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 NH and SiH groups were found to be significantly different in the SiN films. The NH rich films exhibited a lower etch rate at −20 °C than that observed at room temperature or higher, whereas the SiH rich films showed a higher etch rate at −20 °C. We found that the fluorocarbon thickness was thicker in the SiH rich samples than NH rich samples. The fact suggests that hydrogen originated from the broken SiH bonds enhanced the polymerization, which causes the decrease of etch rate. A thinner fluorocarbon thickness was found in the SiH rich samples at low temperature, which results in the higher etch rate. Angular-resolved XPS indicates that NH 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.