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

• Published in: Applied physics letters 2012-11, Vol.101 (22)
• Main Authors: Kumar, K., Lee, K. K. C., Herman, P. R., Nogami, J., Kherani, N. P.
• Format: Article
• Language: English
• Subjects: Cleaning; Density; Etching; Femtosecond; Lasers; Masks; Silicon; Wafers
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.4768689

We report on the fabrication of high-fidelity inverted-pyramids in crystalline silicon (c-Si) at the 1 μm 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 μm diameter laser-ejected aperture in the hard-mask at a single pulse fluence of 0.45 J cm−2, resulting in 1 μm 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 cm2 was produced with a defect density of less than 1 in 104. 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.