Structural properties of the titanium dioxide thin films grown by atomic layer deposition at various numbers of reaction cycles

A dependence of structural properties of TiO₂ films grown on both Si- and Ti-substrates by atomic layer deposition (ALD) at the temperature range of 250-300 °C from titanium ethoxide and water on the number of reaction cycles N was investigated using Fourier-transform infrared (FTIR) spectroscopy and X-Ray diffraction (XRD). TiO₂ films grown on both Si- and Ti-substrates revealed amorphous structure at low values of N < 400. However, an increase of N up to values 400-3600 resulted in the growth of polycrystalline TiO₂ with structure of anatase on both types of substrates and according to XRD-measurements the sizes of crystallites rose with the increase of N. The maximum anatase crystallite size for TiO₂ grown on Ti-substrate was found to be on ∼35% lower in comparing with that for TiO₂ grown on Si-substrate. A use of titanium methoxide as a Ti precursor with the ligand size smaller than in case of titanium ethoxide allowed to observe an influence of the ligand size on both the growth per cycle and structural properties of TiO₂. The average growth per cycle of TiO₂ deposited from titanium methoxide and water (0.052 ± 0.01 nm/cycle) was essentially higher than that for TiO₂ grown from titanium ethoxide and water (0.043 ± 0.01 nm/cycle). Ligands of smaller sizes were found to promote the higher crystallinity of TiO₂ in comparison with the case of using the titanium precursor with ligands of bigger sizes.