INFLUENCE OF O-2 AND H2O2 ON THE METALLIC CONTAMINATION PROCESS OF SILICON-WAFERS IN DILUTE HF SOLUTIONS

Because dilute HF solutions (DHF) are most commonly used for wet clean ing of silicon surfaces, an extensive experimental study has been deve loped to investigate the effect of oxidant additives such as O-2 and H 2O2 The results show that these agents could efficiently prevent conta mination of the silicon surface by trace amounts of metal ions. Moreov er, electrochemical methods were very sensitive and allowed the detect ion of Cu2+ ions at a level of a few tens of ppb, even when a sophisti cated technique, based on the quantification of the fluorescence signa l of metallic elements (TXRF), could not perceive any surface contamin ation. The responses of p- and n-type silicon wafers were investigated in DHF solutions containing O-2 or H2O2 and traces of copper ions. Be cause of the high electron concentration, n-type silicon was very sens itive to cathodic reactions, while p-type silicon was inhibited by the limiting minority carrier current. The electrochemical results were i nterpreted in terms of reactivity of anodic and cathodic sites, the re duction rate of the oxidizing species, O-2 and H2O2, being sharply enh anced by the electrocatalytic properties of the first nanometric coppe r nuclei. The electrochemical response constitutes a powerful tool for monitoring the wet treatment lines for production of ultra large scal e integrated (ULSI) microcircuits.