The effects of gas flow rates on the etch characteristics of silicon nitride with an extreme ultra-violet resist pattern in CH 2F 2/N 2/Ar capacitively coupled plasmas

Abstract

The effects of CH 2F 2 and N 2 gas flow rates on the etch selectivity of silicon nitride (Si 3N 4) layers to extreme ultra-violet (EUV) resist and the variation of the line edge roughness (LER) of the EUV resist and Si 3N 4 pattern were investigated during etching of a Si 3N 4/EUV resist structure in dual-frequency superimposed CH 2F 2/N 2/Ar capacitive coupled plasmas (DFS-CCP). The flow rates of CH 2F 2 and N 2 gases played a critical role in determining the process window for ultra-high etch selectivity of Si 3N 4/EUV resist due to disproportionate changes in the degree of polymerization on the Si 3N 4 and EUV resist surfaces. Increasing the CH 2F 2 flow rate resulted in a smaller steady state CH xF y thickness on the Si 3N 4 and, in turn, enhanced the Si 3N 4 etch rate due to enhanced SiF 4 formation, while a CH xF y layer was deposited on the EUV resist surface protecting the resist under certain N 2 flow conditions. The LER values of the etched resist tended to increase at higher CH 2F 2 flow rates compared to the lower CH 2F 2 flow rates that resulted from the increased degree of polymerization.