An integrated circuit (IC) device includes a conductive region including a first metal on a substrate. An insulating film is on the conductive region. A conductive plug including a second metal passes through the insulating film and extends in a vertical direction. A conductive barrier pattern is between the conductive region and the conductive plug. The conductive barrier pattern has a first surface in contact with the conductive region and a second surface in contact with the conductive plug. A bottom surface and a lower sidewall of the conductive plug are in contact with the conductive barrier pattern, and an upper sidewall of the conductive plug is in contact with the insulating film. The conductive barrier pattern includes a vertical barrier portion between the insulating film and the conductive plug, and the vertical barrier portion has a width tapering along a first direction away from the conductive region.