Patent ID: 7072024

Claim:
A lithographic projection apparatus that projects a pattern on a wafer by a projection beam by preliminarily determining locations of surface points of a surface profile of the wafer on a stage and subsequently introducing the stage with the wafer into the projection beam; said apparatus comprising: a projection station that projects a pattern on the wafer arranged on the stage by the projection beam incident in an incidence direction; and a first measuring station and a second measuring station that are arranged oppositely with respect to said projection station and each serve to measure a height of a wafer and a height of a reference plane of the stage, said first measuring station including a first wafer height sensor and a first stage height sensor, said second measuring station including a second wafer height sensor and a second stage height sensor, said first wafer height sensor and said second wafer height sensor each serving to measure the height of a wafer in said incidence direction, said first stage height sensor and said second stage height sensor emitting light generally towards said projection station and thereby measuring the height of the stage.