Adjustable permanent magnetic lens having shunting device

1 . A charged particle lens configured to modify a charged-particle beam of a charged particle optical system, the lens being provided with a beam passage extending primarily along a longitudinal axis and allowing the passage of a charged-particle beam, said lens including a magnetic circuit assembly comprising:

at least one permanent magnet;

a yoke body; and

at least one shunting device,

said yoke body being composed of at least two yoke components, of which a first yoke component realizes an inner yoke shell, arranged surrounding the passage space, and a second yoke component realizes an outer yoke shell which is arranged surrounding the inner yoke shell, said yoke components being arranged circumferentially around the longitudinal axis and comprise a ferromagnetic or ferrimagnetic material;

said at least one permanent magnet being arranged between the at least two yoke components and circumferentially around the inner yoke shell, said at least one permanent magnet comprising a permanent magnetic material being magnetically oriented with its two magnetic poles towards respective yoke components;

wherein in the magnetic circuit assembly, the at least one permanent magnet and the yoke body form a closed magnetic circuit but having at least two gaps formed between respective axial faces of different yoke components, wherein the closed magnetic circuit is configured to direct a magnetic flux density coming from said at least one permanent magnet through the yoke body and, in said gaps, induce a magnetic field, which reaches inwards into the beam passage, and

said at least one shunting device comprising at least one magnetically permeable shunting component and being arranged in a defined position between the at least two components of the yoke body, said at least one shunting device enabling a defined portion of the magnetic flux density to bypass at least parts of the magnetic circuit assembly;

wherein the at least one shunting component is composed of two or more sector components made of magnetically permeable materials, said sector components being arranged around the longitudinal axis at respectively different azimuthal positions,

wherein at least one of said sector components comprises a magnetically permeable material having a magnetic permeability that is different from the magnetic permeability of the magnetically permeable materials of the other sector components, enabling the charged particle lens to have azimuthal differentially varying magnetic flux densities and thus azimuthally varying magnetic fields around the longitudinal axis.

2 . The charged particle lens of claim 1 , having an overall rotationally symmetric shape along said longitudinal axis, wherein the components of the magnetic circuit assembly, namely,

the at least one permanent magnet;

the yoke body; and

the at least one shunting device, are arranged coaxial with said longitudinal axis and preferably have basic shapes corresponding to hollow cylinders or hollow polygonal prismatic shapes.

3 . The charged particle lens of claim 1 , wherein the at least one shunting component is composed of two or more layers stacked along the longitudinal axis and/or of one or more sectors arranged around the longitudinal axis.

4 . The charged particle lens of claim 1 , wherein the at least one permanent magnet is composed of at least two sub-components arranged around the longitudinal axis at respectively different azimuthal positions, wherein one or more of the at least one shunting device or of the sector components is placed between respective two of said permanent-magnet sub-components.

5 . The charged particle lens of claim 1 , wherein the second yoke component realizes a housing body of the charged particle lens, which surrounds other components of the lens including all other yoke components.

6 . The charged particle lens of claim 1 , wherein the at least one permanent magnet has a magnetization oriented substantially radially, and the at least one shunting device comprises a ferromagnetic or ferrimagnetic material at least along a direction parallel to said substantially radially oriented magnetization.

7 . The charged particle lens of claim 1 , wherein the at least one permanent magnet is composed of at least two sub-components, namely:

segmented according to two or more layers stacked along a longitudinal axis; and/or

split into two or more sectors arranged around a longitudinal axis.

8 . The charged particle lens of claim 7 , wherein at least one shunting device is placed between respective two of said sub-components.

9 . A charged-particle optical apparatus including the charged particle lens of claim 1 , and configured for influencing a charged-particle beam of said apparatus propagating through the lens along the longitudinal axis thereof, wherein said lens is part of a particle-optical system of said apparatus.

10 . The charged-particle optical apparatus of claim 9 , wherein the apparatus is realized as a multi-column system comprising a plurality of particle-optical columns, each column being configured to employ a respective particle beam and comprising a respective particle-optical system which includes a respective instance of a charged particle or electromagnetic lens.

