Electrochimica Acta, Vol.53, No.1, 145-154, 2007
Curvature enhanced adsorbate coverage mechanism for bottom-up superfilling and bump control in damascene processing
Superconformal electrodeposition is explained by the curvature enhanced adsorbate coverage (CEAC) mechanism. A CEAC model is used to quantitatively explain shape evolution during bottom-up "superfill" of trenches and vias. The bottom-up filling dynamic is seen to be a consequence of competitive adsorption between a rate suppressing polyethylene glycol-chloride layer (PEG-Cl) and a depassivating or rate accelerating species comprised of sulfonate-terminated propane thiol/disulfide and chloride (SPS-Cl). The SPS is the stronger surfactant and it adsorbs concurrently with displacement of the more rapidly formed PEG-Cl layer; growth on non-planar geometries thus leads to enrichment of SPS on advancing concave surfaces and dilution on convex sections. Because the metal deposition rate rises monotonically with the local accelerator (SPS-Cl) surface coverage, this yields positive feedback that naturally gives rise to desirable bottom-up superfilling. As the accelerating action of SPS can also be quenched by the addition of a cationic surfactant (LEV), additive concentrations can be optimized to allow SPS derived bottom-up superfilling followed by LEV induced SPS deactivation. The LEV addition can thus be used to inhibit overshoot that otherwise would result in undesirable bump formation above the features. This paper presents a summary of electroanalytical experiments and simulations designed to determine the mechanism and rate constants of the adsorbate interactions during copper deposition in the PEG-Cl-SPS-LEV system as well as predictions of feature filling using the CEAC shape change model. (C) 2007 Elsevier Ltd. All rights reserved.