A Proprietary Chemical Bath Life Study in MHM ULK Scheme Wet Cleaning

As technology evolves to 45nm and beyond, IC companies adopt TiN metal hardmask instead of PR (photo resist) to gain better etching profile, CD uniformity and less low-k material damage. To improve Cu gap fill capability, an in situ TiN pull back is needed in the subsequential wet clean step. This pullback can be done by mixing some additive with clean media, like H2O2. But H2O2 tends to decompose along the time, it also bring the challenges to the wet clean media stability. In this paper, we study a proprietary wet clean chemical behavior with pH, Cu ion concentration, H2O2 additive and bath lifetime. Cu ions content is demonstrated critical to the mixture instability when H2O2 presents. Chemical degradation mechanism is also discussed.