Methods of forming integrated circuit devices include forming an interlayer insulating layer having a trench therein, on a substrate and forming an electrical interconnect (e.g., Cu damascene interconnect) in the trench. An upper surface of the interlayer insulating layer is recessed to expose sidewalls of the electrical interconnect. An electrically insulating first capping pattern is formed on the recessed upper surface of the interlayer insulating layer and on the exposed sidewalls of the electrical interconnect, but is removed from an upper surface of the electrical interconnect. A metal diffusion barrier layer is formed on an upper surface of the electrical interconnect, however, the first capping pattern is used to block formation of the metal diffusion barrier layer on the sidewalls of the electrical interconnect. This metal diffusion barrier layer may be formed using an electroless plating technique.