For microelectronics applications, it is important to have good interfacial properties between copper and parylene-N (Cu/PA-N), and parylene-N and silicon (PA-N/Si). Two of the relevant interfacial properties studied in this article are diffusion of the individual layers into the other layer at application temperatures and adhesion between these layers. The interface between copper and parylene-N, and parylene-N and silicon has been studied using secondary ion mass spectroscopy (SIMS). Scanning electron microscopy (SEM) has also been used to study the PA-N/Si interface. SEM revealed the microstructure at the interface. SIMS was used to tunnel through the composite film in the cross section and get the various elemental concentrations. This gave the average concentrations prevailing, at a particular depth. It was observed that copper diffuses, from the top, through the PA-N film to the silicon substrate at 350 degrees C. Gettering of copper was observed, leading to high concentration of copper at the Cu/PA-N and PA-N/Si interface. A high distribution of silicon was observed in PA-N at the PA-N/Si interface. X-ray photoelectron spectroscopy studies showed that no new chemical bonds were formed. Thus, diffusion resulted in a mixing layer which led to good interfacial adhesion.