Charged particle optical apparatus with aberration corrector
When an accelerating voltage and operating distance are changed, an excitation current and a pole voltage of an aberration corrector must also be changed. Moreover, different multipole voltages or currents must be added individually for each pole in order to superpose multipoles. In view of overcoming the problems explained above, the charged particle optical apparatus of the present invention comprises an excitation device including, to give excitation to form a multipole field to each pole of the multipole lens, electromagnetic type quadrupole of four stages arranged along an optical axis of charged particle beam, electromagnetic type quadrupole of two stages for superposing distribution of voltage similar to distribution of magnetic potential of the electromagnetic type quadrupole of two stages at the center of the electromagnetic type quadrupole of four stages, and electromagnetic type octupole for superposing magnetic potential at least to three multipoles among that of four stages and also comprises a first power supply group for driving the same excitation device and a second power supply group for impressing voltages.
1. A scanning charged particle optical microscope comprising:
an irradiation optical system for scanning a specimen with a charged particle beam;
a specimen stage for supporting the specimen;
a detecting optical system for detecting secondary charged particles generated from the specimen by irradiation with the charged particle beam;
a control unit to control the irradiation optical system; and
a power supply including a current source and a voltage source;
wherein the irradiation optical system includes a charged particle gun, an objective lens, and an aberration corrector arranged between the charged particle gun and the objective lens,
wherein the aberration corrector includes a first pair of multipole lenses, each pole having a first coil, and a second pair of multipole lenses between the first pair of multipole lenses, each pole having a second coil and a voltage input terminal,
wherein the first coils and the second coils are connected to the current source, and the voltage input terminal is connected to the voltage source, and
wherein the control unit is arranged to control whether a voltage of the voltage source is applied to the voltage input terminal, in accordance with an accelerating voltage of the charged particle beam.
2. A scanning charged particle optical microscope according to claim 1 ,
wherein when the accelerating voltage of the charged particle beam is equal to or higher than a predetermined value, the second pair of multipole lenses are operated as only magnetic lenses.
3. A scanning charged particle optical microscope according to claim 1 ,
wherein the first coils are connected to each other and the second coils are connected to each other.
4. A scanning charged particle optical microscope according to claim 1 ,
wherein each pole of the first pair of multipole lenses has a third coil;
wherein each pole of the second pair of multipole lenses has a fourth coil, and
wherein the third coils are connected to each other and the fourth coils are connected to each other.
5. A scanning charged particle optical microscope according to claim 4 ,
wherein each pole of the first pair of multipole lenses has a fifth coil;
wherein each pole of the second pair of multipole lenses has a sixth coil,
wherein the fifth coils are connected to each other and the sixth coils are connected to each other,
wherein the poles having the first coils, the poles having the third coils, and the poles having the fifth coils respectively form a dipole lens, a quadrupole lens, and an octupole lens, and
wherein the poles having the second coils, the poles having the fourth coils, and the poles having the sixth coils respectively form a quadrupole lens, an octupole lens, and a dodecapole lens.
6. A scanning charged particle optical microscope comprising:
an irradiation optical system for scanning a specimen with a charged particle beam,
a specimen stage for supporting the specimen;
a detecting optical system for detecting secondary charged particles generated from the specimen by irradiation with the charged particle beam,
a control unit arranged to control the irradiation optical system; and
a power supply including a current source and a voltage source,
wherein the irradiation optical system includes a charged particle gun, an objective lens, and an aberration corrector arranged between the charged particle gun and the objective lens,
wherein the aberration corrector includes a first pair of multipole lenses, each pole having a first coil, and a second pair of multipoles lenses between the first pair of multipole lenses, each pole having a second coil and a voltage input terminal,
wherein the first coils and the second coils are connected to the current source and the voltage input terminal is connected to the voltage source, and
wherein the control unit is arranged to controllably stop supply of the voltage from the voltage source to the voltage input terminal when an accelerating voltage of the charged particle beam is equal to or higher than a predetermined value.
7. A scanning charged particle optical microscope according to claim 6 ,
wherein when the accelerating voltage of the charged particle beam is equal to or higher than the predetermined value, the second pair of multipole lenses are operated as only magnetic lenses.
8. A scanning charged particle optical microscope according to claim 6 ,
wherein the first coils are connected to each other and the second coils are connected to each other.
9. A scanning charged particle optical microscope according to claim 6 ,
wherein each pole of the first pair of multipole lenses has a third coil;
wherein each pole of the second pair of multipole lenses has a fourth coil, and
wherein the third coils are connected to each other and the fourth coils are connected to each other.
10. A scanning charged particle optical microscope according to claim 9 ,
wherein each pole of the first pair of multipole lenses has a fifth coil;
wherein each pole of the second pair of multipole lenses has a sixth coil,
wherein the fifth coils are connected to each other and the sixth coils are connected to each other,
wherein the poles having the first coils, the poles having the third coils, and the poles having the fifth coils respectively form a dipole lens, a quadrupole lens, and an octupole lens, and
wherein the poles having the second coils, the poles having the fourth coils, and the poles having the sixth coils respectively form a quadrupole lens, an octupole lens, and a dodecapole lens.