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 duri ng the initial stages of the deposition of amorphous hydrogen-free dia mond-like carbon (DLC) films. We employ mass selected ion beams of 50, 100, 500 and 1000 eV C-12(+) ions. The microstructures of the produce d DLC films, of the substrate and of the interface are characterized b y transmission electron microscopy. Electron diffraction exhibits all the DLC films to be amorphous. Parallel electron energy loss spectrosc opy shows plasmon peaks at around 30 eV for all room temperature depos ited DLC films, which indicates sp(3)-coordination of C atoms in the a morphous network. Thus tetrahedrally amorphous carbon has formed. The Si substrates are affected by the DLC deposition as dependent on the d eposition energy. (i) At all energies these are highly strained. After 100 eV deposition they are highly dislocated. (ii) The substrate cont ains a high amount of carbon, according to secondary ion mass spectros copy up to 1 at.%. (iii) The carbon content is found far beyond a dept h of a few nm that is expected for thermal diffusion and for the ion i mplantation range. We discuss the nucleation and growth of the DLC lay er as a function of the deposition energy and find corroboration of th e subplantation model. The unusually deep-reaching carbon in the subst rate is discussed in view of mass transport mechanisms that are enhanc ed by Si point defects created in excessively high densities due to ca rbon ion impact. (C) 1998 Elsevier Science S.A.