Single Patterning Research Articles

Highly Efficient Laser Bidirectional Graphene Printing: Integration of Synthesis, Transfer and Patterning.

Graphene has tremendous potential in future electronics due to its superior force, electrical, and thermal properties. However, the development of graphene devices is limited by its complex, high-cost, and low-efficiency preparation process. This study proposes a novel laser bidirectional graphene printing (LBGP) process for the large-scale preparation of patterned graphene films. In LBGP, a sandwich sample composed of a thermoplastic elastomer (TPE) substrate, carbon precursor powder, and a glass cover is irradiated by a nanosecond pulsed laser. The laser photothermal effect converts the carbon precursor into graphene, with partial graphene sheets deposited directly on the TPE substrate and the remaining transferred to the glass cover via a laser-induced plasma plume. This method simultaneously prepares two face-to-face graphene films in a single laser irradiation, integrating synthesis, transfer, and patterning. The resulting graphene patterns demonstrate good performance in flexible pressure sensing and Joule heating, showcasing high sensitivity (7.7kPa-1), fast response (37ms), and good cycling stability (2000 cycles) for sensors, and high heating rate (1°Cs-1) and long-term stability (3000s) for heaters. It is believed that the simple, low-cost, and efficient LBGP process can promote the development of graphene electronics and laser manufacturing processes.

Self-Mixed Biphasic Liquid Metal Composite with Ultra-High Stretchability and Strain-Insensitivity for Neuromorphic Circuits.

Neuromorphic circuits that can function under extreme deformations are important for various data-driven wearable and robotic applications. Herein, biphasic liquid metal particle (BMP) with unprecedented stretchability and strain-insensitivity (ΔR/R0 = 1.4@ 1200% strain) is developed to realize a stretchable neuromorphic circuit that mimics a spike-based biologic sensory system. The BMP consists of liquid metal particles (LMPs) and rigid liquid metal particles (RLMPs), which are homogeneously mixed via spontaneous solutal-Marangoni mixing flow during coating. This permits facile single step patterning directly on various substrates at room temperature. BMP is highly conductive (2.3 × 106 S/m) without any post activation steps. BMP interconnects are utilized for a sensory system, which is capable of distinguishing variations of biaxial strains with a spiking neural network, thus demonstrating their potential for various sensing and signal processing applications.

Voltage contrast determination of design rules at the limits of EUV single patterning

Voltage contrast determination of design rules at the limits of EUV single patterning

Ultrasensitive metal-organic cluster resist for patterning of single exposure high numerical aperture extreme ultraviolet lithography applications

BackgroundAn incredible increase in the integration of electronic chips has pushed the semicon industries to endorse high numerical aperture (h-NA ∼ 0.5), extreme-ultraviolet (EUV) lithography (EUVL) (λ ∼ 13.5 nm) at the commercial scale. Induction of h-NA postulates EUV resists that could outperform the resolution, line pattern roughness, and sensitivity (RLS) trade-off for chip fabricators, which is currently extremely limited.AimThe development of EUV resist to balance RLS trade-off as well as overcome throughput limitations of h-NA EUV system to facilitate high volume semiconductor manufacturing.ApproachHere, we developed indium-methacrylic acid-based metal-organic clusters resist for h-NA, EUVL. To examine the h-NA single exposure patterning potential of the resist, prescreening by sub-10 nm next-generation lithography (NGL) tools such as electron beam lithography (EBL), and helium ion beam lithography (HIBL) were conducted as a prelude to EUV exposure.ResultsDense ∼13 nm, (l/s) patterns at ∼45 and ∼30 μC / cm2 were well resolved by EBL and HIBL, on the top this the line edge roughness (LER) was 2.48 ± 0.04 nm, and etch resistance ∼1.98 and ∼0.34 times lower than Si and SiO2 / Si systems. Also, In-MAA MOCs resist shows ultra-sensitivity of 2.3 mJ / cm2 towards h-NA EUVL for patterning up to 26 nm half-pitch line patterns with LER ∼2.36 ± 0.16 nm.

