Patent ID: 8610092

Claim:
A charged particle beam system for processing a substrate, comprising: a charged particle column configured to produce a beam of charged particles which can be focused on the surface of the substrate in a vacuum chamber; an in-vacuum optical subsystem positioned inside the vacuum chamber, the optical subsystem configured to collect scattered infrared radiation and visible light from the surface and regions near the surface of the substrate; an illumination subsystem positioned outside the vacuum chamber configured to provide infrared radiation and visible light to the surface of the substrate; an imaging subsystem, configured to focus the scattered infrared radiation and visible light collected by the in-vacuum optical subsystem onto one or more detectors positioned outside the vacuum chamber; and a vacuum viewport to provide an optical path between the inside of the vacuum chamber and the outside of the vacuum chamber, the vacuum viewport including a transparent element that is tilted with respect to the optical path of the light from the illumination system to reduce the amount of reflected radiation entering at least one of the detectors.