Kinetics and microstructure of laser chemical vapor deposition of titanium nitride

Titanium nitride (TiN) films were deposited onto Ti–6Al–4V substrates by laser chemical vapor deposition using a cw CO2 laser and TiCl4, N2 and H2 reactant gases. Laser-induced fluorescence (LIF) and pyrometry determined relative titanium gas phase atomic number density and deposition temperature, respectively. Auger electron spectroscopy found substoichiometric films, caused by diffusion of nitrogen through TiN grain boundaries to the titanium alloy substrate. The morphology is a polyhedral structure with crystallite sizes ranging from 10 to 1000 nm. The activation energy was calculated to be 122 ± 9 kJ mol−1 using growth rates measured by film height and 117 ± 23 kJ mol−1 using growth rates measured by LIF signals. Above N2 and H2 levels of 1.25% and below TiCl4 input of 4.5%, the growth rate has a half-order dependence on nitrogen and a linear dependence on hydrogen. The rate-determining steps of TiN growth are discussed.