Patent ID: 8629418

Claim:
A sensor for use at a substrate level in a lithographic projection apparatus having a projection system configured to project a patterned radiation beam onto a target portion of a substrate, the sensor comprising: a radiation detector; a transmissive plate having a front surface and a back surface, the transmissive plate being positioned such that radiation projected by the projection system passes into the front surface of the transmissive plate and out of the back surface thereof to the radiation detector, the back surface comprising a structure being constructed to improve transmission of the radiation to the radiation detector, the structure being selected from the group consisting of: surface roughness of the back surface, a Fresnel lens, a Winston cone, a cylindrical projection having a distal end comprising a concave shape, or a spherical lens; and a gap region disposed between the transmissive plate and radiation detector, wherein a flowing liquid medium is disposed in the gap region.