Patent Number: 
Section: claims

1. 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; anda 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, andwherein the first and second positions are across from each other with the incident electron beam impinging therebetween. 2. The electron beam apparatus of claim 1, wherein the trap electrode comprises an end portion with a semi-circular shape which increases said range of scattering angles. 3. The electron beam apparatus of claim 1, wherein the substrate surface comprises a semiconductor wafer surface. 4. The electron beam apparatus of claim 1, wherein the device comprises multiple separate trap electrodes, each trap electrode being configured at a position above the substrate surface and below the electron lens closest to the substrate surface, and each trap electrode having a semi-circular end portion. 5. The electron beam apparatus of claim 1 further comprising deflectors to scan the beam across an area of interest, wherein the deflectors are positioned between the source and the electron lens closest to the substrate surface. 6. The electron beam apparatus of claim 5, wherein the apparatus comprises a critical dimension scanning electron microscope (CD-SEM). 7. The electron beam apparatus of claim 5, wherein the apparatus comprises an inspection or review tool. 8. The electron beam apparatus of claim 1, wherein the trap electrode comprises a ring-shaped trap electrode configured circumferentially around the incident electron beam. 9. A method of imaging a surface area, the method comprising:generating an incident beam;focusing the incident beam by a lens closest to a substrate surface so that the beam impinges upon the substrate surface and interacts with surface material so as to cause emission of secondary electrons;detecting the secondary electrons by a secondary electron detector, wherein the detected secondary electrons travel between the substrate surface and the lens closest to the substrate surface; andattracting and capturing the secondary electrons which are emitted within a range of scattering angles extending from a plane of the substrate surface by a trap electrode positioned above the substrate surface and below the lens closest to the substrate surface so that the captured electrons are not detected by the secondary electron detector; andapplying a positive voltage to the trap electrode relative to a substrate potential,wherein said detecting of the secondary electrons and said capturing of the secondary electrons are performed at positions across from each other with the incident beam impinging therebetween. 10. The method of claim 9, wherein-the trap electrode comprises a ring-shaped trap electrode configured circumferentially around the incident electron beam. 11. The method of claim 10, wherein the substrate surface comprises a semiconductor wafer surface. 12. The method of claim 9, further comprising generating an image from the detected secondary electrons. 13. The method of claim 12, further comprising inspecting or reviewing the image for defects. 14. The method of claim 12, further comprising measuring a critical dimension of a feature in the image. 15. The method of claim 9, wherein the trap electrode comprises a ring-shaped trap electrode configured circumferentially around the incident beam. 16. An apparatus for imaging a surface area, the apparatus comprising:means for generating an incident beam;a lens closest to a substrate surface for focusing the incident beam so that the beam impinges upon the substrate surface and interacts with surface material so as to cause emission of secondary electrons;means for detecting secondary electrons traveling between the substrate surface and the lens closest to the substrate surface; anda trap electrode positioned above the substrate surface and below the lens closest to the substrate surface for attracting and capturing the secondary electrons which are emitted within a range of scattering angles extending from a plane of the substrate surface so that the captured electrons are not detected by the means for detecting,wherein said means for detecting and the trap electrode are positioned across from each other with the incident beam impinging therebetween. 17. The apparatus of claim 16, wherein the trap electrode comprises a ring-shaped trap electrode configured circumferentially around the incident beam.