Ruthenium (Ru) films have recently received attention in the microelectronics industry due to their unique physical and chemical properties. In this work, we investigated etching of Ru using an approach that combines surface functionalization using the effluent of a remote plasma source (RPS) fed with Ar/O2/Cl2 gas mixtures and electron beam (EB) irradiation. Simultaneous exposure of the Ru substrate to reactive fluxes from the RPS and the energetic EB source exhibits a synergistic effect: For combined fluxes, the Ru etch rate (ER) is greater than for separate RPS exposure or EB irradiation. The RPS generates reactive neutral species that functionalize the Ru surface through oxidation and chlorination. The flux of energetic (1 keV) electrons incident on the Ru surface induces Ru etching. A parametric study in which the electron flux density [proportional to the electron emission current (EC)], relative Cl2 and O2 flow rates, and RP power were varied was performed to examine the impacts of the neutral and electron fluxes on the Ru ER. The Ru etching reactions change from being electron flux-limited for small EC to neutral flux-limited etching for large EC or for small reactive gas flows. We also show that selective removal of Ru over Ta, which is important for applications like extreme ultraviolet photomask repair, can be realized for these process conditions. For energetic EB bombardment and Ar/O2/Cl2 RP exposure, a Ru/Ta etching selectivity of ∼6 can be realized. Spatially resolved x-ray photoelectron spectroscopy (XPS) has been performed to characterize the surface chemistry for (a) locations exposed to both reactive neutral and energetic electron fluxes and (b) areas only exposed to the reactive neutral flux produced by the RPS. The XPS results support an EB and RP induced Ru etching mechanism where Ru etching is based on the formation of volatile Ru-oxides, and in which the role of Cl is to assist in Ru oxidation. A surface etching model based on the consideration of the incident oxygen and chlorine fluxes, Langmuir adsorption limited surface functionalization, and EB bombardment causing volatilization of RuO4 in the etching process has been developed. The model can successfully account for the major parametric observations of the Ru ER seen for the energetic EB irradiation and RPS-generated reactive neutral-induced etching process.

Patterning of ruthenium (Ru) in the microelectronics industry has become important because of novel Ru applications, including back-end-of-line metallization. Selective etching and deposition of Ru over tantalum (Ta) are crucial for the repair of extreme ultraviolet photomasks. A further challenge is to reduce near-surface damage and interdiffusion at the interfaces of material layers, which is often generated when patterning is performed by ion bombardment. In this work, we investigated the etching of Ru and Ta by exposure to electron beam (EB) irradiation and reactive neutral fluxes provided by a remote plasma source (RPS) fed with Ar/O2 gas mixtures. A synergistic effect is observed for Ru etching for simultaneous EB and remote plasma (RP) exposure as compared to isolated EB using the nonexcited feed gas mixture or RP exposure. The RP exposure functionalizes the Ru surface by oxidizing the Ru to nonvolatile RuO2, and the electron flux can further oxidize the functionalized surface to volatile RuO4 resulting in Ru etching. The Ru etch rate (ER) shows strong dependence on O2 flow and EB emission current, which determine the oxygen neutral and electron fluxes to the Ru surface, respectively. The effect of increasing O flux by adding a small amount of CF4 to the Ar/O2 as a feed gas for RPS does not directly result in Ru ER improvement. This is likely due to the formation of nonvolatile Ru oxyfluoride, which cannot be removed by the electron flux for Ar/O2/CF4 gas mixtures. Following Ar/O2/CF4 remote plasma exposure, Ru etching with Ar/O2 is subsequently enhanced for some time once the CF4 flow is stopped. This effect is likely caused by the passivation of reactor walls by RP-generated fluorocarbon species and reduced recombination of reactive oxygen species necessary for Ru etching on the reactor walls, thus leading to a higher ER. Exposure of Ta to EB and Ar/O2 RPS generated fluxes induces oxidation of Ta to nonvolatile Ta oxide, which is accompanied by an increase in layer thickness. The Ta oxidation rate decreases as the Ta oxide layer grows. With the addition of CF4, RP only exposure induces Ta etching by the formation of volatile Ta fluoride, whereas with EB irradiation, Ta oxide forms. Utilizing the passivation effect induced by CF4 addition and the differing responses of Ru and Ta to EB irradiation, we developed a process that enables selective removal of Ru over Ta. Surface chemistry and thickness measurements by spatially resolved x-ray photoelectron spectroscopy and ellipsometry suggest that the EB-induced materials’ modification likely arises from the promotion of surface oxidation.

