Channel cracking in low-k films on patterned multi-layers

This paper considers cracking of a low-k tensile film fabricated on top of a patterned multilayer. A finite element model has been established to study all the geometry effects of the top film and underlying layers. It is found that the driving force for film cracking, as calculated from the energy release rate, is greatly enhanced by the underlying layers of copper and low-k materials. The geometry dependence has been verified by a test structure. The results indicate that a low-k film that is intact when deposited on silicon may crack when integrated in a multilayer BEOL. IBM has successfully engineered a CVD SiCOH low-k film with reduced film stress and increased modulus without degrading the cohesive strength (or the dielectric constant). Accordingly, cracking of the film has been prevented even for the worst case interconnect structures.