Study on characterizing fluorocarbon polymer films deposited on an inner surface during high-aspect-ratio contact hole etching using secondary ion mass spectroscopy

Abstract

Characterization of fluorocarbon films deposited on sidewall and bottom surfaces during high-aspect-ratio contact hole etching has been investigated by secondary ion mass spectrometry (SIMS). Very high-aspect-ratio contacts, with hole diameters ranging from 0.06 to 0.18 μm, were etched in 1 μm thick SiO2 films with polycrystalline Si hard masks by high density CHF3/CO or C4F8/O2/Ar plasma generated by a dipole ring-type magnetron reactive ion etching reactor. A series of SIMS studies for test element group chips with high density contact holes first reveal that the SIMS profiles obtained from the etched samples qualitatively exhibit a good measure of fluorocarbon profiles on the inner surfaces of the high-aspect-ratio contact holes. Quantitative evaluation is also discussed further. Fluorocarbon films on the sidewalls polymerized from CHF3/CO plasma show a great accumulation of C-rich films at an aspect ratio of around 4. With an increasing aspect ratio of more than approximately 8, the polymers are found to change from C-rich to F-rich films. On the other hand, fluorocarbon films on the sidewalls polymerized from C4F8/O2/Ar plasma are more uniform, much more fluorinated, and much thinner than those of the CHF3/CO plasma. Both polymers show a clear C pileup on the Si substrates at the bottom of the contact holes even for sub-0.1 μm contacts. This work successfully demonstrates the usefulness of the SIMS measurement for characterizing high-aspect-ratio contacts down to sub-0.1 μm diameters.