Patent ID: 8890066

Claim:
An electron beam apparatus comprising: a source for generating an incident electron beam; an electron lens closest to a substrate surface for focusing the incident electron beam so that the beam impinges upon the substrate surface and interacts with surface material so as to cause emission of secondary electrons; a secondary electron detector configured at a first position above a plane of the substrate surface to detect secondary electrons traveling between the substrate surface and the electron lens closest to the substrate surface; and a trap electrode configured at a second position above the plane of the substrate surface and below the electron lens closest to the substrate surface to attract and capture the secondary electrons which are emitted within a range of scattering angles extending from the plane of the substrate surface so that the captured electrons are not detected by the secondary electron detector, wherein a positive voltage is applied to the trap electrode relative to a substrate potential, and wherein the first and second positions are across from each other with the incident electron beam impinging therebetween.