Benzyl-containing quaternary ammonium salt as a new leveler for microvia copper electroplating

Abstract

Recently, quaternary ammonium salt is considered as an effective leveler because of its easy adsorption on the cathode surface. However, quaternary ammonium salt compounds usually have a variety of functional groups with different structures, which may bring different adsorption effects. In this paper, three kinds of benzyl-containing quaternary ammonium compounds with different side chains, i.e., benzyl trimethyl ammonium chloride, tetradecyl dimethyl benzyl chloride ammonium chloride and benzethonium chloride, were selected as potential levelers for microvia overfilling of PCB with high-density interconnect. The wettability and the electrochemical behavior of the three levelers on copper deposition were studied through contact angle measurements and cyclic voltammetry striping tests. It was found that among the three kinds of quaternary ammonium salts, benzethonium chloride (BZC) with three side chains of ether bond, alkyl and benzene ring has the most significant inhibitory effect on copper deposition. Electrochemical tests including cyclic voltammetry striping (CVS) and linear sweep voltammetry (LSV) performed at two different speeds that simulates the microvia filling environment were then used to analyze the effect of the addition concentration of BZC as leveler on the deposition behavior of copper to make sure an optimal concentration. Subsequently, the effect of BZC as leveler on the electrodeposition behavior of copper under the synergistic action of conventional accelerator, suppressor and chloride ion was further analyzed by comparing with traditional leveler based on GM and LSV. The results show that under the synergistic action of other additives, this BZC produces greater inhibition of copper deposition than the traditional JGB, has more obvious convection-dependent adsorption behavior and forms a larger potential difference to meet the super filling. Filling experiment further shows that BZC as a leveler had an excellent filling performance. In addition, Field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were used to analyze the surface morphology and crystal structure of microvia filled copper at different concentrations of BZC. The present results show that benzyl ammonium chloride with ether bond, alkyl and benzene ring is an effective leveler for the microvia filling of PCB.