An optimized passivation mechanism at the copper film recess for achieving efficient planarization of copper chemical mechanical polishing

This article proposed an improvement plan for the slurry to reduce the dishing caused during copper chemical mechanical polishing (CMP) of the interconnect structure. According to the difference in the pressure between the concave and convex parts of the copper film in the high-hardness polishing pad, polishing slurries were designed with a distinct difference in the polishing removal rate under high and low platen pressures to improve their planarization efficiency. 2 wt% GLY (glycine) and 1 wt% H2O2 can provide a chemical dissolution effect, adding 0.1% TAZ (1,2,4-triazole) to slow down the corrosion mainly for the recession, by adjusting the slurry pH to 7. The polishing results showed that the slurry had a high copper removal rate (6772 Å/min) at high pressure (3.0 psi) and a much lower removal rate (3273 Å/min) at low pressure (1.2 psi). The pattern wafer polished with this slurry obtained relatively low dishing. The other comparison groups showed slight differences in copper removal rate at high and low pressure and a deeper dishing of the polished pattern wafer. In this paper, based on the analysis of static dissolution experiments, electrochemical experiments, and XPS experiments of copper films in different slurries, the chemical reaction mechanism of copper films in the solution system of GLY and H2O2 was studied at different pH values. In addition, the inhibition mechanism of TAZ on the copper surface at different slurry pH values was proposed, including the properties of the TAZ molecule adsorption film on the copper surface, the uniformity of the surface coverage, and the thickness of the passivation layer. The results can reflect the polishing results to a certain extent despite some deviations, but it can also be used as a more reasonable argument to explain the optimization scheme of the slurry proposed in this article.