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In this work, we show the feasibility of extreme ultraviolet (EUV) patterning on an HF-treated silicon (100) surface in the absence of a photoresist. EUV lithography is the leading lithography technique in semiconductor manufacturing due to its high resolution and throughput, but future progress in resolution can be hampered because of the inherent limitations of the resists. We show that EUV photons can induce surface reactions on a partially hydrogen-terminated silicon surface and assist the growth of an oxide layer, which serves as an etch mask. This mechanism is different from the hydrogen desorption in scanning tunneling microscopy-based lithography. We achieve silicon dioxide/silicon gratings with 75-nanometer half-pitch and 31-nanometer height, demonstrating the efficacy of the method and the feasibility of patterning with EUV lithography without the use of a photoresist. Further development of the resistless EUV lithography method can be a viable approach to nanometer-scale lithography by overcoming the inherent resolution and roughness limitations of photoresist materials., Science Advances, 9 (16), ISSN:2375-2548

Modern electronics continue to shrink down the sizes while becoming more and more powerful. To improve heat dissipation of electronics, fillers used in the semiconductor packaging process need to possess both high electrical and thermal conductivity. Graphene is known to improve thermal conductivity but suffers from van der Waals interactions and thus poor processibility. In this study, we wrapped silver microflakes with graphene sheets, which can enable intercoupling of phonon- and electron-based thermal transport, to improve the thermal conductivity. Using just 1.55 wt % graphene for wrapping can achieve a 2.64-times greater thermal diffusivity (equivalent to 254.196 ± 10.123 W/m·K) over pristine silver flakes. Graphene-wrapped silver flakes minimize the increase of electrical resistivity, which is one-order higher (1.4 × 10

Dynamic tuning of color filters finds numerous applications including displays or image sensors. Plasmonic resonators are subwavelength nanostructures which can tailor the phase, polarization, and ...

High magnetization materials are in great demand for the fabrication of advanced multifunctional magnetic devices. Notwithstanding this demand, the development of new materials with these attribute...

Significant heat generation in modern high-speed electronic devices requires elevated thermal conductivity of electrically conductive adhesives (ECAs), but the gap between discrete filler materials...

We report on a novel and simple pattern transfer process into Si via fullerene-based spin-on-carbon (SOC) hard masks in this work. Electron beam lithography and extreme ultraviolet interference lithography techniques are used to pattern high-resolution and dense lines on a resist/SOC bilayer. The patterns are subsequently transferred by a low-pressure O2 plasma etching (SOC) and reactive ion etching process with a gas mixture of SF6 and C4F8 (Si). Si sidewall trimming can be controlled by modifying the Si etching rate, achieving Si fins with dimension down to 15 nm half-pitch with aspect ratio as high as of 7:1.

High-NA extreme ultraviolet lithography (EUVL) is going to deliver the high-volume manufacturing (HVM) patterning for sub-3nm technology node for the semiconductor industry. One of the critical challenges is to develop suitable EUV photoresists at high resolution with high sensitivity and low line-width roughness (LWR) at reduced film thickness needed for high-NA by its reduced depth of focus (~1/NA2). The resist performance is generally limited by the resolution-LWR sensitivity (RLS) tradeoff, and it is critical to find new materials to support the future lithography nodes. EUV interference lithography (EUV-IL) is a powerful and efficient technique to test new materials at high resolution. In this work, we evaluate the performance of about 120 EUV resists, including molecular resist, inorganic resist, chemically-amplified resist (CAR), and chemically-amplified resist with a metal sensitizer (metal-CAR). Among all tested resists, we selected and compared six resists with the best performance in dose-to-size, line-width roughness, and maximal exposure latitude for 16 nm and 14 nm half-pitch (HP) lines/spaces (LS). A molecular resist showed the lowest dose to resolve HP 16 nm (29 mJ/cm2) and 14 nm (31 mJ/cm2), still featuring low LWRunbiased (2.7 nm and 3.1 nm, respectively). We observed that there is steady progress in EUV resist development: the LWR of the resists was improved in comparison with the results of the last two years as we noted that the amount of the resists within given dose and LWR threshold increased from 10 % to 33% for HP 14 nm. For contact holes, CAR gave the lowest LCDU of 2.2 nm for HP 20 nm with the lowest doses (21.1 mJ/cm2). While inorganic resists resolved pillars with highest resolution HP down to 18 nm with LCDU of 2.1 nm.

