Microstructuring of silicon with femtosecond laser pulses

Abstract

We report that silicon surfaces develop an array of sharp conical spikes when irradiated with 500 laser pulses of 100-fs duration, 10-kJ/m2 fluence in 500-Torr SF6 or Cl2. The spikes are up to 40-μm tall, and taper to about 1-μm diam at the tip. Irradiation of silicon surfaces in N2, Ne, or vacuum creates structured surfaces, but does not create sharp conical spikes.

Femtosecond laser irradiation-induced infrared absorption on silicon surfaces

“…The absorptance at wavelength of 1.5 µm of the structured silicon is about 50% that is much higher than that of unstructured silicon substrate. In visible wavelengths part, the absorptance increment is mainly originated from the effect of multiple reflections, i.e., the incident light is reflected multiple times on the micro/ nanostructured surface and is absorbed by the silicon [7][8][9][10][11]. In near-infrared (NIR) region, there is an obvious drop in wavelength around 1.1 μm for the unstructured silicon absorptance curve, which is corresponding to the silicon band gap.…”

“…After sulfur atoms were doped into the silicon surface, the band gap of silicon was filled with the sulfur impurity energy states. As a result, the absorption for IR light with photon energy less than 1.1 eV can be obtained [3,7]. The IR absorption has potential applications for the IR optoelectronic devices, such as IR image detector.…”

“…If its wavelength is longer than 1.1 μm, i.e., its photon energy is less than the silicon band gap energy (1.1 eV), the light cannot be absorbed as it passes through silicon solid because the photon energy is not large enough to excite an electron to the conduction band from the valence band of the silicon solid. To improve the optical properties of silicon, femtosecond laser irradiation method has been applied to treat silicon surfaces [3,[7][8][9][10]. In order to increase the silicon absorption in the IR range, the microstructured silicon was formed with femtosecond laser irradiation on silicon surfaces in the presence of the background gas of SF 6 .…”

Overcoming the brittleness of glass through bio-inspiration and micro-architecture

“…Lasers have been widely used in the past to alter the structure of materials and to generate useful structures at small scale and with high accuracy: surface roughness, microfluidic devices or waveguides [36][37][38][39][40] . Here we used a 3D laser engraving technique, which consists of focusing a laser beam at predefined points by using a set of two mirrors and a focusing lens (Fig.…”

Saturation effects in femtosecond laser ablation of silicon-on-insulator

“…2,3 Silicon, as the most important element in today's semiconductor industry, has drawn a lot of attention from researchers to study both the fundamental response to ultrashort pulsed laser radiation [4][5][6][7] and its potential application in direct laser writing of photonic devices, 2 laser fabrication of nano-tips on thin silicon films, 8,9 direct laser amorphization of silicon, 10,11 and microspiked or black silicon. 12,13 Photonic crystal waveguide slabs are usually made out of silicon-on-insulator (SOI) by electron-beam and x-ray lithography, as well as focused ion beam (FIB) milling. 2 The emergence of femtosecond laser microfabrication makes sub diffraction-limited features directly fabricated on SOI wafer possible.…”