A 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.