Characterization of highly oriented (110) TiN films grown on epitaxial Ge/Si(001) heterostructures

Abstract

The characteristics of epitaxial growth of titanium nitride films on Ge/Si(001) have been studied. The growth of titanium nitride and germanium films on (001)Si was carried out in situ in a high vacuum chamber (<10−7 Torr) using a multitarget stage in a pulsed laser deposition system. Electrical resistivity, stoichiometry, crystallinity, and epitaxial relationships as a function of deposition temperature have been studied. Electrical resistivity of the titanium nitride films grown at deposition temperatures in the range of 450 °C–750 °C was measured using a four-point probe. The stoichiometry of these films was investigated using Auger electron spectroscopy and Raman spectroscopy. The crystalline quality and epitaxial nature of TiN films grown at different substrate temperatures were characterized using x-ray diffraction and transmission electron microscopy. Highly oriented titanium nitride films with (110) orientation were obtained on Ge(001) film when the substrate temperature was maintained between 550 °C and 650 °C. The epitaxial growth of the titanium nitride films was found to be a function of two-dimensional or three-dimensional growth mode of germanium film on silicon (001) substrate. Titanium nitride films grown at a substrate temperature of 650 °C exhibited the lowest room temperature resistivity (26 μΩ-cm), highest nitrogen content (close to stoichiometry), and the best epitaxiality with the Ge(001) films on Si(001). The epitaxial relationships for the TiN/Ge/Si(001) heterostructure are found to be [001]TiN‖ [110]Ge‖ [110]Si and [110]TiN‖ [110] Ge‖ [110]Si. To explain the epitaxial growth in a large mismatch system (∼28%) such as TiN/Ge(001), the domain matching mechanism is proposed. Domains of size four (001)TiN by seventeen (220)TiN in the titanium nitride film match closely with domains of size three (220)Ge by sixteen (220)Ge in the germanium film, respectively. The lattice matching epitaxy involving a 4% mismatch between Ge and Si provides a mechanism for epitaxial growth of Ge on Si(001).