A study on etching properties of quartz and silicon by a dual-frequency (60 MHz/400 kHz) capacitively coupled NF3/Ar/O2 plasma: effect of pressure

Influence of pressure variation on the etching characteristics of various materials (including rough quartz, smooth quartz, monocrystalline silicon, polished monocrystalline silicon, and polycrystalline silicon) was investigated in a dual-frequency (60 MHz/400 kHz) capacitively coupled NF3/Ar/O2 plasma. The experimental results indicate that with increasing the pressure, the concentration of the fluorine radical in the plasma increases, which promotes the etching of quartz and silicon. Etching behavior varies for different surface types: for quartz, the rough surface exhibits a higher etch rate than the smooth surface due to the presence of more surface defects that provide additional reactive sites. It is found that after being etched, the rough quartz surface features etch pits and spherical structures. For silicon, polycrystalline silicon demonstrates the highest etch rate, attributed to its abundant grain boundaries, and developed pronounced irregular surface features. Monocrystalline silicon exhibited similar morphology after etching, while polished monocrystalline silicon shows minimal changes in surface structure due to its smoothness, resulting in weaker etching reactions. A comparison between quartz and silicon etching revealed that quartz, with its higher Si–O bond energy, had a relatively lower etch rate. In contrast, silicon, characterized by lower Si–Si bond energy, can react more readily with fluorine atom to form volatile SiF₄, resulting in a higher etch rate. This study elucidates the impact of pressure and surface structure on etching behavior and discusses respective etching mechanisms of quartz and silicon. The findings provide a theoretical foundation for optimizing plasma etching processes and improving material resistance to etching.