Initial growth mechanisms of ZrO ₂ and TiO ₂ thin films using cycloheptatrienyl-cyclopentadienyl heteroleptic precursors: A comparative study by density functional theory

The initial growth mechanisms of atomic layer deposition (ALD) of ZrO ₂ and TiO ₂ thin films using cycloheptatrienyl (CHT)-cyclopentadienyl (Cp) precursors on SiOH surface have been investigated theoretically. The reactions of Cp ^Me Zr(CHT) and CpTi(CHT) with SiOH surface proceed through similar reaction pathways. The reaction of CpTi(CHT) requires much more energies than that of Cp ^Me Zr(CHT). Chemisorption of the CHT-Cp precursors on SiOH surface could not be found. The most stable adsorption states of both Cp ^Me Zr(CHT) and CpTi(CHT) are formed via CHT rings. The previous experiments have shown that an ALD-window has been established when depositing ZrO ₂ thin films, but has not been established when depositing TiO ₂ thin films. Our calculation results show that the adsorption of Cp ^Me Zr(CHT) is energetically favorable, but the adsorption of CpTi(CHT) is thermodynamic unfavorable. One theoretical explanation is given for this observed difference from the viewpoint of precursor adsorption.