Unveiled Understanding on Thermodynamic Mechanisms of Atomic Layer Deposition Based on Trimethylaluminum and Water Precursors

Despite the importance of the atomic layer deposition (ALD) technique for developing thin films of various inorganic materials with the precisely controlled thickness, the detailed mechanistic pathway and thermodynamics of the ALD processes are not fully understood. In this study, the first-principles density functional theory calculations for ALD of Al2O3 are employed to explore the reaction thermodynamics in the chemical adsorption of trimethylaluminum (TMA) and water during the TMA- and H2O-dosed half-cycles of ALD. Three primary conclusions are highlighted from this investigation. (i) Despite the intrinsic nature of the TMA molecule with higher thermodynamic stability in a dimeric form than in a monomeric form, the TMA molecules would prefer to be chemisorbed on Al2O3(0001) surfaces in a monomeric form during the TMA-dosed half-cycle, exhibiting the highest stability for the monomeric TMA adsorbates in bidentate configurations under the assumption of the presence of abundant hydroxyl adsorption sites. (ii) The energy profile for the chemisorption of water molecules during the H2O-dosed half-cycle would strongly rely on the configuration of the TMA adsorbates formed in the previous TMA-dosed half-cycle, especially at the early stage of the H2O-dosed half-cycle. (iii) The thermodynamic feasibility of the water molecules chemisorbed after the early stage of the H2O-dosed half-cycle would not be significantly varied in real ALD processes.