Measurement of Minute Corrosion of Copper Thin Film by a Quartz Crystal Microbalance

Abstract

A quartz crystal microbalance (QCM) technique can detect sensitively a small weight change during minute corrosion of metal thin film from the measurement of change in resonance frequency of quartz crystal. The QCM technique has been applied to monitor the minute corrosion of copper thin film in air or nitrogen gas with different relative humidities containing H2S of 20 ppm at 30°C. The weight gain due to sulfide formation as corrosion products on the copper thin film obeyed a linear rate law at the initial stage and subsequently obeyed a prabolic rate law. The linear and parabolic rate constants obtained from the time-variation of weight gain were influenced by the relative humidity and oxygen in air. The corrosion mechanism was discussed from the view-point of electrochemistry. Furthermore, the QCM technique has been applied to investigate the anodic oxidation process of copper thin film in pH 8.4 borate solution. The real electric current, Ireal measured during anodic oxidation at a constant potential in the passive region was compared with the apparent current, Iapp calculated from the frequency change in QCM. It was shown that the dissolution rate of Cu2+ ions through the passive film into solution and the uptake rate of oxygen in the film could be separately evaluated from the comparison between Ireal and Iapp at the high anodic potential where the dissolution of Cu+ ions was negligibly small. These results has revealed that the QCM technique is one of the most powerful tools for the study on minute corrosion of metal thin film. © 1990, The Society of Materials Science, Japan. All rights reserved.