Apparatus for generating a plurality of beamlets

An apparatus for generating a plurality of charged particle beamlets, comprising:

• a charged particle source for generating a diverging charged particle beam,
• a lens array comprising a plurality of lenses,
• said lens array further comprising an aperture plate, wherein the aperture plate has an electrically conducting surface and means for defining the electrostatic potential of said surface, and
• means for defining an equipotentional surface at a distance from said aperture plate at a different potential than said aperture itself, wherein said means comprises a plate placed at a distance from said aperture plate, wherein said plate having a hole large enough to let the beam pass, and means for defining the electrostatic potential of said plate at a different potential than said aperture plate,
• wherein the apparatus comprises a converging means for refracting said diverging charged particle beam, and
• wherein the converging means is adapted for refracting a diverging charged particle beam into a substantially parallel charged particle beam for generating a plurality of substantially parallel charged particle beamlets,
• wherein said converging means comprises a collimator lens and further comprises an array of converging elements, wherein each element comprises a deflector aligned with a beamlet.