Effect of PEG molecular weight on bottom-up filling of copper electrodeposition for PCB interconnects

摘要

The effect of polyethylene glycol (PEG) molecular weight (Mw) upon the microhole filling by Cu electrodeposition was investigated by cross-sectional images using optical microscopy. The bottom-up filling capability of the electroplating bath was increased clearly with an increase in PEG Mw from 600 to 8000 g mol~(-1), and holes with a diameter of 50 μm and aspect ratio of one were filled completely when PEG Mw was higher than 6000 g mol~(-1). The electrochemical study indicated that the polarisation on the cathode was increased with an increase in PEG Mw, and the Cu deposition rate was inhibited. Furthermore, X-ray diffraction analyses showed the crystallography and the peak intensity ratio I(111)/I(200) of plated Cu film were decreased with an increase in PEG Mw. The surface roughness of deposited Cu film was decreased, and a smooth surface was obtained as the PEG Mw increased. The results present PEG-8000 as an inhibitor which is beneficial for microholes filling for high density interconnections printed circuit board.