Extend 0.33 NA extreme ultraviolet single patterning to pitch 28-nm metal design by low-n mask

Extending 0.33 NA extreme ultraviolet single patterning to 28-nm pitch becomes challenging in stochastic defectivity, which demands high-contrast lithographic images. The low-n attenuated phase-shift mask (attPSM) can provide superior solutions for individual pitches by mitigating mask three-dimensional effects. The simulation and experiment results have shown substantial imaging improvements: higher depth of focus at similar normalized image log slope and smaller telecentricity error values than the best binary mask configuration. In this work, the exploration of low-n attPSM patterning opportunity for pitch 28-nm metal design is investigated. Using generic building block features, the lithographic performance of the low-n attPSM is compared with the standard binary Ta-based absorber mask. In addition, the impact of mask tone (bright field (BF) versus dark field) on the pattern fidelity and process window is evaluated both by simulations and experiments. The results indicate that BF low-n attPSM provides the best patterning performance. Consequently, the BF low-n attPSM patterning performance is assessed with an actual imec N3 pitch 28-nm random logic metal design. The wafer data indicate BF low-n attPSM enables good patterning fidelity, as well as good overall process window with high exposure latitude (∼20 % ).

Exploration of alternative mask for 0.33NA extreme ultraviolet single patterning at pitch 28-nm metal design

Extending 0.33NA extreme ultraviolet (EUV) single patterning to pitch 28 nm will enable significantly shorter process flow for N2 node and cost-efficiency of metal layers patterning. At the same time, EUV single patterning becomes very challenging in terms of stochastic defectivity and process window. To enable EUV single patterning at pitch 28 nm with good process window and patterning fidelity (low defectivity and line edge roughness), three mask candidates are considered: a standard binary Ta-based absorber mask, a high extinction (high-k) absorber mask, and a low-n attenuated phase-shift mask (attPSM). The patterning performance of these three mask candidates is compared by means of source mask optimization. The patterning performance of the candidate masks is assessed using an imec N3 (foundry N2 equivalent) random logic M1 layout. The impact of mask tonality (bright field versus dark field) and insertion of sub-resolution assist features (SRAFs) on pattern fidelity and process window is evaluated. Considering all the aspects, simulations indicate that the low-n attPSM has the best patterning performance both for dark-field mask with SRAFs and bright-field mask without SRAFs.

Pattern Generation for Micropattern Traction Microscopy.

Micropattern traction microscopy allows control of the shape of single cells and cell clusters. Furthermore, the ability to pattern at the micrometer length scale allows the use of these patterned contact zones for the measurement of traction forces, as each micropatterned dot allows for the formation of a single focal adhesion that then deforms the soft, underlying hydrogel. This approach has been used for a wide range of cell types, including endothelial cells, smooth muscle cells, fibroblasts, platelets, and epithelial cells. This review describes the evolution of techniques that allow the printing of extracellular matrix proteins onto polyacrylamide hydrogels in a regular array of dots of prespecified size and spacing. As micrometer-scale patterns are difficult to directly print onto soft substrates, patterns are first generated on rigid glass coverslips that are then used to transfer the pattern to the hydrogel during gelation. First, the original microcontact printing approach to generate arrays of small dots on the coverslip is described. A second step that removes most of the pattern to leave islands of small dots is required to control the shapes of cells and cell clusters on such arrays of patterned dots. Next, an evolution of this approach that allows for the generation of islands of dots using a single subtractive patterning step is described. This approach is greatly simplified for the user but has the disadvantage of a decreased lifetime for the master mold needed to make the patterns. Finally, the computational approaches that have been developed for the analysis of images of displaced dots and subsequent cell-generated traction fields are described, and updated versions of these analysis packages are provided.

