Paper TF-TuA7
Waterless TiO₂ Atomic Layer Deposition using Titanium Tetrachloride and Titanium Tetraisopropoxide

Tuesday, October 19, 2010, 4:00 pm, Room Ruidoso

Most processes for TiO₂ atomic layer deposition (ALD) utilize water or other oxidants that can oxidize some substrates of interest. To avoid this oxidation, waterless or oxidant-free surface chemistry can be used that involves titanium halides and titanium alkoxides. This waterless surface chemistry approach for metal oxide ALD was originally proposed by the University of Helsinki group (M. Ritala et al., Science 288, 319 (2000)). In this study, TiO₂ ALD was accomplished using titanium tetrachloride (TiCl₄) and titanium tetraisopropoxide (TTIP). In situ Fourier transform infrared (FTIR) studies revealed that the mechanism for TiO₂ ALD using TiCl₄ and TTIP changed with temperature. At high temperatures between 250 and 300 ºC, the isopropoxide species after TTIP exposures quickly underwent beta-hydride elimination to produce TiOH species on the surface. The observation of propene by quadrupole mass spectrometry confirmed the beta-hydride elimination reaction pathway. The TiCl₄ exposure then reacted with the TiOH species to deposit TiCl_x species on the surface. At low temperatures between 125 and 200 ºC, the isopropoxide species remained after TTIP exposures to react with TiCl₄. However, this reaction was much less efficient than the reaction of TiCl₄ with TiOH species. Quartz crystal microbalance (QCM) studies were also used to monitor TiO₂ ALD at low and high temperatures. The QCM studies measured low TiO₂ growth rates of ~3 ng/cm² at a low temperature of 150°C. In contrast, much higher TiO₂ growth of ~15 ng/cm² were observed at a higher temperature of 250°C under similar reaction conditions. X-Ray reflectivity measurements determined that TiO₂ ALD using TiCl₄ and TTIP at 250°C produced a growth rate of 0.5-0.6 Å per cycle. X-Ray photoelectron studies also confirmed TiO₂ film growth with a chlorine contamination of less than 0.5 at%. This waterless TiO₂ ALD process using TiCl₄ and TTIP should be valuable for preventing substrate oxidation during TiO₂ ALD on oxygen-sensitive substrates such as cobalt.