High aspect ratio SiO2 contacts are etched with a C4F8/CO/O-2/Ar chemistry using a magnetically enhanced reactive ion etching (MERIE) plasma source with a good selectivity to the underlying silicon. X-ray photoelectron spectroscopy (XPS) studies allow chemical analysis of high aspect ratio SiO2 contact holes. Using the charging effect, a complete separation of the XPS peaks originating from the resist mask and from the bottom of the contact holes is possible. XPS analyses show that the fluorination of the polymer on the bottom of the contact is low (F/C around 0.2) and independent of the aspect ratio of contact holes. Furthermore, XPS spectra also show that the full width at half maximum of the Si 2p doublet measured at the bottom of contact holes strongly increases, showing that the highly energetic ion bombardment induced by the MERIE source lead to a severe amorphization of the silicon surface. Finally, comparisons between MERIE and high density plasma are discussed.