Transient fluorocarbon film thickness effects near the silicon dioxide/silicon interface in selective silicon dioxide reactive ion etching

Abstract

We have utilized an on-line ellipsometer to perform real time measurement of the thickness of fluorocarbon films formed on Si during overetching in selective silicon dioxide reactive ion etching (RIE) using CF4/H2. Employing an ultrahigh vacuum surface analysis system interfaced via a transfer chamber to the RIE system, x-ray photoelectron spectroscopy analysis was also performed on reactive ion etched SiO2 just before the encounter of the SiO2/Si interface (≂3-nm SiO2 remaining) during etching and for Si just after etching through the interface (overetch time <15 s). The SiO2 surface was essentially free of fluorocarbon film. The formation of the fluorocarbon film on Si after etching through the SiO2/Si interface was shown to occur very fast and achieve a near steady-state thickness value within ≂15 s for our etching conditions.