Effect of cupric ion concentration on the etching behavior of copper in Electrogenerated Chemical Polishing (EGCP)

Abstract

Electrogenerated Chemical Polishing (EGCP) is a stress-free polishing method which has been verified to be an effective method to obtain an ultra-flat and ultra-smooth copper (Cu) surface without defects induced by mechanical force. However, the surface roughness deterioration and removal rate decline emerged after polishing for a long time which prevents the application of EGCP in Cu ultra-precision manufacturing. In this study, apparent activation energy experiments and energy dispersive spectrometer (EDS) analysis were carried out to explore the mechanism of the Cu surface roughness deterioration and removal rate decline. With the increasing of cupric ions (Cu2+) concentration, the apparent activation energy of the Cu/Cu2+ reaction increased which inhibited the material removal rate consequently. Furthermore, it was found that Cu micro bumps were generated on the surface which was speculated to result from the disproportionation reaction of cuprous ion (Cu+) induced by high concentration of Cu2+. Based on this study, lifting the working electrode (WE) with a fixed time interval was verified to be an effective way to avoid the deterioration of surface roughness and the decline of the material removal rate. This study contributes to a further understanding of the chemical etching mechanism of Cu in EGCP.