Atomic layer deposition of high-purity palladium films from Pd(hfac)2 and H2 and O2 plasmas

A plasma-assisted atomic layer deposition (ALD) process has been developed that allows for low temperature (100 °C) synthesis of virtually 100% pure palladium thin films with low resistivity of 24 ± 3 µO cm on oxide substrates. This process is based on Pd(hfac)2 (hfac = hexafluoroacetylacetonate) precursor dosing followed by sequential H2 plasma and O2 plasma steps in a so-called ABC-type ALD process. Gas-phase infrared spectroscopy studies revealed that the O2 plasma pulse is required to remove carbon contaminants from the Pd surface that remain after the H2 plasma reduction step. Omitting the O2 plasma step, that is, Pd ALD from Pd(hfac)2 and H2 plasma in a typical AB-like ALD process, leads to a carbon contamination of >10% and significantly higher resistivity values. From transmission electron microscopy, it has also been observed that the ABC-type process leads to a faster nucleation of the Pd nanoparticles formed during the initial stage of film growth. As this novel process allows for the deposition of high-purity Pd at low temperatures, it opens prospects for various applications of Pd thin films and nanoparticles.