An argon electron cyclotron resonance plasma has been applied to the SiO2/Si system, in order to investigate the SiO2 film etching reaction and the Si surface damage using in situ spectroscopic ellipsometry (SE) and single wavelength ellipsometry. Ex situ atomic force microscopy was used to characterize the surface morphology and compare with SE results. Experiments included a range of ion dose rates from 3 X 10(15)-2 X 10(16) ions/cm2 s, at substrate temperatures of floating temperature (< 100-degrees-C) and 700-degrees-C, and doses from 10(16)-10(19) ions/cm2 at low ion energies from 0 to 100 V dc bias. Etch rates of about 20 nm/min for SiO2 have been achieved at - 50 V bias. At floating temperature a critical minimum ion energy for removal of the oxide is about -25 V bias, and the damage includes a roughness layer and an interface amorphous layer which increased with ion energy. At 700-degrees-C no amorphous layer was observed and the Si roughness layer varied with the ion dose from 0.4 to 30 nm for 10(17) and 10(19) ions/cm2, respectively after SiO2 removal. The determination of the optimum cleaning end point was achieved using real time ellipsometry.