Development platform for UV-NIL processes using polymer masters produced by laser ablation and photolithography

Replication of micro- and nanostructures in polymer materials by hot embossing, injection molding, or nanoimprint lithography (NIL) is often used for the efficient fabrication of nano- and microstructures on surfaces.¹ Nanoimprinting enables high-fidelity replication of micro- and nanostructures and can be performed as thermal or UV-assisted NIL (T-NIL and UV-NIL, respectively).² Independent of the specific technique, imprinting is typically performed into a thin polymeric layer on an appropriate substrate, which can be a hard silicon wafer for microtechnical applications or a polymer foil (e.g., for labeling). UV-NIL replication is scalable from plate-to-plate (P2P) fabrication to a roll-to-plate (R2P) or a roll-to-roll (R2R) process.^1–3 Such scalable micropatterning techniques are also of substantial interest for large-area utilization of nanostructures such as antireflection surfaces for glass or solar cells.^4,5 A key requirement for R2R fabrication processes is an appropriate master roller with inverse micro/nanostructures. Fabrication of 15 nm lines in a NIL R2R process has been demonstrated for optical wire polarizers.⁶ Metal master structures are typically used for P2P and R2R imprint techniques.^7–9 Such rigid, high-quality metal masters for high-volume R2R production processes require a cost-intense, time-consuming fabrication process. Although mechanical or etching techniques are still in use for mesoscopic pattern generation on rollers, micro- or nanostructures require alternative techniques borrowed from microelectronics. However, these wafer-level techniques cannot be simply transferred to metallic rollers of large sizes, owing to the need for very specialized equipment.

Microlithography in which mask patterns are copied onto a photosensitive film by UV exposure and subsequent development is a standard technique in microelectronics. Traditional mask printing by UV exposure is usually capable of resolving 1 µm patterns, but electron beam writing resolves patterns below 10 nm. Further, the spin-on photosensitive film feature allows roughness in the range of 1 nm rms and a precise thickness with variations in the range of 10 nm across the wafer.¹⁰ Such a well-defined film thickness defines the height of the final functional pattern, which is important for diffractive optical applications such as gratings or holograms. From any lithographically fabricated pattern (e-beam writing or photolithography), nickel shims, i.e., thin flexible metal foils holding inverse copies of master patterns that can be used as stamps for replication processes, can be fabricated by electroforming of these resist structures.⁸ 

Various approaches have been adopted with the aim of simplifying the master fabrication process in relation to direct patterning of the roller using polymers as master materials. Continuous, seamless patterning can be performed by laser ablation or lithography on the roller.¹¹ Various laser texturing techniques have been used for the fabrication of micropatterns directly on metallic rollers or sleeves by pulsed lasers for applications in printing, embossing, NIL, or UV-NIL.^6,7,12–14 To realize high-quality patterns, ultrashort lasers need to be applied for metals, whereas UV lasers are preferred for patterning of UV-absorbing polymers. In general, during the last few decades, soft masters composed of polymer materials have come into more widespread use.^2,3,15

The structuring of polymer surfaces with short and ultrashort laser pulses is based on material removal caused by decomposition of the polymer resulting from disintegration of the hydrocarbon chains and can be applied to surface pattern fabrication on polymer films and foils.^16–18 The ablation process has already been investigated for various polymers such as polytetrafluoroethylene (PTFE), polyetheretherketone (PEEK), polyethylene terephthalate (PET), polycarbonate (PC),^16,19 and polyimide (PI).²⁰ The lateral resolution of the laser patterning process is given by the optical resolution of the projection optics, whereas the principal vertical precision is represented by the ablation rate. The surface roughness of laser-machined polymer surfaces can be less than 800 nm for Gaussian laser spots and less than 200 nm for excimer lasers.²¹ Polymer machining with excimer lasers using mask projection techniques such as contour masks and/or grayscale masks allows the generation of various 2D and 2.5D microstructures with high surface quality.^21,22 For easy and damage-free demolding, an antisticking layer is usually applied to the master surface. Silicones offer good antisticking properties^23,24 and a high degree of flexibility, allowing forceless replication of sensitive patterns. Therefore, silicone (PDMS) has been widely used as stamp material.^25,26

