Transmission electron microscope study of lattice damage and polymer coating formed after reactive ion etching of SiO2

Abstract

Reactive ion etching (RIE) of SiO2 in a CHF3/O2 plasma provides both high anisotropy and selectivity to the Si substrate. Cross-sectional transmission electron microscopy was used to study the polymer film and the lattice damage induced by this RIE process as well as the effect of post-treatment and annealing conditions. The lattice damage consists mostly of defect clusters which increase both in density and depth with overetching. Post-treatment in an NF3/Ar plasma removes the polymer film as well as the defect zone, but produces surface roughness (up to 5 nm). Annealing at 450 °C (30 min) had only a minor effect on the lattice damage, whereas annealing at 900 °C (30 min) removed all defects. No correlation was found between RIE damage and residual ion implantation damage.