Charging phenomena are investigated using a scanning electron microscope (the Applied Materials VeritySEM),
equipped with an energy filter. Three types of charging are studied: wafer charging, uniform charging of the field-of-view (FOV), and non-uniform charging of the FOV. Wafer charging occurs when the wafer is charged by some source other than the scanning electron beam. Uniform and non-uniform charging of the FOV occur when a wafer is
scanned with a primary electron beam.
On insulating materials, the primary electron density, in units of electrons per unit area, governs whether the
charging regime is uniform or non-uniform. At low electron density, the charging regime is uniform FOV charging.
In this regime, the surface potential increases linearly with FOV size and extraction field, in agreement with
calculations based on an electrostatic simulation. At high electron density, the charging regime changes to a non-uniform
local charging, varying over adjacent pixels within the FOV. The local field attracts the emitted SE's until a
steady state is reached having a local yield of one. In this regime, the FOV charging potential is weakly depend on
FOV size, and it can be either positive or negative, depending on the strength of the applied extraction field.