NIST DEVELOPS TOOL FOR UNDERSTANDING ROLES OF ADDITIVES IN SUPERCONFORMAL ELECTRODEPOSITION OF COPPER.

A multidisciplinary effort is under way at NIST to develop an understanding of superconformal electrodeposition of copper, which recently has been implemented for on chip interconnects. Future demands for high density of interconnects with very short signal delay times require interconnects that are very narrow and have a high electrical conductivity. Superconformal deposition, which is promoted by the presence of small concentrations of additives in the electrolyte, enables the copper to deposit without voids into vias and trenches having high aspect ratios.

Recently NIST researchers have demonstrated superconformal electrodeposition of copper in 500 nm deep trenches ranging from 500 nm to 90 nm in width using an acid cupric sulfate electrolyte containing chloride (Cl), polyethylene glycol (PEG), and 3-mercapto-1-propanesulfonate (MPSA). The behavior of the system is representative of several commercial electrolytes and may be employed usefully as a model or "test bed" for exploring the "superfilling" phenomenon. In contrast, similar experiments using either an additive-free electrolyte, or an electrolyte containing the binary combination Cl-PEG, Cl-MPSA, or simply benzotriazole (BTAH), resulted in the formation of a continuous void within the center of the trench. Examination of the current-potential deposition characteristics of the electrolytes reveals an hysteretic response associated with the Cl-PEG-MPSA electrolyte that can be employed usefully to monitor and explore additive efficacy and consumption. This provides an easily used tool for developing an unde rstanding of the specific roles of the additives in promoting superfill.