Patent ID: 8229207

Claim:
A mask inspection apparatus comprising: a stage having a first mirror and a second mirror and movable in X and Y directions in a state of holding a mask thereon; a first laser interferometer for applying laser light to the first mirror and receiving light reflected therefrom to thereby measure an X-direction position of the stage; a second laser interferometer for applying laser light to the second mirror and receiving light reflected therefrom to thereby measure a Y-direction position of the stage; an optical image acquisition part for moving the stage in the X and Y directions and acquiring optical images of patterns written onto the mask while using the results of measurement by the first and second laser interferometers; a positional displacement amount storage part for storing therein pre-measured amounts of positional displacements of optical images, which are caused by flexure of the mask and distortions of the first and second mirrors; a positional displacement correction part for correcting positional displacements of the optical images acquired by the optical image acquisition part, based on the positional displacement amounts stored in the positional displacement amount storage part; and an image comparison part for comparing each of the optical images corrected by the positional displacement correction part and a predetermined reference image.