Delamination of polyimide/Cu films under mixed mode loading

Organic passivation layers are used as coatings in semiconductor devices for protection of metallization films against a variety of environmental effects. Polyimides (PI) have been used successfully as conformable protection layers on aluminium and also recently on copper metallization. While adhesion properties of Cu interconnects to compliant polymer substrates have been investigated so far, studies on PI/Cu passivation layers are scarce. In this study the adhesion strength of polyimide passivation layer to Cu film stacks on Si has been studied by using different fracture mechanic methods including four point bending, double cantilever beam and single lap shear tests. The focus is investigation of the dependency of the critical energy release rate to the mode mixity obtained by different testing techniques and evaluation of the delamination data using analytical models and by means of FEA and cohesive zone modelling.