Patent ID: 6943360

Claim:
An apparatus for inspecting a substrate using charged particles, the apparatus comprising: an illumination system configured to generate an incident charged-particle beam; an objective lens system configured to receive the incident beam, to focus the incident beam onto the substrate, and to retrieve a scattered beam from the substrate; a projection system configured to receive the scattered beam and to project the scattered beam onto a detector; and a beam separator coupled to and interconnecting the illumination system, the objective lens system, and the projection system, wherein the beam separator is configured to receive the incident beam from the illumination system, bend the incident beam towards the objective lens system, receive the scattered beam from the objective lens system, and bend the scattered beam towards the projection system, wherein the objective lens system includes a magnetic immersion lens causing circumferential velocities in the incident beam, and wherein the illumination system includes another magnetic immersion lens causing circumferential velocities in the incident beam that compensate for the circumferential velocities caused by the magnetic immersion lens in the objective lens system.