Apparatus of plural charged-particle beams

Patent metadata

Field	Value
Publication number	US-9922799-B2
Application number	US-201615213781-A
Country	US
Kind code	B2
Filing date	Jul 19, 2016
Priority date	Jul 21, 2015
Publication date	Mar 20, 2018
Grant date	Mar 20, 2018

Abstract

A multi-beam apparatus for observing a sample with high resolution and high throughput and in flexibly varying observing conditions is proposed. The apparatus uses a movable collimating lens to flexibly vary the currents of the plural probe spots without influencing the intervals thereof, a new source-conversion unit to form the plural images of the single electron source and compensate off-axis aberrations of the plural probe spots with respect to observing conditions, and a pre-beamlet-forming means to reduce the strong Coulomb effect due to the primary-electron beam.

First claim

What is claimed is:

1. A multi-beam apparatus for observing a surface of a sample, comprising:
an electron source;
an adjustable collimating lens below said electron source;
a source-conversion unit below said adjustable 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 adjustable 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 adjustable 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 adjustable 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.

2. The multi-beam apparatus according to claim 1 , wherein said adjustable collimating lens comprises multiple annular electrodes which are placed at different axial positions along and aligned with said primary optical axis, and voltages thereof can be adjusted to move said first principal plane so as to vary said currents of said plurality of beamlets.

3. The multi-beam apparatus according to claim 1 , wherein said adjustable collimating lens comprises at least two single magnetic lenses which are placed at different axial positions along and aligned with said primary optical axis, and excitations thereof can be adjusted to move said first principal plane so as to vary said currents of said plurality of beamlets.

4. The multi-beam apparatus according to claim 1 , wherein said adjustable collimation lens comprises multiple annular electrodes and at least one magnetic lens which are placed at different axial positions along and aligned with said primary optical axis, and voltages of said electrodes and excitations of said at least one magnetic lens can be adjusted to move said first principal plane for varying said currents of said plurality of beamlets.

5. The multi-beam apparatus according to claim 1 , wherein each of said plurality of electron optics elements comprises one or more micro-multipole-lenses which compensate off-axis aberrations of one corresponding probe spot.

6. The multi-beam apparatus according to claim 5 , further comprising a pre-beamlet-forming means for reducing Coulomb effect, which is close to said electron source and has a plurality of beamlet-forming apertures, wherein each of said plurality of beamlets passes through one of said plurality of beamlet-forming apertures and therefore said plurality of beamlet-forming apertures cut off most of those electrons which do not constitute said plurality of beamlets.

7. The multi-beam apparatus according to claim 1 , further comprising a pre-beamlet-forming means for reducing Coulomb effect, which is close to said electron source and has a plurality of beamlet-forming apertures, wherein each of said plurality of beamlets passes through one of said plurality of beamlet-forming apertures and therefore said plurality of beamlet-forming apertures cut off most of those electrons which do not constitute said plurality of beamlets.

8. A multi-beam apparatus for observing a surface of a sample, comprising:
an electron source;
a collimating lens below said electron source;
a source-conversion unit below said 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 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 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 each having a micro-multipole-lens,
wherein said electron source generates a primary-electron beam along said primary optical axis, and said 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, said micro-multipole-lens of said each electron optics element compensates off-axis aberrations of one corresponding probe spot, 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 theref

Assignees

• Hermes Microvision Inc

Inventors

• Li Shuai
• Ren Weiming
• Liu Xuedong
• Dou Juying
• Hu Xuerang
• Chen Zhongwei

Classifications

• H01J37/244

  Detectors; Associated components or circuits therefor · CPC title

• H01J2237/2446

  Position sensitive detectors · CPC title

• H01J2237/2448

  Secondary particle detectors · CPC title

• H01J2237/2817

  Pattern inspection · CPC title

• H01J2237/04924

  electrostatic · CPC title