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

Abstract

The electrochemical open circuit potential response described in a previous publication proved very efficient for the study of silicon wafer contamination by copper traces from HF solutions containing 20 to 800 ppb Cu2+ ions. In pure 0.5% DHF, copper nuclei were immediately generated at the silicon surface. In the same conditions, when the solutions contained 0.5% DHF+HCl 1 M, no electrochemical response was observed leading to the conclusion that silicon contamination was greatly inhibited. Upon NH4F 1 M addition to the 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 64Cu as tracer, confirmed that HCl addition to HF solutions was efficient to generate an extremely passive silicon surface and supported the conclusions derived from the free potential measurements.