Abstract: Niobium and niobium oxides have been used for superconductive structures such as Josephson junctions, SQUIDS and superconductive interconnects in semiconductor devices. In tllls work we had investigated the thermal oxidation of Nb thin-films (deposited by DC - sputtering ou to silicon substrates), at different temperatures (673-1023 K) and times (10-45 min). X-Ray diiffractomerty and ESCA measurements revealed the presence of lhe Nb02 and Nb2O5 layers. The rate of lhe etching of these oxydes in plasmas of CF4- 02 and CF4 - H2gas mixtures have been investigated. The etch curves ot the oxydes thermally grown at different temperatures showed similar behaviour as these of pure Nb films, but with etch rates a factor 012 - 3 higher. Fluorine radicals seem to be the main reactants in the etch chemistry. The etching is anisotropic and the end-point detection can be accurately made by "in situ" laser interferometry Ver menos