Apparatus of plural charged-particle beams

Patent metadata

Field	Value
Publication number	US-10141160-B2
Application number	US-201615365145-A
Country	US
Kind code	B2
Filing date	Nov 30, 2016
Priority date	Nov 30, 2015
Publication date	Nov 27, 2018
Grant date	Nov 27, 2018

Abstract

A secondary projection imaging system in a multi-beam apparatus is proposed, which makes the secondary electron detection with high collection efficiency and low cross-talk. The system employs one zoom lens, one projection lens and one anti-scanning deflection unit. The zoom lens and the projection lens respectively perform the zoom function and the anti-rotating function to remain the total imaging magnification and the total image rotation with respect to the landing energies and/or the currents of the plural primary beamlets. The anti-scanning deflection unit performs the anti-scanning function to eliminate the dynamic image displacement due to the deflection scanning of the plural primary beamlets.

First claim

What is claimed is:

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;
an objective lens below said source-conversion unit;
a deflection scanning unit below said source-conversion unit;
a sample stage below said objective lens;
a beam separator below said source-conversion unit; and
a detection unit above said beam separator and comprising a secondary projection imaging system and an electron detection device with a plurality of detection elements,
wherein said electron source, said condenser lens, said source-conversion unit, said objective lens, said deflection scanning unit and said beam separator are aligned with a primary optical axis of said apparatus, said sample stage is configured to sustain said sample so that said surface faces to said objective lens, said detection unit is aligned with a secondary optical axis of said apparatus, and said secondary optical axis is not parallel to said primary optical axis,
wherein said plurality of detection elements is placed on a detection plane, said secondary projection imaging system comprises a zoom lens, an anti-scanning deflection unit and a projection lens,
wherein said electron source is configured to generate a primary electron beam along said primary optical axis, said condenser lens is configured to focus said primary electron beam, said source-conversion unit is configured to change said primary electron beam into a plurality of beamlets and make said plurality of beamlets form a plurality of first images of said electron source, said objective lens is configured to focus said plurality of beamlets to image said plurality of first images onto said surface and therefore form a plurality of probe spots thereon respectively, and said deflection scanning unit is configured to deflect 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 then incident to said objective lens, said objective lens is configured to in passing focus said plurality of secondary electron beams, and said beam separator is configured to deflect said plurality of secondary electron beams to enter said secondary projection imaging system along said secondary optical axis,
wherein said zoom lens is configured to focus said plurality of secondary electron beams onto a transfer plane, said transfer plane is between said zoom lens and said projection lens, and said plurality of secondary electron beams is configured to form a first crossover between said zoom lens and said transfer plane,
wherein said projection lens is configured to focus said plurality of secondary electron beams onto said detection plane, said plurality of secondary electron beams is configured to form a second crossover between said projection lens and said detection plane and a plurality of secondary-electron spots on said detection plane, said plurality of secondary-electron spots is inside said plurality of detection elements respectively, consequently a corresponding relationship between said plurality of probe spots and said plurality of detection elements is established, and accordingly each detection element is configured to generate an image signal of one corresponding scanned region,
wherein said anti-scanning deflection unit is configured to deflect said plurality of secondary electron beams in step with said plurality of probe spots scanning over said plurality of scanned regions to remain positions of said plurality of secondary-electron spots and thereby keeping said corresponding relationship all the time,
wherein an imaging magnification of said zoom lens is configured to be adjusted to keep said corresponding relationship when observing said surface in different conditions.

2. The apparatus according to claim 1 , further comprising a secondary beam-limit aperture to cut off peripheral electrons of said plurality of secondary electron beams.

3. The apparatus according to claim 1 , further comprising a field lens placed at said transfer plane to reduce off-axis aberrations of said projection lens.

4. The apparatus according to claim 1 , further comprising a stigmator to compensate astigmatism aberrations of said plurality of secondary electron beams due to said beam separator.

5. The apparatus according to claim 1 , further comprising an alignment deflector to compensate a deviation of said corresponding relationship due to manufacturing and/or assembly errors of said detection unit.

6. The apparatus according to claim 1 , wherein said anti-scanning deflection unit is between said beam separator and said zoom lens.

7. The apparatus according to claim 1 , wherein said zoom lens comprises a first zoom sub-lens and a second zoom sub-lens, and said second zoom sub-lens is between said first zoom sub-lens and said transfer plane.

8. The apparatus according to claim 7 , wherein said anti-scanning deflection unit is between said first and second zoom sub-lenses.

9. The apparatus according to claim 8 , wherein said anti-scanning deflection unit is configured to deflect said plurality of secondary electron beams incident to said second zoom sub-lens along said secondary optical axis.

10. The apparatus according to claim 9 , wherein said secondary projection imaging system comprises a field lens placed at said transfer plane to reduce radial shifts and tilt angles of said plurality of secondary electron beams incident to said projection lens.

11. The apparatus according to claim 9 , wherein said secondary projection imaging system comprises a secondary beam-limit aperture plate with one or more openings, and said one or one of said more opening is placed at a position of said second crossover to cut off peripheral electrons of said plurality of secondary electron beams.

12. The apparatus according to claim 11 , wherein said secondary projection imaging system comprises a field lens placed at said transfer plane to bend said plurality of secondary electron beams to keep said position of said second crossover when observing said surface in different conditions.

13. The apparatus according to claim 12 , wherein said secondary projection imaging system comprises a stigmator placed at or close to said first crossover to compensate astigmatism aberrations of said plurality of secondary-electron spots due to said beam separator.

14. The apparatus according to claim 13 , wherein said objective lens has a first magnetic lens.

15. The apparatus according to claim 14 , wherein said field lens has a second magnetic lens which is configured to cancel rotation variations of said plurality of secondary-electron spots when observing said surface in different conditions.

16. The apparatus according to claim 14 , wherein said zoom lens has a second magnetic lens which is configured to cancel rotation variations of said plurality of secondary-electron spots when observing said surface in different conditions.

17. The apparatus according to claim 14 , wherein said projection lens has a second magnetic lens which is configured to cancel rotation variations of said plurality of secondary-electron spots when observing said surface in different conditions.

18. The apparatus according to claim 17 , wherein said secondary projection imaging system comprises an alignment deflector, which is between

Assignees

• Hermes Microvision Inc
• Hermes Microvision Inc

Inventors

• Ren Weiming
• Liu Xuedong
• Hu Xuerang
• Chen Zhongwei

Classifications

• H01J37/244

  Detectors; Associated components or circuits therefor · CPC title

• H01J2237/0453

  multiple apertures · CPC title

• H01J2237/24592

  Inspection and quality control of devices · CPC title

• H01J2237/24465

  Sectored detectors, e.g. quadrants · CPC title

• H01J37/153

  Electron-optical or ion-optical arrangements for the correction of image defects, e.g. stigmators · CPC title