Direct observation of platinum etching during the fluorination of a Pt/LaF3/Si structure

The platinum etching during fluorination of the Pt surface of a Pt/LaF3/Si( 111) sandwich structure is investigated by means of X-ray methods, atomic f orce microscopy (AFM), and quartz crystal microbalance (QCM). XeF2 and F-2 have been used as sources of fluorine atoms. The X-ray triple-crystal rocki ng curve measurements show a smoothing of the rough Pt surface due to the i nteraction with fluorine. AFM observations confirm this change in surface r oughness. For verification of these data, X-ray theta-2 theta scans have be en performed for several samples using a Seeman-Bohlin X-ray diffractometer . The decrease of the integrated Pt peak intensity for a sample that had be en fluorinated for about 30 h in XeF2 shows a decrease of the film thicknes s from initially 40 nm by 25 +/- 5%. QCM measurements showed an initial inc rease of the total mass followed by a decrease after 80 min. We conclude th at the surface smoothing can be explained by the etching of platinum with t he formation of a platinum fluoride layer during the first stage of this pr ocess followed by decomposition and desorption of this PtFx layer.