Infinite etch selectivity and line edge roughness variation during etching of silicon oxynitride with an extreme ultraviolet resist pattern in dual-frequency CH_2F_2/H_2/Ar capacitively coupled plasmas

摘要

The process window for infinitely high etch selectivity of silicon oxynitride (SiON) layers to extreme ultraviolet (EUV) resist and the variation in line edge roughness (LER) of etched EUV resist were investigated in a CH_2F_2/H_2/Ar dual-frequency superimposed capacitively coupled plasma under various process parameters including the gas flow ratio and low-frequency source power (P_(LF))- The CH_2F_2/H_2 gas flow ratio was found to play a critical role in determining the process window for infinite selectivity of the SiON/EUV resist due to the change in the degree of polymerization. The preferential chemical reaction of hydrogen and carbon species in the hydrofluorocarbon (CH_xF_y) layer with nitrogen on the SiON surface led to the formation of HCN etch by-products, resulting in a thinner steady-state CH_xF_y layer. During continuous SiON etching, the thinner steady-state CH_xF_y layer was due to enhanced SiF_4 formation, while the CH_xF_y layer was deposited on the EUV resist surface. In addition, the critical dimension and LER tended to increase with increasing Q(CH_2F_2) flow ratio.