Passivation against Cu contamination is a key technology for realizing multilevel Cu interconnection for ultralarge scale integrated circuits (ULSI). Phosphosilicate glass (PSG) with rapid thermal annealing (RTA) is found to provide no less of a passivation effect than furnace-annealed (FA) PSG films, while significantly reducing the thermal budget of the PSG annealing from 900-degrees-C x 20 min (FA) to 900-degrees-C X 60 s (RTA). This suggests that the PSG-RTA process is applicable to 0.25 mum level metal oxide semiconductor (MOS) ULSIs, since both the amount of Cu diffusion and the thermal budget are within the limits of 0.25 mum MOS device technology.