Both of the standard techniques for micropattern fabrication for masters feature very different characteristics, such as pattern definition flexibility, minimal feature size, and surface roughness and pattern size limitations, and so a combination of the two techniques can prove valuable for specific applications. In the present study, a process chain for inverse master fabrication using structures fabricated by laser ablation in polyimide substrates and by photolithography and the replication of such masters by UV-NIL is demonstrated as part of a development platform. The merger of such different pattern types in one UV-NIL master requires the alignment and sometimes the assembly of patterned areas. This assembly approach enables the use of standard laboratory patterning equipment, which is often limited in patterning field size for the large-area master fabrication needed for R2R replication.

UV-NIL processes are capable of high-volume production of functional surfaces, but need an inverse patterned master. The proposed process chain for the rapid demonstration of UV-NIL replication up to R2R processes is shown in Fig. 1. The process chain comprises primary master fabrication, assembly of differently patterned submasters to the required size, copying onto an inverse master, and final replication by UV-NIL in a P2P or an R2R process. The advantages of this approach are (a) the combination of different primary patterning techniques for one master and (b) the utilization of the flexible silicone copy for UV-NIL replication. Although the assembly processes are challenging, they are needed owing to the size restrictions on the patterning tools (e.g., lithography, e-beam writing, or laser direct writing), especially under laboratory conditions. The laboratory-patterned areas are much less than the size of the master for R2R UV-NIL processes. To achieve precise assembly of different submasters, the sections are aligned with markers and laser-written edges.

The inverse silicone copies, which can hold patterns from different patterning processes, must be flexible to a certain extent not only to enable planar replication but also for wrapping onto a base roller. Therefore, a stable polymer foil was chosen as a supporting material for the micropatterns of the inverse master copy, which must not only provide the flexibility to wind around the roller, but also prevent distortion of the pattern as much as possible.

In the first step, positive master structures were produced according to the patterns required by the particular application. The primary patterning techniques utilized were photolithography and laser direct writing of binary structures with picosecond (ps) lasers and of 2.5D structures, fabricated by mask projection techniques, with UV nanosecond (ns) lasers.

An excimer laser (LPX220, Coherent) running at 248 nm and emitting 20 ns laser pulses was used to fabricate prismatic structures in polyimide foils using a mask-shaped laser beam spot. The basics of this laser spot shaping and 2.5D pattern formation technique are given in Refs. 21 and 22. The basic approach described there was extended for fast direct writing by using an array of identical trapeze-like mask patterns as shown in Fig. 2. This mask was cut from nickel foil (20 µm thick) by a ps laser. The identical mask elements were separated, because the mechanical and thermal stability of the nickel foil mask had to be maintained during laser writing. By imaging this rhomboid mask on the polyimide surface, the homogenized excimer beam was shaped into rhombic spots, and prismatic ablation structures were achieved while the projected contour mask pattern was scanned across the substrate. The design of the whole machining process for prism array writing comprises the definitions of (i) the width of the rhombus shape that defines the width of the prismatic structures, (ii) the number of overlaying identical mask elements during writing, and (iii) the scanning speed. The laser fluence should be optimized to minimize the roughness of the laser-written prismatic structures. The depth of the prism structures can be adjusted by the laser fluence, scanning speed, and the shaped spot height. Considering these requirements, in the present work, the prism arrays were written in polyimide with a scanning velocity of 2 mm/s using a repetition rate of 100 Hz and a pulse energy of 260 mJ. Although this approach is demonstrated here for prismatic structures, other 2D structures such as line gratings or cylindrical structures can also be fabricated.^21,22

