Electrostatic mirror chromatic aberration correctors
Electrostatic mirror chromatic aberration (Cc) correctors, according to the present disclosure, comprise an electrostatic electron mirror that itself comprises a multipole. The electrostatic electron mirror is positioned within the corrector such that, when the corrector is in use, an electron beam passing through the corrector is not incident on the electrostatic electron mirror along the optical axis of the mirror. The mirror object distance of the electrostatic mirror is equal to the mirror image distance of the electrostatic mirror, and the electrostatic mirror is configured such that the electrostatic mirror applies no dispersion or coma aberration to the electron beam. The multipole is positioned in the mirror plane of the electrostatic electron mirror, and in some embodiments the multipole is a quadrupole.
1 . An electrostatic mirror chromatic aberration (Cc) corrector, the corrector comprising:
an electrostatic electron mirror comprising an electrostatic multipole, the electrostatic multipole positioned at or near a mirror plane of the electrostatic electron mirror; and
wherein the electrostatic electron mirror is positioned within the corrector such that, when the corrector is in use, an electron beam passing through the corrector is not incident on the electrostatic electron mirror along a central mirror axis of the mirror.
2 . The electrostatic mirror Cc corrector of claim 1 , wherein the mirror object distance of the electrostatic mirror is equal to the mirror image distance of the electrostatic mirror, such that the electrostatic mirror applies no dispersion or coma aberration to the electron beam.
3 . The electrostatic mirror Cc corrector of claim 1 , wherein the mirror axial potential of the electrostatic mirror is specifically shaped such that the electrostatic mirror induces no chromatic astigmatism to the electron beam.
4 . The electrostatic mirror Cc corrector of claim 1 , wherein the electrostatic mirror Cc corrector is positioned upstream of an accelerator when used in a charged particle system, such that a chromatic aberration of the electron beam is corrected before the electron beam is accelerated by the accelerator.
5 . The electrostatic mirror Cc corrector of claim 1 , wherein the electrostatic mirror CC corrector does not comprise a beam splitter.
6 . The electrostatic mirror Cc corrector of claim 1 , wherein the electrostatic electron mirror comprises a MEMS device.
7 . The electrostatic mirror Cc corrector of claim 1 , wherein the electrostatic electron mirror is a pancake multipole mirror.
8 . The electrostatic mirror Cc corrector of claim 1 , wherein the electrostatic multipole is a quadrupole, and the quadrupole applies a stigmatism to the electron beam without disturbing the symmetry between the object side and image side of the electrostatic electron mirror.
9 . The electrostatic mirror Cc corrector of claim 1 , wherein the diameter of the electrostatic electron mirror is 3 mm or less.
10 . The electrostatic mirror Cc corrector of claim 1 , wherein the electrostatic electron mirror is a first electrostatic electron mirror, the multipole is a first multipole, and the corrector further comprises a second electrostatic electron mirror comprising a second electrostatic multipole.
11 . The electrostatic mirror Cc corrector of claim 10 , wherein the second electrostatic electron mirror is positioned within the corrector such that, when the corrector is in use, the electron beam passing through the corrector is not incident on the second electrostatic electron mirror along the central mirror axis of the second electrostatic electron mirror.
12 . The electrostatic mirror Cc corrector of claim 10 , wherein the first electrostatic electron mirror and the second electrostatic electron mirror use symmetry to correct 2-fold aberrations.
13 . The electrostatic mirror Cc corrector of claim 12 , wherein the first electrostatic electron mirror applies a first 2-fold aberration to the electron beam in a first direction, and the second electrostatic electron mirror applies a second 2-fold aberration to the electron beam in a perpendicular direction such that the first aberration and the second aberration combine to correct each other.
14 . The electrostatic mirror Cc corrector of claim 1 , wherein the corrector further comprises a first set of deflectors and a second set of deflectors, wherein:
the first set of deflectors is configured to selectively deflect the electron beam away from a first beam path where it would strike the first electrostatic electron mirror and to a second beam path where the electron beam travels to the second set of deflectors; and
the second set of deflectors are configured to selectively deflect the electron beam away from the second beam path and to a third beam path.
15 . The electrostatic mirror Cc corrector of claim 14 , wherein when the corrector is operating in a Cc correction mode, the electron beam is reflected by the first electrostatic electron mirror and the second electrostatic electron mirror, and when the corrector is operating in a bypass mode, the electron beam is deflected by the first set of deflectors and the second set of deflectors such that the electron beam is not reflected by the first electrostatic electron mirror and the second electrostatic electron mirror.
16 . The electrostatic mirror Cc corrector of claim 15 , wherein the electron beam exits the corrector along a same beam path whether it is operating in the Cc correction mode or the bypass mode.
17 . The electrostatic mirror Cc corrector of claim 1 , wherein the mirror plane of the electrostatic electron mirror corresponds to a plane at or near the surface of a pancake multipole.
18 . A charged particle system, the system comprising:
a sample holder configured to hold a sample;
a source configured to emit a charged particle beam towards a sample;
an electrostatic mirror chromatic aberration (Cc) corrector, the corrector comprising:
an electrostatic electron mirror comprising an electrostatic multipole, the electrostatic multipole being positioned in a mirror plane of the electrostatic electron mirror; and
wherein the electrostatic electron mirror is positioned within the corrector such that, when the corrector is in use, an electron beam passing through the corrector is not incident on the electrostatic electron mirror along a central mirror axis of the mirror;
a focusing column configured to direct the charged particle beam to be incident on the sample; and
one or more detectors configured to detect emissions resultant from the charged particle beam being incident on the sample.
19 . The charged particle system of claim 18 , wherein the mirror object distance of the electrostatic mirror is equal to the mirror image distance of the electrostatic mirror, such that the electrostatic mirror applies no dispersion or coma aberration to the electron beam.
20 . The charged particle system of claim 18 , wherein the electrostatic electron mirror is a first electrostatic electron mirror, the electrostatic multipole is a first electrostatic multipole, the corrector further comprises a second electrostatic electron mirror comprising a second electrostatic multipole, and wherein the first electrostatic electron mirror and the second electrostatic electron mirror use symmetry to correct 2-fold aberrations.