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High-quality, ultra-precise processing of surfaces is of high importance for high-tech industry and requires a good depth control of processing, a low roughness of the machined surface and as little as possible surface and subsurface damage but cannot be realized by laser ablation processes. Contrary, electron/ion beam, plasma processes and dry etching are utilized in microelectronics, optics and photonics. Here, we have demonstrated a laser-induced plasma (LIP) etching of single crystalline germanium by an optically pumped reactive plasma, resulting in high quality etching. A Ti:Sapphire laser (λ = 775 nm, EPulse/max. = 1 mJ, t = 150 fs, frep. = 1 kHz) has been used, after focusing with a 60 mm lens, for igniting a temporary plasma in a CF4/O2 gas at near atmospheric pressure. Typical etching rate of approximately ~ 100 nm / min and a surface roughness of less than 11 nm rms were found. The etching results were studied in dependence on laser pulse energy, etching time, and plasma – surface distance. The mechanism of the etching process is expected to be of chemical nature by the formation of volatile products from the chemical reaction of laser plasma activated species with the germanium surface. This proposed laser etching process can provide new processing capabilities of materials for ultra—high precision laser machining of semiconducting materials as can applied for infrared optics machining.

Ultrahigh-precision machining of glass is indispensable for optical component fabrication and therefore for applications. In this regard, plasma jet assisted chemical etching technologies enable new fabrication processes for enhanced optical functionalities due to their deterministic localized machining capabilities. This technique has been successfully applied to fused silica and silicon. However, applications require specific glass properties are related to complex material compositions of the glass. Hence, reactive plasma etching of these optical glasses is a challenging task. For instance, etching of metal oxide containing glass like N-BK7 by a fluorine-based reactive atmospheric plasma jet (RAPJ) exhibits currently limitations due to the formation of non-volatile reaction products that remain on the glass surface as a layer. Therefore, a procedure consisting of RAPJ etching and laser ablation is proposed for the machining of N-BK7. The capability of laser-based removal of residual layers is compared to water-based solving of the residual layer. After RAPJ etching of N-BK7 using a CF4–O2 gas mixture with an average microwave power of 16 W, the samples are cleaned either by a water-based solvent or by the ablation with a nanosecond-pulsed ultraviolet laser. The laser irradiation with fluences of 2.8 J/cm2 results in a localized removal of the residual layer. It is demonstrated that the roughness of the laser-cleaned N-BK7 surface is similarly low as solvent-based cleaned samples but the pulsed laser enhanced cleaning allows a dry processing at atmospheric pressure as well as a localized processing with a high lateral resolution.

Dry etching is a prevalent technique for pattern transfer and material removal in microelectronics, optics and photonics due to its high precision material removal with low surface and subsurface damage. These processes, including reactive ion etching (RIE) and plasma etching (PE), are performed at vacuum conditions and provide high selectivity and vertical side wall etched patterns but create high costs and efforts in maintenance due to the required machinery. In contrast to electrically generated plasmas, laser-induced micro plasmas are controllable sources of reactive species in gases at atmospheric pressure that can be used for dry etching of materials. In the present study, we have demonstrated the laser-induced plasma etching of monocrystalline silicon. A Ti:Sapphire laser has been used for igniting an optically pumped plasma in a CF4/O2 gas mixture near atmospheric pressure. The influence of process parameters, like substrate temperature, O2 concentration, plasma-surface distance, etching duration, pulse energy and crystal orientation on etching rate and surface morphology has been investigated. Typical etching rates of 2–12 µm x min−1 can be achieved by varying mentioned parameters with a decreasing etching rate during the process. Different morphologies can be observed due to the parameters set, smooth as well as rough surfaces or even inverted pyramids. The presented etching method provides an approach for precise machining of silicon surfaces with good surface qualities near atmospheric pressure and sufficiently high material removal rates for ultraprecise surface machining.

High-quality, low-defect laser machining of dielectric materials remains challenging due to the high energy densities required for inducing the physical processes of laser ablation. Therefore, experiments were performed to demonstrate the laser-induced frontside etching (LIFE) of silicon by nanosecond laser pulses at a wavelength of 1550 nm, utilizing a thin chromium layer as the absorber. Etching was found at a fluence range from 200 to 700 mJ/cm², where the etched surfaces were smooth in the center (5 to 80 nm rms). The etching process was accompanied by incubation as well as saturation effects. At a fluence of 280 mJ/cm², an averaged etching rate of about 0.05 nm/pulse was determined for a high number of laser pulses (N > 1000). At the edges where the fluence was below the etching threshold of about 200 mJ/cm², chromium film melting and the formation of different kinds of laser-induced periodic surface structures (LIPSS) were observed. The LIFE was accompanied by different surface modifications. The optical absorption of silicon likely increased due to the incorporation of chromium into the silicon and the formed defects near the surface. Further, LIPSS were observed at fluences near the threshold of laser etching. In particular, the formation of regular linear ripples with a period of approximately 1.52 µm was observed. The morphological characteristics of the ripples suggest that the mechanism was related to surface scattering at surface features or small ripples and the hydrodynamic instabilities of the molten silicon. In addition, outside the etching track, periodic but nonlinear LIPSS were observed in the chromium film. These hexagonal arranged dot-like patterns had a period of around 440 nm. It is suggested that the hexagonal dot-like patterns resulted from the multi-pulse irradiation and the sequential stress relaxation in the chromium film below the melting point of chromium during spot movement.

