Characterization of polymer formation during SiO2 etching with different fluorocarbon gases (CHF3, CF4, C 4F8)

Abstract

In this paper, the polymer composition generated by three different combinations of gas chemistries for oxide etch are studied and the effects of different O2 plasma strip duration on polymer removal are also presented. The etch chemistries used were CHF3/CF4, CO/CF4/CHF3 and C4F8/CO/CHF 3 chemistry. From the X-ray photoelectron spectroscopy (XPS) C Is spectra, five distinct peaks are identified which correspond to C-C, C-CF x, CF, CF2 and CF3. The C/F ratio is found to be highest for polymer generated by the C4F4/CO/CHF 3 chemistry, about 0.8, whereas the C/F ratios for those by CHF 3/CF4 and CO/CF4/CHF3 chemistries are about 0.6. Atomic force microscopy (AFM) images show that the polymer generated by the C4F8/CO/CHF3 chemistry is much rougher than that by CHF3/CF4 and CO/CF 4/CHF3 chemistries. The XPS spectra of C Is also show a significant decrease in the intensity of the more fluorinated carbon peaks (CF3 and CF2) after O2 plasma strip. The C/F ratios increased to about 1.4 to 1.8 after O2 plasma strip. The spectra are similar for different O2 strip times, indicating the decrease is independent of O2 strip duration. From the AFM images, all the polymers formed by CHF3/CF4 and CO/CF 4/CHF3 chemistries are rather smooth with no visible change after O2 strip. However, the polymers generated by C 4F4/CO/CHF4 chemistry are flattened with increasing O2 strip duration. The high energy ion bombardment of oxygen ions probably have flattened the rough polymer surface.