Patterning SiO2 thin film on the Si (100) surface was demonstrated by synchrotron radiation (SR) stimulated etching with a contact cobalt mask. The reaction gas was a mixture of SF6 and O-2 The contact cobalt mask was fabricated by sputtering cobalt films on a photolithography resist pattern and lift-off technique. The thickness of the mask was about 145 nm. The SR irradiation with flowing SF6 and O-2 could effectively etch the silicon dioxide and the etching process stopped at the SiO2/Si interface. The etching rate at room temperature was about 2.7 nm per 100 mA min. The etched pattern was evaluated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and step profile meter. Area-selective and anisotropy etching were achieved and the roughness (R-a) with a line profile on the etched surface was about 0.05 nm. (c) 2004 Elsevier B.V. All rights reserved.