Plasma-enhanced atomic layer deposition of titanium molybdenum nitride: Influence of RF bias and substrate structure

In this work, TiMoN thin films were deposited by plasma-enhanced atomic layer deposition with an equal number of Ti and Mo precursor exposures at a substrate temperature of 250 °C. Tetrakis(dimethylamido) titanium and bis(tert-butylimido)bis(dimethylamido) molybdenum were used as sources for Ti and Mo, respectively. N2 and N2/H2 plasma were used, respectively, for TiN and MoN cycles as a source for N. Negative RF substrate bias voltage of magnitude, |Vbias|, of 0, 31, 62, 125, and 188 V were applied during the plasma half cycle. Nanocrystalline rock salt crystal structures were found by x-ray diffraction for films deposited on single-crystal Si and Si-thermal oxide substrates. Applying |Vbias| generated voids by the bombardment of high-energy ions, lowering the density. Further increase of |Vbias| caused the annihilation of voids and a slight increase in density. Four-point probe measurement showed increased electrical resistivity due to a reduction in grain size caused by continuous renucleation during growth. High-energy ions at high |Vbias| sputtered away the films resulting in low growth rates. Stripe test revealed inferior wear rates and coefficients of friction at higher |Vbias| due to low-density porous films. Epitaxial films deposited on c-plane sapphire had (111) orientation and considerable mosaicity with twinned domains rotated at 60° to each other.