US Patent 9318343 Method to improve etch selectivity during silicon nitride spacer etch

Techniques herein include methods to increase etching selectivity among materials. Techniques herein include a cyclical process of etching and oxidation of a silicon nitride (SiN) spacer and silicon (such as polycrystalline silicon). This technique can increase selectivity to the silicon so that silicon is less likely to be etched or damaged while silicon nitride is etched from sidewalls. Techniques and chemistries as disclosed herein can be more selective to silicon oxide and silicon as compared to silicon nitride. An oxidizing step creates an oxide protection film on silicon surfaces that is comparatively thicker to any oxide film formed on nitride surfaces. As such, techniques here enable better removal of silicon nitride and silicon nitride spacer materials.