Patent ID: 6949735

Claim:
A beam source comprising: a discharge tube; a gas inlet for introducing gas into the discharge tube disposed on an upstream side of the discharge tube; three electrodes mounted in the discharge tube downstream from the gas inlet, wherein the upstream electrode has a plurality of openings through which the gas can pass, the middle electrode is a mesh electrode, and the downstream electrode is a beam-emitting electrode having a plurality of beam-emitting holes and is disposed in a plane parallel to the middle electrode; a plasma chamber formed between the upstream electrode and the mesh electrode, the upstream electrode and the mesh electrode connected by wiring for maintaining at approximately the same potential, and plasma-generating means disposed between the upstream electrode and the mesh electrode on the outside of the discharge tube for transforming gas introduced into the discharge tube into plasma; and an accelerating chamber formed between the mesh electrode and the downstream electrode, the mesh electrode and the downstream electrode connected by another wiring to voltage-applying device for accelerating the beam between the mesh electrode and the downstream electrode and emitting the accelerated beam from the downstream electrode; wherein said mesh electrode comprises a cross mesh having a wire thickness and width of 0.1–0.5 millimeters and has an open area ratio of 85% or less and an aspect ratio of open areas provided in said mesh electrode is less than 1; wherein an accelerating voltage of 1 kV or less is applied between the mesh electrode and the downstream electrode, and the two electrodes on the downstream end are separated by a distance of 10–30 millimeters; and wherein each of the beam-emitting holes formed in the beam-emitting electrode on the downstream end has a length-to-diameter ratio of 2 or greater.