Yuniarto Widjaja

Quantum chemical study of the mechanism of aluminum oxide atomic layer deposition

The atomic layer deposition of alumina using water and trimethylaluminum is investigated using the density functional theory. The atomistic mechanisms of the two deposition half-cycles on Al–CH3* and Al–OH* surface sites are investigated. Both half-cycle reactions proceed through the formation of an Al–O Lewis acid-base complex followed by CH4 formation. The Al–O complexes are relatively stable, with formation energies between 0.57 and 0.74 eV. The CH4 formation activation energies range from 0.52 to 0.91 eV and both half-cycle reactions are exothermic with overall enthalpies of reaction between 1.30 and 1.70 eV.

Atomic layer deposition of hafnium oxide: A detailed reaction mechanism from first principles

Atomic layer deposition (ALD) of hafnium oxide (HfO2) using HfCl4 and H2O as precursors is studied using density functional theory. The mechanism consists of two deposition half-reactions: (1) HfCl4 with Hf-OH sites, and (2) H2O with Hf-Cl sites. Both half-reactions exhibit stable intermediates with energies lower than those of the final products. We show that increasing the temperature reduces the stability of the complex. However, increasing temperature also increases the dissociation free-energy barrier, which in turn results in increased desorption of adsorbed precursors. Both half-reactions are qualitatively similar to the corresponding reactions of ZrO2 ALD using ZrCl4 and H2O.

Quantum chemical study of the elementary reactions in zirconium oxide atomic layer deposition

Elementary reactions in atomic layer deposition of zirconia using zirconium tetrachloride and water are investigated using the density functional theory. The atomistic mechanisms of the two deposition half cycles on the Zr–OH and Zr–Cl surface sites are investigated. Both half reactions proceed through the formation of stable intermediates, resulting in high barriers for HCl formation. We find that the intermediate stability is lowered as the surface temperature is raised. However, increasing temperature also increases the dissociation free-energy barrier, which in turn results in increased desorption of adsorbed precursors.

Atomistic mechanism of the initial oxidation of the clean Si(100)-(2×1) surface by O2 and SiO2 decomposition

Density functional theory simulations are used to investigate the reaction mechanism of oxidation of the bare Si(100)-(2×1) surface by molecular oxygen. O2 adsorbs molecularly on the “up” surface Si atom with no activation barrier and an adsorption energy of 35 kcal/mol. Adsorbed O2 is found to be negatively charged. O2(a) then transforms into the peroxide bridge structure with a barrier of 10 kcal/mol and exothermicity of 33 kcal/mol. The bridged peroxide O2 then dissociates by first inserting one oxygen atom into the Si–Si dimer bond followed by insertion of the remaining oxygen atom into a Si–Si backbond. The activation barriers are 36 kcal/mol and 13 kcal/mol for the first and second oxygen insertions, respectively. We have also calculated the activation barriers for SiO2 film decomposition, which becomes prevalent at high temperatures, in which SiO(g) desorbs from SiO2 films. The SiO desorption barriers are found to be in the range of 65–67 kcal/mol.