Multi-axis magnetic lens for focusing a plurality of charged particle beams

1. A multi-axis magnetic lens, comprising:

a pair of parallel magnetic conductor plates with a plurality of through holes in pairs therein, wherein for each pair of through holes, an upper through hole in an upper magnetic conductor plate of said pair of parallel magnetic conductor plates is aligned with a lower through hole in a lower magnetic conductor plate of said pair of parallel magnetic conductor plates;

a plurality of magnetic round rings in pairs, wherein for each pair of magnetic round rings, an upper magnetic round ring is inside said upper through hole of one pair of through holes and forms a first upper radial gap therebetween, a lower magnetic round ring is inside said lower through hole of said pair of through holes and forms a first lower radial gap therebetween, said upper magnetic round ring is aligned with said lower magnetic round ring, and a lower end of said upper magnetic round ring extends downward into said lower magnetic round ring and forms a magnetic-circuit gap therebetween;

a plurality of subsidiary coils between said upper and lower magnetic conductor plates, wherein said upper magnetic round ring of one pair of magnetic round rings is wound by one of said plurality of subsidiary coils,

thereby forming a plurality of magnetic sub-lens modules, wherein each of said plurality of magnetic sub-lens modules comprises one pair of through holes, one pair of magnetic round rings therein and one subsidiary coil winding said upper magnetic round ring of said pair of magnetic round rings, wherein for each magnetic sub-lens module, an optical axis thereof lies on a central axis of said upper magnetic round ring, said upper and lower magnetic round rings function as an upper pole-piece and a lower pole-piece respectively, and said subsidiary coil can be excited to provide a first magnetic flux leaking out through said magnetic-circuit gap and towards said optical axis; and

an annular permanent-magnet unit between said upper and lower magnetic conductor plates, surrounding said plurality of subsidiary coils and having an annular shape in a radial section, wherein said annular permanent-magnet unit is magnetized in a direction perpendicular to said upper magnetic conductor plate to provide a second magnetic flux to said plurality of magnetic sub-lens modules, wherein for each of said plurality of magnetic sub-lens modules, a portion of said second magnetic flux can flow in and leak out through said magnetic-circuit gap and towards said optical axis,

wherein each of said plurality of magnetic sub-lens modules therefore is able to form a magnetic round-lens field with an excitation of said subsidiary coil thereof and/or said annular permanent-magnetic unit, and consequently said multi-axis magnetic lens can provide a plurality of magnetic sub-lenses.

2. The multi-axis magnetic lens according to claim 1 , wherein for said each pair of magnetic round rings, magnetic permeabilities of said upper and lower magnetic round rings are higher than that of said upper and lower magnetic conductor plates respectively.

3. The multi-axis magnetic lens according to claim 2 , wherein said first upper and lower radial gaps can be vacuum or filled with non-magnetic or weakly-magnetic material.

4. The multi-axis magnetic lens according to claim 3 , wherein said annular permanent-magnet unit contacts said upper and lower magnetic conductor plates.

5. The multi-axis magnetic lens according to claim 4 , wherein said annular permanent-magnet unit can be formed by one full annular permanent magnet or several segmented permanent magnets.

6. The multi-axis magnetic lens according to claim 5 , wherein outer radial dimensions of said upper and lower magnetic conductor plates are equal to or larger than that of said annular permanent-magnet unit.

7. The multi-axis magnetic lens according to claim 6 , further comprising a magnetic-shielding tube which encloses said annular permanent-magnet unit with a third radial gap and keeps a fourth gap from one or each of said upper and lower magnetic conductor plates so as to reduce upper and lower stray magnetic fields respectively above and below said plurality of magnetic sub-lens modules.

8. The multi-axis magnetic lens according to claim 6 , further comprising a magnetic short-circuit tube which is initially placed above said upper magnetic conductor plate or below said lower magnetic conductor plate so as not to influence said magnetic round-lens fields, and can be moved to connect peripheral portions of both said upper and lower magnetic conductor plates so as to form an enclosed magnetic bypass to said second magnetic flux and therefore turn off said multi-axis magnetic lens.

