Patent Number: 
Section: abstract

A charged particle shaped beam column includes: a charged particle source; a gun lens configured to provide a charged particle beam approximately parallel to the optic axis of the column; an objective lens configured to form the charged particle shaped beam on the surface of a substrate, wherein the disk of least confusion of the objective lens does not coincide with the surface of the substrate; an optical element with 8N poles disposed radially symmetrically about the optic axis of the column, the optical element being positioned between the condenser lens and the objective lens, wherein N is an integer greater than or equal to 1; and a power supply configured to apply excitations to the 8N poles of the optical element to provide an octupole electromagnetic field. The octupole electromagnetic field is configured to induce azimuthally-varying third-order deflections to the beam trajectories passing through the 8N-pole optical element. By controlling the excitation of the 8N poles a shaped beam, such as a square beam, can be formed at the surface of the substrate. The 8N-pole element can be magnetic or electrostatic.