METHOD TO IMPROVE ETCH SELECTIVITY DURING SILICON NITRIDE SPACER ETCH

摘要

Techniques in the present invention include methods for increasing etching selectivity among materials. The techniques also include a cyclical process of etching and oxidizing 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 in the present invention can be more selective to silicon oxide and silicon as compared to silicon nitride. An oxidizing step creates an oxide protective film on silicon surfaces comparatively thicker to any oxide film formed on nitride surfaces. Therefore, the techniques in the present invention enable better removal of silicon nitride and silicon nitride spacer materials.