Corrosion inhibitors in H2O2 system slurry for Ru based barrier layer Cu interconnect chemical mechanical polishing and optimization

Abstract

Ruthenium (Ru) has the advantages of low resistivity, high thermal stability, and good adhesion and wettability, making it an important solution for breaking through the 14 nm process as a new barrier layer material for multilayer copper interconnect. The purpose of copper (Cu) interconnect Ru-based barrier layer chemical mechanical polishing (CMP) is to obtain a highly flat surface, which not only includes the ideal Ru removal rate and selectivity of the Cu/Ru removal rate, but also inhibition of Cu corrosion. In this article, the corrosion inhibition mechanism of environmentally friendly and highly water-soluble inhibitor 5-methylthio-1 H-tetrazole (MTT) on Cu was studied. The inhibitory effect of MTT on Cu was analyzed through static etching rate testing, electrochemical experiments, and surface characterization. A systematic test was conducted on the planarization performance of the optimized polishing slurry. The corrosion inhibition mechanism of MTT on Cu was revealed through quantum chemical calculations and XPS testing. The experimental results show that the corrosion inhibitor MTT can effectively improve the surface quality of Cu. Quantum chemical calculations and experimental results indicate that MTT can be adsorbed on the surface of Cu through both physical and chemical methods, forming a dense passivation film, thereby inhibiting the corrosion of Cu. The optimized ratio of Ru-based barrier layer CMP polishing slurry was 5 wt% SiO₂, 0.15 wt% H₂O₂, 20 mM ethylenediamine (EDA), 5 mM K₄Fe(CN)₆, and 2000 ppm MTT, resulted in the Cu/Ru removal rate selectivity of 1:1.18 and the Cu/Ru corrosion potential difference of 3 mV. The average correction values for dishing and erosion on the test pattern wafer of the Ru barrier layer were 355 Å and 280 Å, respectively. The results of this study indicate that MTT is an effective copper corrosion inhibitor in alkaline H₂O₂-based polishing slurry, providing meaningful references for Ru-based barrier layer copper interconnect CMP.