Charged particle beam device and electrostatic lens
To provide a charged particle beam device capable of preventing generation of geometric aberration by aligning axes of electrostatic lenses with high accuracy even when center holes of respective electrodes which constitute the electrostatic lens are not disposed coaxially. The charged particle beam device according to the invention includes an electrostatic lens disposed between an acceleration electrode and an objective lens, wherein at least one of the electrodes which constitutes the electrostatic lens is formed of a magnetic body, and two or more magnetic field generating elements are disposed along an outer periphery of the electrode.
1. A charged particle beam device which emits a charged particle beam to a sample, the charged particle beam device comprising:
a charged particle source which emits the charged particle beam;
an acceleration electrode which accelerates the charged particle beam emitted by the charged particle source;
an objective lens which focuses the charged particle beam on the sample;
an electrostatic lens which is disposed between the acceleration electrode and the objective lens; and
a deflector which is disposed between the acceleration electrode and the electrostatic lens, wherein
at least one of electrodes which constitutes the electrostatic lens is formed of a magnetic body, and
the charged particle beam device further comprising:
a magnetic field generating element which is magnetically connected to the electrode and generates a magnetic field having a function of deflecting the charged particle beam, wherein
two or more magnetic field generating elements are disposed along an outer periphery of the electrode; and
a control unit configured to control a current supplied to the magnetic field generating element such that a difference is minimized between a first deflection angle of the charged particle beam caused by the deflector when the charged particle beam passes through a wobbler center of the electrostatic lens and a second deflection angle of the charged particle beam caused by the deflector when a focus correction amount made by the objective lens is minimum.
2. The charged particle beam device according to claim 1 , wherein
the magnetic field generating element is magnetically connected to the electrode by being in contact with and attached to the electrode.
3. The charged particle beam device according to claim 2 , wherein
the magnetic field generating element includes a magnetic bar attached to the electrode and a coil wound around the magnetic bar.
4. The charged particle beam device according to claim 1 , wherein
the magnetic field generating element is disposed to be at least two-fold rotationally symmetric or more around the electrode.
5. The charged particle beam device according to claim 1 , wherein
the objective lens is configured to be able to correct a focusing position when the charged particle beam is emitted to the sample.
6. The charged particle beam device according to claim 5 , wherein
the control unit obtains a first difference between the first deflection angle and the second deflection angle when a first current is supplied to the magnetic field generating element,
the control unit obtains a second difference between the first deflection angle and the second deflection angle when a second current is supplied to the magnetic field generating element, and
the control unit obtains a third current different from the first current and the second current such that the difference is minimized in the third current by performing interpolation between a first pair of the first current and the first difference and a second pair of the second current and the second difference.
7. The charged particle beam device according to claim 1 , further comprising:
a first magnetic member which is disposed to surround the outer periphery of the electrode, wherein
the magnetic field generating element is disposed between the electrode and the first magnetic member, and is disposed to magnetically connect the electrode and the first magnetic member.
8. The charged particle beam device according to claim 3 , further comprising:
a first magnetic member which is disposed to surround the outer periphery of the electrode, wherein
the magnetic bar is disposed between the electrode and the first magnetic member, and connects an outer surface of the electrode and an inner surface of the first magnetic member.
9. The charged particle beam device according to claim 8 , further comprising:
a second magnetic member which is disposed to surround the outer periphery of the electrode.
10. The charged particle beam device according to claim 9 , wherein
the second magnetic member is disposed between the electrode and the first magnetic member.
11. The charged particle beam device according to claim 10 , wherein
the magnetic bar includes a first portion extending from the electrode toward the first magnetic member, and a second portion branched from the first portion,
the second portion extends along an emitting direction of the charged particle beam, and
the second magnetic member is formed by the second portion.
12. The charged particle beam device according to claim 9 , wherein
the second magnetic member is disposed to surround the outer periphery of the first magnetic member.
