Patent ID: 10763120

Abstract:
A technique to inhibit the growth of colloidal silica deposits on surfaces treated in phosphoric acid is described. In one embodiment, the disclosed techniques include the use of a colloidal silica growth inhibitor as an additive to a phosphoric acid solution utilized for a silicon nitride etch. In some embodiments, the additive may have chemistry that may contain strong anionic groups. A method and apparatus is provided that monitors the silica concentration and/or the colloidal silica growth inhibitor concentration in the phosphoric acid solution during processing and adjusts the amount of those components as needed. Techniques are provided for a method and apparatus to control the additive concentration to be used as well as the silica concentration in the phosphoric acid solution. The techniques described herein provide a high selectivity etch of silicon nitride towards silicon dioxide without the growth of colloidal silica deposits on the exposed surfaces.