Mechanical Properties of Atomic-Layer-Deposited Al₂O₃/Y₂O₃ Nanolaminate Films on Aluminum toward Protective Coatings

Atomic layer deposition is an appealing deposition technology for the fabrication of protective coatings for various applications, including semiconductor manufacturing chambers and related metallic parts with complex three-dimensional topographies, where a key requirement is (thermo)mechanical robustness of the coatings. Here, we study the mechanical properties of atomic-layer-deposited Al2O3, Y2O3, and their nanolaminate (NL) coatings on an Al metal substrate. Tensile straining experiments accompanied by in situ optical and scanning electron microscopy indicate that the fragmentation onset of 100 nm thick coatings can be tailored in the strain range of 1.3–2.1% by controlling the layer structure and composition of the NLs, such that a higher Al2O3 content, denser layer spacing, and amorphization favor higher crack onset strain. Although the fracture toughness of Al2O3 and Y2O3 is found to be similar, KIC = 1.3 MPa·m1/2, the (substantially tensile) intrinsic residual stress for Y2O3 is a disadvantage for applications, where applied tensile stresses are to be expected. The films adhere well to the Al substrate as significant delamination of the films is not observed in the tensile experiments; the analysis of the fragmentation patterns indicates that insertion of an Al2O3 layer at the film/substrate interface can enhance the interface toughness. High-temperature (425 °C) tensile experiments for the Al2O3 films indicate good temperature tolerance for the coatings, and in comparison to the room-temperature data, a significant difference is seen in the increase of saturation crack spacing. Moreover, the structure and composition of the films are studied in detail through X-ray reflection and diffraction, transmission electron microscopy, Rutherford backscattering spectrometry, and elastic recoil detection analysis. The results are particularly interesting for protective coating applications.