9. The multi-axis magnetic lens according to claim 6 , further comprising a magnetic-shielding tube and a magnetic short-circuit tube, wherein said magnetic-shielding tube encloses said annular permanent-magnet unit with a third radial gap and keeps a fourth radial gap from one of said upper and lower magnetic conductor plates, and said magnetic short-circuit tube can be moved to fill in said fourth radial gap so as to form an enclosed magnetic bypass to said second magnetic flux and therefore turn off said multi-axis magnetic lens.

10. The multi-axis magnetic lens according to claim 6 , further comprising a magnetic field-adjusting tube which encloses said annular permanent-magnet unit with a third radial gap and keeps a fifth axial gap from one of said upper and lower magnetic conductor plates, wherein said magnetic field-adjusting tube can be moved to change an axial size of said fifth axial gap so as to adjust said magnetic round-lens fields of said plurality of magnetic sub-lenses.

11. The multi-axis magnetic lens according to claim 6 , further comprising an upper magnetic-shielding plate located above said upper magnetic conductor plate with a sixth axial gap and having a plurality of upper through circular openings each aligned with one of said plurality of magnetic sub-lens modules so as to reduce high order harmonics of magnetic fields of said plurality of magnetic sub-lenses.

12. The multi-axis magnetic lens according to claim 11 , further comprising a lower magnetic-shielding plate located below said lower magnetic conductor plate with a seventh axial gap and having a plurality of lower through circular openings each aligned with one of said plurality of magnetic sub-lens modules so as to further reduce high order harmonics of magnetic fields of said plurality of magnetic sub-lenses.

13. The multi-axis magnetic lens according to claim 7 , further comprising an upper magnetic-shielding plate located above said upper magnetic conductor plate with a sixth axial gap and having a plurality of upper through circular openings each aligned with one of said plurality of magnetic sub-lens modules, and a lower magnetic-shielding plate located below said lower magnetic conductor plate with a seventh axial gap and having a plurality of lower through circular openings each aligned with one of said plurality of magnetic sub-lens modules, thereby reducing high order harmonics of magnetic fields of said plurality of magnetic sub-lenses.

14. A multi-axis magnetic lens, comprising:

a pair of parallel magnetic conductor plates with a plurality of through holes in pairs therein, wherein for each pair of through holes, an upper through hole in an upper magnetic conductor plate of said pair of parallel magnetic conductor plates is aligned with a lower through hole in a lower magnetic conductor plate of said pair of parallel magnetic conductor plates;

a plurality of magnetic round rings, wherein each of said plurality of magnetic round rings has an upper end inside said upper through hole of one pair of through holes and forming a first radial gap therebetween, and a lower end inside said lower through hole and forming a magnetic-circuit gap therebetween;

a plurality of subsidiary coils between said upper and lower magnetic conductor plates, wherein said each of said plurality of magnetic round rings is wound by one of said plurality of subsidiary coils,

thereby forming a plurality of magnetic sub-lens modules, wherein each of said plurality of magnetic sub-lens modules comprises one pair of through holes, one magnetic round ring and one subsidiary coil winding said magnetic round ring, wherein for each magnetic sub-lens module, an optical axis lies on a central axis of said magnetic round ring, said magnetic round ring functions as an upper pole-piece and a peripheral portion of said lower through hole in said lower magnetic conductor plate functions as a lower pole-piece, and said subsidiary coil can be excited to provide a first magnetic flux leaking out through said magnetic-circuit gap and towards said optical axis; and

an annular permanent-magnet unit between said upper and lower magnetic conductor plates, surrounding said plurality of subsidiary coils and having an annular shape in a radial section, wherein said annular permanent-magnet unit is magnetized in a direction perpendicular to said upper magnetic conductor plate to provide a second magnetic flux to said plurality of magnetic sub-lens modules, wherein for each of said plurality of magnetic sub-lens modules, a portion of said second magnetic flux can flow in and leak out through said magnetic-circuit gap and towards said optical axis,

wherein each of said plurality of magnetic sub-lens modules therefore forms a magnetic round-lens field with an excitation of said subsidiary coil thereof and/or said annular permanent-magnetic unit, and consequently said multi-axis magnetic lens can provide a plurality of magnetic sub-lenses.

15. The multi-axis magnetic lens according to claim 14 , wherein magnetic permeability of said each magnetic round ring is higher than that of both said upper and lower magnetic conductor plates.

