Diffraction-based overlay marks and methods of overlay measurement

摘要

A method may include forming a first grating and a second grating, disposed in a region of vertical overlap of the first and second gratings on different levels, respectively, having substantially the same pitch, and inclined with respect to each other, such that a bias value between the first and second gratings is changed along a length direction of the first and second gratings, using a lithography process. A method may include emitting a beam to the first and second gratings; and obtaining trend information associated with a diffracted beam from an image pattern of a beam from the first and second gratings, using the emitted beam, in which the trend information may concern changes in the intensity of the diffracted beam according to the bias value. An overlay error in at least one grating may be determined based on the trend information and an intensity of a diffracted beam.