Stress-Related Phenomena in Capped Aluminum-Based Metallizations

Abstract

ABSTRACTThe effect of a TiW capping layer on the mechanical behavior of AlSi(l%)Ou(y2%) thin films was evaluated. The aluminum films studied were deposited at temperatures ranging from 150 to 450°C, on various barrier layers (Ti, TiW, and TiN). Measurement of the stacks stress during anneal up to 450°C revealed that for films deposited at 150°C, the capping layer improved yield strength regardless of the type of barrier layer used. The uncapped stacks exhibited the traditional behavior of hillock formation during heating, and hillock /grain collapse during cooling. The capped stacks, however, showed considerably reduced, or suppressed hillock formation during heating, and active tensile stress relief mechanisms during cooling included cracking, voiding, and grain boundary grooving. These observations correlated well with XRD data characterizing the extent of tensile stress buildup in the aluminum films. For films deposited at 300°C, grain deformation during cooling after deposition presumably caused hardening which prevented cracking as well as changes in texture during anneal. This was observed regardless of the presence of a capping layer. Although the stacks studied were unpassivated, this data suggests that capping. layers may enhance stress migration issues in integrated systems.