In this work, the surface of silicon etched by sulphur hexafluoride (SF6) and carbon tetrafluoride (CF4) plasma jet, pure or mixed with oxygen gas (O2), was investigated by scanning electron microscope (SEM), optical perfilometry and x-ray photoelectron spectroscopy (XPS). Through these techniques it was possible to investigate the etching rate, etched surface roughness and chemistry on Si surface as a function of O2 concentration in the SF6+O2 and CF4+O2 mixture. The results indicate high etching rates of up to 1.0 µm/min obtained for rf power and operating pressure at about 150W and 3.2 mTorr, respectively. The conditions whose etched profile showed higher anisotropy were obtained with CF4. Regarding the chemical analysis of the etched Si surface it was possible to identify elements of the sample surface such as F, C, N and O, as well as, their respective bonds with the Si.