Electron-stimulated etching of surfaces functionalized by remote plasma is a flexible and novel approach for material removal. In comparison with plasma dry etching, which uses the ion-neutral synergistic effect to control material etching, electron beam-induced etching (EBIE) uses an electron-neutral synergistic effect. This approach appears promising for the reduction of plasma-induced damage (PID), including atomic displacement and lateral straggling, along with the potential for greater control and lateral resolution. One challenge for EBIE is the limited selection of chemical precursor molecules that can be used to produce functionalized materials suitable for etching under electron beam irradiation. In this work, we studied a new experimental approach that utilizes a remote plasma source to functionalize substrate surfaces in conjunction with electron beam irradiation by an electron flood gun. Etching rates (ERs) of SiO2, Si3N4, and poly-Si are reported in a broad survey of processing conditions. The parametric dependence of the ER of these Si-based materials on the operating parameters of the flood gun and the remote plasma source is evaluated. We also identified the processing parameters that enable the realization of material selective removal, i.e., the etching selectivity of Si3N4 over SiO2 and poly-Si over SiO2. Additionally, surface characterization of etched materials is used to clarify the effects of the co-introduction of particle fluxes from the remote plasma and flood gun sources on surface chemistry.

The paradigm switch to a reflective mask design for EUV lithography has proven to be challenging. Within the Horizon2020 PIn3S program Zeiss and imec are collaborating to address some of these challenges. In this work, an EUV mask with a collection of programmed defects representative for the 3nm technology node was reviewed. Defect printability at wafer level was analyzed after exposure on the ASML NXE:3400B by SEM. Furthermore, the mask was analyzed on the Zeiss AIMS® EUV platform and by SEM. For P36 (1x) 1:1 L/S programmed extrusions we have demonstrated that AIMS® EUV can be used to predict ADI local defect widths as well as (μ)bridge printability. Moreover, from P36 to P32 the mask spec regarding allowed opaque L/S extrusion widths needs to be tighter considering an earlier onset of ADI (μ)bridge printability and a stronger than expected ADI defect width increase through pitch.

Electron-based surface activation of surfaces functionalized by remote plasma appears like a flexible and novel approach to atomic scale etching and deposition. Relative to plasma-based dry etching that uses ion bombardment of a substrate to achieve controlled material removal, electron beam-induced etching (EBIE) is expected to reduce surface damage, including atom displacement, surface roughness, and undesired material removal. One of the issues with EBIE is the limited number of chemical precursors that can be used to functionalize material surfaces. In this work, we demonstrate a new configuration that was designed to leverage flexible surface functionalization using a remote plasma source, and, by combining with electron beam bombardment to remove the chemically reacted surface layer through plasma-assisted electron beam-induced etching, achieve highly controlled etching. This article describes the experimental configuration used for this demonstration that consists of a remote plasma source and an electron flood gun for enabling electron beam-induced etching of SiO2 with Ar/CF4/O2 precursors. We evaluated the parametric dependence of SiO2 etching rate on processing parameters of the flood gun, including electron energy and emission current, and of the remote plasma source, including radiofrequency source power and flow rate of CF4/O2, respectively. Additionally, two prototypical processing cases were demonstrated by temporally combining or separating remote plasma treatment and electron beam irradiation. The results validate the performance of this approach for etching applications, including photomask repair and atomic layer etching of SiO2. Surface characterization results that provide mechanistic insights into these processes are also presented and discussed.

