Ion-Enhanced Etching Characteristics of sp(2)-Rich Hydrogenated Amorphous Carbons in CF(4) Plasmas and O(2) Plasmas

The sp(2)-rich hydrogenated amorphous carbon (a-C:H) is widely adopted as hard masks in semiconductor-device fabrication processes. The ion-enhanced etch characteristics of sp(2)-rich a-C:H films on ion density and ion energy were investigated in CF(4) plasmas and O(2) plasmas in this work. The etch rate of sp(2)-rich a-C:H films in O(2) plasmas increased linearly with ion density when no bias power was applied, while the fluorocarbon deposition was observed in CF(4) 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 CF(4) plasmas and O(2) plasmas when bias power was applied. An ion-enhanced etching model was suggested to fit the etch rates of a-C:H in CF(4) plasmas and O(2) plasmas. Then, the etch yield and the threshold energy for etching were determined based on this model from experimental etch rates in CF(4) plasma and O(2) plasma. The etch yield of 3.45 was observed in CF(4) plasmas, while 12.3 was obtained in O(2) 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 O(2) plasmas, while the high threshold energy of 156 eV was observed in CF(4) 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.