| 摘要 |
PURPOSE:To accurately judge improper conduction without influence of variation in the surface state of an anode plate by detecting a voltage difference between the electrode plates of a plurality of semiconductor wafers, amplifying them, selecting the maximum and minimum values of the plurality of amplified voltage differences, detecting the value responsive to the difference, and comparing the voltage value responsive to the detected difference with a predetermined set value. CONSTITUTION:An amplifier 10 detects voltage differences V10-V60 between anode plates 1 and semiconductor wafers 2, and amplifies tham. A sending circuit 200 selects the maximum value Vmax and the minimum value Vmin of the differences V10-V60 amplified by the amplifier 100. A voltage difference detector 300 detects the difference (Vmax-Vmin) of the selected Vmax and Vmin by the circuit 200. Then, a comparator 400 compares the value of the voltage difference (Vmax-Vmin) output from the detector 300 with a predetermined set value. When the value is larger than the set value, a signal of 'Hi' level is fed to a warning circuit 600, in which an alarm buzzer is, for example, rung or a lamp is flashed.
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