Etching characteristics of hydrogenated amorphous carbon with different sp2/sp3 hybridization ratios in CF4/O2 plasmas

Abstract 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 sp 2 /sp 3 hybridization ratios was studied for CF 4 /O 2 plasma mixtures. The etch rate of sp 3 ‐rich a‐C:H is 33.7 times higher than that of sp 2 ‐rich a‐C:H in a plasma comprising 50% CF 4 and 50% O 2. The etch rate of the sp 2 ‐rich a‐C:H exhibits a linear correlation with the ion density of CF 4 /O 2 plasma, whereas that of the sp 3 ‐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 sp 2 ‐rich a‐C:H, whereas spontaneous chemical etching is the main reaction mechanism for the sp 3 ‐rich a‐C:H in CF 4 /O 2 plasmas.