Residual chlorine in TiO2 films grown at low temperatures by plasma enhanced atomic layer deposition

We have studied the presence of residual chlorine in thin TiO2 films grown by plasma enhanced atomic layer deposition (PEALD) at temperatures within 40-250 °C range, using x-ray photoemission spectroscopy, secondary ion mass spectrometry, grazing incidence x-ray diffraction and scanning electron microscopy. The source of the residual chlorine is TiCl4, which was used as a titanium precursor in ALD. The PEALD results are compared with the results on ALD films grown thermally in the same reactor. Films deposited by PEALD show a lower amount of residual chlorine, while chlorine concentration decreases with the processing temperature in both ALD techniques. In addition to the standard signal from residual chlorine bonded to Ti, a strong signal from ClO bonds was observed in PEALD samples grown at low temperatures. Our study also shows the development of an anatase phase in TiO2 films grown above 200 °C, which correlates well with the reduction of both types of residual chlorine in PEALD samples.