to thermal cycling reveals the interaction of dislocation-mediated,plastic deformation with the cap/Cuinterface.

Source: Applied Physics Letters - December 7, 2016 Category: Physics Authors: Conal E. Murray, Deepika Priyadarshini, Son Nguyen and E. Todd Ryan Source Type: research