Room Temperature Growth of Epitaxial Titanium Nitride Films by Pulsed Laser Deposition

摘要

Reducing the thermal budget of epitaxial thin film growth has been one of the biggest challenges for the electronics industry. In this report, the room-temperature epitaxial growth of titanium nitride (TiN) thin films (similar to 75 nm) on (0001) Al2O3 substrates is demonstrated using a pulsed laser deposition technique. In TiN thin films, the epitaxial relationship is established by X-ray diffraction for (111)(TiN)//(0001) (Al2O3) and 1(1)over bar0(TiN) // 10(1)over bar0 (Al2O3) which corresponds to a 30 degrees rotation of titanium and nitrogen atoms with respect to the hexagon arrangement of aluminum atoms. An increase in the defect concentration is shown in the room-temperature thin film growth as compared to the ones grown at elevated temperature. A shift and broadening of the diffraction peaks is observed in the thin films as compared to the bulk value, indicating a higher residual tensile strain with decreasing growth temperature and an increase in defect concentration at room temperature. The increased defect concentration observed at lower growth temperature is explained by the lower energy budget that limits defect recombination and film relaxation. The residual strain in all films is dominated by the lattice mismatch (similar to 8.46% misfit) and defects, and not due to the thermal expansion mismatch, as Al2O3 and TiN have similar coefficients of thermal expansion. Raman spectroscopy measurements also confirm an increased concentration of vacancies in TiN films grown at lower temperature. Using atomic resolution scanning transmission electron microscopy, it is shown that the room-temperature grown films contain a lower density of periodic dislocations at the film/substrate interface, a characteristic of the large misfit systems, but have more dislocations trapped within the film. The lower density of dislocations near the film-substrate interface signifies incomplete relaxation at lower temperatures. In view of more defect