11 . An electromagnetic lens including

a charged particle lens and a sleeve insert inserted into the passage space along the longitudinal axis,

wherein the charged particle lens is configured to modify a charged-particle beam of a charged particle optical system, the lens being provided with a beam passage extending primarily along a longitudinal axis and allowing the passage of a charged-particle beam, said lens including a magnetic circuit assembly comprising:

at least one permanent magnet;

a yoke body; and

at least one shunting device,

said yoke body being composed of at least two yoke components, of which a first yoke component realizes an inner yoke shell, arranged surrounding the passage space, and a second yoke component realizes an outer yoke shell which is arranged surrounding the inner yoke shell, said yoke components being arranged circumferentially around the longitudinal axis and comprise a ferromagnetic or ferrimagnetic material;

said at least one permanent magnet being arranged between the at least two yoke components and circumferentially around the inner yoke shell, said at least one permanent magnet comprising a permanent magnetic material being magnetically oriented with its two magnetic poles towards respective yoke components;

wherein in the magnetic circuit assembly, the at least one permanent magnet and the yoke body form a closed magnetic circuit but having at least two gaps formed between respective axial faces of different yoke components, wherein the closed magnetic circuit is configured to direct a magnetic flux density coming from said at least one permanent magnet through the yoke body and, in said gaps, induce a magnetic field, which reaches inwards into the beam passage, and

said at least one shunting device comprising at least one magnetically permeable shunting component and being arranged in a defined position between the at least two components of the yoke body, said at least one shunting device enabling a defined portion of the magnetic flux density to bypass at least parts of the magnetic circuit assembly;

said sleeve insert surrounding a beam passage having a radius smaller than the radius of the beam passage of the charged-particle lens, the sleeve insert extending along a longitudinal axis,

said sleeve insert comprising a mounting body, which is at least partially electrically conductive, and at least one electrically conductive electrode element,

said at least one electrode element being configured to be applied an electric potential via a power supply so as to generate an electrostatic field within the beam passage of the charged particle lens;

wherein the at least one electrode element includes a beam aperture element forming a delimiting opening with a defined radius around the longitudinal axis,

said delimiting opening being configured to limit the lateral width of a charged-particle beam propagating along the longitudinal axis; and

said beam aperture element being connected to a current measurement device configured to measure an amount of the charged-particle beam absorbed at the beam aperture element.

12 . The electromagnetic lens of claim 11 , wherein the longitudinal axis of said sleeve insert coincides with the longitudinal axis of the charged particle lens.

13 . The electromagnetic lens of claim 11 , wherein the at least one electrode element is configured to form a particle optical lens in conjunction with the magnetic field within the beam passage of the charged particle lens at the at least two gaps, wherein a focal length of said particle-optical lens is adjustable through modifying the electric potentials applied to the at least one electrode elements.

14 . The electromagnetic lens of claim 11 , wherein the inner yoke shell extends along the longitudinal axis and surrounds the sleeve insert circumferentially, and the at least two gaps of the closed magnetic circuit are located at either axial end of the inner yoke shell, each gap generating a defined magnetic field, reaching inwards into the beam passage opening, said electrostatic field generated by one or more of the at least one electrode element of the sleeve insert being configured to at least partially overlap with the respective defined fields in each gap.

15 . The charged particle lens of claim 11 , wherein one or more of the at least one electrode element includes an electrostatic multipole electrode, comprising a number of sub-electrodes arranged uniformly around the longitudinal axis along a circumferential direction, said sub-electrodes being connectable to the power supply, which comprises a multi-channel power supply unit feeding potentials to each sub-electrode individually.

16 . A charged-particle optical apparatus including the electromagnetic lens of claim 11 , and configured for influencing a charged-particle beam of said apparatus propagating through the electromagnetic lens along the longitudinal axis thereof, wherein said electromagnetic lens is part of a particle-optical system of said apparatus.

17 . The charged-particle optical apparatus of claim 16 , wherein the apparatus is realized as a multi-column system comprising a plurality of particle-optical columns, each column being configured to employ a respective particle beam and comprising a respective particle-optical system which includes a respective instance of a charged particle or electromagnetic lens.