| 摘要 |
PROBLEM TO BE SOLVED: To make the completion of etching perceivable. SOLUTION: The space between electrodes 4 and 5 in a chamber 3 is applied with high frequency electric power from a high frequency oscillator 1 via a matching box 2 to generate plasma in the chamber 3. By this plasma, the etching of a film formed on the surface of the electrode 5 starts. Self-bias electrode VDC superposed on high frequency voltage to be applied to the electrodes 4 and 5 is detected by a VDC detecting circuit 12. Divided voltage corresponding to the voltage is converted into a digital signal by an AD converter 13. A sampling circuit 14 samples the signal from the AD converter 13 per Δt sec. A variation arithmetic circuit 5 finds the variation per unit time of the signal before and after the sampled signal. A comparator circuit 16 compares the variation per unit time and a reference variation and generates a specified signal in the case it exceeds the reference variation. |
