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

Abstract

AbstractAmorphous 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.