A freestanding ultrathin hybrid membrane was synthesized comprising two functional layers, that is, first, a carbon nanomembrane (CNM) produced by electron irradiation-induced cross-linking of a self-assembled monolayer (SAM) of 4′-nitro-1,1′-biphenyl-4-thiol (NBPT) and second, purple membrane (PM) containing genetically modified bacteriorhodopsin (BR) carrying a C-terminal His-tag. The NBPT-CNM was further modified to carry nitrilotriacetic acid (NTA) terminal groups for the interaction with the His-tagged PMs forming a quasi-monolayer of His-tagged PM on top of the CNM-NTA. The formation of the Ni-NTA/His-tag complex leads to the unidirectional orientation of PM on the CNM substrate. Electrophoretic sedimentation was employed to optimize the surface coverage and to close gaps between the PM patches. This procedure for the immobilization of oriented dense PM facilitates the spontaneous fusion of individual PM patches, forming larger membrane areas. This is, to our knowledge, the very first procedure described to induce the oriented fusion of PM on a solid support. The resulting hybrid membrane has a potential application as a light-driven two-dimensional proton-pumping membrane, for instance, for light-driven seawater desalination as envisioned soon after the discovery of PM.

Electrostatic charging of electrically insulating samples upon electron irradiation plays a large role in the analysis and processing of materials in biosciences and the semiconductor industry. We have analyzed spectral changes of purple membranes (PMs) containing bacteriorhodopsin, an electrochromic biological material, upon irradiation with electrons at an acceleration voltage of 30 kV. We observed a bathochromic shift in the UV/VIS spectrum of PM films, due to internal electric fields generated by charges injected into the films. The experiments demonstrate that spectroscopic changes, accompanying electron beam-induced charge injection into electrochromic materials, enable quantitative analysis of electrostatic charging of insulators upon electron irradiation by optical spectroscopy.

Scaling trends in the semiconductor industry towards smaller technology nodes and feature sizes are continuing and first consumer products manufactured with the help of EUV technology are already on the market. Major industrial players have introduced EUV lithography into their production at the 7nm technology node and with the 5nm node being on its way [1], the amount of EUV lithographic layers is expected to rise significantly and implementation of EUV double patterning is anticipated. These developments lead to more strict technological requirements especially for the corresponding EUV but also for the used high-end DUV photomasks in terms of minimum feature sizes and acceptable Edge Placement Errors (EPE). Moreover, photomask defectivity increases dramatically with shrinking feature sizes. This creates significant challenges to the industry, as in particular the most cost intensive EUV photomasks possess the highest numbers of defects. The current industry standard for high-end photomask repair tools is the MeRiT neXT [2]. To face the upcoming challenges an efficient and reliable way to repair future high-end photomasks is inevitable. A corresponding repair tool must address decreased minimum feature sizes and increased pattern complexity on high-end photomasks. In this paper we present our latest results of high-end EUV repairs carried out on the next generation photomask repair tool MeRiT LE. The tool shows improved system dynamics, makes use of a new electron beam column, which operates at a low electron beam voltage down to 400V and enables the repair of next generation ultra-small defects.

Transmission electron cryo-microscopy (cryoEM) of vitrified biological specimens is a powerful tool for structural biology. Current preparation of vitrified biological samples starts off with sample isolation and purification, followed by the fixation in a freestanding layer of amorphous ice. Here, we demonstrate that ultrathin (∼10 nm) smart molecular nanosheets having specific biorecognition sites embedded in a biorepulsive layer covalently bound to a mechanically stable carbon nanomembrane allow for a much simpler isolation and structural analysis. We characterize in detail the engineering of these nanosheets and their biorecognition properties employing complementary methods such as X-ray photoelectron and infrared spectroscopy, atomic force microscopy as well as surface plasmon resonance measurements. The desired functionality of the developed nanosheets is demonstrated by in situ selection of a His-tagged protein from a mixture and its subsequent structural analysis by cryoEM.

