System and Method for Controlling Charge-up in an Electron Beam Apparatus

An objective lens of a scanning electron microscope for observing a surface of a sample, comprising:

• a magnetic objective lens;
• a first control electrode below said magnetic objective lens;
• and
• a second control electrode below said first control electrode and above said surface,
• wherein said first control electrode and said second control electrode are biased a first voltage and a second voltage with respect to said sample respectively,
• wherein during each period of line-scanning within a frame cycle of imaging scanning, said first voltage and said second voltage are respectively set at a first value u1 and a third value u3 so as to generate an electrostatic extraction field on said surface,
• wherein during each period of beam-retracing within said frame cycle of imaging scanning, said first voltage and said second voltage are respectively set at a second value u2 and a fourth value u4 so as to generate an electrostatic reflection field above said surface.

An objective lens of a scanning electron microscope for observing a surface of a sample, comprising:

• a magnetic objective lens;
• a first control electrode under said magnetic objective lens;
• and
• a second control electrode under said first control electrode and above said surface,
• wherein said first control electrode and said second control electrode are biased a first voltage and a second voltage with respect to said sample respectively,
• wherein said second voltage is set at an extractive value so as to generate an electrostatic extraction field on said surface,
• wherein said first voltage is set at a reflective value so as to generate an electrostatic reflection field to reflect an amount of secondary electrons emitted from said surface back to said surface to make a charge balance thereon.

An electron beam apparatus, comprising:

• an electron source, which emits primary electrons along a direction, wherein said direction is an optical axis of said electron beam apparatus and said primary electrons form a primary electron beam;
• a condenser lens, which is located below said electron source and aligned with said optical axis;
• a beam-limit aperture plate, which is located below said electron source and comprises at least one opening, wherein one opening is aligned with said optical axis and limits a current of said primary charged particle beam;
• a magnetic objective lens, which is located below said beam-limit aperture plate and condenser lens and aligned with said optical axis;
• a control electrode, which is located below said magnetic objective lens and aligned with said optical axis;
• a sample stage, which is located below said control electrode and supports a sample, wherein an interested surface thereof is placed upwards and said control electrode is biased a voltage with respect to said sample;
• a deflection unit, which is above said control electrode and deflects said primary electron beam so as to scan said interested surface in a raster way within a frame cycle of imaging scanning, wherein said frame cycle of imaging scanning comprises a series of alternately distributing periods of line-scanning and beam-retracing, wherein on said interested surface, a path of said primary electron beam during said each period of beam-retracing covers a path thereof during a latest period of line-scanning;
• and
• an electron detector, which is located above said deflection unit and below said beam-limit aperture plate, comprises a hole aligned with said optical axis for said primary electron beam passing therethrough and a detection area facing to said interested surface so as to collect a first amount of secondary electrons emitted therefrom,
• wherein said primary electron beam is not blanked out during said each period of beam-retracing,
• wherein during said each period of line-scanning, said voltage is set at a first value so as to generate an electrostatic extraction field on said interested surface,
• wherein during said each period of beam-retracing, said voltage is set at a second value so as to generate an electrostatic reflection field which reflects a second amount of said secondary electrons back to said interested surface to make a charge balance thereon.

An electron beam apparatus, comprising:

• an electron source, which emits primary electrons along a direction, wherein said direction is an optical axis of said electron beam apparatus and said primary electrons form a primary electron beam;
• a condenser lens, which is located below said electron source and aligned with said optical axis;
• a beam-limit aperture plate, which is located below said electron source and comprises at least one opening, wherein one opening is aligned with said optical axis and limits a current of said primary charged particle beam;
• a magnetic objective lens, which is located below said beam-limit aperture plate and said condenser lens and aligned with said optical axis;
• a first control electrode, which is located below said magnetic objective lens and aligned with said optical axis;
• a second control electrode, which is located below both said magnetic objective lens and said first control electrode, above said interested surface and aligned with said optical axis;
• a sample stage, which is located below said second control electrode and supports a sample, wherein an interested surface thereof is placed upwards;
• a deflection unit, which is above said first control electrode and deflects said primary electron beam so as to scan said interested surface in a raster way within a frame cycle of imaging scanning, wherein said frame cycle of imaging scanning comprises a series of alternately distributing periods of line-scanning and beam-retracing, wherein on said interested surface, a path of said primary electron beam during said each period of beam-retracing covers a path thereof during a latest period of line-scanning;
• and
• an electron detector, which is below said beam-limit aperture plate, comprising a hole aligned with said optical axis for said primary electron beam passing therethrough and a detection area facing to said interested surface so as to collect a first amount of secondary electrons emitted therefrom,
• wherein said first and second control electrodes are biased a first voltage and a second voltage with respect to said sample respectively,
• wherein during said each period of line-scanning, said first voltage and said second voltage are respectively set at a first value and a third value so as to generate an electrostatic extraction field on said surface,
• wherein during said each period of beam-retracing, said first voltage and said second voltage are respectively set at a second value and a fourth value so as to generate an electrostatic reflection field above said surface.

An electron beam apparatus, comprising:

• an electron source, which emits primary electrons along a direction, wherein said direction is an optical axis of said electron beam apparatus and said primary electrons form a primary electron beam;
• a condenser lens, which is located below said electron source and aligned with said optical axis;
• a beam-limit aperture plate, which is located below said electron source and comprises at least one opening, wherein one opening is aligned with said optical axis and limits a current of said primary charged particle beam;
• a magnetic objective lens, which is located below said beam-limit aperture plate and said condenser lens and aligned with said optical axis;
• a first control electrode, which is located below said magnetic objective lens and aligned with said optical axis;
• a second control electrode, which is located below said first control electrode and aligned with said optical axis;
• a sample stage, which is located below said second control electrode and supports a sample, wherein an interested surface thereof is placed upwards and said first and second control electrodes are biased a first voltage and a second voltage with respect to said sample respectively;
• a deflection unit, which is above said first control electrode and deflects said primary electron beam so as to scan said interested surface;
• and
• an electron detector, which is below said beam-limit aperture plate, comprising a hole aligned with said optical axis for said primary electron beam passing therethrough and a detection area facing to said interested surface so as to collect a first amount of secondary electrons emitted therefrom,
• wherein said first and second control electrodes are biased a first voltage and a second voltage with respect to said sample respectively,
• wherein said second voltage is set to generate an electrostatic extraction field on said sample surface,
• wherein said first voltage is set to generate an electrostatic reflection field which reflects a second amount of said secondary electrons back to said interested surface to make a charge balance thereon.

A method for eliminating positive charges on a surface of a sample in a scanning electron microscope, comprising:

• providing an electrostatic extraction field on said surface during a period of line-scanning;
• providing an electrostatic reflection field above said surface during a period of beam-retracing immediately next to said period of line-scanning;
• providing a primary electron beam of said scanning electron microscope to said surface during said period of beam-retracing,
• wherein, on said surface, a path of said primary electron beam during said period of beam-retracing covers a path of said primary electron beam during said period of line-scanning,
• wherein said electrostatic reflection field reflects a desired amount of secondary electrons emitted from said surface back to said surface to neutralize positive charges on said surface to reach a charge balance thereon.