For direct laser writing on polyimide foil, an ultrashort pulsed laser (Super Rapid, Lumera) incorporated into a laser workstation (microSTRUCT, 3D-Micromac) was used. The surfaces were machined with laser radiation of wavelengths 355 and 532 nm, a repetition rate of 100 kHz, and a pulse duration of 12 ps. The Gaussian laser beam was focused on the sample surface by an f-theta lens with focal lengths of 103 and 165 mm for 355 and 532 nm laser wavelengths, respectively. Laser power and scanning speed/number of laser pulses were adapted to the pattern size and/or depth. Intended patterns for writing can be provided as bitmaps or CAD datasets, or, as was done here, programmed directly as parallel lines or a dot pattern with a specific distance. Although the scanner system used for laser writing had a working field of ∼100 × 100 mm², master patterns as large as 600 × 200 mm² were directly written by stitching the scan fields by means of the stages of the workstation. In some cases, stitching of the writing fields was achieved by adjustment of fields on previously written or available markers. The software of the laser machining system together with the precision stages and a camera system returned the offset and rotation parameters for the stitching process. As a consequence, a precision better than 50 µm was realized for the alignment of adjacent areas during laser writing. In this way, primary masters could be laser-written onto polyimide (Kapton) foils of the full size needed for R2R UV-NIL. Laser direct writing, however, can be time-consuming for large patterned areas and small laser spots. All laser-written primary masters were cleaned before further use.

Primary master patterns such as lines, disks, rectangles, and triangles with a minimum feature size of 1 µm were produced with optical lithography as a parallel working patterning technique. In the present study, a mask aligner MA1006 from Süss MicroTec GmbH was used that provided a maximum size for exposure of 150 × 150 mm²; in these experiments, masks with a patterned area of 100 × 100 mm² were utilized. The height of the lithographic pattern can be adapted to the needs of a particular application by choosing an appropriate photoresist and applying suitable spin-on parameters. The well-developed spin-on technique provides photoresist films with low roughness and a high degree of homogeneity. In this study, a positive working photoresist AZ MIR 701 (MicroChemicals GmbH, Germany) was used. A layer thickness of 700 nm was established at a spin coating speed of 3000 rpm. The 5 µm square patterns with a 10 µm period were exposed three times for 2.2 s and then developed for 75 s with AZ-726 developer. In addition, a negative photoresist AR-N 4340 (Allresist GmbH, Germany) with a thickness of 2200 nm spun on at 2000 rpm was used. This resist was exposed three times for 5.7 s using a photomask with line patterns with a period of 15 µm and was then developed for 75 s with AR 300-475 developer, resulting in a linewidth of ∼7.5 µm. Two 5 in. photomasks were utilized to study the replication process with regard to the type and size of structures. One mask containing circular, square, and linear structures of different sizes was used to get an overall view of replication fidelity, and the other mask contained line structures to study homogeneity. The line structures were applied onto 100 × 100 mm² PI foil samples (submasters) in different directions (parallel, perpendicular, and at a 45° angle), which allowed study of the feature-filling behavior of R2R UV-NIL. Deviations in the pattern height of less than 10 nm and a side wall slope of about 80° were achieved by optimizing the whole lithographic process. Two pattern characteristics, namely, the height and the shape of the binary pattern, are important for diffractive optics (e.g., in diffraction gratings): as well as determining the diffracted power at the associated diffraction order, they affect the replication quality because both mold filling and demolding depend on the pattern geometry.

Utilizing both laser direct writing and photolithography, complex patterns were fabricated by combining these techniques in sequence. First, using the scanning contour mask approach described in Sec. II A 1, prismatic structures were laser-written on 10 µm thick AZ 4562 baked at 140 °C. For laser machining, a laser fluence of 112 mJ/cm² and a scanning speed of 0.1 mm/s at a repetition rate of 10 Hz were applied. After removal of some of the debris from the laser ablation process, line patterns with a line/space period of 20 µm were produced lithographically. Then, a 1.5 µm thick photolithographic film (AZ MIR701) was spun-on, exposed, and developed. The resulting surface topography is shown in Fig. 3.