16. The multi-axis magnetic lens according to claim 15 , wherein said first radial gaps can be vacuum or filled with non-magnetic or weakly-magnetic material.

17. The multi-axis magnetic lens according to claim 16 , wherein said annular permanent-magnet unit contacts said upper and lower magnetic conductor plates.

18. The multi-axis magnetic lens according to claim 17 , wherein outer radial dimensions of said upper and lower magnetic conductor plates are equal to or larger than that of said annular permanent-magnet unit.

19. The multi-axis magnetic lens according to claim 18 , further comprising a magnetic-shielding tube which encloses said annular permanent-magnet unit with a third radial gap and keeps a fourth gap from one or each of said upper and lower magnetic conductor plates so as to reduce a upper and lower stray magnetic fields respectively above and below said plurality of magnetic sub-lens modules.

20. The multi-axis magnetic lens according to claim 19 , further comprising an upper magnetic-shielding plate located above said upper plate with a sixth axial gap and having a plurality of upper through circular openings each aligned with one of said plurality of magnetic sub-lens modules, and a lower magnetic-shielding plate located below said lower plate with a seventh axial gap and having a plurality of lower through circular openings each aligned with one of said plurality of magnetic sub-lens modules, thereby reducing high order harmonics of magnetic fields of said plurality of magnetic sub-lenses.

21. A method to configure a multi-axis magnetic lens, comprising:

forming a plurality of magnetic sub-lens modules by a pair of parallel magnetic conductor plates with a plurality of through holes in pairs therein, a plurality of magnetic round rings in pairs and a plurality of subsidiary coils, wherein each of said plurality of magnetic sub-lens modules comprises one pair of through holes, one pair of magnetic round rings and one subsidiary coil,

wherein for said pair of through holes, an upper through hole in an upper magnetic conductor plate of said pair of parallel magnetic conductor plates is aligned with a lower through hole in a lower magnetic conductor plate of said pair of parallel magnetic conductor plates,

wherein for said pair of magnetic round rings, an upper magnetic round ring inside said upper through hole with a first upper radial gap is aligned with a lower magnetic round ring inside said lower through hole with a first lower radial gap, a lower end of said upper magnetic round ring extends downward into said lower magnetic round ring and forms a magnetic-circuit gap therebetween, magnetic permeabilities of said upper and lower magnetic round rings are higher than that of said upper and lower magnetic conductor plates respectively, and said first upper and lower radial gaps can be vacuum or filled with non-magnetic or weakly-magnetic material,

wherein an optical axis of said magnetic sub-lens module lies on a central axis of said upper magnetic round ring,

wherein said subsidiary coil is between said upper and lower magnetic conductor plates, winds around said upper magnetic ring and can be excited to provide a first magnetic flux leaking out through said magnetic-circuit gap and towards said optical axis; and

placing an annular permanent-magnet unit between said upper and lower magnetic conductor plates and surrounding said plurality of subsidiary coils, wherein said annular permanent-magnet unit is magnetized in a direction perpendicular to said upper magnetic conductor plate to provide a second magnetic flux, and for said each magnetic sub-lens module, a portion of said second magnetic flux can flow in and leak out through said magnetic-circuit gap and towards said optical axis,

wherein each of said plurality of magnetic sub-lens modules therefore is able to form a magnetic round-lens field with an excitation of said subsidiary coil and/or said annular permanent-magnetic unit.

22. The method according to claim 21 , wherein said annular permanent-magnet unit contacts said upper and lower magnetic conductor plates.

23. The method according to claim 22 , further placing a magnetic-shielding tube enclosing said annular permanent-magnet unit to reduce upper and lower stray magnetic fields respectively above and below said plurality of magnetic sub-lens modules.

