Charged particle beam tube and method of operating the same.

摘要

An electron beam or other charged particle beam tube (121) of the compound fly's eye type having -many of the features disclosed in U.S. Patent Specification No. 4 142 132, comprises an evacuated housing together with an electron gun (122) or other charged particle beam producing means disposed at one end of the evacuated housing for producing a beam (13) of electrons or other charged particles. A coarse deflector (17a or 17a and 17b), a compound microlens assembly (125), and a fine deflector (124a and 124b) are disposed in the housing in the path of the electron or other charged particle beam (13) for first selecting a lenslet (125) and thereafter finely deflecting an electron or other charged particle beam to a desired spot on a target plane (18). According to the invention the electron or other charged particle beam tube is constructed and operated such that the electron or other charged particle beam (13) is caused to diverge at a small angle of divergence in advance of passing through the coarse deflector (17a or 17a and 17b) by appropriately locating the virtual origin or point source of the charged particle a small distance in advance of the coarse deflector. This divergence causes particle beam spot aberration at the target plane (18) to be minimised.

Beam divergence may be produced by appropriate design of the electron gun means (122) or by providing a condenser lens (123) between the electron gun means and the coarse deflector (17a or 17a and 17b).

The aberration may be further reduced by a dynamic focusing correction potential supplied to the micro lens assembly along with a high voltage energizing potential, with the dynamic focusing correction potential being derived from components of both the coarse deflection potentials and the fine deflection potentials.