Patent ID: 7164139

Claim:
A Wien filter for a charged-particle beam apparatus, the Wien filter comprising: an opening for transmission of the charged-particle beam through the Wien filter in a first direction; a first field generation mechanism comprising a first set of devices configured to generate a first field in a second direction which is perpendicular to the first direction; and a second field generation mechanism comprising second and third sets of devices configured to generate a second field in a third direction which is perpendicular to the first and second directions, wherein one of said fields is a magnetic field and another of said fields is an electrostatic field, and wherein said fields are further configured such that a ratio of electrostatic field strength (E) to magnetic field strength (B) is approximately equal to a speed (v) of charged particles in the beam, and wherein the second and third sets of devices are located along the first direction before and after the first set of devices, and wherein the second and third sets of devices are configured to generate different field strengths relative to each other, such that a first-order chromatic dispersion at a target plane is minimized.