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Silicon dioxide (SiO2) layers using photoresist (PR) masks are etched by inductively coupled plasma in CH4/SF6 under various etching conditions. A thin CHxFy polymer layer which exists on the surface of sample during steady‐state etching is observed. The steady‐state CHxFy layer reduces the physical sputtering of ions, resulting in the etching rate of PR decreases significantly. Although the high‐density plasmas can enhance the physical sputtering to some extent and give SiO2 more opportunities to react with fluorine atoms, it is helpful to improve the etching rate of SiO2. By optimizing process conditions, the thickness of the steady‐state CHxFy layer and the density of ions are regulated, and a reasonable selective etching is obtained.