| 摘要 |
PURPOSE:To prevent deterioration in the beam spots on the periphery by forming apertures long sideways at a low potential applied electrode in a sub lens part and forming apertures long lengthways of a low potential applied electrode in a main-lens part. CONSTITUTION:Electron lenses formed of electrodes G3 3, G4 4, G5 5 are called sub- lenses, and electron lenses formed of the electrodes G5 5 and G3 6 are called main lenses. Normally, the electrode G6 is made equipotential with the G5, and the G4 is made relatively lower in potential than both other electrodes. Since a high voltage is applied to the electrode G5, electron lens focusing force formed between the electrodes G5 and G6 becomes very large. In this composition, flat apertures long sideways are formed at the electrode G4 which serves as a relatively low potential electrode in the sub-lens forming electrodes, and flat apertures long lengthways are formed at the electrode G4 which is on the side of the electrode G5 and serves as a relatively low potential electrode in the main lens forming electrodes. Hence, while electron beam spots in the central parts of both surfaces are kept equivalent in their performance to each other, deterioration in the beam spots can be prevented on the periphery, especially, at upper and lower ends of the screen and on four corners of both the surfaces.
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