Etch characteristics of nanoscale ultra low-k dielectric using C3H2F6

Abstract

Next generation semiconductor devices require ultra low dielectric constant (ULK) materials such as porous SiCOH on the back end of line structure for lower resistance and capacitance (RC) time delay, however, these ULK materials are easily damaged by the exposure to plasmas during the etching. In this study, etch characteristics of nanoscale TiN masked porous SiCOH such as etch rate, etch profile, surface damage, etc. and plasma characteristics by using C3H2F6 based gases have been investigated with a dual-frequency capacitively coupled plasma system (DF-CCP) and the results were compared with those by using conventional C4F8 based gases used for low-k dielectric etching. The results showed that, for the similar etch rates and etch profiles of porous SiCOH, lower sidewall damage was observed for the etching with the C3H2F6 compared to the C4F8. The analysis showed that it was related to less UV (less than 400 nm) emission and less fluorine radicals in the plasma for C3 H2F6 compared to C4F8, which leads to less fluorine diffusion to the sidewall surface of the etched porous SiCOH by the fluorine scavenging by hydrogen in C3H2F6.