Evolution of stress gradients in Cu films and features induced by capping layers

The presence of voids in Cu metallization represents a key reliability issue for ultra-large scale integration technology. In particular, the interface between the Cu and capping layers represents a critical location where the stress state of the Cu must be experimentally determined. Glancing-incidence X-ray diffraction (GIXRD) can be used to investigate depth-dependent stress distributions within electroplated Cu films induced by overlying capping layers. A combination of conventional X-ray diffraction measurements and GIXRD results revealed that strain gradients were created in Cu films and patterned features possessing a SiC xN yH z cap, where an increased in-plane tensile stress was generated near the film/cap interface due to the constraint imposed by the SiC xN yH z layer during cooling from the cap deposition temperature. Cu films possessing a CoWP cap, deposited at lower temperatures where the Cu experienced only elastic deformation, did not exhibit depth-dependent stress distributions. However, all Cu samples exposed to the SiC xN yH z deposition temperature developed stress gradients regardless of the capping material. Although in situ annealing of SiC xN yH z capped Cu films decreased the stress gradient as the sample temperature approached that of the cap deposition, the gradient reappeared upon cooling to room temperature. © 2011 Elsevier B.V. All rights reserved.