Surface reaction processes in C 4F 8 and C 5F 8 plasmas for selective etching of SiO 2 over photo-resist

Abstract

Surface reactions induced by fluorocarbon plasmas were studied on Si substrates with SiO 2 and photo-resist overlayers using an inductively coupled plasma source. As source gases, C 4F 8 and C 5F 8 were employed to investigate their differences in the etching performance and the selectivity between SiO 2 and photo-resist. Deposition of fluorocarbon polymer was noticed in both gases by Fourier-transform infrared ellipsometric measurements when substrate bias was not applied. With the bias application, etching started on both substrate from certain threshold values of the bias voltage and the rate increased with increase of the voltage. However, in C 5F 8 plasma the increasing tendency on photo-resist was much less than on SiO 2, while in C 4F 8 plasma the difference is small. This difference is attributed to a larger deposition ability of C 5F 8 plasma with higher content of fluorine atoms in the polymer than that of C 4F 8 plasma as confirmed by X-ray photoelectron spectroscopy.