Synthesis and characterization of low pressure chemically vapor deposited titanium nitride films using TiCl₄ and NH₃

This study investigates the inter-relationships governing the growth kinetics, composition, and properties of titanium nitride (TiN) films synthesized by low pressure chemical vapor deposition (LPCVD) using titanium tetrachloride (TiCl₄) and ammonia (NH₃) as reactants. In the deposition temperature regime of 450 to 600 °C, an Arrhenius dependence was observed from which an activation energy of 42 kJ/mol was calculated. The growth rate dependencies on the partial pressures of NH₃ (50 to 100 mTorr) and TiCl₄ (1 to 12 mTorr) yielded reaction rate orders of 1.37 and -0.42, respectively. RBS spectrometry was used for establishing the Ti/N ratio and the chlorine content of the films as a function of the processing variables. Films with compositions trending towards stoichiometry were produced as the deposition temperature was decreased and the NH₃ partial pressure was increased. The chlorine concentration in the films was observed to decrease from 7.2% (a/o) at the deposition temperature of 450 °C down to 0.15% at 850 °C. The film density values increased from 3.53 to 5.02 g/cm³ as the deposition temperature was increased from 550 to 850 °C. The resistivity of the films was dependent on changes in deposition temperature and flow rate ratios. The lowest resistivity value of 86 μΩ cm was measured for a deposition temperature of 600 °C and an NH₃/TiCl₄ flow ratio of 10/1. The film stress was found to be tensile for all deposits and to decrease with higher deposition temperatures. Nano-indentation measurements yielded values for the hardness and Young's modulus of the films to be around 15 and 250 GPa, respectively. X-ray diffraction measurements revealed in all cases the presence of cubic TiN phase with a preferred (200) orientation. For the investigated aspect ratios of up to 4:1, the deposits were observed to exhibit conformal step coverage over the investigated range of processing conditions.