Atomic layer deposition of titanium dioxide using titanium tetrachloride and titanium tetraisopropoxide as precursors

Most atomic layer deposition (ALD) processes for metal oxides involve the use of a metal precursor and an oxygen source, such as H₂O, O₃, or an O₂ plasma. These ALD processes lead to the formation of an undesirable interfacial oxide during deposition on semiconductor surfaces. As an alternative, some metal oxides other than TiO₂ have been deposited using metal alkoxides as the oxygen source. In this article, we report on the ALD of TiO₂ using TiCl₄ and titanium tetraisopropoxide (TTIP) as precursors. Our surface infrared spectroscopy data shows that over the temperature range of 150–250 °C and the duration of a typical ALD cycle (∼1–10 s), in both half-reaction cycles, the surface reaction mechanism is dominated by alkyl-transfer from the TTIP ligands to Ti-Cl species. At 250 °C, which is the onset for TTIP thermal decomposition, the contribution of the direct decomposition reaction to film growth is negligible. The growth per cycle, ∼0.7 Å at 200 °C, is higher than H₂O-based ALD of TiO₂ from either TiCl₄ or TTIP, but similar to O₂-plasma-based processes. X-ray photoelectron spectroscopy data show TiO₂ films with only the +4 oxidation state of Ti, and the Cl content is estimated to be 2.5–3.5%. UV–Vis spectroscopy shows a band gap of ∼3.0 eV, which is comparable to the values reported in the literature for amorphous TiO₂ thin films.