Fabrication and surface modification of micro/nanoporous silicon

We have studied surface and structural properties of micro/nanoporous silicon, synthesized by electrochemical etching of ptype Si (100) with different etching conditions. SEM studies reveal tunable pore sizes from 200 nm to 1.5 μm for etching time 5 to 30 min, and the thickness of pore walls decreases upto 20 nm for 30 min etching. AFM investigations reveal increase in roughness of the porous structure with increase in etching time and saturate around 250 nm at higher etching time. X-ray diffractogram of porous Si surface for etching time 20 min shows the appearance of two peaks at 2θ = 69.13° and 69.33°. For 30 min etching time a broad peak is observed at 2θ = 69.39°. The broadening may due to the size distributions of pore walls, and up ward shifts may due to relaxation of strain in the porous structure. FTIR investigations show the presence of Si-H bending in Si₃-SiH groups at 624 cm^-1, Si-O stretching in O-Si-O in between 1056-1160 cm ^-1. The bands at 2958, 2927, and 2856 cm^-lare related to C-H stretching of CH₃, CH₂, and CH groups, which probably come from residual of HF-dimethylformamide.