Electrochemical test for silicon surface contamination by copper traces inHF, HF plus HCl and HF+NH4F dilute solutions

The electrochemical open circuit potential response described in a previous publication proved very efficient for the study of silicon wafer contamina tion by copper traces from HF solutions containing 20 to 800 ppb Cu2+ ions. In pure 0.5% DHE copper nuclei were immediately generated at the silicon s urface. In the same conditions, when the solutions contained 0.5% DHF + HCl 1 M, no electrochemical response was observed leading to the conclusion th at silicon contamination was greatly inhibited. Upon NH4F 1 M addition to t he 0.5% DHF solution, the surface seems to be transiently contaminated and then tends to be partly cleaned. Further studies, of surface contamination, using radioactive Cu-64 as tracer, confirmed that HCl addition to HF solut ions was efficient to generate an extremely passive silicon surface and sup ported the conclusions derived from the free potential measurements.