V. Bertagna et al., COPPER CONTAMINATION MECHANISM OF SILICON SUBSTRATES FROM HF SOLUTIONS, Zeitschrift fur Naturforschung. A, A journal of physical sciences, 52(6-7), 1997, pp. 465-476
The contamination of silicon wafers from dilute HF solutions containin
g ultratrace levels of metallic ion impurities is a subject of constan
t interest. The mechanism of copper electroless deposition from HF ont
o monocrystalline silicon was investigated using a new electrochemical
cell, which proved to be a very sensitive detector for in situ charac
terization of silicon surfaces. Upon addition of copper trace amounts,
the open-circuit potential was observed to shift rapidly towards more
positive values at a rate nearly proportional to the copper concentra
tion. All potential/time curves tend to reach a limiting value of the
potential, while quantitative measurements of radioactive tracers reve
aled that during a few tens of minutes, copper ions were continuously
reduced on the silicon surface. Electrochemical potentials and voltamm
etric measurements were interpreted in terms of the mixed potential th
eory and led to the conclusion that copper nuclei act as a catalyst wh
ich enhances the cathodic activity for protons reduction. The model wa
s supported by AFM observations which demonstrated the initiation of c
orrosion pits around the nuclei.