A method of manufacturing an integrated circuit (IC) device includes forming a photoresist layer on a substrate, and exposing the photoresist layer to light by using a photolithographic apparatus including a light generator. The light generator includes a chamber having a plasma generation space, an optical element in the chamber, and a debris shielding assembly between the optical element and the plasma generation space in the chamber, and the debris shielding assembly includes a protective film facing the optical element and being spaced apart from the optical element with a protective space therebetween, the protective space including an optical path, and a protective frame to support the protective film and to shield the protective space from the plasma generation space.