Method and apparatus for detecting positional deviation by using diffraction gratings with a compensation delay determining unit

摘要

A method and apparatus for measuring relative positional deviation between first and second diffraction gratings formed on an object is disclosed, wherein, in detection of a signal corresponding to the relative positional deviation between the first and second diffraction gratings, a suitable delay is determined in accordance with a signal corresponding to a relative positional deviation between third and fourth diffraction gratings formed on the object and having a predetected relative positional deviation, and wherein the measurement of the positional deviation between the first and second diffraction gratings is done on the basis of a signal corresponding to that deviation and of the delay thus determined.