| 摘要 |
PURPOSE:To obtain good convergence and high resolution by a method wherein the mutually facing surfaces of two electrodes for forming main lenses are provided with the horizontally long oval openings while the spaces inside of electrodes are horizontally trisected avoiding the vicinity of the openings and forming three vertically long lens spaces. CONSTITUTION:A G3 electrode 12 and a G4 electrode 13 serving as electrodes for forming main lenses are provided with the horizontally long oblong rectangular openings 14 and 15 respectively on the mutually facing surfaces while the G3 electrode 12 and the G4 electrode 13 are partitioned by separators 16-19 respectively. While the oblong opening 14 of the electrode 12 is not made to be rectangular but elliptic (oval) by combining a straight line 32 with a circular arc 33, the oblong opening 15 of the elctrode 13 is equally formed oval. Therefore, aberration of a high order through the main lenses on both sides can be reduced as well as the beam spot shape formed by the electron beams on both sides can be made satisfactory. |
