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Abstract: Laser-induced backside dry etching (LIBDE) is a promising technique for micro- and nanomachining of transparent materials. Although several experiments have already proved the suitability and effectiveness of the technique, there are several open questions concerning the etching mechanism and the concomitant processes. In this paper time-resolved light transmission investigations of etching process of fused silica are presented. 125nm thick silver coating was irradiated through the carrying 1mm thick fused silica plate by single pulses of a nanosecond KrF excimer laser. The applied fluences were 0.38, 0.71 and 1J/cm2. During the etching process the irradiated spots were illuminated by an electronically delayed nitrogen laser pumped dye laser. The delay between the pump and probe pulses was varied in the range of 0ns and 20μs. It was found that the transmitted probe beam intensity strongly depends on the applied delays and fluences. Scanning electron microscopy and energy dispersive X-ray spectrometry of the etched surface showed the existence of silver droplets and fragments on the illuminated surfaces and silver atoms built into the treated surface layer influencing the transmission behavior of the studied samples. [Copyright &y& Elsevier]

Abstract: Laser induced backside dry etching method (LIBDE) was developed – analogously to the well-known laser induced backside wet etching (LIBWE) technique – for the micromachining of transparent materials. In this procedure, the absorbing liquid applied during LIBWE was replaced with solid metal layers. Fused silica plates were used as transparent targets. These were coated with 15–120nm thick layers of different metals (silver, aluminium and copper). The absorbing films were irradiated by a nanosecond KrF excimer laser beam through the quartz plate. The applied fluence was varied in the 150–2000mJ/cm2 range, while the irradiated area was between 0.35 and 3.6mm2. At fluences above the threshold values, it was found that the metal layers were removed from the irradiated spots and the fused silica was etched at the same time. In our experiments, we investigated the dependence of the main parameters (etch rate and threshold) of LIBDE on the absorption of the different metal layers (silver, copper, aluminium), on the size of the irradiated area, on the film thickness and on the number of processing laser pulses. [Copyright &y& Elsevier]

Nanostructures exhibit a raised importance in manifold application fields like electronics and optics. The laser irradiation of thin metal layers allows the fabrication of metal nanostructures induced by a melting and deformation process where the resultant structures are dependent on the laser and metal layer parameters. However, for an optimization of this process a detailed physical understanding is necessary. Therefore, the dynamics of the metal layer deformation process was measured by time-dependent reflection and transmission as well as shadow graph measurements at different KrF excimer laser parameters (laser fluence and number of laser pulses) and metal layer thicknesses were used. Magnetron-sputtered thin chromium films with a thickness from 10 to 100 nm on fused silica substrates were studied. Based on the optical measurements the liquid phase lifetime of the metal was estimated and compared with the calculated lifetime using a simple thermodynamic model. [ABSTRACT FROM AUTHOR]

Abstract: Laser-induced backside dry etching (LIBDE) method has proved to be capable of micro- and nanomachining of transparent materials. In present study the applicability of this technique was tested to prepare surface structures that are suitable for surface enhanced Raman scattering (SERS) spectroscopy. Fused silica plates were coated with 16nm thick silver layer by pulsed laser deposition (PLD) method. The metal absorbing film was irradiated and removed by 10 ArF excimer laser (λ =193nm, FWHM=20ns) pulses perpendicularly through the transparent samples at 1200mJ/cm2 fluence. The remaining part of the silver coating was dissolved chemically shortly after the experiment using nitric acid. After this the etched holes were re-coated with 10, 20 and 40nm thick silver layers by PLD, respectively. SERS activity of the different parts of the holes was investigated by a Thermo Scientific DXR Raman Microscope at 785nm wavelength using 10−3 M aqueous solution of Rhodamin 6G as reference sample. SERS spectra were recorded at different areas of the holes having various roughness parameters. It was found that the intensity of the main peaks depended significantly on the surface morphology of the tested area and the thickness of its silver coating. [Copyright &y& Elsevier]

Experimental investigations and thermal calculations of laser induced backside wet etching (LIBWE) of fused silica are presented. Fused silica plates having 1 mm thickness were irradiated by an ArF excimer laser in the presence of liquid absorber. The absorbing liquids were naphthalene–methyl-methacrylate solutions with different concentrations (0, 0.21, 0.43, 0.85 and 1.71 mol/dm3). The absorption coefficients (α) of these solutions at the applied wavelength were determined using a plano–concave microcuvette. It was found that the value of α could be varied in the range of 39400–62300 cm−1 by the change of the naphthalene content. The dependence of the etch rate on both the absorption coefficient of the liquid absorbers and the applied fluence was studied. The etch depths were measured by an atomic force microscope. At 450 mJ/cm2 laser fluence, the etch rates were found to be between 13.3 and 22.2 nm/pulse depending on the actual absorption coefficient. In the next experiment the laser fluence was varied from 110 to 860 mJ/cm2 and the etch rate was found to vary between 4.7 and 49.5 nm/pulse when the concentration of the applied solution was constant 0.85 mol/dm3. The mechanism of the LIBWE can be explained in the first approximation by thermal effects and their consequences. We calculated the maximal depth of melted fused silica layer by numerical solution of the one-dimension heat flow equation taking into account the phase transformations of the liquid reagents and the fused silica target. These calculations proved that the thickness of the melted quartz layer depends linearly on both of the absorption coefficient of the liquid and the laser fluence. Our calculations give an upper estimation of the etch rate. On the basis of our results a possible interpretation of the LIBWE was suggested. [Copyright &y& Elsevier]