Single, binary and successive patterning of charged nanoparticles by electrophoretic deposition

Deposition of nanoparticles on a substrate in a controlled manner leads to the formation of multifunctional surfaces and therefore devices. Electrostatic forces can be utilized to manipulate different types of materials such as magnetic, insulating, conducting, semiconducting, organic and inorganic, without altering the chemistry of the surface. However, simultaneous and successive electrophoretic deposition (EPD) methods are not fully utilized for nanoparticles with different characteristics. In this work, electrostatic forces are applied to direct and position charged nanoparticles suspended in aqueous dispersions on desired areas of the surface. Assemblies of particles are obtained by electrostatic attraction generated by gold electrodes of sizes from 500 nm to 50 µm that are fabricated by thermal evaporation. Different types of charged nanoparticles were simultaneously attracted towards different locations of the surface by means of EPD; as a result, alternating nanoparticle patterns and particle deposition on the same designated areas for forming composite areas are obtained. Assemblies formed from positively charged silver nanoparticles and negatively charged fluorescent latex and silica nanoparticles are demonstrated. The position of metallic-, polymeric- and inorganic-based nanoparticles is controlled by the design of electrode geometry.

Multi-Wavelength Optical Patterning for Multiscale Materials Design

Laser interferometry is a consolidated technique for materials structuring, enabling single step and large area patterning. Here we report the investigation of the morphological modification encoded on a thin film of a photosensitive material by the light interference pattern obtained from a laser operating in multiline mode. Four lines with equal intensity are retained, with the same p linear polarization. An azopolymer is exploited as medium for the holographic recording. Optical microscopy and profilometer measurements analyze the modification induced in the bulk and on the surface of the irradiated area. We show that the intensity profile of the interference patterns of two laser beams is the one obtained assuming each line of the laser as an independent oscillator of given intensity and wavelength, and how these light structures are faithfully replicated in the material bulk and on the topography of the free surface. Patterns at different length scales are achievable in a single step, that can be traced back to both interference fringes and wave envelopes. The proposed multi-wavelength holographic patterning provides a simple tool to generate complex light structures, able to perform multiscale modifications of photoresponsive materials

Exploiting Substrate Cues for Co-Culturing Cells in a Micropattern.

Spatial distribution of cells and their interactions between neighboring cells in native microenvironments are of fundamental importance in determining cell fate decisions such as migration, growth, and differentiation. Controlling the spatial distribution of different cell types in defined geometries can replicate these native environments, which can be a useful model for several studies. While spatiotemporal control over multiple cell arrangements is required to achieve the complex tissue architecture, unfortunately, conventional cell patterning techniques usually allow only single patterning with a single cell type. In the present study, we introduce a simple lithographic method to pattern multiple cell types in a spatially controlled manner by utilizing the biophysical cues present at the corners of the patterned geometry. By fabricating micropatterns of different shapes, we demonstrate how the cell can be constrained to pattern along the corners of patterned geometries owing to the presence of topographical cues, leaving empty voids in the center that can be further utilized for patterning a second cell type. We also demonstrate that the cell alignment along the pattern is a dynamic process and the cells migrate from a more uniform cell-adhesive region toward the topographical cues. The cytoskeleton arrangement was geometry-dependent, which was confirmed through a series of in vitro evaluations, such as scanning electron microscopy and fluorescence microscopy. These findings have not only helped us in exploring the importance of these cues in guiding the cell fate but have also allowed us to develop a technique, which self-patterns the cells without any expensive exogenous cues and can be used as a model protocol to eventually organize cells into a specific pattern with micron-scale precision in vitro.

