| 摘要 |
PURPOSE:To reduce the diameter of beam-spot on a target, by providing an eletrode between 5th grid and 6th grid of the main lens part and applying an intermediate potential between the potential of the 5th grid and that of the 6th grid onto said electrode. CONSTITUTION:An electron gun is built up with a 4 poles part 56 containing a cathode 9 and 1st-3rd grid 12-14 and a main lens part 57 containing 3rd-7th grid 14-18, and 6th grid 17 is provided between 5th grid 16 and 7th grid 18. An intermediate potential of about 8kV is given to the 3rd grid 14 and the 5th grid 16. A low-grade potential of about 700V is given to the 4th grid 15, a high- grade potential of about 25kV is given to the 7th grid 18, and further an intermediate potential of about 16.5kV which is between the potential of the 5th grid 16 and that of the 7th grid 18 is given to the 6th grid 17. Consequently, the lens performance can be greatly enhanced and the diameter of beam-spot can be remarkably reduced by using the beam of best quality. |
