Previous work has shown that epoxy siloxane polymer can inherently resist Cu diffusion. However, the adhesion between Cu and fully cured polymer is poor due to the nature of chemically inert organic groups on the polymer surfaces. In the present work it is shown that this polymer surface, before being fully cured/annealed, can provide adhesion to Cu. Rutherford backscattering spectroscopy (RBS) spectra of the as-spun polymer/Cu stacks followed by a thermal annealing show that Cu can diffuse into the as-spun polymer film readily upon thermal annealing indicating that the polymer with incomplete curing process remains active, thus providing a route for Cu to react with polymer. As a result, the adhesion at Cu-polymer interface is obtained by mechanical interlock and chemical reaction attributed to the formation of a diffused layer and Cu-polymer complex, respectively. Therefore, we propose a two-layer polymer stack strategy consisting of an adhesion layer (not fully cured) that is adjacent to Cu and a fully cured/annealed polymer film that retains its resistance to Cu diffusion. Triangular-voltage sweep (TVS) curves show that this scheme can retain its resistance to Cu diffusion under a bias-temperature stress (BTS) of 0.5 MV/cm at 150 degrees C. Current-voltage (I-V) and BTS current-time (I-t) curves further demonstrate that the polymer layer fully cured at 250 degrees C in the two-layer stack can effectively block the conduction paths generated during the formation of the interfacial bonding at Cu-polymer interface.