A COMPARATIVE ELECTRCHEMICAL STUDY OF COPPER DEPOSITION ONTO SILICON FROM DILUTE AND BUFFERED HYDROFLUORIC ACIDS

An electrochemical direct current polarization method was used to inve stigate characteristics of copper deposition onto silicon from dilute and buffered hydrofluoric acid solutions. The corrosion current densit y and corrosion potential of silicon were not very sensitive to the Cu 2+ concentration, up to 1000 parts per billion, in buffered hydrofluor ic acid. However, the extent of copper deposition, as measured by tota l reflection X-ray fluorescence, increased as the Cu2+ concentration i n solution increased. In dilute hydrofluoric acid, Cu2+ addition had a significant and systematic effect on the corrosion potential and corr osion current density of silicon. However, in both types of solution, the cathodic current calculated from the measured copper deposition wa s found to be only a small fraction of the corrosion current (less tha n 1%). This indicates that the primary cathodic reaction is not copper ion reduction but hydrogen ion reduction. Illumination affected the e lectrochemical behavior of both p- and n-type silicon in Cu2+ spiked d ilute hydrofluoric acid, but only that of p-type silicon in buffered h ydrofluoric acid.