Scanning electron microscope

1. A scanning electron microscope comprising:

an electron optical system that includes an electron source generating an irradiation electron beam and an objective lens focusing the irradiation electron beam on a sample;

a detector that is arranged outside an optical axis of the electron optical system and detects a signal electron generated when the sample is irradiated with the irradiation electron beam;

a deflection electrode that forms a deflection field to guide the signal electron to the detector;

a disk-shaped electrode that is arranged to be closer to the electron source than the deflection field and has an opening through which the irradiation electron beam passes;

first and second control electrodes arranged along the optical axis to be closer to the sample than the deflection field; and

a controller,

wherein the sample and the objective lens are adapted to be set to a reference potential by the controller, and

wherein the controller is configured to cause a potential lower than the reference potential to be applied to the disk-shaped electrode, and potentials, which are higher than the reference potential and different from each other, to be applied to the first and second control electrodes, respectively.

2. The scanning electron microscope according to claim 1 , wherein

the second control electrode is arranged to be closer to the deflection electrode than the first control electrode, and

the controller is configured to apply a potential to the second control electrode is that is higher than the potential applied to the first control electrode.

3. The scanning electron microscope according to claim 2 , wherein

the first control electrode controls a trajectory of the signal electron so as to guide the signal electron emitted from the sample to the objective lens, and

the second control electrode controls the trajectory of the signal electron that has passed through a pole piece of the objective lens.

4. The scanning electron microscope according to claim 1 , wherein

the controller is configured to cause a voltage applied to the first and second control electrodes to be lower by one digit or more than an acceleration voltage of the irradiation electron beam.

5. The scanning electron microscope according to claim 1 , wherein

the deflection field is formed by a first deflection electrode and a mesh-shaped second deflection electrode which are arranged to oppose each other, and

the second deflection electrode is arranged to be close to the detector and is set to a higher potential than the first deflection electrode.

6. The scanning electron microscope according to claim 1 , wherein

the deflection field is formed by a first deflection electrode and a hollow second deflection electrode which are arranged to oppose each other, and

the second deflection electrode is arranged to be close to the detector and is set to a higher potential than the first deflection electrode.

7. The scanning electron microscope according to claim 1 , further comprising:

a lens electrode arranged between the deflection field and the detector; and

a deceleration electric field filter arranged between the lens electrode and the detector.

8. The scanning electron microscope according to claim 1 , further comprising:

a lens electrode arranged between the deflection field and the detector; and

an energy analyzer arranged between the lens electrode and the detector.

9. The scanning electron microscope according to claim 1 , wherein

the sample is placed inside a magnetic field of the objective lens.

10. The scanning electron microscope according to claim 1 , wherein

the electron optical system is configured to not include a deceleration function.

11. A scanning electron microscope comprising:

an electron optical system that includes an electron source generating an irradiation electron beam and an objective lens focusing the irradiation electron beam on a sample;

a detector that is arranged outside an optical axis of the electron optical system and detects a signal electron generated when the sample is irradiated with the irradiation electron beam;

a deflection electrode that forms a deflection field to guide the signal electron to the detector;

a disk-shaped electrode that is arranged to be closer to the electron source than the deflection field and has an opening through which the irradiation electron beam passes;

a control electrode that is arranged along the optical axis to be closer to the sample than the deflection field;

a lens electrode arranged between the deflection field and the detector;

a deceleration electric field filter or an energy analyzer arranged between the lens electrode and the detector; and

a controller,

wherein the controller is configured to set the sample and the objective lens to a reference potential, and

wherein the controller is configured to apply a potential lower than the reference potential to the disk-shaped electrode, and to apply a potential higher than the reference potential to the control electrode.

12. The scanning electron microscope according to claim 11 , wherein

the controller is configured to cause a voltage applied to the control electrode to be lower by one digit or more than an acceleration voltage of the irradiation electron beam.

13. The scanning electron microscope according to claim 11 , wherein

the deflection field is formed by a first deflection electrode and a mesh-shaped or hollow second deflection electrode which are arranged to oppose each other, and

the second deflection electrode is arranged to be close to the detector and is set to a higher potential than the first deflection electrode.

14. The scanning electron microscope according to claim 11 , wherein

the sample is arranged inside a magnetic field of the objective lens.

15. The scanning electron microscope according to claim 11 , wherein

the electron optical system is configured to not include a deceleration function.