13. The charged particle beam device according to claim 1 , wherein
the magnetic field generating element includes a magnetic bar attached to the electrode and a coil,
the charged particle beam device further includes a first magnetic member disposed to surround the outer periphery of the electrode,
the magnetic bar is disposed between the electrode and the first magnetic member, and magnetically connects an outer surface of the electrode and the first magnetic member, and
the coil is wound around the first magnetic member.
14. The charged particle beam device according to claim 1 , wherein
the electrode and the two magnetic field generating elements form a magnetic circuit from one of the magnetic field generating elements to the other of the magnetic field generating elements via the electrode.
15. The charged particle beam device according to claim 14 , wherein
the electrode has a hole through which the charged particle beam passes, and
the electrode and the two magnetic field generating elements are disposed to form the magnetic circuit around the hole.
16. An electrostatic lens which focuses a charged particle beam, the electrostatic lens comprising:
a first electrode which is formed of a magnetic body;
a second electrode which generates an electric field interlocking with the first electrode; and
a magnetic field generating element which is magnetically connected to the first electrode, generates a magnetic field having a function of deflecting the charged particle beam, and is configured to receive a current supplied to the magnetic field generating element such that a difference is minimized between a first deflection angle of the charged particle beam caused by a deflector when the charged particle beam passes through a wobbler center of the electrostatic lens and a second deflection angle of the charged particle beam caused by the deflector when a focus correction amount made by the objective lens is minimum;
wherein two or more magnetic field generating elements are disposed along an outer periphery of the electrode.
17. The electrostatic lens according to claim 16 , wherein
the magnetic field generating element is magnetically connected to the first electrode by being in contact with and attached to the first electrode.
18. The electrostatic lens according to claim 17 , wherein
the magnetic field generating element includes a magnetic bar attached to the first electrode and a coil wound around the magnetic bar.
19. The electrostatic lens according to claim 16 , wherein
the magnetic field generating element is disposed to be at least two-fold rotationally symmetric or more around the first electrode.
20. The electrostatic lens according to claim 16 , further comprising:
a first magnetic member which is disposed to surround the outer periphery of the first electrode, wherein
the magnetic field generating element is disposed between the first electrode and the first magnetic member, and is disposed to magnetically connect the first electrode and the first magnetic member.
21. The electrostatic lens according to claim 18 , further comprising:
a first magnetic member which is disposed to surround the outer periphery of the first electrode, wherein
the magnetic bar is disposed between the first electrode and the first magnetic member, and connects an outer surface of the first electrode and an inner surface of the first magnetic member.
22. The electrostatic lens according to claim 21 , further comprising:
a second magnetic member which is disposed to surround the outer periphery of the first electrode.
23. The electrostatic lens according to claim 22 , wherein
the second magnetic member is disposed between the first electrode and the first magnetic member.
24. The electrostatic lens according to claim 23 , wherein
the magnetic bar includes a first portion extending from the first electrode toward the first magnetic member, and a second portion branched from the first portion,
the second portion extends along an emitting direction of the charged particle beam, and
the second magnetic member is formed by the second portion.
25. The electrostatic lens according to claim 22 , wherein
the second magnetic member is disposed to surround the outer periphery of the first magnetic member.
26. The electrostatic lens according to claim 16 , wherein
the magnetic field generating element includes a magnetic bar attached to the first electrode and a coil,
the electrostatic lens further includes a first magnetic member disposed to surround the outer periphery of the first electrode,
the magnetic bar is disposed between the first electrode and the first magnetic member, and magnetically connects an outer surface of the first electrode and the first magnetic member, and
the coil is wound around the first magnetic member.
27. The electrostatic lens according to claim 16 , wherein
the first electrode and the two magnetic field generating elements form a magnetic circuit from one of the magnetic field generating elements to the other of the magnetic field generating elements via the first electrode.
28. The electrostatic lens according to claim 27 , wherein
the first electrode has a hole through which the charged particle beam passes, and
the first electrode and the two magnetic field generating elements are disposed to form the magnetic circuit around the hole.