Patent ID: 8536538

Claim:
A focused electron beam imaging apparatus comprising: an electron source configured to emit electrons; a gun lens configured to focus the electrons into an electron beam which travels down an optical axis of the apparatus; a pre-scanning deflector configured to controllably deflect the electron beam away from the optical axis, wherein the pre-scanning deflector comprises a 12-pole electrostatic deflector; a main scanning deflector configured to controllably deflect the electron beam back towards the optical axis; an objective lens configured to focus the electron beam onto a spot on a surface of a target substrate; and a detector configured to detect scattered electrons from the surface of the target substrate, wherein the 12-pole electrostatic deflector comprises a first electrode plate configured to span a radial angle of 2α 1 , a first gap adjacent to the first electrode plate, the first gap spanning a radial angle of 2δ, a second gap adjacent to the second electrode plate, the second gap spanning a radial angle of 2δ, a third electrode adjacent to the second gap, the third electrode being configured to span a radial angle of α 2 , and a third gap adjacent to the third electrode plate, the third gap spanning a radial angle of 2δ, wherein together the first electrode plate, the first gap, the second electrode plate, the second gap, the third electrode plate, and the third gap span a radial angle of 90 degrees, wherein α 1 =23 degrees, α 2 =16 degrees, and δ=2 degrees.