Low-blur electrostatic transfer lens for multi-beam electron gun

A multi-beam field emission gun (FEG) for a multi-beam apparatus, the FEG comprising:

• an electron source;
• a micro-hole array beam splitter disposed downstream of the electron source, being configured to receive a beam from the electron source and to produce multiple beams;
• an electrostatic beam transfer lens comprising a series of multiple, successive, electrodes, each electrode being spaced apart from each other, the electrodes being disposed along a column such that an aperture bore of said each electrode is aligned along a central axis and is configured to allow multiple beams to pass therethrough;
• a first electrode in the series being a cylindrical electrode configured to receive the multiple beams from the beam splitter at an entrance plane that is perpendicular to the central axis and upstream of the successive electrodes of the series along the column, and to prevent lens focusing fields of the electrostatic beam transfer lens from extending through the first electrode and beyond the entrance plane,
• wherein the first electrode has a bore length and a bore diameter such that a ratio of bore diameter/bore length<0.3;
• and
• a differential pumping aperture configured to receive a focused beam from the electrostatic beam transfer lens, and to produce an array of focused beams at an image plane.