US Patent 8089056 Projection lens arrangement

A charged particle multi-beamlet system for exposing a target using a plurality of beamlets. The system comprises a first plate having a plurality of holes formed in it, with a plurality of electrostatic projection lens systems formed at the location of each hole so that each electron beamlet passes through a corresponding projection lens system. The holes have sufficiently uniform placement and dimensions to enable focusing of the beamlets onto the surface of the target using a common control voltage. Preferably the electrostatic projection lens systems are controlled by a common electrical signal to focus the electron beamlets on the surface without correction of the focus or path of individual electron beamlets.