Patent ID: 7408646

Claim:
A method for determining a local variation of reflection or transmission behavior over a surface of a mask for projecting a structure onto a wafer, comprising: providing the mask in a measuring device including at least one detector for measuring the intensity of a light beam that is diffracted at the structure on the mask; irradiating the mask with a light beam incident on the structure, so that the light beam is decomposed at the structure into at least two partial beams each representing an order of diffraction; measuring intensities of a first of the partial beams and of a second of the partial beams on the basis of the at least one detector; comparing the first intensity with the second intensity; determining a local variation of the reflection or transmission behavior over a surface of the mask from a result of the comparison for projecting the structure onto a wafer; setting the light beam to impinge on a surface patch of the mask in which portions of the structure to be projected are formed; and determining a local fluctuation of a line width, wherein the line width is measured with a high resolution microscope in a manner dependent on the determined fluctuation of the line width for at least one of the surface patches.