ELECTROCHEMICAL CONTROL FOR WORKING LIQUID

PURPOSE:To accurately detect the concentration of a component in working liquid such as a plating solution or an etching solution with an electrochemical element under a stable condition, when the working liquid is controlled, by making the pressure of the liquid in contact with the element lower than the internal pressure of a reference electrode. CONSTITUTION:Working liquid 12, e.g. a chemical copper plating solution, in a working vessel 11 is sucked through an electrochemical detection element 14 and returned into the working vessel 11 by a quantitative pump 15. Thus, the working liquid is circulated. In this case, the pH value of the plating solution is detected with the element 14. The detected value is introduced into a controller 16, amplified and compared with a preset pH value. Another quantitative pump 17 is driven with the comparison value, and an aqueous NaOH solution in a supplemental liquid vessel 18 is added as supplemental liquid 19 to the plating solution in the working vessel 11 to hold the pH value of the plating solution at a fixed level. In this case, the element 14 is constructed by an indication electrode such as a glass electrode and a reference electrode such as a silver-silver chloride electrode, and located at the suction side of the quantitative pump 15 so that liquid in contact with the element is constantly maintained in a pressure-reduced state. Consequently, the pH value can be accurately detected at any moment, and components in the liquid can be controlled under a stable condition.