
The first chamber cleaning gas and the first silicon-containing film-etching gas of the present invention comprise at least one compound selected from the group consisting of FCOF, CF.sub.3 OCOF and CF.sub.3 OCF.sub.2 OCOF, and O.sub.2 in the specific amount, and optionally other gases. The second chamber cleaning gas and the second silicon-containing film-etching gas comprise CF.sub.3 COF, C.sub.3 F.sub.7 COF or CF.sub.2 (COF).sub.2 and O.sub.2 in specific amounts, and optionally may comprise o...











