Paper TF-ThP15
Reaction Mechanism for the Atomic Layer Deposition of Titanium Dioxide using Titanium Tetrachloride and Titanium Tetraisopropoxide as Precursors

Thursday, November 1, 2012, 6:00 pm, Room Central Hall

Atomic layer deposition (ALD) is a thin film deposition technique widely used to deposit highly conformal thin films of a wide range of materials including metal oxides and nitrides, metals and more recently, polymers. Most ALD processes for the deposition of metal oxides require the use of H₂O, O₂ plasma, O₃, or H₂O₂ as the oxygen source. ALD processes for depositing metal oxides using metal halides and metal alkoxides as the oxygen source were first reported by Ritala (Science 288, 319 (2000)) to mitigate the problem of an interfacial oxide formation during deposition on semiconductor surfaces such as Si and Ge. Herein, we report an ALD process to deposit titanium dioxide using TiCl₄ and titanium tetraisopropoxide (Ti[(OC₃H₇)₄], TTIP) as the oxygen source. We have used in situ attenuated total reflection Fourier transform infrared spectroscopy to probe the corresponding surface reactions during film growth over a temperature range of 150-250 °C. Depending on the surface temperature, alkyl-transfer and β-hydride elimination have been proposed as two possible reaction pathways for TTIP on a TiCl_x-terminated surface. However, our infrared data show that alkyl-transfer is the only reaction pathway for this ALD process even at temperatures of up 250 °C, which is close to the decomposition temperature of TTIP. We also report the growth per cycle, stiochiometry, and the band gap for these TiO₂ films grown over the above temperature range. Finally, we discuss the growth of these TiO₂ films on Cl-terminated Ge nanoparticle surfaces.