  A new method of introducing nanopores with spongy morphology during
fabrication of size and pitch controlled flexible silicon microwires (SiMWs) in
wafer scale is presented using nanosphere lithography technique in addition to
metal catalyzed electroless etching technique by varying concentration of
oxidant and introducing surfactant or co-solvents to the etching solution. For
achieving self-assembled monolayer closed-pack pattern of SiO2 microparticles
in wafer-scale simple spin coating process was used. The effect of variation of
the etchant, oxidant and surfactant on the morphology and optical properties of
SiMWs were studied. By simply controlling the diameter of SiO2 microparticles
and concentration of H2O2 the size of the MWs as well as the introduction of
pores could be controlled in wafer-scale. Average reflectance suppressed to
below 8% in the broad spectral range of 400-800 nm for these porous, spongy and
flexible SiMW arrays in wafer scale. The mechanism behind this formation of
spongy, porous and flexible nature of the SiMWs is also demonstrated for a
better understanding of the etching process.
