Electron-optical system and inspection method using the same

An electron-optical system, comprising:

• an irradiating beam source;
• an irradiation optical system which causes an irradiating electron beam emitted from the irradiating beam source to be incident on a beam separator;
• an objective optical system which causes an irradiating electron beam that passes through the beam separator to be incident on a surface of a sample, the observation means including a cathode lens;
• an image-focusing optical system which causes an observational electron beam that is emitted from the surface of the sample, and that passes through the beam separator in a direction that is different from the direction leading to the irradiating beam source, to be incident on electron beam detection means;
• and
• an accelerating electric field is formed by the surface of the sample and the cathode lens,
• the surface of the sample is biased to a negative potential (−V1, V1>0), the cathode lens has a plurality of electrodes, at least one of said plurality of electrodes is biased to a positive potential (V2, V2>V1), so that the observational electron beam that has just been emitted from the surface of the sample is accelerated monotonically, without a decrease in velocity, to the energy of approximately (V1+V2).

An inspection method using an electron-optical system, comprising steps of:

• guiding an irradiating electron beam emitted from an irradiating beam source via an irradiation optical system so as to be incident on a beam separator;
• guiding the irradiating electron beam that has passed through the beam separator via an objective optical system so as to be incident on a surface of a sample and so as to emit an observational electron beam from the surface of the sample;
• guiding the observational electron beam via the objective optical system so as to be incident on the beam separator;
• guiding the observational electron beam via the beam separator in a direction that is different from the direction leading to the irradiating beam source;
• and
• guiding the observational electron beam that has passed through the beam separator via an image-focusing optical system so as to be incident on electron beam detection means,
• wherein the objective optical system includes a cathode lens,
• an accelerating electric field is formed by the surface of the sample and the cathode lens, and
• the surface of the sample is biased to a negative potential (−V1, V1>0), the cathode lens has a plurality of electrodes, at least one of said plurality of electrodes is biased to a positive potential (V2, V2>V1), so that the observational electron beam that has just been emitted from the surface of the sample is accelerated monotonically, without a decrease in velocity, to the energy of approximately (V1+V2).