High-quality submicron pattern formation in dielectrics by lasers is challenging, in particular with regard to large areas. Self-assembly and self-organization mechanisms, which arise from the interaction of the laser photons with the material of the sample, can provide conditions for efficient micron patterning of large surface areas. This study demonstrates the formation of submicron ripples in fused silica (SiO2) by nanosecond laser irradiation, which extends the category of lasers capable of the controllable manufacturing of laser-induced surface structures (LIPSS). A newly designed layer system was deposited on the surface of samples, comprising, on top of the dielectric substrate, an interlayer, an absorber, and a confinement layer. The samples were irradiated though the dielectric substrate with single nanosecond (λ = 1064) nm laser pulses. It was found that the period of the LIPSS can be tuned by changing the nanosecond laser energy, the confinement strength, and the laser pulse length from 5 ns to 25 ns. LIPSS with periods in the range of 400–600 nm, with a depth of up to 140 nm and with an orientation perpendicular to the polarization direction of the laser light, were found experimentally. The design of the sample finally enables an intra-pulse modification of the dielectric surface that provides temporal conditions near the dielectric substrate surface for surface plasmon polaritron (SPP) generation. The proposed mechanism of LIPSS formation thus comprises the ablation of the absorber layer and a plasma formation confined between the substrate surface and the confinement layer. This process causes a modification of the substrate surface. In consequence, temporary SPP generation occurs at the modified SiO2 surface, resulting in a lateral intensity modulation of the nanosecond laser beam within the pulse duration. This lateral intensity modulation of the laser pulse causes localized variation of the ablation, which finally results in the LIPSS found. The experimentally observed dependencies of the LIPSS period on the pulse energy, the confinement layer thickness, and the pulse length can be explained with the proposed model. The findings of this work provide a method of enabling local adjustment of the LIPSS period, which can be used in applications such as writing hierarchical structures of variable sizes.

The fabrication of sub-micron and nanopatterns at large surface areas by lasers is still a challenge, but the use of laser-induced, self-organized processes provides a promising approach. Here, the guided formation of nanodroplets ordered in two directions during irradiation of 15 nm thick molybdenum (Mo) film on Al2O3 (1–102) substrate with a fibre laser having a wavelength of 1064 nm and selectable pulse duration from 5 to 600 ns is demonstrated. The two-step process comprises laser-induced ripple formation and remelting of the ripples for nanodroplet generation. The ripples with period of ∼1.1 µm are oriented perpendicularly to the laser polarization. The ripples are fabricated by irradiation with 46 laser pulses with a duration between 25 to 100 ns and fluences of 0.3 to 1.3 J/cm², respectively. After a subsequent laser irradiation with 10 pulses at fluences above 1 J/cm² and a pulse duration of 100 ns, two kinds of Mo droplets are observed: (i) large, periodically ordered droplets with a diameter of ∼360 nm and a distance along and orthogonal to the laser-generated ripples of about 1 µm and 1.1 µm, respectively, in addition to (ii) small, less-ordered droplets with a size of about 120 nm localized in the former ripple valleys.

The laser structuring of CIGS (copper indium gallium (di)selenide) solar cell material without influence and damaging the functionality of the active layer is a challenge for laser methods The shock-wave-induced thin-film delamination (SWIFD) process allows structuring without thermal modifications due to a spatial separation of the laser absorption from the functional layer removal process. In the present study, SWIFD structuring of CIGS solar cell stacks was investigated. The rear side of the polyimide was irradiated with a KrF-Excimer laser. The laser-induced ablation process generates a traverse shock wave, and the interaction of the shock wave with the layer-substrate interface results in a delamination process. The effect of a water confinement on the SWIFD process was studied where the rear side of the substrate was covered with a ∼2 mm thick water layer. The resultant surface morphology was analysed and discussed. At a sufficient number of laser pulses N and laser fluences Φ, the CIGS layer can be selectively removed from the Mo back contact. The water confinement, as well as the increasing laser beam size A0 and N, results in the reduction of the necessary minimal laser fluence Φth. Further, the delaminated CIGS area increased with increasing Φ, N, and A0.

The machining of optical glass materials with beam technologies enables novel fabrication processes for innovative optical elements with freeform surfaces. However, the complex material composition of optical glass such as N-BK7® is challenging for non-abrasive, pure chemical machining. N-BK7 can be machined utilizing reactive atmospheric plasma jet (RAPJ) etching. However, the etching mechanism results in process-inherent surface composition changes that limit potential applications of RAPJ-machining. A residues layer is formed which causes a temporally changing etching behavior and an increased roughness. Therefore, a process sequence of utilizing RAPJ etching and laser cleaning is proposed and demonstrated that enables to overcome the stated limitations. In this cyclic sequence, N-BK7 optical glass is etched first with a fluorine-containing reactive atmospheric plasma jet resulting in an etched but also residues-modified surface. Thereafter, the residues are removed by pulsed UV laser irradiation without ablation of the glass. This combined laser-enhanced reactive plasma jet etching allows etching of optical glass with a higher average etching rate and smoother machined surfaces.

The well-reproducible, fast and cost-effective nanostructuring is a big challenge for laser methods. The laser nanostructuring of fused silica assisted by chromium nanotriangles was studied using a KrF excimer laser (λ = 248 nm, Δtp = 25 ns, top hat beam profile). Therefore, a fused silica substrate was covered with periodically ordered polystyrene (PS) spheres with a diameter of 1.59 μm. Subsequently, this system was covered with 30 nm chromium by electron beam evaporation. Afterwards the PS spheres were removed and the bare and resultant periodic Cr triangles were irradiated. The laser irradiation with high laser fluences resulted in a removal of the chromium and in localized modifications of the fused silica like a localized ablation of the fused silica. The resultant structures were studied by scanning electron (SEM) and atomic force microscopy (AFM) as well as the surface composition was analysed by energy-dispersive X-ray spectroscopy (EDX). The laser process allows the production of well-defined periodic hole structures into the fused silica surface where the resultant surface structure depends on the laser parameters. The multi-pulse irradiation of the Cr/SiO2 sample with moderate laser fluences (Φ ∼ 650 mJ/cm2) allows the fabrication of periodic pyramidal-like structures (depth Δz = 130 nm).

