Studies in highly-developed functionalizing of titanium nitride thin films by reflection high energy electron diffraction and electron spectroscopy

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The property of titanium nitride, TiN_y, gradually changes from metallic to covalent and then to ionic with increasing the ratio of N to Ti, which makes TiN_y fascinating for both points of view of technological applications such as diffusion barriers in microcircuits and fundamental research. In order to elucidate the interesting physical properties of TiN_y films, investigation of bonding properties between Ti and N atoms by in-situ observations during the growth of TiN_y films is necessary. However, knowledge of changes in the crystallographic and electronic structures during nitriding of Ti films, is not complete yet. Thus, to obtain the knowledge, in the 400 kV analytical and high resolution transmission electron microscope (TEM) combined with ion accelerators, nitrogen ions (N_2^+) with 62 keV were implanted into 100 nm-thick Ti films, which were grown in ultra-high vacuum with evaluation of the crystallinity by reflection high energy electron diffraction (RHEED). Observations by … More in-situ TEM equipped with electron energy loss spectrometer and by RHEED and Auger electron spectroscopy, along with the results of the discrete variational Xα molecular orbital calculations, revealed changes in the crystallographic and electronic structures of evaporated-Ti films due to N-implantation. As-grown Ti films consist of (110)-oriented TiH_x and (03・5)-oriented hcp-Ti. Heating of evaporated Ti films up to 350℃ gives rise to release of H from TiH_x and transformation or TiH_x to hcp-Ti. A (001)-oriented NaC1-type TiN_y is epitaxially formed by the transformation of (03・5)-oriented hcp-Ti to (001)-oriented fcc-Ti and by the occupation of N in the octahedral (O-) sites, whereas a (110)-oriented TiN_y is formed by nitriding a (110)-oriented TiH_x. The release of H from the TiH_x precedes the occupation of N in the O-sites of fcc-Ti sublattice. The energy loss peak due to plasmon excitation of the areas where TiH_x has grown in the as-grown films shifts to lower loss energy in the early N-implanting stage, while that of the areas, where hcp-Ti has grown, gradually shifts to higher loss energies with increasing N-dose. Analysis of Mulliken bond overlap populations revealed that occupation of N in the O-sites gives rise to weakening of Ti-Ti bonds and forming of Ti-N covalent bonds. Less