Well-defined multiwalled carbon nanotube structures are generated on stainless steel AISI 304 (EN AW 1.4301) by chemical vapor deposition. Pulsed laser-induced dewetting (PLiD) of the surface, by 532 nm nanosecond laser pulses, is utilized for the preparation of metal oxide nanoparticle fields with a defined particle number per area. The reduction of the precursor particles is achieved in an Ar/H2 (10% H2) atmosphere at 750 °C, thereby generating catalytic nanoparticles (c-NPs) for carbon nanotube (CNT) growth. Ethylene is used as a precursor gas for CNT growth. CNT lengths and morphology are directly related to the c-NP aerial density, which is dependent on the number of dewetting cycles during the PLiD process. Within a narrow window of c-NP per area, vertically aligned carbon nanotubes of great lengths are obtained. For more intense laser treatments, three-dimensional dewetting occurs and results in the formation of cauliflower-like structures. The laser process enables the creation of all kinds of CNT morphologies nearby on the microscale.

A self‐organization phenomenon named laser‐induced periodic surface structures (LIPSS) is utilized for pattern formation in indium–tin oxide (ITO) transparent conductive films coated on borosilicate glass. Stripe patterns with periodicities down to 175 nm are created by scanning the focused beam (30 µm spot diameter 1 e −2 ) of a nanosecond pulsed laser operating at 532 nm wavelength over ITO films. Highly ordered ITO‐LIPSS are generated at a pulse duration of 6 ns, pulse frequencies between 100 and 200 kHz, pulse energies around 20 µJ, and laser spot scan speeds in the range of 50–80 mm s −1 . Resulting nanopatterns are electrically conductive and feature improved optical transparency as well as stability against strong acids such as hydrochloric acid, sulfuric acid, and even aqua regia. The formation of mixed phases between ITO and silicon is considered to be the origin for the chemical robustness of laser patterned transparent conductive electrodes.

Living Micrococcus luteus (M. luteus) and Escherichia coli (E. coli) are encapsulated in poly(vinyl alcohol), poly(vinylpyrrolidone), hydroxypropyl cellulose, and gelatin by high-temperature spray drying. The challenge is the survival of the bacteria during the standard spray-drying process at temperatures of 150 degrees C (M. luteus) and 120 degrees C (E. coli). Raman imaging and transmission electron microscopy indicate encapsulated bacteria in hollow composite microparticles. The versatility of the spray-dried polymer bacteria microparticles is successfully proved by standard polymer solution-processing techniques such as electrospinning, even with harmful solvents, to water-insoluble polyacrylonitrile, polystyrene, poly(methyl methacrylate), and poly(vinyl butyrate) nanofiber nonwovens, which opens numerous new opportunities for novel applications.

In electron cryo-microscopy, structure determination of protein molecules is frequently hampered by adsorption of the particles to the support film material, typically amorphous carbon. Here, we report that pyrene derivatives with one or two polyglycerol (PG) side chains bind to the amorphous carbon films, forming a biorepulsive hydrogel layer so that the number of protein particles in the vitreous ice drastically increases. This approach could be extended by adding a hydrogel-functionalized carbon nanotube network (HyCaNet, the hydrogel again being formed from the PG-pyrene derivatives), which stabilized the protein-containing thin ice films during imaging with the electron beam. The stabilization resulted in reduced particle motion by up to 70%. These substrates were instrumental for determining the structure of a large membrane protein complex.

Carbon nanomembranes (CNMs) are a class of two-dimensional materials, which are obtained by electron beam-induced crosslinking of aromatic self-assembled monolayers (SAMs) on solid substrates. CNMs made from a single type of precursor molecule are uniform with homogeneous chemical and physical properties. We have developed a method for the fabrication of internally patterned CNMs resembling a key feature of biological membranes. Direct laser patterning is used to obtain multicomponent patterned SAMs on gold, which are subsequently crosslinked by electron irradiation. We demonstrate that the structure of internally patterned CNMs is preserved upon transfer to different substrates. The method enables rapid fabrication of patterned 2D materials with local variations in chemical and physical properties on the micrometer to centimeter scale. (C) 2017 Elsevier B.V. All rights reserved.

