In Situ Mass Spectrometry Study on Atomic Layer Deposition from Metal (Ti, Ta, and Nb) Ethoxides and Water

Reaction mechanisms between titanium, tantalum, and niobium ethoxides and deuterated water in the atomic layer deposition (ALD) of TiO 2, Ta 2 O 5, and Nb 2 O 5 were studied with a mass spectrometer. The amounts of the reaction product CH 3 CH 2 OD + ( m / z = 47) and its main fragment CH 2 OD + ( m / z = 32) increased up to about 300 °C where all the metal precursors started to thermally decompose. Despite the decomposition, significant amounts of the ligands still remained on the surface and were released in the exchange reactions with D 2 O. It was also observed that in the titanium dioxide process titanium ethoxide adsorbs on the water-treated TiO 2 surface mostly without obvious exchange reactions, and over 90% of the ligands were released during the water pulse. The adsorption of C 2 H 5 OH on the TiO 2 surface was also examined, and it can partially explain the low amount of ligands released during the metal precursor pulses. At 325 °C the ALD growth of Ta 2 O 5 and Nb 2 O 5 can mainly be described as an alternate release of (C 2 H 5 ) 2 O during the Ta(OC 2 H 5 ) 5 or Nb(OC 2 H 5 ) 5 pulses and C 2 H 5 OD during the D 2 O pulse.