A method of stabilizing plating film impurities in an electrochemical plating bath solution is disclosed. The method includes providing an electrochemical plating machine in which an electrochemical plating process is carried out. A by-product bath solution is formed by continually removing a pre-filtered bath solution from the machine and removing an additive from the pre-filtered bath solution. A clean bath solution is formed by removing an additive by-product from the by-product bath solution. An additive bath solution is formed by adding a fresh additive to the clean bath solution. The additive bath solution is added to the electrochemical plating machine. An apparatus for stabilizing film impurities in an electrochemical plating bath solution is also disclosed.