Insight into the structural evolution during TiN film growth via atomic resolution TEM

Although the microstructure evolution during TiN film growth has been extensively studied, how the atomic-resolution structure of the films changes with the deposition conditions remains unclear. Here, a series of TiN films were prepared on silicon substrates at different bias voltages (V-b) by magnetron sputtering. The microstructure and atomic resolution structures of the films were systematically investigated with transmission electron microscopy (TEM) and high resolution TEM (HRTEM), complemented by X-ray photoelectron spectroscopy measurement and density functional theory (DFT) calculations. With increasing the bias voltage, the morphology of columnar grain evolves, and grain size and dislocation density increase, and films become much dense. HRTEM observations reveal that the boundaries between two neighboring grains are dominated by low-angle grain boundaries in the case of floating bias conditions. Numerous twins surprisingly form in the TiN films under certain bias voltage. The initiation of twins in TiN films can be attributed to the reduction of stacking fault energy (SFE) caused by non-stoichiometry to a certain degree, i.e., N/Ti atomic ratio, as validated by theoretical calculations. Moreover, the mechanisms of hardness alterations under different bias-voltages are discussed. (C) 2018 Elsevier B.V. All rights reserved.