Silicon nitride (SiNx) thin film layers were deposited on Cu/Ta/SiO2/Si multilayer structures by Plasma Enhanced Chemical Vapor Deposition at the temperature 285degreesC. The influence of post deposition thermal annealing treatments on the micro-structural, compositional and thermal stability study of SiNx/Cu/Ta/SiO2/Si multilayer structure was studied and compared with unpassivated, Cu/Ta/SiO2/Si multilayer structure. It was found that after SiNx 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 SiNx/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 750degreesC due to the formation of TaxNy, at the interface of SiNx/Cu.