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

摘要

The present invention provides means and corresponding embodiments to control charge-up in an electron beam apparatus, which can eliminate the positive charges soon after being generated on the sample surface within a frame cycle of imaging scanning. The means are to let some or all of secondary electrons emitted from the sample surface return back to neutralize positive charges built up thereon so as to reach a charge balance within a limited time period. The embodiments use control electrodes to generate retarding fields to reflect some of secondary electrons with low kinetic energies back to the sample surface.

主权项

1. 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.