Reaction mechanism studies on the zirconium chloride–water atomic layer deposition process

Reaction mechanisms in the zirconium chloride–water atomic layer deposition (ALD) process have been studied with a quartz crystal microbalance (QCM) and quadrupole mass spectrometer (QMS) at 250–500 °C. The only observed reaction byproduct was HCl. Both the growth rate and the amount of reaction byproduct were the highest at 300 °C as measured with QCM and QMS, respectively. The reaction temperature had no major effect on the reaction mechanism: half of the chloride ligands were released during the ZrCl4 pulse and the other half during the water pulse. However, at higher temperatures the process was slowly moving towards a mechanism where only one chlorine is released during the zirconium pulse and the other three during the D2O pulse. This was suggested to be due to a lowered amount of OD groups on the surface at high temperatures. The results were compared with the earlier TiO2, ZrO2 and HfO2 ALD processes.