Early-stage modification of a silicon oxide surface in fluorocarbon plasma for selective etching over silicon

Abstract

During the etching of the film of silicon dioxide in an Ar-diluted octafluoro cyclobutane (c-C4F8) plasma, infrared spectra were obtained every half a second by using in situ time-resolved attenuated total reflection infrared (IR-ATR) spectroscopy. With IR-ATR, it was possible to separately observe the bands of absorption by carbon fluorine and silicon oxygen. These time-resolved spectroscopic observations enabled us to characterize the formation of the film of amorphous fluorinated carbon (a-C:F) during the etching process. Experimental results for the etching of a-C:F on the silicon oxide indicated that the thickness of the film of a-C:F on silicon-oxide surface reached steady-state value that was one fifth of the steady-state value on a silicon surface. The modification of the surface in the early stages was characterized in terms of the balance between the rates of deposition and sputtering of the film of a-C:F. Infrared analysis is shown to be a powerful tool for characterizing the film of a-C:F film that is formed during oxide etching.