Influences of substrate temperatures on etch rates of PECVD-SiN thin films with a CF_4/H_2 plasma

摘要

The dependence of substrate temperatures (50 to -20 degrees C) on etch rate in two kinds of PECVD SiN films were investigated by a CF4/H-2 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 degrees C than that observed at room temperature or higher, whereas the Si-H rich films showed a higher etch rate at -20 degrees 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 SiH 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 degrees 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.