Patent ID: 7420676
Filing Date: 2008-09-02
Classification: G03F

Abstract:
1. A method of measuring an alignment error, said method comprising: using a first patterning structure to impart a beam of radiation with a first pattern in its cross-section; projecting the beam having the first pattern onto a first side of a substrate to create a first mark; subsequent to said projecting the beam having the first pattern, turning said substrate over; aligning said substrate with respect to a reference position; using a second patterning structure to impart a beam of radiation with a second pattern in its cross-section; projecting the beam having the second pattern onto a second side of said substrate, said second side being substantially opposite to said first side, to create a second mark; detecting a position of said first mark on said first side of said substrate in a plane substantially parallel to said first side; and detecting a position of said second mark on said second side of said substrate in a plane substantially parallel to said second side, wherein said substrate is transparent to the beams of radiation, and wherein, between said detecting a position of said first mark and said detecting a position of said second mark, the substrate remains stationary relative to a substrate table holding said substrate.