In this work, we present a novel resistless patterning technique on hydrogen-terminated Si (100) using EUV-induced surface reaction. We has successfully demonstrated a direct Si pattern transfer of half-pitch 75 nm Si gratings using the EUV resistless patterning technique. The EUV-induced surface reactions could achieve direct patterning on functionalized Si surface and potentially overcome the resolution limitations of conventional photoresists in the semiconductor industry. Moreover, this approach can be used for better understanding of EUV exposure mechanisms by preparing simple molecular systems and studying the EUV-induced reactions.

High aspect ratio nanostructuring requires high precision pattern transfer with highly directional etching. In this work, we demonstrate the fabrication of structures with ultra-high aspect ratios (up to 10 000 : 1) in the nanoscale regime (down to 10 nm) by platinum assisted chemical etching of silicon in the gas phase. The etching gas is created by a vapour of water diluted hydrofluoric acid and a continuous air flow, which works both as an oxidizer and as a gas carrier for reactive species. The high reactivity of platinum as a catalyst and the formation of platinum silicide to improve the stability of the catalyst pattern allow a controlled etching. The method has been successfully applied to produce straight nanowires with section size in the range of 10–100 nm and length of hundreds of micrometres, and X-ray optical elements with feature sizes down to 10 nm and etching depth in the range of tens of micrometres. This work opens the possibility of a low cost etching method for stiction-sensitive nanostructures and a large range of applications where silicon high aspect ratio nanostructures and high precision of pattern transfer are required., Nanoscale Horizons, 5 (5), ISSN:2055-6756, ISSN:2055-6764

An electrically tunable filter based on a plasmonic phase retarder and liquid crystal cells is reported. The plasmonic phase retarder consists of a periodic array of deep-subwavelength metallic nanostructures. A first entrance polarizer prepares the incident light in a polarization state oriented at 45° from the nanowires orientation. A strong phase retardation between TM and TE polarizations is induced by the plasmon resonances. A polarization analyzer based on liquid crystal cells allows to project the transmitted light onto a polarization state whose orientation depends on the applied voltage. Using this approach, a range of 8V is enough to span more than 70% of the area covered by standard RGB filters in CIE color coordinates with a single filter, including yellow, orange, red, magenta, purple, blue, cyan and green as well as different tones of white. In order to ensure the applicability to large area production, UV nanoimprint lithography (UV-NIL) and thin film coatings have been used to fabricate the plasmonic phase retarder. The evaporation is performed with an angle, so that a self-shadowing effects prevents full coverage of the surface. The resulting structure consists in a periodic array of silver nanowires. Multiple interfering resonances are observed so that the nominal transmission can reach levels above 70%. The construction of the colors transmitted by the tunable filter is modeled and validated through a series of optical characterization of the individual elements.

Background: Reliable photomask metrology is required to reduce the risk of yield loss in the semiconductor manufacturing process as well as for the research on absorber materials. Actinic pattern inspection (API) of EUV reticles is a challenging problem to tackle with a conventional approach. For this reason, we developed RESCAN, an API platform based on coherent diffraction imaging. Aim: We want to verify the sensitivity of our platform to absorber and phase defects. Approach: We designed and manufactured two EUV mask samples with absorber and phase defects, and we inspected them with RESCAN in die-to-database mode. Results: We reconstructed an image of an array of programmed absorber defects, and we created a defect map of our sample. We inspected two programmed phase defect samples with buried structures of 3.5 and 7.8 nm height. Conclusions: We verified that RESCAN, in its current configuration, can detect absorber defects in random patterns and buried (phase) defects down to 50 × 50 nm2.

Room temperature ferromagnetism has been observed in the Cu doped ZnO films deposited under an oxygen partial pressure of 10−3 and 10−5 torr on Pt (200 nm)/Ti (45 nm)/Si (001) substrates using pulsed laser deposition. Due to the deposition at relatively high temperature (873 K), Cu and Ti atoms diffuse to the surface and interface, which significantly affects the magnetic properties. Depth sensitive polarized neutron reflectometry method provides the details of the composition and magnetization profiles and shows that an accumulation of Cu on the surface leads to an increase in the magnetization near the surface. Our results reveal that the presence of the copper at Zn sites induces ferromagnetism at room temperature, confirming intrinsic ferromagnetism.