Central to the use of Ge-Sb-Te based phase-change materials for data storage applications is their crystallization capability since it determines memory writing time. Although being intensively studied to identify intrinsic limits and develop strategies to enhance memory performance, the crystallization process in these materials is still not fully explored. Therefore, this study focuses on the determination of crystal growth dynamics in an epitaxial phase-change material thin film model system offering the advantage of high crystalline quality and application-relevant sizing. By introducing a method that combines time-resolved reflectivity measurements with high-resolution scanning transmission electron microscopy, crystal growth velocities upon fast cooling after single ns-laser pulse irradiation of the prototypical phase-change material Ge2Sb2Te5 are determined. As a result, an increase in crystal growth velocity from 0.4 to 1.7 m/s with increasing laser fluence is observed with a maximum rate of 1.7 m/s as the upper detectable limit of the studied material.

Metal surfaces can be nanostructured by laser irradiation making use of different effects ranging from thin film generation to nanostructures formation. Here, the colorization of pure nickel surfaces by nanosecond laser irradiation in air is demonstrated and studied in detail. Correlations between chromaticity coordinates and laser-processing parameter show that the accumulated fluence is the dominating factor in creation of a specific colored surface. The color of the laser-irradiated surfaces shows both angle-dependent and angle-independent in reliance on the processing conditions. The examination of the laser-colored surface demonstrates that lateral and vertical organized, laser-induced structures with nano-, micro-, and mesoscopic scales can be found simultaneously which contribute to the colorization in a particular manner. A comprehensive analysis of the processes involved in the color formation at nickel was performed by examining the surfaces by SEM, reflectometry, XPS, and XRD to verify the multi-process mechanisms of color formation. The most saturated colors result from interference effects within the redeposited layers. It was found that controlling the hatching distance applying optimized laser fluence enables a wider color range and allows a very precise setting of the color. Based on the extracted laser-processing parameters, the surface coloration of arbitrary pattern with desired optical properties becomes practicable, and nanosecond laser color marking can, therefore, be expanded to potentially new applications.

Self-organized processes are of special interest for the laser-induced nanostructuring of surfaces. In this study we combined two self-organized processes: the microsphere lithography and the molten phase transformation for the nanostructuring of dielectrics. A fused silica substrate was covered with periodically ordered polystyrene (PS) spheres and the system was subsequently covered with 30 nm chromium. Afterwards the PS spheres were removed and the bare and resultant periodic Cr triangles were irradiated in two steps using a KrF excimer laser. First step: A low laser fluence treatment results in a melting and shape transformation of the triangles. Second step: A high laser fluence treatment of the pre-treated surface results in a nanostructuring of the dielectric surface (and removal of the metal). The surface topography was studied by scanning electron microscopy. Furthermore, the different steps were simulated and compared with the experimental results.

Laser-induced etching techniques feature several unique characteristics that enable ultraprecise machining of transparent materials. However, LIBDE (laser-induced back side dry etching) and LIBWE (laser-induced back side wet etching) are preferentially studied due to experimental feasibilities either using a very thin or a bulk absorber at the rear side of the transparent material. This study aims to fill the gap by examining the thickness dependence of the absorbing material. Multi-pulse-LIBDE (MP-LIBDE) of fused silica using different thick photoresist absorber layers ( d L = 0.2–11.7 μm) was performed with a KrF excimer laser ( λ = 248 nm, t p ≈ 20 ns). The influence of several experimental parameters, such as laser fluence, pulse number, film thickness, on the ablation morphology and the etching rate were investigated. Especially at moderate fluences ( F = 0.7–1.5 J/cm 2 ) MP-LIBDE and LIBWE show several similar process characteristics such as the etching rate dependence on the laser fluence and the pulse number with a typical etching rate of approx. 12 nm at 1 J/cm 2 . However, the specific etching rate values depend on the absorber layer thickness, for instance. The morphology of the etched surface is smooth with a roughness of below 5 nm rms. Further, the modification of the surface has been observed and will be discussed in relation to the multi-pulse laser etching mechanism.

In this paper, the authors report a method for continuous trench micromachining on polymethylmethacrylate (PMMA). Visible laser-induced backside wet etching (v-LIBWE) on PMMA using a potassium permanganate (KMnO4)-based absorber liquid was studied. PMMA is widely used in microfluidic devices for chemical and biological applications. Conventional micromachining of channels in the PMMA substrate using CO2 lasers achieves the smallest feature of approximately 85 μm. In this study, a continuous 12 μm-wide trench etching on PMMA was achievable by v-LIBWE using a 532 nm nanosecond pulsed laser. The etching threshold is ∼10 J/cm2, which corresponds to the average power of 58 mW for the repetition rate of 10 kHz. The authors also determined that the lowest scanning speed of 2 mm/s was necessary for the v-LIBWE of PMMA to generate the crack-free surface. Our study provides a new perspective and a convenient approach for the micromachining of the polymer substrate using v-LIBWE.

LIPSS (Laser Induced Periodic Surface Structures) formation at pre-patterned photoresist films was investigated using a partial polarized excimer laser beam (λ = 248 nm, tp = 20 ns). These line and dot pre-patterns were fabricated by the lithography in a photoresist films and have widths of 1–3 µm and 1–5 µm, respectively. LIPSS with a period of 195 nm and a direction along the laser polarization were formed at very low laser fluences (threshold 7 mJ/cm2) and high pulse numbers. With increasing fluence first LIPSS appear at the top surface, extend than to the sidewalls and finally at fluences higher than (F ∼ 17 mJ/cm2) found only at the sidewalls while the top surface is smooth. The height of the LIPSS increases with the pulse number and saturates at approximately 65 nm. The degree of LIPSS order depends on the alignment of the laser polarization to the pattern direction and shape. For parallel alignment of polarization and pattern edges, a high degree of order was found over several hundreds of micrometers along the stripe structure. This order mechanism can accept alignment mismatches up to 10°. This approach may serve as a general guideline for forming well-ordered LIPSS on large areas.

