Patent ID: 8278623

Claim:
An apparatus for imaging a surface of a manufactured substrate, the apparatus comprising: a source for generating a beam; a vacuum chamber; a variable aperture mechanism within the vacuum chamber which is configured to select a spot size for the beam, wherein the variable aperture mechanism has diagonal symmetry in relation to the beam; a lens system configured to focus the beam onto a surface of the substrate; a detector configured to detect radiation emitted from the substrate as a result of the beam impinging onto the surface; a stage configured to hold the substrate and controllably move the substrate under the beam; and a system controller configured to execute an imaging application, wherein the variable aperture mechanism comprises: a first support; a first blade attached to the first support and having a first edge; a second blade attached to the first support and having a second edge, wherein the first blade is spaced vertically above the second blade on the first support; a second support; a third blade attached to the second support and having a third edge; and a fourth blade attached to the second support and having a fourth edge, wherein the fourth blade is spaced vertically above the third blade on the second support, wherein there is a partial horizontal overlap between the first and third blades and between the fourth and second blades, and wherein an opening of the variable aperture mechanism has a perimeter defined by the first, second, third and fourth edges from a top-down view.