Microstructural studies of reactive ion etched silicon

The structures of Si near-surface damage induced after the removal of a thick SiO2 layer on Si using reactive ion etching with various etching gases were studied by transmission electron microscopy. Cross-sectional micrographs showed the presence of a fluorocarbon film on the Si surface after the SiO2 layer is etched away. No extended defects were observed in Si etched utilizing pure CF4 or CF4/20% H2 etching gas, even after a 25-min overetch into Si. For a CF4/40% H2 etching gas, no extended lattice defects were evident for overetch times of up to 5 min. However, extensive damage was found in the Si surface layer after a 10-min or longer overetch. This extensive damage consists of {111} planar defects distributing underneath the Si surface to a depth of 300 Å. The planar defects are highly decorated by impurities, likely H and possibly C, F. A pure H2 etching gas was found to introduce a heavily damaged layer and a high density of extended defects near the Si surface after only a 5-min overetch. These observations indicate that H ion bombardment plays an important role in the formation of Si near-surface damage during reactive ion etching.