Apparatus of Plural Charged-Particle Beams

摘要

A multi-beam apparatus for observing a sample with oblique illumination is proposed. In the apparatus, a new source-conversion unit changes a single electron source into a slant virtual multi-source array, a primary projection imaging system projects the array to form plural probe spots on the sample with oblique illumination, and a condenser lens adjusts the currents of the plural probe spots. In the source-conversion unit, the image-forming means not only forms the slant virtual multi-source array, but also compensates the off-axis aberrations of the plurality of probe spots. The apparatus can provide dark-field images and/or bright-field images of the sample.

主权项

1. A multi-beam apparatus for observing a surface of a sample, comprising:
an electron source; a condenser lens below said electron source; a source-conversion unit below said condenser lens; a primary projection imaging system below said source-conversion unit and comprising an objective lens and a transfer lens; a deflection scanning unit inside said primary projection imaging system; a sample stage below said primary projection imaging system; a beam separator above said objective lens; a dark-field secondary projection imaging system above said beam separator; and a dark-field electron detection device with a plurality of dark-field detection elements,
wherein said source-conversion unit comprises an image-forming means with a plurality of image-forming elements and a beamlet-limit means with a plurality of beam-limit openings, said image-forming means is above said beamlet-limit means, and each image-forming element comprises a micro-deflector and a micro-round-lens,wherein said electron source, said condenser lens, said source-conversion unit, said primary projection imaging system, said deflection scanning unit and said beam separator are aligned with a primary optical axis of said apparatus, said sample stage sustains said sample so that said surface faces to said objective lens and is slant to said primary optical axis, said dark-field secondary projection imaging system and said dark-field electron detection device are aligned with a dark-field secondary optical axis of said apparatus, and said dark-field secondary optical axis is not parallel to said primary optical axis,wherein said electron source generates a primary electron beam along said primary optical axis, a plurality of micro-deflectors of said plurality of image-forming elements deflects a plurality of beamlets of said primary electron beam to form a plurality of parallel virtual images of said electron source and therefore a virtual multi-source array is converted from said electron source, a plurality of micro-round-lenses of said plurality of image-forming elements respectively focuses said plurality of beamlets to tilt said virtual multi-source array slant to said primary optical axis, said plurality of beamlets passes through said plurality of beam-limit openings respectively, a current of each beamlet is therefore limited by one corresponding beam-limit opening, and currents of said plurality of beamlets can be varied by adjusting said condenser lens,wherein said primary projection imaging system images said virtual multi-source array onto said slant surface, said virtual multi-source array is tilted to make an image plane of said primary projection imaging system coincident with said slant surface, a plurality of probe spots is therefore formed 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 dark-field signal electron beams generated by said plurality of probe spots respectively from said plurality of scanned regions is in passing focused by said objective lens, deflected by said beam separator to said dark-field secondary projection imaging system, focused onto and kept within said plurality of dark-field detection elements by said dark-field secondary projection imaging system, and therefore said plurality of dark-field detection elements respectively provides a plurality of dark-field images with respect to said plurality of scanned regions.