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

The chemical dry etching of Si in a fast discharge flow was studied using a low-power (80 W) microwave discharge of Ar/CF 4 /O 2 mixtures. The variation of etch rate was measured as a function of the O 2 or Ar flow rate in order to determine the effects of the addition of O 2 and Ar. The maximum etch rate was about 3600 Å/min at the Ar, CF 4 and O 2 flow rates of 2500, 100 and 10 sccm, respectively. This etch rate was larger than those obtained without the addition of O 2 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 O 2 on the Si surface and discharge. The marked enhancement of the etch rate at low O 2 /CF 4 flow ratios below 10% was explained by an increase in the F concentration and a decrease in the concentrations of carbons and CF n ( n =1,2). The decrease in the etch rate at high O 2 /CF 4 flow ratios above 10% was attributed to the formation of SiO 2 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.