24. A method to configure a multi-axis magnetic lens, comprising:

forming a plurality of magnetic sub-lens modules by a pair of parallel magnetic conductor plates with a plurality of through holes in pairs therein, a plurality of magnetic round rings and a plurality of subsidiary coils, wherein each of said plurality of magnetic sub-lens modules comprises one pair of through holes, one magnetic round ring and one subsidiary coil,

wherein for said pair of through holes, an upper through hole and a lower through hole are respectively in an upper magnetic conductor plate and a lower magnetic conductor plate of said pair of parallel magnetic conductor plates and aligned with each other, said magnetic round ring has an upper end inside said upper through hole with a first radial gap and a lower end inside said lower through hole and forming a magnetic-circuit gap therebetween, said magnetic round ring has permeability higher than that of said upper and lower magnetic conductor plates, and said first radial gap can be vacuum or filled with non-magnetic or weakly-magnetic material,

wherein an optical axis of said magnetic sub-lens module lies on a central axis of said magnetic round ring,

wherein said subsidiary coil is between said upper and lower magnetic conductor plates, winds around said magnetic round ring and can be excited to provide a first magnetic flux leaking out through said magnetic-circuit gap and towards said optical axis; and

placing an annular permanent-magnet unit between said upper and lower magnetic conductor plates and surrounding said plurality of subsidiary coils, wherein said annular permanent-magnet unit is magnetized in a direction perpendicular to said upper magnetic conductor plate to provide a second magnetic flux, and for said each magnetic sub-lens module, a portion of said second magnetic flux can flow in and leak out through said magnetic-circuit gap and towards said optical axis,

wherein each of said plurality of magnetic sub-lens modules therefore is able to form a magnetic round-lens field with an excitation of said subsidiary coil and/or said annular permanent-magnetic unit.

25. The method according to claim 24 , wherein said annular permanent-magnet unit contacts said upper and lower magnetic conductor plates.

26. The method according to claim 25 , further placing a magnetic-shielding tube enclosing said permanent-magnet unit to reduce upper and lower stray magnetic fields respectively above and below said plurality of magnetic sub-lens modules.

27. A method for forming a multi-axis magnetic lens with stable performance, comprising:

providing a pair of parallel magnetic conductor plates with a plurality of through holes in pairs therein, wherein for each pair of through holes, an upper through hole and a lower through hole are respectively in an upper magnetic conductor plate and a lower magnetic conductor plate of said pair of parallel magnetic conductor plates and aligned with each other;

providing a plurality of magnetic rings respectively inside said plurality of through holes, wherein each magnetic ring has an upper end inside said upper through hole of one pair of through holes with a first radial gap and a lower end inside said lower through hole of said pair of through holes and forming a magnetic-circuit gap therebetween, said magnetic ring has permeability higher than that of said upper and lower magnetic conductor plates, and said first radial gap can be vacuum or filled with non-magnetic or weakly-magnetic material;

configuring a plurality of subsidiary coils, between said upper and lower magnetic conductor plates, respectively winding said plurality of magnetic rings; and

providing an annular permanent-magnet unit between said upper and lower magnetic conductor plates and surrounding said plurality of subsidiary coils, wherein said annular permanent-magnet unit is magnetized in a direction perpendicular to said upper magnetic conductor plate.

28. A method for forming a multi-axis magnetic lens with stable performance, comprising:

providing a pair of parallel magnetic conductor plates with a plurality of through holes in pairs therein, wherein for each pair of through holes, an upper through hole in an upper magnetic conductor plate of said pair of parallel magnetic conductor plates is aligned with a lower through hole in a lower magnetic conductor plate of said pair of parallel magnetic conductor plates;

providing a plurality of magnetic rings in pairs respectively inside said plurality of through holes in pairs, wherein for each pair of magnetic rings, an upper magnetic ring inside said upper through hole of one pair of through holes with a first upper radial gap is aligned with a lower magnetic ring inside said lower through hole of said pair of through holes with a first lower radial, a lower end of said upper magnetic ring extends downward into said lower magnetic ring and forms a magnetic-circuit gap therebetween, magnetic permeabilities of said upper and lower magnetic rings are higher than that of said upper and lower magnetic conductor plates respectively, and said first upper and lower radial gaps can be vacuum or filled with non-magnetic or weakly-magnetic material;

configuring a plurality of subsidiary coils, between said upper and lower magnetic conductor plates, respectively winding said plurality of upper magnetic rings; and

providing an annular permanent-magnet unit between said upper and lower magnetic conductor plates and surrounding said plurality of subsidiary coils, wherein said annular permanent-magnet unit is magnetized in a direction perpendicular to said upper magnetic conductor plate.