The invalidated process and related mechanism of PEG during copper via-filling process were investigated by means of electrochemical polarization and electrochemical impedance (EIS) measurements, and infra-red spectrum (IR) measurement was employed to analyses the invalidated products of PEG. The results suggest that the adsorption strength of PEG on cathode surface and its inhibition to copper reduction decrease gradually with the increase of passed charges (PC). Both the anodic and the cathodic electrifying process can cause the invalidation of PEG, but their invalidated courses are different. PEG will further polymerize to form new PEG with bigger MW on the anode surface, which causes the dispersive ability of plating solution to decrease. As a result, super-filling behavior cannot be obtained and many small wales formed on the specimen surface during copper via-filling process. Inversely, PEG will decompose to form new PEG with smaller MW on the cathode surface, which results in the decrease of PEG adsorption ability and inhibition. As a result, super-filling behavior cannot be obtained and the brightness of the specimen surface decreases during copper via-filling process. The decomposition of PEG is easily to happen than its polymerization when the anodic and cathodic reactions happen in the same plating solution simultaneously. So the main invalidated product of PEG during copper via-filling process is PEG with smaller MW. (C) 2008 Elsevier B. V. All rights reserved.