Apparatus of plural charged-particle beams
A multi-beam apparatus for observing a sample with high resolution and high throughput and in flexibly varying observing conditions is proposed. The apparatus uses a movable collimating lens to flexibly vary the currents of the plural probe spots without influencing the intervals thereof, a new source-conversion unit to form the plural images of the single electron source and compensate off-axis aberrations of the plural probe spots with respect to observing conditions, and a pre-beamlet-forming means to reduce the strong Coulomb effect due to the primary-electron beam.
1. A pre-beamlet-forming aperture array comprising:
multiple beamlet-forming apertures configured to cut off a portion of electrons of a primary electron beam emitted by an electron source to form a set of multiple electron beamlets,
wherein the pre-beamlet-forming aperture array is configured to be positioned proximate to the electron source and between the electron source and a source-conversion unit, and the source-conversion unit is configured to manipulate the set of multiple electron beamlets.
2. The pre-beamlet-forming aperture array of claim 1 , wherein the primary electron beam when it passes between the electron source and the pre-beamlet-forming aperture array has a shape of a wide and uncollimated beam.
3. The pre-beamlet-forming aperture array of claim 1 , wherein the pre-beamlet-forming aperture array is configured to limit currents of the set of multiple electron beamlets to a first set of current levels, and the source-conversion unit is configured to further limit currents of the set of multiple electron beamlets to a second set of current levels.
4. The pre-beamlet-forming aperture array of claim 1 , wherein the pre-beamlet-forming aperture array is configured to reduce Coulomb effect in an area between the electron source and the source-conversion unit.
5. The pre-beamlet-forming aperture array of claim 1 , wherein source-conversion unit is configured to cut off a portion of electrons of the set of multiple electron beamlets.
6. A multi-beam apparatus for observing a surface of a sample, comprising:
an electron source configured to emit a primary electron beam;
a pre-beamlet-forming aperture array comprising multiple beamlet-forming apertures configured to cut off a portion of electrons of the primary electron beam to form a set of multiple electron beamlets, and
a source-conversion unit configured to manipulate the set of multiple electron beamlets,
wherein the pre-beamlet-forming aperture array is positioned proximate to the electron source and between the electron source and the source-conversion unit.
7. The multi-beam apparatus of claim 6 , wherein the primary electron beam between the electron source and the pre-beamlet-forming aperture array has a shape of a wide and uncollimated beam.
8. The multi-beam apparatus of claim 6 , wherein the pre-beamlet-forming aperture array is configured to limit currents of the set of multiple electron beamlets to a first set of current levels, and the source-conversion unit is configured to further limit currents of the set of multiple electron beamlets to a second set of current levels.
9. The multi-beam apparatus of claim 6 , wherein the pre-beamlet-forming aperture array is configured to reduce Coulomb effect in an area between the electron source and the source-conversion unit.
10. The multi-beam apparatus of claim 6 , wherein source-conversion unit is configured to cut off a portion of electrons of the set of multiple electron beamlets.
11. The multi-beam apparatus of claim 6 , further comprising an adjustable collimating lens having a principal plane moveable along a primary optical axis of the multi-beam apparatus.
12. The multi-beam apparatus of claim 11 , wherein the adjustable collimating lens is positioned between the pre-beamlet-forming aperture array and the source-conversion unit.
13. The multi-beam apparatus of claim 12 , wherein the adjustable collimating lens is configured to change paths of electrons of the set of multiple electron beamlets based on the position of the principal plane.
14. The multi-beam apparatus of claim 13 , wherein the adjustable collimating lens is configured to change a current density of the set of multiple electron beamlets based on the position of the principal plane.
15. The multi-beam apparatus of claim 13 , wherein the adjustable collimating lens is configured to move the principal plane closer to the pre-beamlet-forming aperture array to enable the current density of the set of multiple electron beamlets to increase.
16. The multi-beam apparatus of claim 13 , wherein the adjustable collimating lens is configured to move the principal plane closer the source-conversion unit to enable the current density of the set of multiple electron beamlets to decrease.
17. The multi-beam apparatus of claim 11 , wherein the adjustable collimating lens comprises multiple magnetic lenses that are positioned along the primary optical axis.
18. The multi-beam apparatus of claim 11 , wherein the adjustable collimating lens comprises multiple annular electrodes that are positioned along the primary optical axis.