In situ quadrupole mass spectrometry and quartz crystal microbalance studies on the atomic layer deposition of titanium dioxide from titanium tetrachloride and water

The atomic layer deposition (ALD) of TiO2 from TiCl4 and D2O at 150-400 degreesC was studied in situ with a quadrupole mass spectrometer (QMS) and a quartz crystal microbalance (QCM). The ALD growth proceeds via exchange reactions on the film surface. In the first step, TiCl4 is introduced on a surface covered with -OD groups which then become replaced with -O-TiClx species, and DO is released as a volatile byproduct. In the second step, the incoming D2O reacts with the surface -Cl atoms replacing them with -OD groups and, again, DCl is released. When the temperature is increased from 150 to 250 degreesC, the number of -Cl ligands released during the TiCl4 pulse decreases from about two to one. At temperatures higher than 250 degreesC, less than one -Cl ligand is released, indicating molecular adsorption of TiCl4.