Patent ID: 7333174
Filing Date: 2008-02-19
Classification: B23D,G03F

Abstract:
1. A lithographic projection apparatus comprising: a substrate table configured to hold a substrate, the substrate table defining a Z-direction substantially perpendicular to a surface of the substrate table that is configured to hold 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, to determine coordinates of the substrate along the Z-direction; a system for determining the position of the substrate table in at least the Z-direction; a controller configured to cause relative movement between the substrate table and the plurality of level sensors, so that each of the plurality of the level sensors is able to assume a first position relative to the substrate to make a measurement at a first measurement point on the substrate, thereby to provide a first set of overlapping measurements, and so that each of the plurality of level sensors is able to assume a second position relative to the substrate to make a measurement at a second measurement point on the substrate, thereby to provide a second set of overlapping measurements; and a calculator for calculating at least one of a measure of position errors, a measure of substrate table unflatness and a measure of the level sensor position/offset using the first and second sets of overlapping measurements and position determinations from said system for determining the position of the substrate table.