Magnetic lenses, charged particle microscope systems including the same, and associated methods

A magnetic lens comprising:

• a lens body;
• a first coil supported by the lens body and configured to generate a first magnetic field;
• and
• a second coil supported by the lens body and configured to generate a second magnetic field, overlapping the first magnetic field to form a total magnetic field that is a sum of the first magnetic field and the second magnetic field;
• wherein the lens body comprises:
• a central bore configured to receive a charged particle beam passing through the magnetic lens;
• a first pole piece extending circumferentially around the central bore;
• a second pole piece extending circumferentially around the central bore and at least partially disposed radially exteriorly of the first pole piece;
• and
• a third pole piece extending circumferentially around the central bore and at least partially disposed radially exteriorly of the second pole piece,
• which together configure the magnetic lens to operate as a single objective lens with a variable main objective plane.

A charged particle microscope system comprising:

• a charged particle source configured to emit a charged particle beam along an optical axis and toward a sample;
• a sample holder configured to support the sample;
• and
• a magnetic objective lens configured to focus the charged particle beam to a focus location corresponding to a location of the sample;
• wherein the magnetic objective lens comprises:
• a lens body with a central bore through which the charged particle beam extends;
• a first coil supported by the lens body and configured to generate a first magnetic field with a first field magnitude;
• and
• a second coil supported by the lens body and configured to generate a second magnetic field with a second field magnitude, overlapping the first magnetic field to form a total magnetic field magnitude that is a sum of the first field magnitude and the second field magnitude,
• which together configure the magnetic lens to operate as a single objective lens with a variable main objective plane, wherein the magnetic objective lens is configured such that adjusting a ratio between the first field magnitude and the second field magnitude operates to adjust a magnification of the magnetic objective lens, wherein the focus location is positioned exteriorly of the lens body, and wherein each of the first magnetic field and the second magnetic field is localized to a region away from the focus location.

A method, comprising:

• positioning a sample relative to a magnetic lens;
• and
• operating the magnetic lens to focus a charged particle beam to a focus location, comprising:
• generating, with a first coil of the magnetic lens, a first magnetic field;
• and
• generating, with a second coil of the magnetic lens, a second magnetic field, overlapping the first magnetic field to form a total magnetic field that is a sum of the first magnetic field and the second magnetic field,
• wherein the magnetic lens comprises:
• a plurality of pole pieces defining at least two axial gaps;
• and
• at least two independent coils in respective communication with the at least two axial gaps such that the magnetic lens operates as a single objective lens with variable main objective plane.