PASSIVATION EFFECT OF SILICON-NITRIDE AGAINST COPPER DIFFUSION

The use of Cu in ultralarge scale integrated (ULSI) conductors has res ulted in the need to prevent Cu diffusion. We evaluated the passivatio n 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 amou nt of Cu diffused through PECVD-SiN films during the heat treatments o f 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-tempe rature stressing tests of Cu/PECVD-SiN/SiO2/Si capacitors 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 io ns. Although the degradation of electrical characteristics is not expl icitly observed in simulation using Cu/PECVD-SiN/SiO2/Si capacitors, C u atoms reach Si devices in the actual process. Therefore, the passiva tion effect of PECVD-SiN films is insufficient to allow application to ULSI devices. (C) 1997 American Institute of Physics.