Several inverse silicone copies for R2R UV-NIL were fabricated by molding of (i) laser-written primary masters with a length of ∼600 mm or (ii) assembled primary masters comprising six submasters. All submasters were fabricated on polyimide foils by laser ablation of the foil or lithography onto the foil as described earlier. These patterned foils were laser-cut in relation to the patterned edges or markers of the primary pattern. The polyimide foil with the primary pattern was fixed on the laser workstation stage, the patterns were recognized by the calibrated camera system, and finally the submaster edges were cut, aligned at the submaster pattern. In addition, inverse apertures with the size of the submasters were laser-cut into a polymer foil of the same thickness. For assembly, the submasters were bonded to the polyimide carrier foil by Mount (3M) adhesive spray: first the foil with the inverse apertures and then the submasters. The gap remaining between adjacent submasters that is shown in Fig. 4(a) was filled with AR-N 4400-50 photoresist (Allresist GmbH, Germany) to smooth out the slit. From these assembled submasters, inverse copies were prepared by molding into two-component silicone or OrmoStamp hybrid polymer. For production of the inverse silicone copies, a two-component silicone (RepliSet-F5, Struers GmbH) with a curing time of ∼20 min was used. The replication of patterns down to 100 nm was guaranteed by the use of this commercially available black silicone. A 125 µm thick polyimide foil was used to stabilize the very flexible silicone pattern of the rear side, and this allowed the inverse silicone copies to be attached to the roller without distortion. Before molding into silicone, the carrier foil was first activated by corona treatment, and an adhesion promoter was applied. For inverse replica molding, the silicone was poured onto the assembled primary master before the polyimide carrier film was applied by rolling from the side. The 3D structures on the inverse silicone copy were elastic, which facilitated their demolding.²⁶ Several copies of the assembled primary master could be obtained by molding into silicone. Finally, the inverse silicone copies were laser-cut to a length of 565.5 mm that fitted exactly on the circumference of the 180 mm diameter roller.

The silicone copy was fixed to the roller of the UV-NIL system by Mount adhesive spray. Markers on the roller were used for accurate alignment of the inverse master copy perpendicular to the axis of the roller. A 50 µm thick PET foil was used as the carrier for UV-NIL, which was activated by corona exposure in the R2R system before imprinting. An LED lamp (FL 400, Phoseon Technology, USA) with wavelength of 395 nm and an irradiation window of 225 × 20 mm² was used as the UV source for curing the acrylates. Typical UV-NIL conditions chosen here were a UV dose of 4 W/cm² and a web speed of ∼1 m/min. However, the required dose depends on various parameters, including the precursor material, the machining parameters, and the environmental conditions, all of which ultimately determine the throughput of the R2R system. The precursor applicator realized a uniform distribution of the UV-curable polymer across the web. In particular, for the demonstration of the final R2R UV-NIL process, curable MIRAMER M 3130 acrylate (Miwon Specialty Chemical Co. Ltd., Korea) was used. Under these conditions, a final coating thickness of ∼15 µm was achieved.

The surface morphology of the structures was imaged by scanning electron microscopy SEM (Zeiss Gemini Ultra 55) after sputtering with ∼20 nm gold film. The surface topography was analyzed by white light interferometry (WLI, Bruker NPFlex) to acquire quantitative results on the pattern width and height. In some cases, additional markers were written by laser on the primary master to enable comparative measurements of master and replica at the same position.

Each of the primary patterning techniques has its own advantages that enable the fabrication of specific functional patterns for particular applications. Hence, a combination of these techniques—and possibly other patterning techniques in addition—provides a valuable route for the further development of master rollers for R2R UV-NIL processes. For optical applications, both photolithography and laser patterning are useful. The benefit of photolithography is the lower edge rippling and surface roughness of the structures created, as well as the defined depth of the pattern.

