Apparatus and method for measuring an aerial image using transmitted light and reflected light

An aerial image measuring apparatus for inspecting effects of defects on a photomask on which predetermined patterns are formed on an upper surface thereof, the apparatus comprising:

• an optical transmitting section for irradiating light emitted from an optical source to a lower surface of the photomask and forming transmitted light passing through the photomask;
• an optical reflecting section for irradiating the light emitted from the optical source to the upper surface of the photomask and forming reflected light reflected from the upper surface on which the patterns are formed. the optical reflecting section comprising:
• a beam splitter for splitting the light emitted from the optical source into a transmitted light path along which the transmitted light is advanced and a reflected light path along which the reflected light is advanced, and
• a reflecting mirror, installed in the reflected light path between the optical source and the upper surface of the photomask, for altering the reflected light path to irradiate the reflected light to the upper surface of the photomask on which the patterns are formed;
• and
• an aerial image forming device for forming an aerial image by converting one of the transmitted light and the reflected light into an electrical signal.