Lithographic apparatus and method for determining z position errors/variations and substrate table flatness

Abstract

A lithographic projection apparatus including an illumination system configured to provide a beam of radiation, a support configured to support a patterning device, the patterning device configured to impart the beam with a pattern in its cross section, a substrate table configured to hold a substrate, a projection system configured to project the patterned radiation onto a target portion of the substrate, a plurality of level sensors for sensing a level of a substrate carried on the substrate table at a plurality of different positions, and a system for determining the position of the substrate table. Also provided is a controller that is configured to cause relative movement between the substrate and the level sensor array from a first position at which a first measurement is taken to a plurality of overlapping positions at which further measurements are taken, and a calculator for calculating a measure of Z position errors and/or substrate table unflatness and/or a measure of the level sensor position/offset using the plurality of overlapping measurements.