Influence of EDTA/THPED Dual-Ligand on Copper Electroless Deposition

摘要

Single ligand electroless plating process has been studied extensively in the past decades, this studyinvestigates the advantages of using a dual ligand system (EDTA/THPED) on electroless platingprocess. Electrochemistry techniques including mixed potential and linear sweep voltammetry (LSV)are used to examine the fundamental deposition mechanism of dual ligand system, providing criticalinformation for dual ligand formulation design. Mixed potential tests indicated that increasing theTetrakis (2-hydroxypropyl) ethylenediamine （THPED） concentration negatively shifts the electrodepotential. The overall process was divided into three regions: induction, transition and stability. Thedegree of potential negatively shifted at each region was related to absorption, the type of redoxreaction, ion diffusion and migration. Electrochemical analyses showed that there was an obvious peakfor all anodic and cathodic reactions, respectively at around -0.42V and -0.57 V, whereby the currentdensity depended on the THPED concentration. Moreover LSV study demonstrated control factor ofautocatalytic reactions is cathodic reduction process of copper ion. The electroless deposition rateresults were also in good agreement with mixed potential and electrochemical measurements, and thecopper deposition rate increased significantly with the addition of THPED, and showed parabolicgrowth pattern. Metallographic studies of the dual-ligand electroless copper deposits revealed that theirtopographic structures had uniform and fine particle distribution, and a high-purity product withoutCu2O inclusions was detected. Copper layers displayed that the addition of THPED favored theformation of the preferred orientation on the (220) lattice plane.