Patent ID: 8742361
Filing Date: 2014-06-03
Classification: H01J

Abstract:
1. A charged particle column for focusing charged particles over a range of energies from a lowest beam energy to a highest beam energy at a target, comprising: an optical axis; a charged particle source for generating the charged particles, the source being located on the optical axis; an objective lens for focusing the charged particles onto the target, the objective lens comprising at least a first electrode, a second electrode, a third electrode, and a fourth electrode, the electrodes arranged sequentially along the optical axis, with the first electrode closest to the charged particle source and the fourth electrode closest to the target, and with a first gap between the first and second electrodes, a second gap between the second and third electrodes, and a third gap between the third and fourth electrodes; wherein the first and second gaps are substantially equal and the third gap is no more than ⅓ the size of either the first or second gaps; and wherein the first and fourth electrodes are biased to a first voltage by a first voltage supply, and wherein the objective lens is configured to be switchably operated as a three electrode symmetric lens by switchably biasing the second electrode to a second voltage and the third electrode to the first voltage and as a three electrode asymmetric lens by switchably biasing the second electrode to the first voltage and the third electrode to a third voltage.