Mechanism of highly selective etching of SiCN by using NF3/Ar-based plasma

As part of the self-aligned processes to fabricate a 3D device, highly selective SiCN etching using NF3/Ar-based gas plasma generated by microwave electron-cyclotron resonance was investigated. The etching rate of SiCN etched by NF3/Ar plasma was higher than that of various other materials, namely, SiO2, Si3N4, poly-Si, TiN, and Al2O3. Extremely highly selective etchings of SiCN with regard to various materials are possible by forming protective layers on nonetched materials by adding gases to the NF3/Ar plasma. The effects of adding gases to the NF3/Ar plasma on various other materials were studied by analysis using optical emission spectroscopy and x-ray photoelectron spectroscopy (XPS). The three key findings of these analyses are summarized as follows. First, highly selective etching of SiCN to poly-Si was achieved by adding oxygen to the NF3/Ar etching plasma. This etching was made possible because poly-Si etching was inhibited by forming a 1.0-nm-thick oxidized layer to protect the poly-Si surface from the etching reaction with fluorine radicals. Second, highly selective etching of SiCN to SiO2 and Si3N4 was achieved by using NF3/Ar-based plasma with added SiCl4. In this etching, silicon-containing deposited layers were formed on the SiO2 and Si3N4 surfaces. The deposited layers protected the surfaces from being etched by reacting with fluorine radicals. Third, highly selective etching over TiN was achieved by using hydrogen-added plasma. The XPS results show that a thin protective layer containing TiNxFy and ammonium fluoride was formed on the TiN surface. The protective layer formed on the TiN surface effectively protects the TiN from being etched by fluorine radicals.