Stain etching of silicon pillars and macropores


We used a XeCl excimer laser (308 nm, ∼3 J cm–2) and chemically enhanced laser ablation in the presence of SF6 to create arrays of silicon pillars. Etching of these pillars with KOH leads to arrays of macropores whose morphology depends on surface crystallography. Several new stain etchants – containing some combination of HF, NH4HF2, HCl, HNO3, Fe(III), Mn(VII) and water – have been used to cover these structures with a layer of microporous silicon. Both pillars and macropores are black, i.e., exhibit low reflectivity across the visible spectrum. When porosified, pillars exhibit visible photoluminescence whose angular distribution differs from that of planar porous silicon with significantly more intensity at high angles. The peak photoluminescence wavelength depends on the stain etchant composition and exposure to air. The use of metal ions in place of HNO3 in the stain etchant ameliorates the production of gas bubbles and leads to more uniform films.

Physica Status Solidi (A) Applications and Materials 202(8):1422 - 1426 · June 2005