Abstract: A position measurement system for measuring a position of an object is described, the system including: a first incremental measurement unit for measuring a first number of first distance steps in a distance between a reference frame and the object, wherein the first number equals a first integer value plus a first fraction, and a second incremental measurement unit for measuring a second number of second distance steps in a distance between the reference frame and the object, wherein the second number equals a second integer value plus a second fraction, wherein the position measurement system is constructed and arranged to initialize the second incremental measurement unit on the basis of the first number and the second fraction.

Abstract: A position measurement system includes a first position measurement unit configured to measure a position of an object in a first and a second direction, the first position measurement unit including a first sensor and a first grating that extends in a first direction, a second position measurement unit configured to measure the position of the object in the first and the second direction, the second position measurement unit including a second sensor and a second grating that extends in the first direction. The position measurement system is configured to initialize the second position measurement unit based on a position measurement of the first position measurement unit.

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.

Abstract: In a lithographic apparatus, a measurement of the position of an object in an ambient space by an object position measuring system which is influenced by pressure variations in the ambient space, is corrected by an accurate measurement of the pressure in the ambient space. A reference pressure volume may be provided, having a fluid connection with predetermined flow characteristics to the ambient space. A pressure difference is measured between a pressure in the reference pressure volume and an ambient pressure in the ambient space. The absolute pressure in the reference pressure volume is added to the pressure difference to determine a change of pressure in the ambient space. Alternatively, the pressure difference is integrated over time for determining a change of pressure in the reference pressure volume, and this change of pressure in the reference pressure volume is added to the pressure difference to determine a change of pressure in the ambient space.

Abstract: A lithographic apparatus includes an interferometer configured to measure a position of a mirror of the lithographic apparatus. For measuring unflatness of the mirror the interferometer includes a modulator configured to modulate a position of an input beam of the interferometer, a synchronous detector configured to synchronously detect an interfered, modulated beam, and a calculator configured to calculate an unflatness of an area of the mirror from an effect of the modulation of the position of the input beam on an output signal of the synchronous detector. The modulator can include a rotatable, tilted, plan plate.

Abstract: A lithographic apparatus is presented that includes a substrate holder configured to hold a substrate, an illuminator configured to condition a beam of radiation, a support structure configured to support a patterning device that imparts a desired pattern to the beam of radiation, a projection system that projects the patterned beam onto a target portion of the substrate, and an interferometer system configured to measure a position of the object to assist in positioning the object.