First principle calculations are employed to calculate the electronic structure and magnetic properties of transition-metal doped MoS2 considering the effects of defect/defect complex. It shows that pure MoS2 with both Mo and S vacancy are nonmagnetic. Mn, Fe, Co and Ni substitution in Mo site all lead to spin polarized state. Considering defect complex, the results show that (TMMo + TMMo) defect complex has the lowest formation energy at high S pressure and prefers close to each other except for (CoMo + CoMo). Experimentally, we doped Mn, Co, Ni and Fe into MoS2 single crystals. The doping leads to room temperature ferromagnetic ordering and clustering, agreeing well with the first principle calculations. Keywords: Defect engineering, 2D materials, Ferromagnetism, First principle calculations

Sm-doped TiO2 nanorods are synthesized by a molten salt method. The expansion of lattice parameters of Sm-doped TiO2 samples verified by XRD and TEM characterizations suggests the successful incorporation of Sm ions into TiO2 matrix. M-H loops show weak room temperature ferromagnetism in Sm-doped samples. Sm and N co-doped TiO2 nanorods are also prepared to study the magnetic behaviour. The results indicate that the co-doping does not enhance the room temperature ferromagnetism but leading to a strong paramagnetic signal at 5 K.

High magnetization materials are in great demand for the fabrication of advanced multifunctional magnetic devices. Notwithstanding this demand, the development of new materials with these attributes has been relatively slow. In this work, we propose a new strategy to achieve high magnetic moments above room temperature. Our material engineering approach invoked the embedding of magnetic nanoclusters in an oxide matrix. By precisely controlling pulsed laser deposition parameters, Co nanoclusters are formed in a 5 at % Co-TiO

We investigated how the processing parameters, including post exposure baking (PEB), and resist film thickness (FT) influence the dose and line width roughness (LWR) of different types of EUV resists, targeted for the high-NA EUV lithography. We compared the dose and LWR of molecular, inorganic and CAR resists at half-pitch (HP) of 16 and 14 nm for different PEB temperatures. The results show that without PEB or at lower PEB temperature, resists require higher doses, as expected. We also observed the different behavior of various resist platforms in response to variation of the film thickness. The results showed that there is a room for the optimization of the processing parameters to improve dose and LWR of molecular, inorganic and CAR resists for line/space printing at high resolution.

The EUV photomask is a key component of the lithography process for semiconductor manufacturing. A critical defect on the mask could be replicated on several wafers, causing a significant production yield reduction. For this reason, actinic patterned mask inspection is an important metrology component for EUV lithography. The RESCAN microscope is a lensless imaging platform dedicated to EUV mask defect inspection and metrology. The resolution of the tool is about 35 nm, which is similar to that of state-of-the-art EUV microscopes. To improve the resolution of RESCAN, we designed an upgraded optical layout for the illumination system and we developed a coherent diffraction imaging-compatible method to synthesize a custom pupil structure. This new scheme will enable a lensless EUV microscope with a resolution down to 20 nm and thereby allow mask review capabilities for future technology nodes with EUV lithography.

Using high-resolution extreme ultraviolet interference lithography (EUV-IL), we investigated contact hole/pillars printing performance of several EUV resist platforms for the high-NA EUV lithography. We compared the dose and local critical dimension uniformity (LCDU) of the three chemically-amplified resists (CARs) with the best performance for printing contact holes (CHs) at half pitch (HP) of 24 and 20 nm. One of the CARs showed the lowest LCDU, 2.3 and 2.2 nm with lowest dose 16.4 and 21.1 mJ/cm2 for HP 24 and 20 nm, respectively. With the inorganic resist we obtained 38.8 mJ/cm2 with an LCDU of 1.3 nm for HP 20 nm pillars. We have also studied the effects of the resist thickness and post-exposure baking (PEB) temperature on the dose and LCDU. These results show that there are promising CAR and non-CAR resists for CH printing towards high-NA EUVL.

The production of modern semiconductor devices is based on photolithography, a process through which a pattern engraved on a mask is projected on a silicon wafer coated with a photosensitive material. In the past few decades, continuous technological progress in this field allowed the industry to follow Moore’s law by reducing the size of the printed features. This was achieved by progressively increasing the numerical aperture of the projection system and reducing the wavelength. The latest lithography platforms for semiconductor manufacturing employ Extreme Ultra Violet (EUV) light at a wavelength of 13.5 nm. The metrology for the optics and the components of such platforms is not fully mature yet. Specifically, the inspection of the EUV photomask is still an open issue as no commercial solutions are currently available. Here we describe a lensless approach to this problem, based on coherent diffraction imaging at EUV that overcomes the main technological issues linked to the conventional mask inspection approach.

