Photoresist ashing technology using N2/O2 ferrite-core ICP in the dual damascene process

The characteristics of the photoresist (PR) ashing process with respect to the dual damascene structure in its low-k materials scheme were investigated. The O2 plasma used in the conventional PR ashing oxidizes low-k material and makes an SiO2-like layer, which causes the increase of the dielectric constant and the leakage current. The oxygen contributes to damaging the low-k material by breaking the Si-CH3 and C-H bonds and thus by changing the low-k dielectric layer to the SiO2-like material, which can be easily removed by the HF solution. The optimized condition for high PR ashing rate and low ashing damage was achieved with the help of O2/(N2 + O2) gas flow ratio of 0.1. It was observed that the ashing process removes both PR on top of the structure and inside the via hole.