Described herein is an integrated circuit device comprising a conductive line structure including a bit line and an insulating capping pattern; and an insulating spacer covering a side wall of the conductive line structure, the insulating spacer including an inner spacer and a char spacer. To form the insulating spacer, a polymer brush pattern may be chemically bonded to the inner spacer to cover a side wall of the conductive line structure; a first insulating spacer film covering the inner spacer and the polymer brush pattern may be formed; and a char spacer may be formed from the polymer brush pattern by pyrolyzing the polymer brush pattern in the absence of oxygen.