Reliable photomask metrology is required to reduce the risk of yield loss in the semiconductor manufacturing process. Actinic pattern inspection (API) of EUV reticles is a challenging problem to tackle with a conventional approach. For this reason we developed an API platform based on coherent diffraction imaging. Aim: We want to verify the sensitivity of our platform to absorber and phase defects. Approach: We designed and manufactured two EUV mask samples with absorber and phase defects and we inspected them with RESCAN in die-to-database mode. Results: We reconstructed an image of an array of programmed absorber defects and we created a defect map of our sample. We inspected two programmed phase defect samples with buried structures of 3.5 nm and 7.8 nm height. Conclusions: We verified that RESCAN in its current configuration can detect absorber defects in random patterns and buried (phase) defects down to 50 × 50 nm2.

Sm doped ZnO nanorods with various concentrations have been successfully synthesized using a hydrothermal method. XRD analysis indicates that there are no impurities or secondary phases in all the samples. The continuous expansion of d-spacing from XRD and TEM analysis suggests the effective corporation of Sm ions in ZnO. It is found that pure ZnO is paramagnetic. Both 1% and 5% Sm doped ZnO nanorods are ferromagnetic at room temperature. 5% Sm doped ZnO has a large paramagnetic signal at low temperature, suggesting the formation of the precipitation or clusters of samarium oxide.

High-resolution patterning of periodic structures over large areas has several applications in science and technology. One such method, based on the long-known Talbot effect observed with diffraction gratings, is achromatic Talbot lithography (ATL). This method offers many advantages over other techniques, such as high resolution, large depth-of-focus, and high throughput. Although the technique has been studied in the past, its limits have not yet been explored. Increasing the efficiency and the resolution of the method is essential and might enable many applications in science and technology. In this work, the authors combine this technique with spatially coherent and quasimonochromatic light at extreme ultraviolet (EUV) wavelengths and explore new mask design schemes in order to enhance its throughput and resolution. They report on simulations of various mask designs in order to explore their efficiency. Advanced and optimized nanofabrication techniques have to be utilized to achieve high quality and efficient masks for ATL. Exposures using coherent EUV radiation from the Swiss light source have been performed, pushing the resolution limits of the technique for dense hole or dot patterning down to 40 nm pitch. In addition, through extensive simulations, alternative mask designs with rings instead of holes are explored for the efficient patterning of hole/dot arrays. They show that these rings exhibit similar aerial images to hole arrays, while enabling higher efficiency and thereby increased throughput for ATL exposures. The mask designs with rings show that they are less prone to problems associated with pattern collapse during the nanofabrication process and therefore are promising for achieving higher resolution.

Five percent Fe-doped In

Na doped ZnO films were fabricated via a hydrothermal process. The films have shown room temperature ferromagnetism and p-type conductivity. Crossover of positive to negative magnetoresistance has been observed with the variation of Na doping concentrations. The positive MR is due to p-p exchange interaction induced Zeeman splitting to suppress the hopping path of holes. The ferromagnetism is attributed to the formation of a Zn vacancy complex. The negative magnetoresistance is due to the minimization of spin-dependent scattering by the applied magnetic field.

NiO films were deposited by sputtering with a relatively high oxygen partial pressure, followed by subsequent annealing in air. The as-deposited film is amorphous. The amorphous film gradually turns to crystalline structure with the increase in annealing temperature. The film annealed at 673 K shows strong ferromagnetism at room temperature, whereas, there is no room-temperature ferromagnetic ordering for the as-deposited amorphous NiO film or the film after annealed at 873 K. The ferromagnetism is due to the finite size effect and the high Curie temperature above room temperature is associated with the interaction between ferromagnetic NiO crystalline nanoclusters and antiferromagnetic amorphous matrix.

Background: Hybrid inorganic-organic materials have emerged as promising candidates for EUV resists. However, knowledge on their stability when deposited as thin films is essential for their performance in EUV lithography. Aim: We investigate whether the molecular structure of Zn-based metal oxoclusters is preserved upon thin film deposition and study aging processes of the thin film under different atmospheres, since these chemical changes affect the solubility properties of the material. Approach: A hybrid cluster that combines the high EUV photon absorption cross-sections of zinc and fluorine with the reactivity of methacrylate organic ligands was synthesized. The structural modifications upon thin film formation and after aging in air, nitrogen, and vacuum were studied using a combination of spectroscopic techniques. Preliminary studies on the lithographic performance of this material were performed by EUV interference lithography. Results: The Zn-based compound undergoes structural rearrangements upon thin film deposition as compared to the bulk material. The thin films degrade in air over 24 h, yet they are found to be stable for the duration and conditions of the lithography process and show high sensitivity. Conclusions: The easy dissociation of the ligands might facilitate hydrolysis and rearrangements after spin-coating, which could affect the reproducibility of EUV lithography.