Electrochemical metallization memories have received much attention as candidates for next generation non-volatile memory applications, due to their fast switching speed, simple structure, high scalability and low energy consumption. Chalcogenide compounds like Ge–Sb–Te-based materials are extensively studied solid electrolytes for such devices and considered within the most promising candidates. In this work, the influence of different electrode materials on bipolar resistive switching characteristics of amorphous Ge–Sb–Te thin films with close composition to 2:2:5, prepared by pulsed laser deposition, is studied. Detailed investigations by current-voltage measurements, secondary ion mass spectrometry and cross-sectional transmission electron microscopy in conjunction with energy-dispersive x-ray spectroscopy are presented. Depending on the utilized electrode material, analog switching (Cu, Ag, Ti), digital switching (Co, Cr, Ta, Al) or no switching (Pt, Au and Cr-CrO x ) occurs. This work shows that the switching behavior of Ge–Sb–Te strongly depends on the solubility and reactivity of the electrode material.

Large area, high speed, nanopatterning of surfaces by laser ablation is challenging due to the required high accuracy of the optical and mechanical systems fulfilling the precision of nanopatterning process. Utilization of self-organization approaches can provide an alternative decoupling spot precision and field of machining. The laser-induced front side etching (LIFE) and laser-induced back side dry etching (LIBDE) of fused silica were studied using single and double flash nanosecond laser pulses with a wavelength of 532 nm where the time delay ∆τ of the double flash laser pulses was adjusted from ∼50 ns to ∼10 μs. The fused silica can be etched at both processes assisted by a 10 nm chromium layer where the etching depth ∆z at single flash laser pulses is linear to the laser fluence and independent on the number of laser pulses, from 2 to 12 J/cm2, it is ∆z = δLIFE/LIBDE ⋅ Φ with δLIFE ∼ 16 nm/(J/cm2) and δLIBDE ∼ 5.2 nm/(J/cm2) ∼ 3 ⋅ δLIFE. At double flash laser pulses, the ∆z is dependent on the time delay ∆τ of the laser pulses and the ∆z slightly increased at decreasing ∆τ. Furthermore, the surface nanostructuring of fused silica using IPSM-LIFE (LIFE using in-situ pre-structured metal layer) method with a single double flash laser pulse was tested. The first pulse of the double flash results in a melting of the metal layer. The surface tension of the liquid metal layer tends in a droplet formation process and dewetting process, respectively. If the liquid phase life time ∆tLF is smaller than the droplet formation time the metal can be "frozen" in an intermediated state like metal bare structures. The second laser treatment results in a evaporation of the metal and in a partial evaporation and melting of the fused silica surface, where the resultant structures in the fused silica surface are dependent on the lateral geometry of the pre-structured metal layer. A successful IPSM-LIFE structuring could be achieved assisted by a 20 nm molybdenum layer at ∆τ ≥ 174 ns. That path the way for the high speed ultra-fast nanostructuring of dielectric surfaces by self-organizing processes. The different surface structures were analyzed by scanning electron microscopy (SEM) and white light interferometry (WLI).

The fast laser drilling of dielectric surfaces with hole diameters in the sub-μm range and a high aspect ratio is a challenge for laser methods. In this study, a novel laser structuring method for the production of randomly and periodically distributed holes in a fused silica surface will be presented using a self-assembling process. A fused silica surface was covered with a 10 nm thick magnetron-sputtered molybdenum film. The metal film was irradiated by a KrF excimer laser (wavelength λ = 248 nm, pulse duration Δ t p = 25 ns) with low laser fluences ( Φ 2 ) and the laser-induced heating resulting in a melting of the metal film and finally in a self-assembled formation of randomly distributed metal droplets due to the surface tension of the metal liquid phase using a top hat beam profile. Furthermore, the usage of a periodically modulated laser beam profile allows the fabrication of periodically distributed droplet pattern. The multi-pulse irradiation of the laser-generated metal droplets with higher laser fluences results in a stepwise evaporation of the metal and in a partial evaporation of the fused silica near the metal droplets. Finally, the laser-induced stepwise evaporation process results in a formation of cone-like holes in the fused silica surface where the resultant holes are dependent on the size of the generated metal droplets and on the laser parameters. The “drilling” process allows the fabrication of holes with a depth up to 1 μm at a hole radius in the sub-μm range. Furthermore, the hole density can be adjusted by the laser fluence where a hole density up to ∼1.3 μm −2 can be achieved. Furthermore, the process was simulated by finite element method using a simple thermodynamic model and the theoretical results were compared with the experimental findings.

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.

Three-dimensional micro- and nanostructuring of metal surfaces is requested due to the ongoing miniaturization and is therefore of great interest for microelectromechanical systems (MEMS), micro-optics, and precision machining. One promising fabrication method for low-cost, high-quality micro- and nanostructured metal surfaces is laser microembossing. Recent experimental results of laser embossing of submicron structures are presented to discuss the processes and characteristics of laser micro-embossing. Basically, laser embossing shows almost no modification caused by thermal effects of the laser pulses. Therefore, almost no burr, recast droplets, or near-surface material modifications have been found at the embossed structures. The elastoplastic deformation at incomplete submicron pattern embossing is probably the reason for the differences between the replicated pattern and the master structures. Unintended patterns like scratches and satellite patterns may occur in the case of multi-pulse laser embossing without carefully fixing the sample and master positions.

