Apparatus of plural charged-particle beams
A multi-beam apparatus for observing a sample with high resolution and high throughput is proposed. In the apparatus, a source-conversion unit forms plural and parallel images of one single electron source by deflecting plural beamlets of a parallel primary-electron beam therefrom, and one objective lens focuses the plural deflected beamlets onto a sample surface and forms plural probe spots thereon. A movable condenser lens is used to collimate the primary-electron beam and vary the currents of the plural probe spots, a pre-beamlet-forming means weakens the Coulomb effect of the primary-electron beam, and the source-conversion unit minimizes the sizes of the plural probe spots by minimizing and compensating the off-axis aberrations of the objective lens and condenser lens.
1. An apparatus for reducing aberrations of beamlets of a multi-beam apparatus, the apparatus comprising:
a plurality of electron optics elements configured to direct a plurality of beamlets generated by the multi-beam apparatus towards a primary optical axis of the multi-beam apparatus with different deflection angles, wherein the deflection angles of the plurality of beamlets are individually set to reduce aberrations of a plurality of probe spots formed by the plurality of beamlets respectively; and
a plurality of beam-limit openings configured to limit currents of the plurality of probe spots.
2. The apparatus of claim 1 , wherein the plurality of electron optics elements is below and aligned with the plurality of beam-limit openings respectively.
3. The apparatus of claim 2 , wherein the plurality of beam-limit openings is configured to form the plurality of beamlets from a substantially parallel beam generated by the multi-beam apparatus.
4. The apparatus of claim 2 , further comprising a plurality of pre-bending micro-deflectors respectively above the plurality of beam-limit openings, configured to:
form the plurality of beamlets from a substantially parallel beam generated by the multi-beam apparatus; and
direct the plurality of beamlets to be perpendicularly incident into the plurality of beam-limit openings.
5. The apparatus of claim 2 , wherein each of the plurality of electron optics elements is a 4-pole lens.
6. The apparatus of claim 2 , wherein the plurality of electron optics elements compensates at least one of field curvature, astigmatism, or distortion aberrations of the plurality of probe spots to further reduce sizes and distortions of the plurality of probe spots.
7. The apparatus of claim 6 , wherein each of the plurality of electron optics elements is an 8-pole lens.
8. The apparatus of claim 7 , wherein each of the plurality of electron optics elements comprises one micro-lens and two 4-pole lenses which are aligned with and placed along an optical axis of the each element, and the two 4-pole lenses have a 45° difference in azimuth.
9. The apparatus of claim 8 , wherein for the each of the plurality of electron optics elements, one of the two 4-pole lenses is on a beamlet exit side and one corresponding beamlet is deflected by the one 4-pole lens.
10. The apparatus of claim 9 , wherein landing energies of the plurality of beamlets are varied by changing a potential of the plurality of beamlets.
11. The apparatus of claim 2 , further comprising a condenser lens between the plurality of beam-limit openings and the plurality of electron optics elements, configured to focus the plurality of beamlets to be directed by the plurality of electron optics elements respectively towards the primary optical axis.
12. The apparatus of claim 1 , wherein the plurality of electron optics elements is above and aligned with the plurality of beam-limit openings respectively.
13. The apparatus of claim 12 , wherein the plurality of electron optics elements is configured to form the plurality of beamlets from a substantially parallel beam generated by the multi-beam apparatus.
14. A method for reducing aberrations of beamlets of a multi-beam apparatus, the method comprising:
generating a plurality of beamlets of charged-particles;
directing, using a plurality of electron optics elements, the plurality of beamlets towards a primary optical axis of the multi-beam apparatus with different deflection angles; and
individually setting the deflection angles to reduce aberrations of a plurality of probe spots formed by the plurality of beamlets respectively.
15. The method of claim 14 , further comprising:
compensating, using the plurality of electron optics elements, at least one of field curvature, astigmatism, or distortion aberrations of the plurality of probe spots to further reduce sizes and distortions of the plurality of probe spots.
16. The method of claim 14 , wherein generating the plurality of beamlets of charged-particles comprises:
forming, using the plurality of electron optics elements, the plurality of beamlets from a substantially parallel beam generated by the multi-beam apparatus.
17. The method of claim 14 , wherein generating the plurality of beamlets of charged-particles comprises:
forming, using a plurality of beam-limit openings respectively above and aligned with the plurality of electron optics elements, the plurality of beamlets from a substantially parallel beam generated by the multi-beam apparatus.
18. The method of claim 14 , wherein generating the plurality of beamlets of charged-particles comprises:
forming, using a plurality of pre-bending micro-deflectors respectively above and aligned with the plurality of electron optics elements, the plurality of beamlets from a substantially parallel beam generated by the multi-beam apparatus.
19. The method of claim 18 , further comprising:
directing the plurality of beamlets to be perpendicularly incident into a plurality of beam-limit openings respectively above and aligned with the plurality of electron optics elements.
20. The method of claim 14 , further comprising:
varying landing energies of the plurality of beamlets by changing a potential of the plurality of beamlets.