Laser Patterned Alumina Mask and Mask-less Dry Etch of Si for Light Trapping

Ultra-short 230 fs laser pulses of 515 nm wavelength were tightly focused into 700 nm focal spots and utilised in opening ~ 0.4 − 1 μm holes in alumina Al2O3 etch masks with 20-50 nm thickness. Such dielectric masks simplify fabrication of photonic crystal (PhC) light trapping patterns for the above-Lambertian performance of high efficiency solar cells. Conditions of laser ablation of transparent etch masks and effects sub-surface Si modifications were revealed by plasma etch- ing, numerical modeling, and minority carrier lifetime measurements. Mask-less patterning of Si is proposed using fs-laser direct writing for dry plasma etch of Si.