A method of manufacturing an integrated circuit (IC) device including forming an etching target structure on a substrate, forming an etching mask pattern having an opening on the etching target structure, etching a portion of the etching target structure through the opening to form a first hole in the etching target structure, forming a conductive polymer layer to cover the etching target structure inside the first hole, and etching another portion of the etching target structure through the first hole, in a state in which the etching target structure is covered by the conductive polymer layer inside the first hole, to form a second hole in the etching target structure and extending from the first hole toward the substrate may be provided.