Role of Nonplasma Oxidizing Agent on the Reaction Step in Atomic Layer Deposition of Titanium Oxide Thin Films

High Resolution Image Download MS PowerPoint Slide Atomic layer deposition (ALD) is a key technique for fabricating high-quality metal oxide thin films via sequential surface reactions between precursors and oxidizing agents. In the thermal (nonplasma) ALD process for TiO 2 thin films, Titanium(IV) chloride (TiCl 4 ), Titanium(IV) isopropoxide (TTIP), and Tetrakis(dimethylamido)titanium(IV) (TDMAT) are among the most widely used precursors, while H 2 O and H 2 O 2 serve as the primary oxidizing agents. This study carried out a theoretical investigation of the oxidation step in ALD–TiO 2, focusing on the reaction mechanisms and energetics using density functional theory (DFT). The simulations revealed that H 2 O oxidizes the surface via O–H bond dissociation, whereas H 2 O 2 proceeds through either O–H or O–O bond cleavage, each with distinct activation barriers and resulting surface structures. The activation barriers for H 2 O oxidation on TDMAT, TTIP, and TiCl 4, were approximately 24, 50, and 92 kJ/mol, respectively, while for H 2 O 2, the O–H bond cleavage pathway required barriers of about 36, 64, and 87 kJ/mol, respectively, and the O–O cleavage pathway required 77, 190, and 170 kJ/mol, respectively. Despite its higher energy requirement, the O–O pathway of H 2 O 2 enables the oxidation of two precursor species with a single molecule, effectively halving the oxidant consumption─an important advantage for industrial-scale applications. Furthermore, this pathway generates twice as many reactive –OH adsorption sites compared to H 2 O, directly impacting film growth kinetics and quality. This study provided valuable insight for optimizing ALD process parameters and selecting synergistic precursor-oxidant pairs, thereby advancing the fundamental knowledge and practical capabilities of ALD technology.