Adhesion Strength Evaluation of Low-k Interconnect Structures Using a Nanoscratch Method

Abstract

AbstractA convenient nanoscratch method was combined with atomic force microscope (AFM) and transmission electron microscope (TEM) observations to conduct the first-ever evaluation of the adhesion strength of a complicated microstructure Cu/Ta/TaN/pSiO2/low-k/SiC/pSiO2/Si-substrate with the aim of correlating the fracture strength with the results of chemical mechanical polishing (CMP) tests. Concretely, this evaluation focused on the fact that specimens having a low-k layer pretreated with rare-gas plasma prior to the deposition of the SiO2 layer exhibited low delaminated densities in the Cu CMP process. It was found that a specimen with the rare-gas plasma pretreatment exhibited a higher friction coefficient, a higher critical load and brittle adhesive failure resulting from delamination at the interface between the low-k and SiC layers. A specimen without the rare-gas plasma pretreatment displayed a lower friction coefficient, a lower critical load, and ductile cohesive failure in the low-k layer. Because less plastic deformation was observed in the low-k layer subjected to the rare-gas plasma pretreatment, it is assumed that the pretreatment reinforced the mechanical properties of the low-k layer, making it more resistant to ductile cohesive failure. These results agreed with the CMP test data and indicated that the nanoscratch method makes it possible to predict the ability of complicated Cu/low-k interconnect structures to withstand the CMP process.