Enhancement of Etch Rate by the Addition of O2 and Ar in Chemical Dry Etching of Si Using a Discharge Flow of Ar/CF4 and CF4/O2 Gas Mixtures

Abstract

The chemical dry etching of Si in a fast discharge flow was studied using a low-power (80 W) microwave discharge of Ar/CF4/O2 mixtures. The variation of etch rate was measured as a function of the O2 or Ar flow rate in order to determine the effects of the addition of O2 and Ar. The maximum etch rate was about 3600 Å/min at the Ar, CF4 and O2 flow rates of 2500, 100 and 10 sccm, respectively. This etch rate was larger than those obtained without the addition of O2 by a factor of 8 and without the addition of Ar by a factor of 23. Auger and XPS spectra of Si substrates and emission spectra of discharges were measured in order to examine the effects of the addition of O2 on the Si surface and discharge. The marked enhancement of the etch rate at low O2/CF4 flow ratios below 10% was explained by an increase in the F concentration and a decrease in the concentrations of carbons and CFn (n=1,2). The decrease in the etch rate at high O2/CF4 flow ratios above 10% was attributed to the formation of SiO2 on the substrate. The marked enhancement of the etch rate by the addition of Ar was explained by the generation of active Ar species which enhance [F] and [O] in the discharge flow.