| 摘要 |
PURPOSE:To simplify a circuit construction and prevent contamination due to impurities, by detecting the ratio of an electrical current flowing through a mask, to a faradaic current and detecting the deflection of an ion beam to monitor it. CONSTITUTION:An ion beam 3 produced by an ion beam generator 1 collides against a mask plate 4 to cause an electrical current Im. This current Im and a current If from a Faraday chamber 6 are applied to current integrators 9, 8 so that these currents are averaged. The averaged value is applied to a divider 10 which performs division to generate an output eo. When this output falls below a set level, a Schmitt trigger circuit 12 produces an alarm signal. The current If is converted into a voltage signal by a voltage converter 14. The voltage signal is applied to an averaging circuit 17 or 18 through an analogue switch 16 depending on the positive or negative part of the output scanning waves of a zero detection circuit 13 which detects the zero level of the potential on a deflection electrode 2. An output produced as a result of the averaging by the circuits 17, 18 is applied to a subtraction circuit 19. When the difference output of the circuit 19 exceeds a set value, another zero detection circuit 21 produces an alarm signal. |
