A mass spectrometrical surface chemistry study of aluminum nitride ALD from tris-dimethylamido aluminum and ammonia

Abstract

Dialkylamido compounds, such as tris-dimethylamido aluminum (TDMAA, Al(NMe₂)₃) and tetrakis-dimethylamido titanium (TDMAT, Ti(NMe₂)₄) are interesting precursors for depositing nitrides using atomic layer deposition (ALD) due to their high volatility and reactivity at low temperatures. In this study, we explored surface chemistry using mass spectrometry and discovered that the surface mechanisms involved β-hydride elimination and ligand decomposition, as well as transamination and hydrogenation reactions which facilitate ligand exchange. This is mainly based on the –N(Me)₂ and HN(Me)₂ detected during both TDMAA and NH₃ pulses, and CH₄ signals detected during the NH₃ pulse stage. The expected reductive elimination of the two dimethylamido ligands, via a direct nitrogen–nitrogen coupling reaction was not observed, suggesting that it is less thermodynamically favorable compared to reduction by NH₃. Arrhenius analysis between 150 and 300 °C found activation energies (E_a) = 27–30 kJ mol⁻¹ and pre-exponential factors (A) = 3–5 s⁻¹ for the reaction between TDMAA and NH₃.