In Situ Mass Spectrometry Study on Surface Reactions in Atomic Layer Deposition of Al₂O₃ Thin Films from Trimethylaluminum and Water

The surface reactions between trimethylaluminum (TMA) and deuterated water (D 2 O) in the deposition of Al 2 O 3 were studied by using a mass spectrometer to determine the amount of the reaction product, methane (CH 3 D), produced in a flow-type atomic layer deposition (ALD) reactor during each deposition step. At low temperatures (<200 °C) more CH 3 D was produced during the TMA pulse whereas at higher temperatures when the dehydroxylation is more extensive more CH 3 D was produced during the D 2 O pulse. In addition to the temperature, the hydroxyl coverage was also noticed to depend on the D 2 O dose, since D 2 O reacts with dehydroxylated alumina sites producing adsorbed −OD groups. According to our results, which agree quite well with previous studies carried out by other methods, the dehydroxylation of the alumina surface seems to play a key role in the surface chemistry of the atomic layer deposition of Al 2 O 3 .