Influence of and on the metallic contamination process of silicon wafers in dilute HF solutions

Abstract

Because dilute HF solutions (DHF) are most commonly used for wet cleaning of silicon surfaces, an extensive experimental study has been developed to investigate the effect of oxidant additives such as and . The results show that these agents could efficiently prevent contamination of the silicon surface by trace amounts of metal ions. Moreover, electrochemical methods were very sensitive and allowed the detection of ions at a level of a few tens of ppb, even when a sophisticated technique, based on the quantification of the fluorescence signal of metallic elements (TXRF), could not perceive any surface contamination. The responses of p- and n-type silicon wafers were investigated in DHF solutions containing or and traces of copper ions. Because of the high electron concentration, n-type silicon was very sensitive to cathodic reactions, while p-type silicon was inhibited by the limiting minority carrier current. The electrochemical results were interpreted in terms of reactivity of anodic and cathodic sites, the reduction rate of the oxidizing species, and , being sharply enhanced by the electrocatalytic properties of the first nanometric copper nuclei. The electrochemical response constitutes a powerful tool for monitoring the wet treatment lines for production of ultra large scale integrated (ULSI) microcircuits.