Formation and characterization of porous silicon films obtained by catalyzed vapor-chemical etching

Porous silicon films obtained by the metal-assisted vapor-chemical etching technique have been characterized. For the film formation, epitaxial (100) N/P+, 1-5 Ω cm monocrystalline silicon wafers were used. The vapors of an alcoholic solution of H2O2/HF were drawn towards the silicon surface, which was previously covered with a thin layer of gold (~8 nm) for the catalytic etching. For the optical and morphological characterization of porous films, Raman spectroscopy, Ellipsometry, FTIR spectroscopy and SEM images were used. The films thickness kept a linear relationship with etching time. A porosity gradient from the surface towards the interface (65% to 12%) was observed in the films. A large amount of Si-H bonds as related to O-Si-O bonds were observed and the pore size depends on the HF concentration. Irregular morphology was found in films formed with 50% HF.