Particle-beam column corrected for both chromatic and spherical aberration
OwnerFrederick Wight Martininventor
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Abstract
An objective lens for use in probe-forming particle-optical columns such as focused ion beam equipment, scanning electron microscopes, and helium microscopes is described. It comprises two interleaved (quadrupole/octopole) lenses and two or three ancillary octopole lenses, and is capable of simultaneous compensation of spherical (Cs) and chromatic (Cc) aberrations of the objective lens alone or of the complete particle-optical column. Additional apparatus comprising a gridded aperture and position-sensitive detector is specified, together with a method to measure and minimize all of the five independent third-order aberration coefficients of the objective lens.
Claims21
An improved particle-optical column comprising a needle-type particle source, an extraction electrode, a condensing lens, and an objective lens system comprising two interleaved quadrupole lenses for forming a finely focused particle beam, wherein the improvement comprises
- two normal octopole correctors inside the objective lens system,
- comprising means to superimpose voltages of one polarity to all poles and of the opposite polarity to all electrodes of each interleaved lens, thereby forming normal octopole lenses within each interleaved lens;
- and
- two skew correctors, consisting of skew octopole lenses,
- situated at any location along the axis of the column,
- wherein the skew correctors are rotated 22.5 degrees about the axis with respect to the normal correctors and
- wherein the normal correctors and skew correctors function to compensate for intrinsic and parasitic third-order aberrations caused in each interleaved quadrupole lens.
An improved particle-optical column comprising a needle-type particle source, an extraction electrode, a condensing lens, and an objective lens system comprising two interleaved quadrupole lenses for forming a finely focused particle beam, wherein the improvement comprises
- two normal octopole correctors inside the objective lens system,
- comprising means to superimpose voltages of one polarity to all poles and of the opposite polarity to all electrodes of each interleaved lens,
- thereby forming normal octopole lenses within each interleaved lens;
- and
- two skew correctors, consisting of skew octopole lenses, situated at any location along the axis of the column,
- wherein the skew correctors are rotated 22.5 degrees about the axis with respect to the normal correctors;
- and
- a third ancillary normal octopole lens, wherever located along the axis of the column;
- and wherein the normal correctors and skew correctors function to compensate for intrinsic and parasitic 3rd-order aperture aberrations of the entire column.
An improved particle-optical column comprising a needle-type particle source, an extraction electrode, a condensing lens, and an objective lens system comprising two magnetic quadrupole lenses for forming a finely focused particle beam, wherein the improvement comprises
- an electric multipole lens structure placed inside the poles of each magnetic lens, functioning simultaneously as
- an electric quadrupole lens,
- a normal octopole corrector lens, and
- a skew corrector octopole lens,
- wherein the skew lenses are rotated 22.5 degrees about the axis with respect to the normal fields;
- and
- wherein the normal correctors and skew correctors function to compensate for intrinsic and parasitic third-order aberrations caused in each quadrupole lens.
Dependencies are inferred from the claim text.