Patent ID: 7227142

Claim:
An electron beam system comprising: an assembly for use in applying an electron beam onto a substrate and detecting backscattered electrons and secondary electrons, said assembly including: (a) a first field-free tunnel electrode having a first inside surface forming a first wall of a field-free tunnel for passage of an electron beam; (b) a second field-free tunnel electrode having a second inside surface, facing and spaced apart from said first inside surface to form said field-free tunnel; (c) a backscattered electron detector disposed on an opposite side of a lower end portion of said first field-free tunnel electrode from said first inside surface; and (d) a secondary electron detector disposed on an opposite side of a lower end portion of said second field-free tunnel electrode from said second inside surface; wherein said first inside surface of said first field-free tunnel electrode and said second inside surface of said second field-free tunnel electrode are substantially parallel.