The barrier properties of plasma-enhanced chemical vapor deposited (PECVD) SiN thin films capped on post chemical mechanical polishing Cu film were investigated by various analytical techniques, such as secondary-ion mass spectrometry (SIMS), transmission electron microscopy, and atomic force microscopy, focusing on the effect of NH3 plasma pretreatment. SiN films were deposited at 400 degreesC in a sequential multistage deposition system. Much less Cu contamination was detected at the surface of SiN deposited with plasma pretreatment, compared to that without plasma pretreatment. Also, the amount of Si diffused into Cu during deposition was found to be significantly reduced after NH3 plasma pretreatment. Similar Cu diffusion behavior was observed in SiN films deposited with or without plasma pretreatment, after being annealed at 450 degreesC. However, SIMS analysis revealed that Cu diffused faster in SiN deposited with plasma pretreatment than in SiN deposited without plasma pretreatment, after being annealed at 550 degreesC.