Patent ID: 6747729
Filing Date: 2004-06-08
Classification: C01B,G03F

Abstract:
A lithographic projection apparatus comprising:a radiation system to provide a projection beam of radiation; patterning structure to pattern the projection beam according to a desired pattern; a substrate table to hold a substrate; a projection system to image the patterned beam onto a target portion of the substrate, a displacement measuring interferometer having an operating wavelength &lgr;1 for measuring at least one of the position of said substrate table and the position of a table which is a part of said patterning structure; a purge gas source to supply purge gas to a space, to displace therefrom ambient air, said space accommodating at least one of at least a part of said substrate table and at least a part of said table which is a part of said patterning structure, wherein said purge gas is substantially non-absorbent of said projection beam of radiation and has a refractive index at a wavelength &lgr;1 which is substantially the same as that of air when measured at equal wavelength, temperature and pressure.