Patent ID: 8009272

Claim:
An image measurement method for measuring an image of a pattern of a mask projected with a projection optical system, the method comprising: detecting light transmitted through an aperture while a substrate is arranged at an image plane of the projection optical system, the substrate having a slit and the aperture; adjusting an alignment angle of the slit on the basis of a signal related to the light detected in the detecting; and measuring the image by detecting light transmitted through the slit while moving the slit, the alignment angle of which has been adjusted in the adjusting, in the image plane of the projection optical system, wherein the width of the slit is smaller than a wavelength of light for illumination of the mask, wherein the width of the aperture is larger than the wavelength of the light for the illumination of the mask, and wherein the light transmitted through the aperture and the light transmitted through the slit are detected by a photodetector array.