Direct laser-writing on polyimide allows the fabrication of different millimeter to sub-micrometer structures, depending on the laser machining process.^27,28 To fabricate well-defined 2.5D structures, a first set of structures were created on the polyimide surface with a shaped ns-laser beam spot. A second set of submasters were then patterned by a Gaussian UV ps-laser beam to fabricate simple but also hierarchical surface structures with adjustable geometry. In all three approaches to primary master fabrication, the primary laser-written master, the inverse silicone copy, and the final replica with positive pattern were imaged to enable comparison and evaluation of the step-by-step replication process.

For the fabrication of prismatic structures for optical applications (the principles of which are described in Ref. 22), the polyimide surface was ablated by a shaped ns-laser beam with a wavelength of 248 nm. The contour mask used for laser beam shaping is shown in Fig. 2. As shown in Fig. 5(a), laser patterning process caused the formation of defined prismatic structures with a depth of ∼4 µm and a periodicity of ∼525 µm. Periodic line structures are present on top of the prismatic structures as a result of the discontinuity of the patterning process with a pulsed laser. As the projected image of the contour mask was moved during the mask scanning, each laser pulse caused the formation of shallow grooves whose edges are shifted with respect to each other.

The topography of the laser-structured polyimide was molded into an inverse silicone copy as shown in Fig. 5(b). This molding allowed high-quality transfer of the prismatic structure, retaining its depth, lateral size, and surface morphology. However, a detailed examination of the surface reveals some smoothing effect due to reduction of the laser writing marks of the contour mask. The measured roughness along the prism surface is given in Table I for all stages of the process.

The roughness increases with prism depth and correlates with the number of applied laser pulses. Basically, the roughness increases slightly in the course of replication. To evaluate the visually observable reduction of the contour mask marks in relation to smoothing effects, the surfaces of the master, the inverse silicone copy, and the final replica were subjected to fast Fourier transform (FFT) as shown in Fig. 5(d). The master and the silicone mold (replica 1) surfaces exhibit typical 1/f noise spectra in which the microroughness amplitude of the silicone replica is lower than that of the laser-patterned master.

Laser ablation of polyimide with ten pulses of a UV ps-laser at a laser power of ∼54 mW resulted in grooves with a depth of ∼2.5 µm and a diameter of ∼5 µm. The bottom surface of the grooves shows a rather rough surface. Periodically ordered groove arrays, one of which is shown in Fig. 6(a), could be fabricated by computer-controlled positioning of the laser spot in a step-and-repeat process. Here, a hexagonal array with a groove distance of 30 µm was chosen for imaging. The geometric properties of the 2D array could be easily modified by altering the laser machining process parameters such as the position list of machining points, the laser power, or the number of laser pulses. The groove dimension is basically determined by the spot size and can be fine-tuned by applying optimized laser power and pulse number. The ps-laser ablation of polyimide for drilling of microholes has been systematically studied in Ref. 27.

Similar to ns-laser written prismatic structures, 2D groove arrays can be transferred very well into an inverse silicone copy and finally into acrylate by UV-NIL (see Fig. 6). The hole geometry (depth and diameter) is copied well into the final acrylate surface by the R2R UV-NIL process. Beside 2D arrays, 1D gratings can also be fabricated by UV ps-laser ablation. To that end, the laser spot was moved with a constant velocity of 100 mm/s across the sample. At a laser power of 85 mW, trenches with a depth of ∼2.5 µm and a width of ∼20 µm having a rough surface were formed [see Fig. 7(a)]. As with 2D arrays, the properties of 1D hierarchical gratings can also be controlled by altering the parameters of the laser machining process. Similarly, 1D gratings can be transferred to silicone and finally to acrylate, with preservation of their depth and width.

