A secondary reaction pathway for the alumina atomic layer deposition process with trimethylaluminum and water, revealed by full-range, time-resolved in situ mass spectrometry

A method to obtain full mass over charge (m/z), time-resolved quadruple mass spectrometry (QMS) spectra of an atomic layer deposition (ALD) cycle is proposed. This method allows one to circumvent the limitations of traditional approaches for obtaining QMS information in ALD as all m/z values can be simultaneously screened for the formation of reaction products in an efficient way. As a proof of concept, this method was applied to the trimethylaluminum (TMA)-water process. This process has been studied extensively over the past decades. Besides the expected formation of CH4, formation of gaseous HOAI(CH3)(2) during the water pulse is observed, revealing a secondary reaction pathway for the water. The reaction energy and Gibbs free energy for different reactions are investigated computationally using density functional theory calculations and confirm that the secondary reaction pathway is thermodynamically allowed for certain surface conditions