| 摘要 |
PURPOSE:To prevent outside noise and thereby to measure a very small current precisely, by giving a Faraday cup a double structure consisting of an outer cup and an inner cup housed in the former, by connecting the inner cup to an ammeter, and by earthing the outer cup. CONSTITUTION:An ion supply port 12 is formed at one end of a vacuum vessel 10, and ions are sent in the direction of an arrow through the supply port 12. A cup 18 is held open, in the vessel 10, in the direction of the supply port 12, e.g. in the direction of the incidence of ions, by an insulator. The cup 18 is made to have a double structure consisting of the cup 18 for holding an article, such as a semiconductor wafer 16, in which the ions are driven, and of an outer cup 20 holding the cup 18, while a shield plate 22 setting the diameter of the opening is arranged in front of the opening. The cup 18 is connected to an ammeter 24 of a measuring system, while the cup 20 is earthed. In addition, an electrode for adsorbing secondary electrons, which is impressed with positive potential, may be provided in the vicinity on the side of the supply port 12 of the shield plate 22. In this way, outside noise is prevented, and thus a very small current can be measured precisely. |
