Nanostructure of the Surface and Interface and Mechanisms of Thermal Growth of Ultrathin Films of Si₃N₄ on Si(001)

Abstract

The chemical situation of the Si atoms at the surface of Si,N, ultrathin films thermally grown onto Si(O01) substrates 2 x 1 reconstructed in a NH, atmosphere has been recently studied in detail by core-level spectroscopy using synchrotron radiation, as well as the chemical situation of the Si atoms at the film/substrate interface. The Si atoms at the 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 NH,. The Si atoms at the interface present intermediate oxidation states. Also recently high resolution isotopic tracing studies of N and H showed that nitrogeneous species (most probably NH, radicals, 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 transport processes taking place during nitride growth, led us to develop a model for the mechanism of thermal growth of Si,N, ultrathin films on Si( loo), that is capable to explain the self-limited character which makes them extremely attractive for applications in the VLSI and ULSI technologies for microfabrication of silicon devices.