No changes in the surface microroughness of the laser-written patterns are visible in the images. The surface roughness (as represented by, e.g., the averaged roughness Ra) along the bottoms of the grooves shows no significant differences along the stages of the step-by-step replication process. To quantify changes in quality, the roughness and the average height of the structures were determined from the WLI measurements and are listed in Table II. Owing to the mechanism of material removal during laser ablation, the surface of the ablated polyimide master samples feature different micro- and nanoroughnesses. These roughnesses of the lines originate from explosive material removal during laser ablation, redeposition of debris, and the discontinuous pulsed laser ablation process. The roughness data in Table II show a slight increase in the surface roughness of both the line and space structures during the course of replication. However, it is the molding into the silicone that contributes the majority of the roughness, and this can be attributed to the type of silicone used. The reason for this is probably related to the different morphologies of the ps-laser-produced roughness that cannot be smoothed completely during replication. Hence, the ps-laser written pattern can be replicated without any loss of quality.

Both line and dot arrays were chosen for replication of simple photolithographic patterns. The square dot arrays featured a 5 µm pattern size and 700 nm pattern height with a period of 10 µm. The line pattern was slightly wider, with a 20 µm period, but allowed height and roughness measurements. All photolithographic patterns featured slightly inclined sidewalls with a slope of roughly 80°. The flexibility of the soft PDMS stamp and the slight inclination of the photoresist sidewalls facilitated defect-free demolding of the inverse silicone copy from the polymer master as well as demolding of the final acrylate replica from the silicone master.

The WLI measurements show some roughness features or rounded edges of the pattern at all stages of the replication process. These features can be related to the limited optical resolution of the WLI microscope and to errors in phase recognition at the steep edges of the patterns. The lateral size of the resist pattern is reproduced well.

The height variation across a measured sample area of 47.5 × 63.5 µm² was evaluated from a histogram of the height distribution. The full width at half maximum (FWHM) of the two main peaks of the histogram was determined. For the master, both peaks (line and spaces) show a height variation of ∼25 nm, which is surprising, since the silicon wafer was plain and smooth. For the final acrylate replica, both plane and bow corrections were performed before the histogram evaluation. The height variations for the spaces and the lines were determined to be 28 and 54 nm, respectively. In the spaces, almost the same height variations as determined for the masters are found, whereas the line height variation has nearly doubled. The height differences of the line gratings were also determined from the histogram and are listed in Table III. These height differences do not include the rounded edges of the line pattern.

The reduction in height in the course of replication might be explained by shrinkage of material during replication. However, as the shrinkage is fixed for a given process and material, it can be taken into account during master fabrication by increasing the photoresist film thickness slightly.

Similar results are obtained for lithographic line gratings. The slightly rounded edges of the lines can be attributed to the limited optical resolution of the WLI measurements. Such line gratings allow better evaluation of the imprint results, since the roughness can be determined along the line direction. The line structures can be transferred to silicone and to the final acrylate polymer. Although the depth and width of the structures are maintained, the surface roughness is slightly changed (Fig. 8). Again, the higher roughness of the lines of the inverse silicone copy, which correspond to the spaces in the primary master, can be attributed to the roughness of the polyimide foil used as the lithographic substrate.

The roughnesses of the lithographically patterned master and the inverse and final replicas were measured by WLI along the line structures at the tops of the lines and the bottoms of the spaces. The measured roughness data are summarized in Table III.

The very low roughness found at the primary lithographic master surface, which may be influenced by the waviness of the measured surface data, increases in the course of replication. The greatest effect on the surface roughness is that of the replication process into the silicone, which might be related to the type of silicone used, since PDMS is capable of copying with a precision down to 1 nm rms.²⁹ Considering the marginal rise in the roughness in the range of 10 nm rms, a significant impact on the roughness of laser patterned surfaces cannot be expected, as indeed has been found to be the case.

Finally, the replication of complex shaped surfaces is demonstrated. The structure shown in Fig. 3 was used as master for step-by-step replication first into silicone and then acrylate. For comparison, cross-sections along and perpendicular to the line pattern were extracted from WLI measurements of the complex structure. In Fig. 9, these data are shown for the master, the silicone stamp, and the final replica.

The replication of complex hierarchical structures shows that the fidelity of replication is also good for different sizes of the pattern. The deviations in height can be attributed to uncertainties in position for the extracted profiles.

