The microstructure of beta-FeSi2 films grown on Si using magnetron sputtering has been examined using various electron microscopy techniques. After annealing, the differences in interfacial roughness and grain size with different target materials are investigated using secondary electron and transmission electron microscopy techniques. Here, we study the variation in microstructures with sputtered materials. We observed, for Fe sputtered onto Si followed by rapid thermal anneal, the formation of nanosized FeSi2 grains (similar to 120 nm) with a rough surface and film/Si interface. These morphologies and microstructure are very different when FeSi2 is sputtered onto Si and annealed; instead, the formation of micrometer FeSi2 grains (similar to 1 to 5 mu m) with sharp surfaces and interfaces is observed. In addition, the effect of oxygen on the growth of FeSi2 has also been studied. Our results show that oxygen impurities in the films result in the formation of SixOy nanoparticles in the FeSi2 matrix upon anneal. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3454741] All rights reserved.