| 摘要 |
PROBLEM TO BE SOLVED: To improve focus during heavy-current and downsize an electron beam spot from light-current to heavy-current, by providing an opening-type corrective electrode in a low-voltage-side first focusing electrode in focusing electrodes and in a main lens electric field region. SOLUTION: Openings 7a-7c adjusted according to a corrected electron beam spot shape are formed on the lower voltage side than standing electrodes 3, 4 in a focusing electrode 1. A high-voltage-side end 8 of a final accelerating electrode 2 is shielded by a flat plate having an opening for penetrating an electron beam, and a horizontal flat electrode 9 is mounted so as to project a pair of upper and lower flat plates from vertical ends of this opening in an eaves shape. In the so constituted focusing electrode 1 and the final accelerating electrode 2, electric fields from standing electrodes 3-6 are overlapped on each other to be enlarged, electric fields from the openings 1a, 2a are synthesized with these, and a main electric field forming three main lenses are formed. In addition, lens operations of an opening-type electrode 7 and the horizontal flat electrode 9 are synthesized with this to constitute three main lenses having one center lens and two side lenses.
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