Patent Number: 
Section: claims

1. An electron beam column for automated inspection of manufactured substrates, the electron beam column comprising:an electron gun including a source for emitting electrons and a gun lens for focusing the electrons into an electron beam;an objective lens for focusing the electron beam onto a beam spot on a surface of a target substrate;a continuously-variable aperture configured to select a beam current;a ground plate below the objective lens;a charge-control plate above the surface of the target substrate; anda pre-charge control plate between the ground plate and the charge-control plate. 2. The electron beam column of claim 1, wherein the continuously-variable aperture is formed by overlapping blades. 3. The electron beam column of claim 2, wherein the overlapping blades form a square aperture. 4. The electron beam column of claim 3, wherein V-cut edges of two blades form the square aperture. 5. The electron beam column of claim 3, wherein edges of four blades form the square aperture. 6. The electron beam column of claim 1, further comprising:a gate valve configured between the electron gun and the continuously-variable aperture. 7. A method of using an electron beam column for automated inspection of manufactured substrates, the method comprising:emitting electrons from a source;forming an electron beam using a gun lens to focus the electrons;selecting a beam current using a continuously-variable aperture;focusing the electron beam onto a beam spot on a surface of a target substrate using an objective lens;applying a voltage to a pre-charge control plate between a ground plate below the objective lens and a charge control plate above the target substrate;scanning the beam spot over the surface of the target substrate; anddetecting secondary electrons from the beam spot using a detector. 8. The method of claim 7, further comprising:adjusting an aperture size of the continuously-variable aperture by changing an amount of overlap between overlapping blades. 9. The method of claim 8, wherein the overlapping blades form a square aperture.