Patent ID: 7566893

Claim:
A best focus detection method in which a best focus position of a projection optical system that forms an image of a pattern placed on a first surface onto a second surface is detected, the method comprising: a first process in which while illuminating a mark placed on the first surface with an illumination light, a pattern plate on which an aperture pattern is formed is scanned in a predetermined measurement direction with respect to an image of the mark formed by the projection optical system within a two-dimensional plane that is orthogonal to an optical axis of the projection optical system and is in a vicinity of the second surface, the illumination light via the aperture pattern is received during the scanning, and position information of the image of the mark related to the measurement direction is detected; a second process in which a position of the pattern plate is set within the two-dimensional plane based on the position information, the pattern plate is moved in the optical axis direction while illuminating the mark placed on the first surface with the illumination light, and position data of the pattern plate related to the optical axis direction and intensity data of the illumination light are obtained during the movement; and a third process in which a best focus position of the projection optical system is computed based on the obtained position data and the obtained intensity data, wherein in the second process, the position data related to the optical axis direction and the intensity data of the illumination light are obtained at predetermined sampling intervals, and in the third process, the best focus position of the projection optical system is computed based on a plurality of position data obtained at the predetermined sampling intervals and a plurality of intensity data obtained at the predetermined sampling intervals.