A method of forming a contact hole on a substrate by using a projection aligner comprising a lighting system including a light source, an aperture, and a condenser lens, a photo mask on which light from the lighting system is incident, and a projection lens for projecting the light from the photo mask onto the substrate, comprises forming a first photosensitive resist film on the substrate; exposing the first photosensitive resist film by using a photo mask in which mask patterns are cyclically arranged in a first direction and a second direction which is orthogonal to the first direction and a first aperture having light transmission parts arranged symmetrically with respect to a center point in the first direction; developing the exposed first photosensitive resist film to form first lines and linear spaces; forming a second photosensitive resist film on the substrate; exposing the second photosensitive resist film by using the photo mask and a second aperture having light transmission parts arranged symmetrically with respect to a center point in the second direction; and developing the second photosensitive resist film to form second lines and linear spaces which are orthogonal to the first lines and linear spaces.