Apparatus of plural charged-particle beams
A multi-beam apparatus for observing a sample with high resolution and high throughput is proposed. In the apparatus, a source-conversion unit changes a single electron source into a virtual multi-source array, a primary projection imaging system projects the array to form plural probe spots on the sample, and a condenser lens adjusts the currents of the plural probe spots. In the source-conversion unit, the image-forming means is on the upstream of the beamlet-limit means, and thereby generating less scattered electrons. The image-forming means not only forms the virtual multi-source array, but also compensates the off-axis aberrations of the plurality of probe spots.
1. A method to configure a source-conversion unit for forming a virtual multi-source array from an electron source, comprising:
providing an image-forming means which comprises an upper layer with a plurality of upper 4-pole structures and a lower layer with a plurality of lower 4-pole structures; and
providing a beamlet-limit means which is below said image-forming means and comprises a plurality of beam-limit openings,
wherein each upper 4-pole structure is above and aligned with one corresponding lower 4-pole structure, both have a 45° difference in azimuth and form a pair of 4-pole structures, and therefore said plurality of upper 4-pole structures and said plurality of lower 4-pole structures form a plurality of pairs of 4-pole structures,
wherein said plurality of beam-limit openings is aligned with said plurality of pairs of 4-pole structures respectively,
wherein one pair of 4-pole structure functions as a micro-deflect to deflect one beamlet of an electron beam generated by said electron source to form a virtual image thereof, a micro-lens to focus said one beamlet to a desired degree, and/or a micro-stigmator to add a desired amount of astigmatism aberration to said one beamlet.
2. The method according to claim 1 , wherein said source-conversion unit comprises an upper electric-conduction plate with a plurality of upper through-holes respectively aligned with said plurality of pairs of 4-pole structures.
3. The method according to claim 2 , wherein said source-conversion unit comprises a lower electric-conduction plate with a plurality of lower through-holes respectively aligned with said plurality of pairs of 4-pole structures.
4. A method for forming a virtual multi-source array from an electron source, comprising:
deflecting an electron beam from said electron source into a plurality of beamlets by using an upper layer with a plurality of upper 4-pole structures and a lower layer with a plurality of lower 4-pole structures, wherein each upper 4-pole structure is above and aligned with one corresponding lower 4-pole structure, and both have about 45° difference in azimuth and form a pair of 4-pole structures; and
limiting said plurality of beamlets by using a plurality of openings.
5. A source-conversion unit comprises:
an image-forming means which comprises an upper layer with a plurality of upper 4-pole structures and a lower layer with a plurality of lower 4-pole structures; and
a beamlet-limit means which is below said image-forming means and comprises a plurality of beam-limit openings,
wherein each upper 4-pole structure is above and aligned with one corresponding lower 4-pole structure, both have about 45° difference in azimuth and form a pair of 4-pole structures, and therefore said plurality of upper 4-pole structures and said plurality of lower 4-pole structures form a plurality of pairs of 4-pole structures,
wherein said plurality of beam-limit openings is aligned with said plurality of pairs of 4-pole structures respectively,
wherein one pair of 4-pole structure functions as a micro-deflect to deflect one beamlet of an electron beam generated by said electron source to form a virtual image thereof, a micro-lens to focus said one beamlet to a desired degree and/or a micro-stigmator to add a desired amount of astigmatism aberration to said one beamlet.