Reticle focus measurement method using multiple interferometric beams

摘要

A first set of interferometric measuring beams is used to determine a location of a patterned surface of a reticle and a reticle focus plane for a reticle that is back clamped to a reticle stage. A second set of interferometric measuring beams is used to determine a map of locations of the reticle stage during scanning in a Y direction. The two sets of interferometric measuring beams are correlated to relate the reticle focal plane to the map of the reticle stage. The information is used to control the reticle stage during exposure of a pattern on the patterned surface of the reticle onto a wafer.