Patent ID: 7633618

Claim:
A method of measuring relative positions of a first alignment mark and a second alignment mark located on a substrate and oriented in a first direction that is substantially parallel to a surface of the substrate, the first alignment mark includes a periodic structure that is oriented substantially in the first direction having a first portion with a first periodicity and an adjacent second portion with a second periodicity, the second alignment mark including a periodic structure that is oriented substantially in the first direction having a first portion with the second periodicity and an adjacent second portion with the first periodicity, the first and second alignment marks being arranged such that the first portion of the first alignment mark and the first portion of the second alignment mark are substantially located one over the other, and the second portion of the first alignment mark and the second portion of the second alignment mark are substantially located one over the other, the method comprising: directing an alignment beam to the first and second alignment marks; measuring a Moiré pattern generated by interference between respective first portions of the first and second alignment marks, and interference between respective second portions of the first and second alignment marks; and determining the relative positions of the first and second alignment marks based on the measured Moiré pattern.