Insights into the role of Basic Blue 7 as a leveler in copper superfilling within microvias

Abstract

Achieving metal interconnects for printed circuit boards (PCBs) is pivotal for the electronics industry. Through electrochemical analysis of Basic Blue 7 (BB7), an excellent suppressing effect was observed. Chronopotentiometry was used to study the possible concentration range of BB7 for microvia filling and a BB7 concentration range of 50–150 mg L⁻¹ was selected to achieve superfilling electrodeposition. A difunctional mechanism of coordination and adsorption of BB7 during electrodeposition is proposed based on density functional theory (DFT) calculations and in situ Raman spectroscopy analysis. The interaction among BB7, the copper substrate and Cu²⁺ leads to the suppression of copper growth. The superfilling electroplating process is optimized and high filling performance can be achieved at 100 mg L⁻¹ with filling percentage (FP) values of 80.19%, 84.70% and 87.90% for microvias with diameters of 150 μm, 125 μm and 100 μm, respectively. Besides, a differential diffusion filling mechanism is proposed for the blind microvia filling process of the newly proposed electroplating system based on the analyses of the interaction among additives and diffusion kinetics. Furthermore, the performance of the copper interconnect layer, including surface morphology, phase structure and signal transmittance, is evaluated.