Patent ID: 6376850
Filing Date: 2002-04-23
Classification: H01J

Abstract:
An electron beam column comprising:a casing; a generator arranged in the casing and operable to generate an electron beam; and an aperture element arranged in the casing in the path of the electron beam, the aperture element (10) comprising a body (11) provided with a passage (12) having an axis (13) for travel therethrough in a given direction of at least part of the electron beam (E) arriving from the generator and with a blocking surface (15) adjoining an entry opening (14) of the passage to block travel of part or all of the beam in that direction for beam shaping or blanking, wherein the blocking surface (15) is arranged to cause blocked electrons derived from the beam or part of the beam to be directed at an angle away from the axis (13) of the passage, a shutter portion (19) extending towards the axis (13) of the passage and terminating at a radial spacing from the entry opening (14), and a screening member (17) having a wall which is co-operable with the blocking surface (15) and the shutter portion (19) to bound a trap cavity (21) for blocked electrons and which is arranged to return electrons to the blocking surface (15) for redirection back into the trap cavity (21), wherein the body (11) has a thickness between the blocking surface (15) and an interior surface of the passage (12) sufficient to shield electrons within the passage from influence of charge build up in the trap cavity (21).