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Amorphous carbon is used as a hard mask for dielectric etching with a high aspect ratio in the fabrication processes of semiconductor devices. The dependence of the etching characteristics of hydrogenated amorphous carbon (a‐C:H) films on the sp2/sp3 hybridization ratios was studied for CF4/O2 plasma mixtures. The etch rate of sp3‐rich a‐C:H is 33.7 times higher than that of sp2‐rich a‐C:H in a plasma comprising 50% CF4 and 50% O2. The etch rate of the sp2‐rich a‐C:H exhibits a linear correlation with the ion density of CF4/O2 plasma, whereas that of the sp3‐rich a‐C:H exhibits a second‐order exponential correlation with O radical density. A combined etch rate model was suggested to explain the etch rates of a‐C:H. Ion‐enhanced etching is identified as the dominant etching mechanism for the sp2‐rich a‐C:H, whereas spontaneous chemical etching is the main reaction mechanism for the sp3‐rich a‐C:H in CF4/O2 plasmas.

The sp2-rich hydrogenated amorphous carbon (a-C:H) is widely adopted as hard masks in semiconductor-device fabrication processes. The ion-enhanced etch characteristics of sp2-rich a-C:H films on ion density and ion energy were investigated in CF4 plasmas and O2 plasmas in this work. The etch rate of sp2-rich a-C:H films in O2 plasmas increased linearly with ion density when no bias power was applied, while the fluorocarbon deposition was observed in CF4 plasmas instead of etching without bias power. The etch rate was found to be dependent on the half-order curve of ion energy in both CF4 plasmas and O2 plasmas when bias power was applied. An ion-enhanced etching model was suggested to fit the etch rates of a-C:H in CF4 plasmas and O2 plasmas. Then, the etch yield and the threshold energy for etching were determined based on this model from experimental etch rates in CF4 plasma and O2 plasma. The etch yield of 3.45 was observed in CF4 plasmas, while 12.3 was obtained in O2 plasmas, owing to the high reactivity of O radicals with carbon atoms. The threshold energy of 12 eV for a-C:H etching was obtained in O2 plasmas, while the high threshold energy of 156 eV was observed in CF4 plasmas. This high threshold energy is attributed to the formation of a fluorocarbon layer that protects the a-C:H films from ion-enhanced etching.

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