Extreme ultraviolet interference lithography (EUV-IL) is relatively simple and inexpensive technique that can pattern high resolution line/space and has been successfully used for the resist performance testing. While the aerial image in EUV-IL formed by two beams is straightforward to understand and has contrast of 1, the aerial image formed by four beams providing contact holes (CHs) is rather complicated. The phases of the interfering beams as well as by the polarization play big roles in the image of the interference pattern and its contrast. To understand thoroughly the formation of CH, we investigate theoretically polarization effect on the aerial image generated with two and four-beam interference. We show the coherent four-beam interference provides the highest contrast (1) with zero initial phase. But the interference pattern strongly depends on the phase difference and switch from one to another when the phase difference between the two pairs of gratings is π/2. Consequently, the contrast also decreases and interference pattern could end with random form when the relative phase of the beams cannot be fully controlled. We propose an incoherent four-beam interference model by intentionally designing the grating with a slightly different pitch to create an optical path difference that is longer than the coherence length of the EUV light (13.5 nm). We also discuss the polarization-induced contrast loss. We verify our analytical model by printing both positive tone chemically amplified resist (CAR) and a negative tone inorganic resist.

Here we present a study of magnetism in Co_{0.05}Ti_{0.95}O_{2-δ} anatase films grown by pulsed laser deposition under a variety of oxygen partial pressures and deposition rates. Energy-dispersive spectrometry and transmission electron microscopy analyses indicate that a high deposition rate leads to a homogeneous microstructure, while a very low rate or postannealing results in cobalt clustering. Depth resolved low-energy muon spin rotation experiments show that films grown at a low oxygen partial pressure (≈10^{-6} torr) with a uniform structure are fully magnetic, indicating intrinsic ferromagnetism. First principles calculations identify the beneficial role of low oxygen partial pressure in the realization of uniform carrier-mediated ferromagnetism. This work demonstrates that Co:TiO_{2} is an intrinsic diluted magnetic semiconductor.

Co-doped titanium dioxide (TiO2) nanorods with different doping concentrations were fabricated by a molten salt method. It is found that the morphology of TiO2 changes from nanorods to nanoparticles with increasing doping concentration. The mechanism for the structure and phase evolution is investigated in detail. Undoped TiO2 nanorods show strong ferromagnetism at room temperature, whereas incorporating of Co deteriorates the ferromagnetic ordering. X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) results demonstrate that the ferromagnetism is associated with Ti vacancy.

Na-doped ZnO nanorods have been fabricated through a hydrothermal method. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses indicate that the d spacing of ZnO increases with increasing doping concentration, suggesting the effective incorporation of dopant Na in the samples. Electron paramagnetic resonance (EPR) measurements indicate that there are shallow donors in pure ZnO samples and the shallow donors are strongly prohibited by Na doping. In addition, the resonance at g = 2.005 suggests the formation of Zn vacancies. Magnetic measurements indicate that pure ZnO is paramagnetic and Na doping leads to ferromagnetism at room temperature. Moreover, 0.5% Na-doped ZnO nanorods exhibits the largest saturation magnetization.

Conventional sintering and direct ball milling of Bi 2 O 3 + Fe 2 O 3 mixture were used for the fabrication of BiFeO 3 powders. The fabricated powders were performed annealing or high energy ball milling to vary the grain size from bottom-up or top-down. It was found that the magnetization of the powders synthesized by both methods plotted with the reciprocal of the grain size could be linearly fitted, indicating that the magnetism is from the finite size effect. Exchange bias phenomenon was observed after field cooling (FC) of the powders, confirming the magnetization is due to the uncompensated or canted surface spins. No spin glass behavior was found in these powders.

The emission behavior of C-doped ZnO films, which were prepared by implantation of carbon into ZnO films, is investigated. Orange/red emission is observed for the films with the thickness of 60–100 nm. However, the film with thickness of 200 nm shows strong green emission. Further investigations by annealing bulk ZnO single crystals under different environments, i.e. Ar, Zn or C vapor, indicated that the complex defects based on Zn interstitials are responsible for the strong green emission. The existence of complex defects was confirmed by electron spin resonance (ESR) and low temperature photoluminescence (PL) measurement.