Silicon nitride (SiN x ) thin film layers were deposited on Cu/Ta/SiO2/Si multilayer structures by Plasma Enhanced Chemical Vapor Deposition at the temperature 285°C. The influence of post deposition thermal annealing treatments on the micro-structural, compositional and thermal stability study of SiN x /Cu/Ta/SiO2/Si multilayer structure was studied and compared with unpassivated, Cu/Ta/SiO2/Si multilayer structure. It was found that after SiN x passivation, the formation of Cu2O and Ta2O5 was significantly reduced and the structure becomes more stable than unpassivated one. The reaction between Cu, Ta and O was not found in this SiN x /Cu/Ta/SiO2/Si multiplayer structure but the out diffusion of Ta to the Cu surface was unable to be suppressed. The Ta barrier was observed to fail at temperatures above 750°C due to the formation of Ta x N y , at the interface of SiN x /Cu.