Carbon transport in Si(001) and nucleation of diamond-like carbon layers during mass selected carbon ion beam deposition

We investigate the transport of carbon into the Si(001) substrate during the initial stages of the deposition of amorphous hydrogen-free diamond-like carbon (DLC) films. We employ mass selected ion beams of 50, 100, 500 and 1000 eV C-12(+) ions. The microstructures of the produced DLC films, of the substrate and of the interface are characterized by transmission electron microscopy. Electron diffraction exhibits all the DLC films to be amorphous. Parallel electron energy loss spectroscopy shows plasmon peaks at around 30 eV for all room temperature deposited DLC films, which indicates sp(3)-coordination of C atoms in the amorphous network. Thus tetrahedrally amorphous carbon has formed. The Si substrates are affected by the DLC deposition as dependent on the deposition energy. (i) At all energies these are highly strained. After 100 eV deposition they are highly dislocated. (ii) The substrate contains a high amount of carbon, according to secondary ion mass spectroscopy up to 1 at.%. (iii) The carbon content is found far beyond a depth of a few nm that is expected for thermal diffusion and for the ion implantation range. We discuss the nucleation and growth of the DLC layer as a function of the deposition energy and find corroboration of the subplantation model. The unusually deep-reaching carbon in the substrate is discussed in view of mass transport mechanisms that are enhanced by Si point defects created in excessively high densities due to carbon ion impact. (C) 1998 Elsevier Science S.A.