Fabrication of nanostructured titanium thin films via N ion implantation and postannealing treatment

Supersaturated Ti(N) thin films have been prepared by the combination of low temperature nonequilibrium processes of ion beam sputtering (IBS) and ion implantation method. Ti thin films of 150 nm in thickness have been deposited on (001) Si substrate by IBS. N+ ions have been penetrated into the films with the dose of 1×1017∼2×1018 ion/cm2. The structural changes due to the N-implantation and successive heat treatments have been evaluated by X-ray photoelectron spectroscopy (XPS) chemical analysis and cross-sectional transmission electron microscopy (TEM) observation. The distribution of N atoms in N-implanted Ti films has been measured by XPS. The maximum concentration of N was achieved at the Ti/Si interface with beam energy of 100 keV. The linear increase of the binding energy shift in proportion to the N concentration suggests that N-implanted Ti films consist of Ti(N) supersaturated solid solution. From TEM observation, as-deposited Ti films show the conventional hcp structure with columnar grains 10 nm in diameter. These grains with growth direction of [0001]α develop perpendicular to the (001) Si substrate. N-implantation results in the film having the complex structure of α-Ti(N) solid solution with small amounts of ɛ-Ti2N and δ-TiN. Formation of the ɛ-Ti2N is recognized from electron diffraction for the N-implanted specimen with 1×1017 ion/cm2 and the δ-TiN phase for the specimen with 5×1017 ion/cm2. The lattice constant has been measured from electron diffraction and the c/a ratio of hcp-Ti(N) increases in proportion to the N concentration toward the theoretical value for cubic structure. The XPS compositional measurement suggests that N-implantation induces the anomaly saturated N in hcp-Ti(N) lattice. The lattice constant of hcp-Ti(N) decreases by postannealing treatment at 773 K. Postannealing promotes the phase decomposition of supersaturated solid solution of hcp-Ti(N) into meta-stable nitrides.