Growth and thermal annealing of Cu on HfO2

The interface between Cu and HfO2 synthesized using physical vapor deposition at 300 K has been examined with in situ low-energy ion scattering (LEIS), in situ X-ray photoelectron spectroscopy (XPS) and ex situ scanning transmission electron microscopy (STEM). Cu deposited on HfO2 at 300 K readily forms three-dimensional clusters. LEIS and XPS data show that the Cu is not oxidized at the Cu–HfO2 interface. A proposed model allows simulation of the coverage of Cu as a function of Cu dosing time before and after thermal annealing. At 300 K, the model fits the data when two-dimensional islands cover no more than 90% of the HfO2 surface. After thermal annealing at 673 K for 10 min under vacuum (1×10−8 Torr), large Cu clusters are formed from smaller ones, but there is no evident diffusion into the HfO2. For this annealed sample, STEM shows a narrow cluster diameter distribution (10–12 nm). Strain fields at the hafnia–copper interface may help limit the cluster size distribution.