Interactions between brightener and chloride ions on copper electroplating for laser-drilled via-hole filling

Abstract

Blind vias with hole sizes of 85 and 110 μm formed by laser ablation on printed circuit boards were employed for investigation of filling by copper electroplating. The plating solution formulated was composed of acid copper sulfate, polyethylene glycol, 3-mercapto-1-propanesulfonate (MPS), and chloride ions. A "bottom-up" filling behavior had been observed with an appropriate MPS concentration. When MPS concentration was higher than 5.6 × 10-6 mol/L, conformal deposition occurred. However, this situation could be altered by adding more chloride ions into the plating solution to recover the behavior of bottom-up filling. Scanning electron microscopy showed that the recovery of bottom-up filling behavior is due to CuCl crystals formed by a synergistic effect between MPS and chloride ions. The synergistic effect results in acceleration of copper growth in via holes. These experimental results agree with the curvature-enhanced accelerator coverage mechanism. © 2003 The Electrochemical Society. All rights reserved.