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 Cl−O 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. - Highlights: • Cl in (Cl−Ti)-groups was observed in PEALD and tALD TiO₂ films at all temperatures. • Cl in (Cl−O)-configuration was observed only in films grown by PEALD bellow 200 °C. • PEALD films show lower concentration of residual Cl compared to tALD. • Residual Cl inhibits formation of TiO₂ crystallites and growth of an anatase phase.