A process chain for the micropatterning of web materials in a UV-NIL process that can also be run as an R2R process comprising primary master patterning, copying into an inverse silicone copy, and UV-NIL of acrylate as a final replication step has been demonstrated. An approach combining different standard patterning techniques to fulfill the requirements for fabrication of highly complex patterns and to fit the required sizes of R2R UV-NIL masters has been proposed and realized by assembly of submasters and subsequent replication into an inverse silicone copy for final UV-NIL of acrylate. Laser-written prismatic structures, laser-machined line and dot patterns, and photolithographic dot and line structures were chosen as primary masters. The capabilities of a highly sophisticated ps-laser workstation enable (i) writing of arbitrary structures on full-size R2R masters (200 × 600 mm²) and (ii) laser cutting of polymer submasters (made by different patterning techniques) to enable an assembly precision of these submasters of better than 50 µm. The assembly of submasters allows the use of standard laboratory equipment for primer patterning and thus a rapid R2R master holding the required structures. It further enables the inverse silicone copies attached to polymer carrier foil to be wrapped around the roller for the R2R UV-NIL process without significant distortions of the patterns. It has been shown that the feature sizes of all structures are maintained during the step-by-step replication process. An increase in the roughness by 10 nm rms has been observed for lithographic line structures that possess sufficient smoothness. A light smoothing process has been observed for prismatic structures. Both the slight increase in roughness and the smoothing effect can be attributed to the silicone molding process.

Partial support of this work within the GRAVOmer network as part of the funding initiative “WIR!—Wandel durch Innovation in der Region” by the BMBF under Contract 03WIR20IL1 is gratefully acknowledged. The authors thank U. Trimper for detailed help with the operation of the R2R nanoimprint machine during the process development. The authors are grateful to Dr. U. Helmstedt for her efforts in the development of the GRAVOmer project. We would also like to thank Mr. Naumann for providing the standard acrylate formulation and I. Mauersberger for support with the topographical analyses of the structures.

The authors have no conflicts to disclose.

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Joachim Zajadacz is a Senior Researcher at the Leibniz Institute of Surface Engineering (IOM), focusing on the development of micro- and nanoprocessing by lithography, nanoimprinting, and etching. He obtained the Diploma degree in Microelectronic Engineering from the University of Applied Science Mittweida. His interests include applications of micro- and nanopatterning of surfaces and thin films for optics, sensing, and microsystems.

Pierre Lorenz studied physics at the Friedrich Schiller University of Jena and received his diploma in 2005 with a thesis entitled “High temperature superconducting Josephson junctions on large area substrates.” In 2006, he moved to the Technical University of Ilmenau, where he obtained his Ph.D. in 2010 with a thesis on the surface and interfacial properties of polar gallium nitride. Since 2010, he has been employed at the Leibniz Institute of Surface Engineering (IOM), where his research has concentrated on laser–solid-state interactions. The objective of this research is to investigate the interactions of ultrashort laser pulses with solid surfaces, both theoretically and experimentally. He has contributed to over 100 scientific publications and currently has an h-index of 20.

Martin Ehrhardt joined the Leibniz Institute of Surface Engineering (IOM) after graduating from the Technical University of Applied Sciences Wildau with a Diploma in Engineering and a Master’s degree in Physics from the Technische Universität Clausthal. He completed his Ph.D. at the University of Leipzig and his postdoctoral studies at the Nanjing University of Science and Technology. His scientific and technological interests are related to ultrahigh-precision laser surface machining for applications in optics and micrometer systems technology.

Klaus Zimmer is Senior Scientist at the Leibniz Institute of Surface Engineering (IOM) and heads the Laser-Based Micro- and Nanostructuring group in the Department of Ultra-Precision Surfaces. He has authored more than 250 papers, including three book chapters, has an h-index of 29, and is Editor of Surfaces and Interfaces. His scientific interests include micro- and nanopatterning by lithography, self-organization, and replication, including film deposition and pattern transfer, laser–matter interactions, and laser processing for high-precision surface machining and applications of these techniques.