Study of metal adhesion on porous low-k dielectric using telephone cord buckling

The interfacial adhesion energy between metal and porous low-k dielectrics is an important parameter for the reliability study of back-end of line integration. In this work, we have observed the spontaneous film delamination with telephone cord morphology after 130 nm thick Ta was sputtered onto methyl silsesquioxane (MSQ) low-k dielectric. The highly compressive stress inside the Ta film is the driving force for the spontaneous buckling. The adhesion failure was identified to be at Ta/MSQ interface by using focused ion beam and scanning electron microscopy. Pinned circular blister model was applied to fit the buckling morphology. The interfacial adhesion energy was extracted to be 7.90 J/m2 at 87° phase angle. The Cu/MSQ interface was evaluated in a similar fashion by using a stressed overlayer Ta/Cu. The fracture energy was calculated to be 3.34 J/m2 with the similar phase angle. The results suggest that an adhesion promoter between Cu and low-k dielectrics is essential for a mechanically stable structure.