A method of inspecting a photomask includes directing radiation from a radiation source onto a photomask so that at least a portion of the radiation is transmitted through the photomask. A first photomask image is detected from the transmitted portion of the radiation transmitted through the photomask and perceptible at a second side of the photomask. A second photomask image is created by applying an exposure simulation model to a photomask design. A difference between the first photomask image and the second photomask image is then determined.
