System and method for controlling charge-up in an electron beam apparatus
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.
1. 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.
2. 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 and an electrostatic reflection field above said surface simultaneously,
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.