Interface properties and structural evolution of TiN/Si and TiN/GaN heterostructures

Spectroscopic ellipsometry (SE) is employed to study the evolution of microstructure, stoichiometry, and electron-transport properties of titanium nitride (TiN) heterostructures grown on Si and gallium nitride (GaN) by reactive magnetron sputtering. In order to achieve subnanometer resolution for the SE analysis, we developed and validated the appropriate methods of interpreting the optical data. Thus, we used (a) effective medium theories describing the heterostructures in terms of their constituent materials (Si, GaN, TiN, over-stoichiometric TiNx, and voids), and (b) a combined Drude-Lorentz model describing the optical response of the conduction and valence electrons of TiN and TiNx. In the case of TiN/Si, the SE results indicate a pure Volmer-Weber type of growth with four distinct growth stages. A TiNx layer is formed before TiN due to the stress variations during growth. On the other hand, TiN/GaN exhibits a quasi two-dimensional growth character. In both cases, the TiN resistivity is very high for films thinner than the critical thickness for homogeneous growth. Thus, for practical applications in electronic devices the thickness of the TiN layer should be at least 4 and 14 nm for TiN/GaN and TiN/Si, respectively. (C) 2003 American Institute of Physics.