Anisotropic etching of deep SiO2 has been obtained using electron cyclotron resonance-reactive ion beam etching with C2F6 gas. The influence of total gas pressure and gas flow rate on the profile control and the roughness due to the etching have been determined. The sidewall angle of etched profile can be tailored by adjusting the processing conditions, and it is found that a sidewall angle of 90 degrees for an etching of deepness around 18 mu m is obtained at a pressure of 1.0 mTorr and a gas flow rate of 35 sccm. Low roughness has also been achieved for a pressure of 1.0 mTorr with the gas flow rate ranging from 25 to 40 sccm. Here, the scanning electron microscope and the scanning tunneling microscope have been used to study the etched profile and the roughness, respectively.