NANOSTRUCTURE OF THE SURFACE AND INTERFACE AND MECHANISMS OF THERMAL GROWTH OF ULTRATHIN FILMS OF SI3N4 ON SI(001)

The chemical situation of the Si atoms at the surface of Si3N4 ultrath in films thermally grown onto Si(001) substrates 2x1 reconstructed in a NH3 atmosphere has been recently studied in detail by core-level spe ctroscopy using synchrotron radiation, as well as the chemical situati on of the Si atoms at the film/substrate interface. The Si atoms at th e surface are assigned to be either bonded to N atoms that are located in the layer just below the surface and having one dangling bond, or terminated by NH2. The Si atoms at the interface present intermediate oxidation states. Also recently high resolution isotopic tracing studi es of N and H showed that nitrogeneous species (most probably NHx radi cals, x < 3) are mobile during thermal growth of silicon nitride films , while isotopic tracing of Si showed that this species appears to be immobile during growth. This newly built experimental scenario for the nanostructure of the surface and interface, and for the atomic transp ort processes taking place during nitride growth, led us to develop a model for the mechanism of thermal growth of Si3N4 ultrathin films on Si(100), that is capable to explain the self-limited character which m akes them extremely attractive for applications in the VLSI and ULSI t echnologies for microfabrication of silicon devices.