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.