Abstract: A point-diffraction interferometer having a source (1) of electromagnetic radiation, a perforated mask (2) on its entrance end, an optics-testing space (4) into which the optics (9) to be tested may be inserted, elements (5, 6) that create a testing beam and a reference beam using a perforated mask (6) on its exit end, and a component (7, 8) that analyzes an interference pattern (16) created by superimposing its testing beam and reference beam. One-dimensional or two-dimensional arrays (12, 15) of nearly point-like through holes are incorporated into the perforated masks (2, 6) on the interferometer's entrance end and exit end. The interferometer has particular application to testing optical systems employed on photolithographic exposure systems.

Abstract: In a lithographic projection apparatus, an object such as a mask is shielded from stray particles by a particle shield using electromagnetic fields. The fields may be a uniform electric field, a non-uniform electric field or an optical breeze. The particle shield is fixed to the mask holder rather than the mask.

Abstract: In a lithographic projection apparatus, a grating spectral filter is used to filter an EUV projection beam. The grating spectral filter is preferably a blazed, grazing incidence, reflective grating. Cooling channels may be provided in or on the rear of the grating spectral filter. The grating spectral filter may be formed of a material effectively invisible to the desired radiation.

Abstract: In a lithographic projection apparatus, an object such as a mask is shielded from stray particles by a particle shield using electromagnetic fields. The fields may be a uniform electric field, a non-uniform electric field or an optical breeze. The particle shield means are fixed to the mask holder rather than the mask.