The use of Cu in ultralarge scale integrated (ULSI) conductors has resulted in the need to prevent Cu diffusion. We evaluated the passivation effect of plasma-enhanced chemical-vapor-deposited silicon nitride (PECVD-SiN) using secondary ion mass spectrometry and atomic absorption spectrometry. From these measurements, it was found that a large amount of Cu diffused through PECVD-SiN films during the heat treatments of the metallization process, probably due to the rapid diffusion paths along the microdefects of PECVD-SiN films. However, Cu contamination was barely detected in the current–voltage measurements and bias-temperature stressing tests ofCu/PECVD-SiN/SiO2/Sicapacitors because the leakage current through SiN films slightly increased as a result of Cu diffusion. This result is attributed to the electric-field relaxation caused by a large number of electrons trapped in the PECVD-SiN films, of which the negative charge compensates the positive charge of Cu ions. Although the degradation of electrical characteristics is not explicitly observed in simulation usingCu/PECVD-SiN/SiO2/Sicapacitors, Cu atoms reach Si devices in the actual process. Therefore, the passivation effect of PECVD-SiN films is insufficient to allow application to ULSI devices. ©1997 American Institute of Physics.