First-principles mechanistic study of the initial growth of SRO by atomic layer deposition on TiO₂-terminated SrTiO₃ (001)

Perovskite oxides with a high dielectric constant such as SrTiO₃ have received much attention as alternative dielectrics for next generation semiconductor devices. The growth of SrTiO₃ thin films by atomic layer deposition (ALD) is commonly achieved by alternating deposition cycles of SrO and TiO₂. However, the underlying reaction mechanisms remain rather poorly understood despite their importance in optimizing the ALD process for desired film properties. In this work, we investigate the adsorption and reaction of Sr(Cp)₂ as a Sr precursor and H₂O as an oxidizer on TiO₂-terminated SrTiO₃ (001) using dispersion-corrected density functional theory calculations. The adsorption energy of Sr(Cp)₂ is predicted to be E_ads = −2.70 eV at low coverage and its magnitude decreases only by 0.16 eV until the surface is fully saturated at 0.25 monolayer (ML) coverage. The Sr(Cp)₂ adsorption on the first adsorption layer is found to be much weaker, yielding E_ads = −1.11 eV. The significant difference in E_ads can contribute favorably to single-layer SrO growth on the TiO₂-terminated surface. In addition, the low saturation coverage of 0.25 ML may suggest that at least four successive cycles of Sr(Cp)₂ dose would be required to form a single SrO layer. Our calculations also demonstrate that the kinetics and energetics of Sr(Cp)₂ decomposition depend strongly on H₂O coverage and the resulting Sr atoms may hardly undergo surface diffusion at typical ALD temperatures (< 300 °C). Our work highlights that a deeper understanding of surface chemistry evolution during the ALD process still needs to be developed to better predict and control the growth behavior and resulting properties of SrTiO₃ thin films, warranting further systematic investigation.