An EPD system with a long service life that enables accurate etch endpoint detection is disclosed. The EPD system according to the present invention is a view port having a groove for receiving the optical cable and the light emitted in the chamber in which the etching process proceeds, the light inserted into the groove of the view port and connected to the view port Cable, and an analyzer for analyzing the wavelength of light transmitted from the optical cable to detect an etch endpoint. Here, the optical cable is composed of a plurality of parallel optical fibers and a coating that fixes and surrounds the optical fiber, the portion of the optical cable connected to the view port is characterized in that the concave (concave) type.
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