Influences of substrate temperatures on etch rates of PECVD-SiN thin films with a CF4/H2 plasma

Abstract The dependence of substrate temperatures (50 to −20 °C) on etch rate in two kinds of PECVD SiN films were investigated by a CF4/H2 mixture plasma. The XRR and XPS results indicate that the chemical composition and film density were almost identical for the films. The FTIR shows that the ratio of N H and Si H groups were found to be significantly different in the SiN films. The N H rich films exhibited a lower etch rate at −20 °C than that observed at room temperature or higher, whereas the Si H rich films showed a higher etch rate at −20 °C. We found that the fluorocarbon thickness was thicker in the Si H rich samples than N H rich samples. The fact suggests that hydrogen originated from the broken Si H bonds enhanced the polymerization, which causes the decrease of etch rate. A thinner fluorocarbon thickness was found in the Si H rich samples at low temperature, which results in the higher etch rate. Angular-resolved XPS indicates that N H bonding formed easier on film surface at −20 °C. These results indicate that the bonding structure and substrate temperature affected the fluorocarbon thickness, fluorine reaction probability and hydrogen dissociation during the SiN etching.