Femtosecond laser direct hard mask writing for selective facile micron-scale inverted-pyramid patterning of silicon

We report on the fabrication of high-fidelity inverted-pyramids in crystalline silicon (c-Si) at the 1 mu m scale through the selective removal of a silicon nitride (SiNx) hard-mask with a 522 nm femtosecond (fs) laser and subsequent alkaline potassium hydroxide (KOH) etching. Through a series of systematic experiments on a range of hard-mask thicknesses, the use of 20 nm thick SiNx film yielded a 0.6 mu m diameter laser-ejected aperture in the hard-mask at a single pulse fluence of 0.45 J cm(-2), resulting in 1 mu m wide inverted-pyramid structure in c-Si after KOH etching. Anisotropic KOH etching of the partially amorphized c-Si underlying the fs-laser patterned hard mask was found to render clean (111) planes of c-Si. An array of inverted-pyramids on c-Si surfaces as large as 4 cm(2) was produced with a defect density of less than 1 in 10(4). This facile, non-contact, and cleanroom-independent technique serves a variety of applications including anti-reflective texturing of thin c-Si for photovoltaics, wafer marking, labeling, and fabrication of microfluidic and optical devices or laboratories on silicon wafers. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4768689]