ELECTROCHEMICAL AND RADIOCHEMICAL STUDY OF COPPER CONTAMINATION MECHANISM FROM HF SOLUTIONS ONTO SILICON SUBSTRATES

The mechanism of copper contamination of silicon wafers from dilute HF solutions containing ultratrace levels of metallic ion impurities, wa s investigated using a new electrochemical cell, which proved to act a s a very efficient sensor for in situ characterization. Upon copper co ntamination, the open-circuit potential was observed to shift rapidly toward more positive values at a rate nearly proportional to the coppe r concentration. All potential/time curves tend to reach a plateau, wh ile quantitative measurements using radioactive tracers revealed that during a few tens of minutes, copper ions were continuously reduced on the silicon surface. Results are interpreted in terms of the mixed-po tential theory and lead to the conclusion that copper nuclei act as a catalyst which enhances the cathodic activity for proton reduction. Th e model was supported by atomic force microscopy observations which sh owed the initiation of corrosion pits around the nuclei.