Plasma enhanced atomic layer deposition of copper: A comparison of precursors

The growth of Cu films by atomic layer deposition using hydrogen plasma has been investigated. To obtain continuous films at sub 5 nm thicknesses the two dimensional coalescence of Cu nucleation sites formed at the start of the deposition process must be enhanced in preference to three dimensional island growth. Thermal energy reduction in the growth process is a key parameter. In this work hydrogen plasma is used to allow the reduction of the adsorbed precursor to metallic Cu at a range of low temperatures. Therefore, precursors can be compared at their low temperature limit, which is mainly determined by transport issues due to their relatively low vapor pressures. The structure of the deposited Cu films varies strongly with the substrate material used highlighting the importance of the nucleation mechanisms. On metallic substrates such as Ru and Pd continuous conductive thin films could be obtained, island formation and slow coalescence were observed on Si, TaN and CDO substrates even at temperatures low as 30 °C; therefore conductive films could only be obtained for relatively thick deposits.