Cationic Surfactants for the Control of Overfill Bumps in Cu Superfilling

Electroanalytical measurements and feature-filling experiments have been conducted to study the effect of dodecyltrimethylammonium chloride (DTAC), a quaternary ammonium cationic surfactant, on Cu deposition in the presence of various combinations of superfilling additives. A variety of other surfactants, cetyltrimethylammonium chloride, cetyltrimethylammonium hydrogen sulfate, and sodium dodecyl sulfate were examined to reveal the significance of head group charge, counterion, and chain length for the adsorption and interaction of levelers with the accelerator bis(3-sulfopropyl) disulfide (SPS). Dodecyltrimethylammonium chloride (DTAC)-saturated surfaces yield substantial inhibition of Cu deposition that is similar in magnitude to that provided by polyethylene glycol (PEG)–Cl. This suggests that such layers operate by physically limiting access of to the Cu surface. However, the addition of DTAC and related cationic surfactants quench the characteristic voltammetric hysteresis of the PEG–Cl–SPS system. This is attributed to ion-pairing between the cationic head group of the surfactants and the anionic tail group of SPS, resulting in the deactivation of SPS. Deactivation may occur either by DTAC accumulation from the electrolyte or by lateral interaction during area reduction that occurs on advancing concave surfaces in accordance with the curvature-enhanced adsorbate coverage mechanism. The combined process may be optimized to enable the superfilling dynamic to be sustained while overfill bump is effectively attenuated.