Colloidal silica growth inhibitor and associated method and system

A method for wet etching of structures on a microelectronic substrate, comprising:

• loading the microelectronic substrate into a wet chemical processing system, the microelectronic substrate having a first structure of silicon nitride and a second structure of silicon oxide, each having an exposed surface;
• using a wet etching solution, selectively etching the first structure of silicon nitride over the second structure of silicon oxide for a time duration until the first structure is removed, wherein the wet etching solution comprises water, phosphoric acid, and a concentration of a colloidal silica growth inhibitor that is increased during the time duration from an initial concentration to a final, higher concentration to inhibit growth of colloidal silica deposits on the exposed surfaces of the first and second structures;
• and
• monitoring the concentration of colloidal silica and the concentration of the colloidal silica growth inhibitor during the etching and increasing the concentration of the colloidal silica growth inhibitor as the concentration of colloidal silica increases.