Thin anodic oxides on n-InP studied by photocurrent transients and surface analysis

Surface reactions induced by fluorocarbon plasmas were studied on Si substrates with SiO₂ and photo-resist overlayers using an inductively coupled plasma source. As source gases, C₄F₈ and C₅F₈ were employed to investigate their differences in the etching performance and the selectivity between SiO₂ 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 C₅F₈ plasma the increasing tendency on photo-resist was much less than on SiO₂, while in C₄F₈ plasma the difference is small. This difference is attributed to a larger deposition ability of C₅F₈ plasma with higher content of fluorine atoms in the polymer than that of C₄F₈ plasma as confirmed by X-ray photoelectron spectroscopy.