Application of Nano-indentation method to characterize adhesion strength of polyimide film

Thick polyimide layer has been used as buffer layer to absorb stress imposed by molding compounds for many years. This paper studied the adhesion strength of the thick polyimide layer under different process conditions. The stress was induced by indentation, and delamination was confirmed by FIB and SEM imaging. The calculated adhesion energy for polyimide film was highest, around 30 J/m2, for the wafer processed with an extra pad protection layer Nblok (Nitrogen-doped barrier on top of copper, SiCN) plasma clean before the spin coating of polyimide film.