Through-Co self-forming-barrier (tCoSFB) metallization scheme is introduced, with Cu gap-fill capability down to 7 nm-node dimensions. Mn atoms from doped-seedlayer diffuse through CVD-Co wetting layer, to form TaMn x O y barrier, with integrity proven by vertical-trench triangular-voltage-sweep and barrier-oxidation tests. tCoSFB scheme enables 32% and 45% lower line and via resistance, respectively at 10 nm node dimensions, while achieving superior EM performance to competitive TaN/Co and TaN/Ru-based barriers.
The microstructure of Cu interconnects fabricated with Ta and Co liner materials had been examined by transmission electron microscopy and correlated to the electrical characteristics. Cu lines of 40 nm width were fabricated on 300 mm Si wafers by conventional CMOS backend processing. Electrical measurements performed immediately after fabrication of these Cu lines showed similar electrical resistance for Co and Ta liners. However, a 2.5-hour anneal at 375°C led to 5% more resistance reduction for Cu lines with the Ta liner than with the Co liner. Microstructure analyses showed that Cu lines with the Ta liner had 24% coherent Σ3 grain boundaries while lines with the Co liner yielded only 6% of coherent grain boundaries. In addition, Cu with Ta liner had a stronger 〈111〉 texture along the line width direction. However, the overall grain size distribution was similar between Ta and Co liners. These results suggest Co liner has some impact on Cu microstructures, which may be a root cause for the relatively higher line resistance.
In this study, we characterize the anodic dissolution behavior of thin PVD Cu/CVD Co bilayer films using linear sweep amperometry in a potassium nitrate electrolyte. The Co and Cu dissolution peaks are well separated, enabling an assessment of the continuity of the Cu overlayers. Complete coverage of the Co film is attained at a PVD Cu overlayer nominal thickness of ~20 nm. Exposing the bilayer films to various wet solutions (as a "pretreat") followed by a linear potential sweep allows measurement of the Co loss during pretreatment. The impact of a pretreat in Cu plating chemistries with different cupric ion concentrations and various organic additive packages is characterized on the Cu/Co bilayer stack. Electrical data are presented for 24 nm CD dual Damascene BEOL test structures for Cu plating chemistries with different Cu contents. The influence of the plating bath Cu concentration on yield is discussed with respect to the observed dependency of Co loss on the pretreat solution Cu content.
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