Substrate processing method and substrate processing apparatus

A substrate processing apparatus, comprising:

• a processing tub;
• a preparing unit configured to prepare a phosphoric acid processing liquid by supplying a precipitation inhibitor configured to inhibit precipitation of silicon oxide into a phosphoric acid aqueous solution;
• a supplying unit configured to supply the precipitation inhibitor into the processing tub;
• and
• a controller configured to perform preparing the phosphoric acid processing liquid by controlling the preparing unit, etching a substrate having a silicon oxide film and a silicon nitride film by immersing the substrate in the processing tub in which the phosphoric acid processing liquid is stored, and increasing a concentration of the precipitation inhibitor in the phosphoric acid processing liquid by controlling the supplying unit to additionally supply the precipitation inhibitor into the phosphoric acid processing liquid in the processing tub when a number of substrates etched by the phosphoric acid processing liquid has reached a first threshold value or when a silicon concentration in the phosphoric acid processing liquid has reached a second threshold value,
• wherein the etching of the substrate comprises, after the increasing of the concentration of the precipitation inhibitor is performed, etching a new substrate by immersing the new substrate in the processing tub in which the phosphoric acid processing liquid with the increased concentration of the precipitation inhibitor is stored.