Laser-induced back side wet and dry etching (LIBWE and LIBDE) were developed for precise etching of transparent materials. However, LIBWE and LIBDE feature characteristics such as incubation effects and etching depth saturation, respectively, that can be unfavourable for applications in ultra-precision machining. Therefore, the techniques of LIBDE and LIBWE were combined in such a manner that the dielectric material was supplied with a thin-film-modified surface before etching by LIBWE. With this goal fused silica samples were covered with a thin chromium film for surface modification before LIBWE etching in acetone with 25 ns KrF excimer laser pulses. Etching with the first pulse was observed. At laser fluences adequate for hydrocarbon LIBWE (1 J/cm 2 ) the etching rate for LIBDE is much higher than for LIBWE. In consequence, the etching rate decreases with increasing pulse number up to ten. The surface morphology depends very strong on the laser fluence and the pulse number. Smooth etchings were achieved at high fluences and low pulse numbers. However, uneven, wavy etched surfaces and micron pattern formation were observed for moderate and low laser fluences.

The optimization of laser scribing for the interconnection of CIGS solar cells is a current focus of laser process development. In addition to the geometry of the laser scribes the impact of the laser patterning to the electrical properties of the solar cells has to be optimized with regards to the scribing process and the laser sources. In-process measurements provide an approach for reliable evaluation of the electrical characteristics. In particular, the parallel resistanceR p that was calculated from the measured I–V curves was measured in dependence on the scribing parameters of a short-pulsed ns laser in comparison to a standard ps laser at a wavelength of 1.06 μm. With low pulse overlap of ∼20% a reduction of R p to 2/3 of the initial value has been achieved for ns laser pulses. In comparison to ps laser slightly more defects were observed at the investigated parameter range.

Laser patterning of thin films is essential for the future development of flexible electronic devices. The damage-free scribing of thermally sensitive thin films such as copper–indium–gallium diselenide (CIGS) that is required for solar module fabrication by integrated interconnections is still challenging. In this study a new approach for non-thermal, damage-free scribing of CIGS films on polyimide foil is proposed and demonstrated. In contrast to the usually used direct laser ablation of the thin-film stack, laser ablation of the polyimide carrier foil at laser fluences higher than 3 J/cm2 is utilized to achieve CIGS film delamination and thus the patterning of the thin film. The edges of the patterned CIGS films do not show typical laser-ablation-induced modifications like melting, debris contamination, or crack formation. The mechanism of the thin-film removal is of non-thermal origin and is probably due to stress formation at the CIGS/Mo interface resulting from secondary processes of polyimide laser ablation like shock-wave formation or local sample deformation.

Nanostructures have a widespread field of applications and are of growing industrial importance. However, the economic fabrication of nanostructures poses a critical challenge. In this work, a fundamental research of a laser-induced surface nanostructuring of fused silica using the dynamic self-assembling structure formation in metal layers is presented. This method may offer promising opportunities for nanostructuring of dielectrics. This new approach is demonstrated by the formation of randomly distributed concentric nanostructures into fused silica. The irradiation of chromium-covered fused silica samples with a KrF excimer laser results in melting, partial ablation, restructuring, and resolidification of both the metal layer and the dielectric surface. In this way, concentric circular structures into the dielectric were formed with dimensions that can be controlled by the laser fluence Φ and by the pulse number N . The distance of the concentric rings increases with increasing laser fluence. The experimental results were compared with simulated structure dimensions taking into account the heat equation and the Navier–Stokes equation. Despite the currently applied decoupled approach for the simulations, i.e. separating the heat equation and the fluid flow, a good agreement of simulation results with experimental data was achieved.

Laser-induced front side etching (LIFE) is a method for laser etching of transparent materials using thin absorber layers. In this study, chromium layers were applied as absorber for etching trenches in fused silica with femtosecond Ti:sapphire laser radiation ( λ = 780 nm, Δ t p = 150 fs, f = 1 kHz). The etching process of fused silica is studied in dependence on the laser fluence, the laser pulse numbers as well as metal absorber layer thicknesses. Especially the influence of the varied parameters on the surface morphology, the etching depth, and the surface modification is presented and discussed. The etched trenches were analyzed with white light interferometry. A fluence window from 0.5 to 2.5 J/cm 2 for the LIFE process of fused silica with a single laser pulse using a metal layer with a thickness from 5 to 50 nm was found. The measured maximum etching depth of approximately 100 nm suggests that the LIFE process is appropriated for precision machining. The attempt to simulate the fs laser LIFE process by a thermodynamic model was moderate successfully and exhibits significant differences within the experimental results.

Laser technology is of increasing interest for the improvement of photovoltaic generators also for mass production. Copper–indium–gallium–diselenide (CIGS) thin film solar cells on flexible polyimide (PI) foil have great potential for specific applications requiring mechanical flexibility. To reduce the dead area of solar modules especially that of the serial interconnection shingling of the solar cells is one encouraging approach. The former developed back side opening process is utilized for via preparation to realize the serial interconnection at the rear side of the solar cells. Arrays of square vias that were fabricated into the polyimide foil by UV laser ablation were filled with a silver-based conductive adhesive for realizing the electrical and mechanical interconnection. Contact resistance of the silver-based adhesive to the solar cell back contact of less than 0.2 Ω mm2 has been measured. Shingled CIGS modules with a size of 100 cm2 having an open circuit voltage of 2.3 V and a short circuit current of more than 500 mA demonstrate the great potential of this interconnection approach for flexible electronic applications.

