Role of a novel imidazolium-based leveler on the Cu electroplating for ultra-high aspect ratio through-silicon-vias

Leveler additives for Cu electrodeposition are critical for achieving bottom-up filling in micrometer scale and high aspect ratio (AR) through-silicon vias (TSVs). This study explores a highly effective imidazolium-based leveler electroplating formulation, which successfully achieves void-free filling of TSVs with a diameter of 3 μm and a depth of 45 μm (with an ultra-high AR of 15:1). Molecular dynamics simulations reveal that the leveler, 1,2-dimethyl-3-propylimidazolium iodide (DMPII), demonstrates a strong adsorption effect on the Cu surface. Electrochemical tests show that DMPII enhances the inhibitory effect of polyethylene glycol (PEG) while simultaneously amplifying the accelerating effect of bis-(sodium sulfopropyl)-disulfide (SPS). The complex interplay among these additives ultimately leads to a significant inhibitory effect on the electrochemical reduction of Cu ions at the TSV sidewalls, while promoting deposition at the bottom of the TSV. Furthermore, minimal impurities are detected in the electroplated Cu layer. These findings suggest that this DMPII-based electroplating formulation holds significant promise for the fabrication of ultra-high AR TSVs to enable future high-density 3D integration.