Growth of ZnO/Al₂O₃ Alloy Films Using Atomic Layer Deposition Techniques

TLDR

Atomic layer deposition enables fabrication of composite thin films, but their thickness and stoichiometry depend on surface chemistry during growth. The study aims to explain why measured ZnO/Al₂O₃ alloy film thicknesses and compositions deviate from predictions. ZnO/Al₂O₃ alloy films were grown by alternating Zn(CH₂CH₃)₂/H₂O and Al(CH₃)₃/H₂O ALD cycles in a viscous flow reactor, varying the ZnO cycle fraction from 0 to 100%, and film thickness and composition were measured by profilometry, ellipsometry, and atomic emission spectroscopy. Measured thicknesses and Zn contents were significantly lower than rule‑of‑mixtures predictions, indicating systematic deviations in the alloy films.

Abstract

Atomic layer deposition (ALD) is an ideal technique for fabricating composite thin films. The thickness and stoichiometry of composite thin films prepared using ALD is dependent on the underlying surface chemistry during ALD film growth. A set of ZnO/Al2O3 alloy films was prepared by ALD in a viscous flow reactor using alternating Zn(CH2CH3)2/H2O exposures for ZnO ALD and alternating Al(CH3)3/H2O exposures for Al2O3 ALD. The ZnO reaction cycle percentage was varied from 0 to 100%. The composite film thicknesses were measured using ex situ stylus profilometry and ellipsometry. The atomic composition of the composite films was established by atomic emission spectroscopy. Large deviations were found when the measured thicknesses and compositions were compared with “rule of mixtures” predictions. Many of the ZnO/Al2O3 alloy films showed lower than expected Zn film content and were thinner than predicted by the ALD growth rates of the pure ZnO and Al2O3 films. To understand these discrepancies, in situ quartz ...