Chemistry of selective metal ions adsorption and loading onto PVAc polymer brush during advanced metal post-CMP cleaning

초록

Metal ion contamination during post-chemical mechanical planarization (post-CMP) cleaning is an increasingly critical issue, particularly for advanced semiconductor devices with smaller node sizes. Post-CMP cleaning with a poly(vinyl acetal) (PVAc) brush can lead to contamination and cross-contamination, resulting in higher defect levels, lower device yield, and reduced brush lifetime. In this study, the interactions of metal ions, including titanium (Ti), cobalt (Co), copper (Cu), molybdenum (Mo), and tungsten (W), with PVAc brushes were systematically investigated through experimental measurements and theoretical calculations. Inductively coupled plasma mass spectrometry (ICP-MS) analysis revealed that Cu ions within the contaminated PVAc brushes exhibited the highest concentration at pH 7 (178 ppb), whereas W ion concentration remained relatively low. Density functional theory (DFT) calculations showed that the specific metal complexes, modeled as [Ti(H2O)6]3+, [Co(H2O)6]2+, [Cu(H2O)4]2+, MoO42−, and WO42−, exhibit distinct electronic characteristics upon interaction with PVAc. The calculated interaction energies (Eint) indicated thermodynamically favorable interactions for Ti (−5.685 eV), Co (−4.182 eV), and Cu (−5.151 eV), whereas Mo (+4.408 eV) and W (+5.057 eV) anions exhibited thermodynamically unfavorable interactions with the PVAc brush. Notably, although Ti showed the strongest intrinsic interaction among the investigated metal species, Cu exhibited the highest experimental loading at pH 7, highlighting the important role of pH and solution chemistry. Overall, these findings elucidate the metal-specific interactions governing the selective adsorption and loading of metal species onto PVAc brushes.

키워드