We developed a method to improve specimen preparation for electron cryo-microscopy of membrane proteins. The method features a perforated hydrogel nanomembrane that stabilizes the thin film of aqueous buffer spanning the holes of holey carbon films, while at the same time preventing the depletion of protein molecules from these holes. The membrane is obtained by cross-linking of thiolated polyglycerol dendrimer films on gold, which self-perforate upon transfer to holey carbon substrates, forming a sub-micron-sized hydrogel network. The perforated nanomembrane improves the distribution of the protein molecules in the ice considerably. This facilitates data acquisition as demonstrated with two eukaryotic membrane protein complexes.

Polycystin-2 (PC2), a calcium-activated cation TRP channel, is involved in diverse Ca2+ signaling pathways. Malfunctioning Ca2+ regulation in PC2 causes autosomal-dominant polycystic kidney disease. Here we report two cryo-EM structures of distinct channel states of full-length human PC2 in complex with lipids and cations. The structures reveal conformational differences in the selectivity filter and in the large exoplasmic domain (TOP domain), which displays differing N-glycosylation. The more open structure has one cation bound below the selectivity filter (single-ion mode, PC2(SI)), whereas multiple cations are bound along the translocation pathway in the second structure (multi-ion mode, PC2(MI)). Ca2+ binding at the entrance of the selectivity filter suggests Ca2+ blockage in PC2(MI), and we observed density for the Ca2+-sensing C-terminal EF hand in the unblocked PC2(SI) state. The states show altered interactions of lipids with the pore loop and TOP domain, thus reflecting the functional diversity of PC2 at different locations, owing to different membrane compositions.

In this paper we introduce a versatile tool for the controlled growth and alignment of copper-silicide nanocrystals. The method takes advantage of a unique self-organization phenomenon denoted as laser-induced periodic surface structures (LIPSS). Copper films (3 perpendicular to 0.2 nm) are sputter-deposited onto single crystal silicon (100) substrates with a thin oxide layer (4 +/- 0.2 nm), and subsequently exposed to linearly polarized nanosecond laser pulses (tau approximate to 6 ns) at a central wavelength of 532 nm. The irradiation triggers dewetting of the Cu film and simultaneous formation of periodic Cu nanowires (LIPSS), which partially penetrate the oxide layer to the Si substrate. These LIPSS act as nucleation centers for the growth of Cu-Si crystals during thermal processing at 500 degrees C under forming gas 95/5 atmosphere. Exemplified by our model system Cu/SiO2/Si, LIPSS are demonstrated to facilitate the diffusion reaction between Cu and underlying Si. Moreover, adjustment of the laser polarization allows us to precisely control the nanocrystal alignment with respect to the LIPSS orientation. Potential applications and conceivable alternatives of this process are discussed. (C) 2017 Elsevier B.V. All rights reserved.

Saccharomyces cerevisiae harbors a family of GPI-anchored cell wall proteins for interaction with its environment. The flocculin Flo11, a major representative of these fungal adhesins, confers formation of different types of multicellular structures such as biofilms, flors, or filaments. To understand these environment-dependent growth phenotypes on a molecular level, we solved the crystal structure of the N-terminal Flo11A domain at 0.89-Å resolution. Besides a hydrophobic apical region, the Flo11A domain consists of a β sandwich of the fibronectin type III domain (FN3). We further show that homophilic Flo11-Flo11 interactions and heterophilic Flo11-plastic interactions solely depend on the Flo11A domain and are strongly pH dependent. These functions of Flo11A involve an apical region with its surface-exposed aromatic band, which is accompanied by acidic stretches. Together with electron microscopic reconstructions of yeast cell-cell contact sites, our data suggest that Flo11 acts as a spacer-like, pH-sensitive adhesin that resembles a membrane-tethered hydrophobin.