The nanostructuring of dielectrics is a big challenge for laser patterning methods. In this study a novel laser structuring method for the fabrication of randomly distributed nanostructures, called laser-induced front side etching using in situ pre-structured metal layers (IPSM-LIFE), is presented. The pulsed laser irradiation of a thin metal film deposited onto a dielectric substrate with fluences below the ablation threshold results in the formation of randomly distributed metal structures by self-assembly processes. Further pulsed laser irradiation of these metal structures with higher or equal laser fluences causes the formation of complex patterns at the surface of the dielectric due to localized ablation and melting processes of the dielectric surface induced by the absorption of the laser energy by the metal structures and the local energy transfer into the dielectric surface.

In the recent decades the importance of nanostructured surfaces has rapidly grown due to the large range of applications of these improved surfaces in the fields of, e.g. optics, biology, and microelectromechanical systems. However, a flexible and low-cost manufacturing process which is suitable for large-scale solid metal surfaces is not introduced yet. Laser microembossing is a nonthermal manufacturing technology which enables the direct fabrication of three-dimensional microand nanostructures. In the present study nanostructures with periods down to 82 nm were successfully replicated from a fused silica master mould into a copper foil surface by laser embossing. The replicated structures were examined by atomic force microscopy. The results show that the replicated structures have a high resolution and the shape of the replicated structures is similar to the master mould.

Three-dimensional micro and nanostructuring of metal surfaces is of great interest due to the ongoing miniaturization and increasing complexity of functional surface structures for microoptics, micromechanic, or even microelectromechanical systems (MEMS). One promising fabrication method for micro and nanostructured metal surfaces is laser embossing. Laser embossing is a flexible nonthermal process, which enables three-dimensional microforming of thin metal sheets. In this paper, an improved embossing process is proposed and demonstrated, which is based on the reverse arrangement of master and workpiece enabling the embossing into thick metallic samples by an advanced laser embossing methodology. The influence of the laser fluence and the pulse number on the height of the embossed structures is presented for a square micron pattern. In order to investigate the size effect and capability of submicron pattering of metallic surfaces by inverse laser embossing a sub-micrometer 2D-sine grating was formed in a copper surface. The topography of the structured surfaces was investigated by a scanning electron and scanning force microscopy. The cross section shape of the replica correlates well with the inverse master within the embossed depth; the full depth could not be embossed due to the laser fluence limitations.

The laser assisted micro structuring of thin films especially for electronic applications without influence the functionality of the multi-layer system e.g. due to melting products is a challenge for the laser micro machining techniques. The P2 scribing of copper indium gallium selenide (CIGS) solar cells on stainless steel carrier foil was studied using shockwave- induced film delamination (SWIFD) patterning. The delamination process is induced by a shock wave generated by the laser ablation of the rear side of the carrier foil. In the present study UV nanosecond laser pulses provided by a KrF excimer laser were used to induce the SWIFD process. The morphology and size of the achieved thin-film structures were studied in dependence on various laser irradiation parameters by optical and scanning electron microscopy (SEM). Furthermore, the materials composition after the laser patterning was analyzed by energy dispersive X-ray spectroscopy (EDX). The temporal sequences of processes involved in the SWIFD process were analyzed with high speed shadowgraph experiments. The results of the present study shows that in dependence on the laser parameter used a large process window exist in which the CIGS thin film can be removed from the substrate without visible thermal modification of the CIGS thin film.

Nanostructures have a widespread field of applications. The structuring of sapphire assisted by a nanosecond laserinduced self-organized molten molybdenum layer deformation process was studied. At low laser fluence the irradiation of a thin metal layer on dielectric surface results in a melting and nanostructuring of the metal layer and partially of the dielectric surface. Furthermore, a subsequent high laser fluence treatment of the metal nanostructures results in different features: (i) pattern transfer, (ii) self-organized surface nanostructuring, and (iii) nanodrilling. (i) Pattern transfer: The irradiation of the pre-structured metal layer with high laser fluences allows the transfer of the lateral geometry of the metal nanostructures into the dielectric surface. (ii) Self-organized surface nanostructuring: The multi-pulse irradiation of the metal layer/dielectric system with moderate laser fluences results in a selforganized nanostructuring of the dielectric surface. (iii) Nanodrilling: The multi-pulse low laser fluence irradiation of the metal layer results in the formation of metal droplets and a further high fluence irradiation of the laser-generated metal droplets results in a stepwise evaporation of the metal and in a partial evaporation of the dielectric and, finally, in the formation of cone-like holes. The resultant structures were investigated by scanning electron microscopy (SEM).

Laser-induced front side (LIFE) and back side etching (LIBDE) are methods for nanometer-precision laser etching of transparent materials using thin absorber layers. The etching behaviour of fused silica at a laser wavelength of 248 nm (KrF) and 351 nm (XeF excimer laser) with a pulse duration of 25 ns using a chromium absorber layer was analysed and compared for front and back side etching geometry. For both wavelengths as well as for both processes the etching depth d increases almost linearly in dependence on the laser fluence (it is: d ≈ δ *( Φ − Φ th )). The etching depth at the same laser fluence is higher for 248 nm compared to 351 nm as well as for back side etching compared to the front side etching process (LIFE: δ (248 nm) = 20 nm/(J/cm 2 ), δ (351 nm) = 15 nm/(J/cm 2 ), LIBDE: δ (248 nm) = 38 nm/(J/cm 2 ), δ (351 nm) = 8 nm/(J/cm 2 ) with Φ th,m from 0.3 to 2.65 J/cm 2 ). Furthermore, the measured depths were evaluated with the estimated etching depth calculated by a thermal model. The simple thermodynamic model allows a good qualitative description of the etching depth behaviour; however, the model does not allow the quantitative calculation of the etching depth.

