Patent ID: 8049189

Claim:
A charged particle inspection system, comprising: at least one charged particle source for generating one or more beams of charged particles; a focusing first magnetic lens having a main axis and comprising an outer pole piece and an inner pole piece, the focusing first magnetic lens having a focusing power; a focusing first electrostatic lens having at least a first electrode and a second electrode spaced apart in a direction of said main axis, said focusing first electrostatic lens having a focusing power; a substrate mount configured to hold a substrate to be inspected relative to the first magnetic lens and the first electrostatic lens, wherein the one or more beams of charged particles are focused onto the substrate by a combination of the focusing power of the first magnetic lens and the focusing power of the first electrostatic lens; and a controller having a first control portion configured to control the focusing power of the first focusing electrostatic lens based on a signal indicative of a distance between the lowermost end of said focusing magnetic lens disposed closest to the substrate and a region of the substrate onto which the one or more beams are focused, wherein the controller is configured to dynamically adjust the focusing power of the focusing first electrostatic lens a plurality of times during inspection of the substrate.