Atomic Layer Deposition of High-Purity Palladium Films from Pd(hfac)₂ and H₂ and O₂ Plasmas

Abstract

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 μΩ cm on oxide substrates. This process is based on Pd(hfac) 2 (hfac = hexafluoroacetylacetonate) precursor dosing followed by sequential H 2 plasma and O 2 plasma steps in a so-called ABC-type ALD process. Gas-phase infrared spectroscopy studies revealed that the O 2 plasma pulse is required to remove carbon contaminants from the Pd surface that remain after the H 2 plasma reduction step. Omitting the O 2 plasma step, that is, Pd ALD from Pd(hfac) 2 and H 2 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.