Laser patterning of thin-film solar cells is essential to perform external serial and integrated monolithic interconnections for module application and has recently received increasing attention. Current investigations show, however, that the efficiency of thin-film Cu(In,Ga)Se2 (CIGS) modules is reduced due to laser scribing also with ultrashort laser pulses. Hence, to investigate the reasons of the laser-induced material modifications, thin-film CIGS solar cells were laser-scribed with femto- and picosecond laser pulses using different scribing procedures and laser processing parameters. Besides standard electrical current voltage (I–V) measurements, additional electrical and optical analysis were performed such as laser beam-induced current (LBIC), dark lock-in thermography (DLIT), and electroluminescence (EL) measurements to characterize and localize electrical losses due to material removal/modifications at the scribes that effecting the electrical solar cell properties. Both localized as well as distributed shunts were found at laser scribe edges whereas the laser spot intensity distribution affecting the shunt formation. Already laser irradiation below the ablation threshold of the TCO film causes material modification inside the thin film solar cell stack resulting in shunt formation as a result of materials melting near the TCO/CIGS interface that probably induces the damage of the pn-junction.

Laser-induced front side etching (LIFE) is a method for laser etching of transparent materials using thin absorber layers, e.g., for precision engineering or even optical applications. Aluminium, chromium, molybdenum, silver as well as titanium with various layer thicknesses (5–100 nm) were applied as absorber for etching trenches in fused silica with nanosecond XeF excimer laser radiation. The sample surfaces were processed at laser fluences up to 10 J/cm 2 and laser pulse numbers from 1 to 10 pulses. A linear growth of the etching depth at rising laser fluence was found. The film thickness dependency is more complex and mostly influenced by the optical properties of the thin metal films. The influence of the laser fluence, the number of pulses, the absorber material as well as the absorber layer thickness on the etching process, the etching depth, and the surface modification were presented and discussed. A simple model is given that allows the discussion of the etching depth in dependency on the laser fluence and the metal film thickness. The measurements represented a good agreement with the calculated results by a thermal model. The LIFE method allows nm-precision etching of fused silica with etching depths up to 150 nm.

Micro- and submicrometer structures have been transferred from nickel foils into solid copper surfaces by laser microembossing. The developed arrangement for laser microembossing allows a large-area replication using multi- pulse laser scanning scheme, guaranties a low contamination of the embossed surface and enables the utilization of thick workpieces. In the micrometer range the replicated patterns feature a high accuracy regarding the shape. A significant difference between the master and the replication pattern could be observed for the laser embossing of submicrometer patterns. In conclusion, the results show that the proposed laser embossing process is a promising method with a number of applications in microengineering.

In consequence of high interest in micro- and nanomachining of transparent materials by laser irradiation, studies on the mechanism of laser-induced backside wet etching (LIBWE) are presented. To reveal the role of the surface modification due to LIBWE the backside ablation (BSA) of LIBWE-modified fused silica (mFS) surfaces at 248 nm was investigated. The threshold fluence and the etch rate of BSA are similar to that of LIBWE and amount ∼250 mJ/cm2 and 30 nm for 1 J/cm2, respectively. The sample transmission after backside ablation of mFS increases and proves the decreasing thickness of the absorbing layer. Time-resolved reflection studies at LIBWE and BSA of mFS show similar patterns in the backside reflection that can be assigned an ablation process as the comparison to thin polymer films demonstrates. By fitting the BSA data to an exponential decay absorption model a modification depth and a surface absorption of about 38 nm and α S ∼1.3×107 m−1 were calculated, respectively. In conclusion of the results a new model for LIBWE is proposed.

Nanostructuring of dielectric surfaces has a widespread field of applications. In this work the recently introduced laser method validates this novel concept for complex nanostructuring of dielectric surfaces. This concept combines the mechanism of self-assembly of metal films due to laser irradiation with the concept of laser-assisted transfer of these patterns into the underlying material. The present work focuses on pattern formation in fused silica near the border of the laser spot, where distorted nested ring-like patterns were found in contrast to concentric ring patterns at homogeneous laser irradiation. For the experiments a lateral homogeneous spot of a KrF excimer laser (λ = 248 nm) and a Gaussian beam Yb fiber laser (λ = 1064 nm) was used for irradiation of a thin chromium layer onto fused silica resulting in the formation of different ring structures into the fused silica surface. The obtained structures were analysed by AFM and SEM. It is found that the mechanism comprises laser-induced metal film melting, contraction of the molten metal, and successive transfer of the metal hole geometry to the fused silica. Simulations taking into account the heat and the Navier-Stokes equations were compared with the experimental results. A good agreement of simulation results with experimental data was found. These first results demonstrate that the variation of the laser beam profile allows the local control of the melt dynamics which causes changes of the shape and the size of the ring patterns. Hence, a light-controlled self-assembly is feasible.

Micro- and nanostructures exhibit a growing commercial interest where a fast, cost-effective, and large-area production is attainable. Laser methods have a great potential for the easy fabrication of surface structures into flexible polymer foils like polyimide (PI). In this study two different concepts for the structuring of polymer foils using a KrF excimer laser were tested and compared: the laser-induced ablation and the laser-induced shock wave structuring. The direct front side laser irradiation of these polymers allows the fabrication of different surface structures. For example: The low laser fluence treatment of PI results in nano-sized cone structures where the cone density can be controlled by the laser parameters. This allows inter alia the laser fabrication of microscopic QR code and high-resolution grey-tone images. Furthermore, the laser treatment of the front side of the polymer foil allows the rear side structuring due to a laserinduced shock wave. The resultant surface structures were analysed by optical and scanning electron microscopy (SEM) as well as white light interferometry (WLI).

