A plasma-etching apparatus is provided to detect the plasma potential through the plug for the measurement and to continually monitor the plasma state while progressing the etching process. The first electrode is arranged inside the chamber(10) for the plasma. The substrate is mounted on the first electrode. The shield ring(30) surrounds the edge part of the first electrode. The second electrode is arranged in order to be faced with the first electrode. The spraying plate(50) sprays the process gas to the inside of chamber. The via hole is formed in order to expose a part of the first electrode to the shield ring. The plug(40) for measurement is formed in the via hole in order to be connected with the first electrode.
