Initial growth mechanisms of ZrO_2 and TiO_2 thin films using cycloheptatrienyl-cyclopentadienyl heteroleptic precursors: A comparative study by density functional theory

摘要

The initial growth mechanisms of atomic layer deposition (ALD) of ZrO_2 and TiO_2 thin films using cydoheptatrienyl (CHT)-cyclopentadienyl (Cp) precursors on Si-OH surface have been investigated theoretically. The reactions of Cp~(Me)Zr(CHT) and CpTi(CHT) with Si-OH 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 Si-OH 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.