Mixing apparatus, mixing method and substrate processing system

A mixing apparatus, comprising:

• a tank configured to mix a phosphoric acid aqueous solution and an additive configured to suppress precipitation of a silicon oxide;
• a phosphoric acid aqueous solution supply configured to supply the phosphoric acid aqueous solution to the tank;
• an additive supply having multiple supply openings provided at an upper portion of the tank and arranged in a horizontal direction, and configured to supply the additive;
• a circulation path through which the phosphoric acid aqueous solution stored in the tank comes out of the tank and returns to the tank;
• wherein the circulation path has an inlet provided at a lower portion of the tank and an outlet provided at the upper portion of the tank,
• a pump provided on the circulation path and configured to form a circulation flow of the phosphoric acid aqueous solution which comes out of the tank and returns to the tank through the circulation path;
• and
• a controller configured to:
• supply the phosphoric acid aqueous solution to the tank from the phosphoric acid aqueous solution supply to store a predetermined amount of the phosphoric acid aqueous solution in the tank;
• operate the pump to form the circulation flow of the phosphoric acid aqueous solution such that a fluidity is imparted to the phosphoric acid aqueous solution;
• supply, from the multiple supply openings of the additive supply, the additive from above a liquid surface of the phosphoric acid aqueous solution to the liquid surface of the phosphoric acid aqueous solution to which the fluidity is imparted;
• and
• control a nozzle of the additive supply to diffuse the additive on the liquid surface of the phosphoric acid aqueous solution to suppress a concentration of the additive from being locally increased.