Irregular interface artifacts were observed in secondary ion mass spectroscopy depth profiling of a Ta thin film on Si by O-2(+) ion beam. They were correlated with the formation of an abnormal surface topography. Volcano-type round craters were developed by sputtering with a 7 keV oxygen ion beam at an incidence angle of 45 degrees. The surface topographic development on a Ta thin film was negligible before approaching the interface. However, scanning electron microscopy study as a function of sputter depth showed that the craters were developed abruptly near the interface, A blistering mechanism is proposed for the crater formation. The buildup of compressive stress caused by volume increase of the Ta layer near the interface due to oxidation is suggested to be a driving force for the crater formation.