Waterless TiO2 atomic layer deposition using titanium tetrachloride and titanium tetraisopropoxide

The surface chemistry for TiO2 atomic layer deposition (ALD) typically utilizes water or other oxidants that can oxidize underlying substrates such as magnetic disks or semiconductors. To avoid this oxidation, waterless or oxidant-free surface chemistry can be used that involves titanium halides and titanium alkoxides. In this study, waterless TiO2 ALD was accomplished using titanium tetrachloride (TiCl4) and titanium tetraisopropoxide (TTIP). In situ transmission Fourier transform infrared (FTIR) studies were employed to study the surface species and the reactions during waterless TiO2 ALD. At low temperatures between 125 and 225 degrees C, the FTIR absorbance spectra revealed that the isopropoxide species remained on the surface after TTIP exposures. The TiCl4 exposures then removed the isopropoxide species and deposited additional titanium species. At high temperatures between 250 and 300 degrees C, the isopropoxide species were converted to hydroxyl species by beta-hydride elimination. The observation of propene gaseous reaction product by quadrupole mass spectrometry (QMS) confirmed the b-hydride elimination reaction pathway. The TiCl4 exposures then easily reacted with the hydroxyl species. QMS studies also observed the 2-chloropropane and HCl gaseous reaction products and monitored the self-limiting nature of the TTIP reaction. Additional studies examined the waterless TiO2 ALD growth at low and high temperature. Quartz crystal microbalance measurements observed growth rates of similar to 3ng/cm(2) at a low temperature of 150 degrees C. Much higher growth rates of similar to 15 ng/cm(2) were measured at a higher temperature of 250 degrees C under similar reaction conditions. X-ray reflectivity analysis measured a growth rate of 0.55 +/- 0.05 angstrom/cycle at 250 degrees C. X-ray photoelectron depth-profile studies showed that the TiO2 films contained low Cl concentrations <1 at. %. This waterless TiO2 ALD process using TiCl4 and TTIP should be valuable to prevent substrate oxidation during TiO2 ALD on oxygen-sensitive substrates. (C) 2014 American Vacuum Society.