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Magnetic lens and method for focusing charged particle beams

A technology of charged particle beam and magnetic lens, applied in the field of magnetic lens, can solve problems such as impact

Active Publication Date: 2018-02-16
FEI COMPANY
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Such vertical fields (including 50Hz magnetic fields) can undesirably affect the beam passing through the lens and can be an additional source of distortion

Method used

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  • Magnetic lens and method for focusing charged particle beams
  • Magnetic lens and method for focusing charged particle beams
  • Magnetic lens and method for focusing charged particle beams

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0069] figure 1 A cross-sectional view of a (rotationally symmetric) magnetic lens 10 according to an embodiment of the invention is schematically shown.

[0070] A beam 1 of charged particles (eg electrons) travels along an optical axis 2 . Composite yokes 13 , 16 and electric coils (magnetic field generating means) 12 are provided around the optical axis 2 . The yoke includes a central (axial) bore 11 and includes an outer main part 13 and an inner secondary part 16, the latter (secondary part 16) being mounted as a single insert within the former (main part 13). The secondary portion 16 comprises a waist region 15 (with a reduced outer diameter) which surrounds the hole 11 and acts as a magnetic constriction. In operation (when the coil 12 is energized), the waist region 15 is magnetically saturated, so an axial (focusing) magnetic field is formed in the focusing region 14 . The secondary part 16 (and in particular the waist region 15 ) has high magnetic quality, wherea...

Embodiment 2

[0075] image 3 A lens 10 with an auxiliary electrical coil 18 and a secondary part (insert) 16 for performing high frequency lens modulation is shown schematically.

[0076] The figure shows the secondary part / insert 16 with the waist part 15 . The auxiliary electrical coil 18 is close to (in this case around) the waist portion 15 . During operation of the lens, the auxiliary coil 18 will thus surround the saturated material, and thus the inductance of the coil 18 will be relatively low, allowing the lens power to vary with relatively high frequencies. For axial fields along optical axis 2, shielding due to eddy currents does not occur.

Embodiment 3

[0078] Figure 4 Schematically shown including an alternative secondary part / insert 16 figure 1 details.

[0079]Here, the insert 16 includes a groove 19 which results in the isolation of the peninsula 20 from the rest of the yoke (primary 13, secondary 16). Because such a peninsula is magnetically "free-standing", it shields the axial region from stray magnetic fields. Preferably, the freestanding peninsula-like portion of the insert extends beyond the joint where the insert 16 sits on the rest of the yoke (13, 17), thus avoiding unwanted escape of the magnetic field at said joint.

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PUM

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Abstract

The invention relates to magnetic lenses for focusing beams of charged particles. Prior art charged particle magnetic lenses include a yoke and an air gap. This air gap defines the location where the magnetic field exists on the optical axis of the lens. According to the invention, a magnetic lens for focusing a beam of charged particles traveling along an optical axis comprises: - an axial aperture arranged around said optical axis to accommodate said beam; - magnetic field generating means for generating a magnetic field and - a magnetic yoke for directing and concentrating said magnetic field towards said optical axis so as to form a focal region for said beam, wherein - said yoke has a composite structure comprising an outer main part and an inner second part; - the secondary part is mounted as a one-piece insert within the main part so as to be arranged around the focal area; - the secondary part comprises a waist region surrounding the aperture and acting as a magnetic constriction zone, which is The magnetic field is configured such that the magnetic field is subjected to saturation in the waist region such that magnetic flux exits the waist region and forms a focusing field in the focusing region. Such a waist region takes over the role of the air gap in prior art lenses.

Description

technical field [0001] The present invention relates to a magnetic lens for focusing a beam of charged particles traveling along an optical axis, the lens comprising: [0002] - an axial hole arranged around the optical axis to accommodate the beam; [0003] - a magnetic field generating device for generating a magnetic field; and [0004] - a magnetic yoke to guide and concentrate the magnetic field towards the optical axis so as to form a focal region for the beam. [0005] The invention also relates to a method of focusing a charged particle beam using such a magnetic lens. [0006] The invention additionally relates to a method of manufacturing such a magnetic lens. [0007] The present invention also relates to charged particle microscopes, including: [0008] - a charged particle source for generating a radiation beam of charged particles propagating along the optical axis; [0009] - a sample holder for holding the sample to be irradiated; [0010] - a particle-op...

Claims

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Application Information

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IPC IPC(8): H01J37/14
CPCH01J37/141H01J2237/26H01J2237/1415H01F2003/106Y10T29/4978G21K1/093H01J37/26
Inventor O.沙内尔
Owner FEI COMPANY