Multi-axis Magnetic Lens for Focusing a Plurality of Charged Particle Beams

摘要

A multi-axis magnetic lens with stable performance in focusing a plurality of charged particle beams is provided. The multi-axis magnetic lens comprises a plurality of magnetic dub-lens modules. On the one hand, the multi-axis magnetic lens employs an annular permanent-magnet unit to provide a basic and stable magnetic flux to the plurality of magnetic sub-lens modules. One the other hand, the multi-axis magnetic lens uses a plurality of subsidiary coils to provide additional and adjustable magnetic flux to the plurality of magnetic sub-lens modules respectively. The invention also proposes a method to turn off or adjust the basic and stable magnetic flux for some applications. Hence, this invention will benefit the applications which need to execute in a long time period while keeping a high stabilization in performance.

主权项

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.