| 主权项 |
1. A multi-beam apparatus for observing a surface of a sample, comprising:
an electron source; a movable collimating lens below said electron source; a source-conversion unit below said movable collimating lens; a primary projection imaging system below said source-conversion unit; a deflection scanning unit below said source-conversion unit; a sample stage below said primary projection imaging system; a beam separator below said source-conversion unit; a secondary projection imaging system above said beam separator; and an electron detection device with a plurality of detection elements,
wherein said electron source, said movable collimating lens and said source-conversion unit are aligned with a primary optical axis of said apparatus, and said sample stage sustains said sample so that said surface faces to said primary projection imaging system,wherein a first principal plane of said movable collimating lens can be moved along said primary optical axis, and said source-conversion unit comprises a beamlet-forming means with a plurality of beam-limit openings and an image-forming means with a plurality of electron optics elements,wherein said electron source generates a primary-electron beam along said primary optical axis, and said movable collimating lens collimates said primary-electron beam into said source-conversion unit,wherein a plurality of beamlets of said primary-electron beam respectively passes through said plurality of beam-limit openings and is focused to form a plurality of parallel images of said electron source by said plurality of electron optics elements respectively, and said plurality of beam-limit openings limits currents of said plurality of beamlets,wherein said primary projection imaging system projects said plurality of parallel images onto said surface and therefore said plurality of beamlets forms a plurality of probe spots thereon, and said deflection scanning unit deflects said plurality of beamlets to scan said plurality of probe spots respectively over a plurality of scanned regions within an observed area on said surface,wherein a plurality of secondary electron beams is generated by said plurality of probe spots respectively from said plurality of scanned regions and directed into said secondary projection imaging system by said beam separator, said secondary projection imaging system focuses and keeps said plurality of secondary electron beams to be detected by said plurality of detection elements respectively, and each detection element therefore provides an image signal of one corresponding scanned region,wherein when said first principal plane is moved from one place to another place along said primary optical axis, a current density of said collimated primary-electron beam changes accordingly and consequently said currents of said plurality of beamlets vary. |