The laser-assisted microstructuring of thin films especially for electronic applications without damaging the layers or the substrates is a challenge for the laser micromachining techniques. The laser-induced thin-film patterning by ablation of the polymer substrate at the rear side that is called ‘SWIFD’ – shock-wave-induced film delamination patterning has been demonstrated. This study focuses on the temporal sequence of processes that characterize the mechanism of this SWIFD process on a copper indium gallium selenide (CIGS) solar cell stacks on polyimide. For this purpose high-speed shadowgraph experiments were performed in a pump probe experimental set-up using a KrF excimer laser for ablating the rear side of the polyimide substrate and measuring the shock wave generation at laser ablation of the polymer substrate as well as the thin-film delamination. The morphology and size of the thin-film structures were studied by scanning electron microscopy (SEM). Furthermore, the composition after the laser treatment was analyzed by energy dispersive X-ray (EDX) spectroscopy. The shadowgraph experiments allow the time-dependent identification and evaluation of the shock wave formation, substrate bending, and delamination of the thin film in dependence on the laser parameters. These results will contribute to improve the physical understanding of the laser-induced delamination effect for thin-film patterning.

Cost-efficient machining of dielectric surfaces with high-precision and low-roughness for industrial applications is still challenging if using laser-patterning processes. Laser induced back side wet etching (LIBWE) using UV laser pulses with liquid heavy metals or aromatic hydrocarbons as absorber allows the fabrication of well-defined, nm precise, free-form surfaces with low surface roughness, e.g., needed for optical applications. The copper-sulphatebased absorber CuSO4/K-Na-Tartrate/NaOH/formaldehyde in water is used for laser-induced deposition of copper. If this absorber can also be used as precursor for laser-induced ablation, promising industrial applications combining surface structuring and deposition within the same setup could be possible. The etching results applying a KrF excimer (248 nm, 25 ns) and a Nd:YAG (1064 nm, 20 ns) laser are compared. The topography of the etched surfaces were analyzed by scanning electron microscopy (SEM), white light interferometry (WLI) as well as laser scanning microscopy (LSM). The chemical composition of the irradiated surface was studied by energy-dispersive X-ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FT-IR). For the discussion of the etching mechanism the laser-induced heating was simulated with finite element method (FEM). The results indicate that the UV and IR radiation allows micro structuring of fused silica with the copper-based absorber where the etching process can be explained by the laser-induced formation of a copper-based absorber layer.

Micro-structured dielectric surfaces in combination with electrode structures are promising in the field of rapid prototyping of micro-sensors. In this work laser-induced back side etching and back side deposition using aqueous copper sulfate in form of a tartrate complex with formaldehyde as absorber liquid has been investigated regarding this aim. Results obtained with different laser systems ranging from UV to Near-IR and with pulse lengths from femtoseconds to nanoseconds will be presented, in order to give a wide-spread overview of the different observable effects. Depending on the specific setup and laser parameters, either well-defined compact Cu deposits, micro- or nanoscaled Cu droplets or ablation of the dielectric substrate was observed. Best quality crystalline and conducting Cu structures were achieved using ns pulses at 532 nm wavelength. Droplet formation with UV excimer laser was observed. Parameters influencing each configuration will be discussed.

Nanostructures are of increasing importance in manifold application fields such as electronics, optics and beyond. However, the fast and cost-effective production of nanostructures is a big technological challenge for laser machining. One promising approach is laser irradiation of thin metal layers, which allows the fabrication of metal nanostructures induced by a melting and transformation process. The influence of laser parameters (laser fluence, laser pulse number) on the morphology of the nanopatterned film and the dynamics of the nanostructure formation during excimer laser irradiation of a 20 nm chromium film on fused silica were studied. The dynamics of nanopatterning, comprising hole and droplet formation, were investigated by time-dependent reflection and transmission measurements as well as time-dependent optical microscopy. The resulting patterns were investigated by optical and scanning electron microscopy (SEM). However, for an optimization of this process a better understanding of the underlying physical phenomena is necessary. Therefore, experimental data of laser-induced nanopatterning were compared with results of physical simulations that consider the heat equation (laser–solid interaction including melting and evaporation) and the Navier–Stokes equation (transformation processes of the molten phase). The simulations, making use of laser fluence-dependent effective material parameters (surface tension and viscosity), are in good agreement with the experimental results.

Laser embossing allows the micron and submicron patterning of metal substrates that is of great interest in a wide range of applications. This replication process enables low-cost patterning of metallic materials by non-thermal, high-speed forming which is driven by laser-induced shock waves. In this study the surface topography characteristics as well as the material structure at laser embossing of sub-micrometre gratings into solid copper is presented. The topography of the laser-embossed copper pattern is analysed with atomic force microscopy (AFM) in comparison to the master surface. The height of the embossed structures and the replicated pattern fidelity increases up to a laser fluence of F∼10 J/cm 2 . For higher laser fluences the height of the embossed structures saturates at 75% of the master pattern height and the shape is adequate to the master. Structural modifications in the copper mono crystals after the laser embossing process were investigated with transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). Almost no modifications were detected. The residual stress after laser embossing of 32 MPa(F = 30 J/cm 2 ) has only a limited influence on the surface pattern formation.

Laser-induced front side etching (LIFE) is a method for the nanometer-precision structuring of dielectrics, e.g. fused silica, using thin metallic as well as organic absorber layer attached to the laser-irradiated front side of the sample. As laser source an excimer laser with a wavelength of 248 nm and an pulse duration of 25 ns was used. For sub-μm patterning a phase mask illuminated by the top hat laser beam was projected by a Schwarzschild objective. The LIFE process allows the fabrication of well-defined and smooth surface structures with sub-μm lateral etching regions (Δx 350 nm) and vertical etching depths from 1 nm to sub-mm.