The surface pores of a porous low-k dielectric layer were sealed by a smooth coating of silica just a few nanometers thick. Atomic layer deposition (ALD) of tungsten nitride (WN) onto the smooth silica surface provided a very thin (1.5 nm) barrier to the diffusion of copper. Without the silica sealing layer, ALD WN penetrated through the low-k dielectric. Strong adhesion was demonstrated for the structure Si/porous dielectric/SiO2/WN/Co/Cu, in which the top four layers were formed by ALD. This structure is stable to at least 400 degrees C and is suitable for making narrow interconnects for future microelectronics. (C) 2004 The Electrochemical Society.