Initial growth mechanisms of ZrO2 and TiO2 thin films using cycloheptatrienyl–cyclopentadienyl heteroleptic precursors: A comparative study by density functional theory

The initial growth mechanisms of atomic layer deposition (ALD) of ZrO2 and TiO2 thin films using cycloheptatrienyl (CHT)–cyclopentadienyl (Cp) precursors on Si-OH surface have been investigated theoretically. The reactions of CpMeZr(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 CpMeZr(CHT). Chemisorption of the CHT–Cp precursors on Si-OH surface could not be found. The most stable adsorption states of both CpMeZr(CHT) and CpTi(CHT) are formed via CHT rings. The previous experiments have shown that an ALD-window has been established when depositing ZrO2 thin films, but has not been established when depositing TiO2 thin films. Our calculation results show that the adsorption of CpMeZr(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.