Phosphoric Acid Wet Etching of Sandwiched Silicon Nitride Nanolayers

Abstract Wet etching of Silicon nitride (Si 3 N 4 ) by phosphoric acid (H 3 PO 4 ) is one of the key steps in the semiconductor fabrication process, especially for three‐dimensional integrated circuits (ICs). Unfortunately, few systematic studies of phosphoric acid etching of Silicon nitride are available. Summarizing how various factors affect etching and determining the reaction mechanism behind the etching process will help further optimize the etching process. In this work, how the boiling point of hydrous phosphoric acid solutions depends on phosphoric acid concentration is firstly investigated. Next, the etching of over 100 samples of Silicon nitride by H 3 PO 4 at different concentrations and temperatures is systematically studied. The results show that the etching rate increases nearly linearly in both temperature and H 3 PO 4 concentration, while temperature play more important role as compared to concentration. For each concentration, the reaction rate is maximal at the boiling point of the hydrous H 3 PO 4 solution. Moreover, the etching rate of 85 wt % phosphoric acid is analyzed using the Arrhenius equation, yielding an apparent activation energy E a =57.28 KJ/mol. Finally, a mechanism of Silicon nitride etching in phosphoric acid is proposed which explains the prior studies well. This work contributes to precisely control semiconductor processing for three‐dimensional ICs.