A method of operating a semiconductor apparatus includes generating an electric field in peripheral areas of a first covering structure and a second covering structure; causing a photomask to move to a position between the first and second covering structures such that the photomask at least partially vertically overlaps the first and second covering structures and such that particles attached to the photomask are attracted to the first and second covering structures by the electric field; and irradiating the photomask with light through light transmission regions of the first and second covering structures.