Selective plasma nitridation and contrast reversed etching of silicon

Abstract

A new method of selectively patterning a silicon substrate with silicon dioxide and silicon nitride is demonstrated. An oxide patterned silicon substrate is directly nitrided using a microwave generated nitrogen plasma. Upon subsequent selective wet chemical etching using KOH, the oxide is removed and etching proceeds into the silicon, revealing a contrast reversed pattern of the oxide. The etch resistance of the nitrided surface is maximized by increasing the microwave power, pressure, and nitridation duration. The etch rate of silicon dioxide is negligibly affected and its etch rate is nearly the same as before nitridation. Compositional analysis of the nitride and the nitrided oxide using x-ray photoelectron spectroscopy confirms that microwave plasma nitridation produces Si–N covalent bonds.