| Summary: | There has been a rising trend in miniaturisation of devices, which leads to an increase in demand for thin and ultrathin films. There are several techniques to deposit thin films, one of which is Atomic Layer Deposition (ALD), which has been growing in popularity in recent times. ALD can deposit thin films of high uniformity, and with accurate thickness control by modifying the number of deposition cycles.
In this study, deposition of noble metal thin films was investigated. More specifically, palladium (Pd) and platinum (Pt) thin films were deposited via ALD, with ozone as the co-reactant. Sapphire (α-Al2O3(0001)), Si (111) and SiO2 (100) were used as the substrates.
For Pd thermal ALD, this is the first instance that palladium(II) hexafluoroacetylacetonate, Pd(hfac)2, has been used together with ozone as the precursors, without using hydrogen. Hydrogen is highly flammable and explosive, thus posing potential safety hazards. In contrast, ozone is a safer option and allows for lower deposition temperatures. The optimum deposition temperature was from 180°C to 220°C. There was successful Pd film deposition, where films with no fluorine impurity, high crystallinity, high uniformity, smooth surfaces and constant growth rate were obtained. As for Pt thermal ALD, platinum (II) acetylacetonate, Pt(acac)2, and ozone were used as the precursors. The substrates required surface pre-treatment of oxygen plasma for Pt film growth and the optimum deposition temperature was between 140°C and 200°C. Pt thin films were deposited successfully, where films of high uniformity and smooth surfaces were achieved. However, more research has to be done to further investigate the film properties and deposition conditions.
The fabrication of Pd and Pt thin films via ALD lays the foundation for producing noble metal high entropy alloys (HEAs) in the future. ALD can fabricate thin films of high uniformity and precise thickness control, thus able to produce high-quality films on high aspect ratio 3D substrates for HEAs. ALD will be used as a novel approach for producing noble metal HEAs, which have many desirable properties such as high strength and high ductility, for applications like catalysis.
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