X-ray photoelectron spectroscopy (XPS) has been used to investigate the thermodynamic stability of Cu layers deposited onto Mn silicate (MnSiO 3) barrier layers formed on SiO 2 surfaces. Using a fully in situ growth and analysis experimental procedure, it has been shown that ∼1 nm Cu layers do not chemically react with ultra thin (∼2.6 nm) MnSiO 3 surfaces following 400 °C annealing, with no evidence for the growth of Cu oxide species, which are known to act as an intermediate step in the Cu diffusion process into silica based dielectrics. The effectiveness of MnSiO 3 as a barrier to Cu diffusion following high temperature annealing was also investigated, with electron energy loss spectroscopy suggesting that a ∼2.6 nm MnSiO 3 layer prevents Cu diffusion at 400 °C. The chemical composition of a barrier layer formed following the deposition of a partially oxidised Mn (MnO x)/Cu alloy was also investigated using XPS in order to determine if the presence of Cu at the Mn/SiO 2 interface during MnSiO 3 growth inherently changes the chemical composition of the barrier layer. In contrast to previous publications, it has been shown that Mn oxide species do not form in the barrier region during thermal annealing, with Cu appearing to be chemically inert in the presence of Mn and SiO 2. © 2012 American Institute of Physics.