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1554952 
Journal Article 
Etching Silicon with HF-HNO3-H2SO4/H2O Mixtures - Unprecedented Formation of Trifluorosilane, Hexafluorodisiloxane, and Si-F Surface Groups 
Lippold, M; Boehme, Uwe; Gondek, C; Kronstein, M; Patzig-Klein, S; Weser, M; Kroke, E 
2012 
Yes 
European Journal of Inorganic Chemistry
ISSN: 1434-1948
EISSN: 1099-0682 
WILEY-V C H VERLAG GMBH 
WEINHEIM 
34 
5714-5721 
WOS:000311564900015 
The etching behaviour of sulfuric-acid-containing HFHNO3
solutions towards crystalline silicon surfaces has been studied over a wide range of H2SO4
concentrations. For mixtures with low sulfuric acid concentration, NO2/N2O4, N2O3, NO and N2O
have been detected by means of FTIR spectroscopy. Increasing concentrations of nitric acid lead
to high etching rates and to an enhanced formation of NO2/N2O4. Different products were observed
for the etching of silicon with sulfuric-acid-rich mixtures [c(H2SO4) > 13 mol?L1].
Trifluorosilane and hexafluorodisiloxane were identified by FTIR spectroscopy as additional
reaction products. In contrast to the commonly accepted wet chemical etching mechanism, the
formation of trifluorosilane is not accompanied by the formation of molecular hydrogen (according
to Raman spectroscopy). Thermodynamic calculations and direct reactions of F3SiH with the etching
solution support an intermediate oxidation of trifluorosilane and the formation of
hexafluorodisiloxane. The etched silicon surfaces were investigated by diffuse reflection FTIR
and X-ray photoelectron spectroscopy (XPS). Surprisingly, no SiH terminations were observed after
etching in sulfuric-acid-rich mixtures. Instead, a fluorine-terminated surface was found. 
Silicon; Silanes; Fluorine; Hydrofluoric acid; Wet chemical etching; Surface analysis