| 摘要 |
PURPOSE:To maintain an etching rate constant by a method wherein a cooling water piping for cooling an electrode plate is composed of a plurality of pipes and cooling water is run through the respective pipes independently. CONSTITUTION:A plurality of pipes are provided inside at least one electrode 2b among 1st and 2nd electrodes. Cooling water is passed through the respective pipes independently and simultaneously. For instance, as the lengths of the four pipes 10-13 provided at the different positions inside the electrode 2b are not so different from each other, the cooling water flowing through the pipes 10-13 is drained out from the pipe ends 10b-13b at approximately the same temperature. Therefore, the bottom of the electrode 2b is cooled so as to make the difference in temperature zero over the whole bottom surface from the inner circumference part to the outer circumference part. As the temperature of the cooling water is constant, a constant etching rate and a constant selection ratio can be obtained.
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