Strain-induced yellow to blue emission tailoring of axial InGaN/GaN quantum wells in GaN nanorods synthesized by nanoimprint lithography

GaN nanorods (NRds) with axial InGaN/GaN MQWs insertions are synthesized by an original cost-effective and large-scale nanoimprint-lithography process from an InGaN/GaN MQWs layer grown on c-sapphire substrates. By design, such NRds exhibit a single emission due to the c-axis MQWs. A systematic study of the emission of the NRds by time-resolved luminescence (TR-PL) and power dependence PL shows a diameter-controlled luminescence without significant degradation of the recombination rate thanks to the diameter-controlled strain tuning and QSCE. A blueshift up to 0.26 eV from 2.28 to 2.54 eV (543 nm to 488 nm) is observed for 3.2 nm thick InGaN/GaN QWs with an In composition of 19% when the NRds radius is reduced from 650 to 80 nm. The results are consistent with a 1-D based strain relaxation model. By combining state of the art knowledge of c-axis growth and the strong strain relieving capability of NRds, this process enables multiple and independent single-color emission from a single uniform InGaN/GaN MQWs layer in a single patterning step, then solving color mixing issue in InGaN based nanorods LED devices.

Deterministic Assembly of Single Sub-20nm Functional Nanoparticles Using a Thermally Modified Template with a Scanning Nanoprobe.

A deterministic assembly technique for single sub-20nm functional nanoparticles is developed based on nanostructured templates fabricated by hot scanning nanoprobes. With this technique, single nanoparticles including quantum dots, polystyrene fluorescent nanobeads, and gold nanoparticles are successfully assembled into 2D arrays with high yields. Experimental and theoretical analyses show that the key for the high yields is the hot-probe-based template fabrication technique, which creates geometrical nanotraps and modifies their surface energy simultaneously. In addition to single nanoparticle patterning, further experiments demonstrate that this technique is also capable of building complex nanostructures, such as nanoparticle clusters with well-defined shapes and heterogeneously integrated nanostructures consisting of quantum dots and silver nanowires. It opens the door to many important applications.

Scanning digital oil immersion lithography providing high-speed large area patterning with diffraction limited sub-micron resolution

A high numerical aperture (NA) scanning digital oil immersion lithography scheme is proposed and demonstrated in this study. To successfully conduct the scanning digital oil immersion lithography, immersion oil should be removed from the photoresist layer before the development process. Also, uniformity of the projected light patterns becomes crucial in the quality of this high NA photolithography. To solve these issues, we developed a cleaning procedure for the immersion oil and an intensity calibration scheme to achieve a highly uniform intensity distribution of the projected patterns. With these preparations, we were able to achieve 400 nm resolution large area patterning with the developed scanning digital oil immersion lithography system and a better than 200 nm resolution in the single line patterning. Also, with a double layered photoresist scheme and our lab-prepared photoresist, we successfully achieved large area lift-off patterns of 400 nm metallic dot arrays through the scanning digital oil immersion lithography system.

Three-dimensional Fabry–Pérot cavities sculpted on fiber tips using a multiphoton polymerization process

This paper presents 3D Fabry–Pérot (FP) cavities fabricated directly onto cleaved ends of low-loss optical fibers by a two-photon polymerization (2PP) process. This fabrication technique is quick, simple, and inexpensive compared to planar microfabrication processes, which enables rapid prototyping and the ability to adapt to new requirements. These devices also utilize true 3D design freedom, facilitating the realization of microscale optical elements with challenging geometries. Three different device types were fabricated and evaluated: an unreleased single-cavity device, a released dual-cavity device, and a released hemispherical mirror dual-cavity device. Each iteration improved the quality of the FP cavity’s reflection spectrum. The unreleased device demonstrated an extinction ratio around 1.90, the released device achieved 61, and the hemispherical device achieved 253, providing a strong signal to observe changes in the free spectral range of the device’s reflection response. The reflectance of the photopolymer was also estimated to be between 0.2 and 0.3 over the spectrum of interest. The dual-cavity devices include both an open cavity, which can interact with an interstitial medium, and a second solid cavity, which provides a static reference reflection. The hemispherical dual-cavity device further improves the quality of the reflection signal with a more consistent resonance, and reduced sensitivity to misalignment. These advanced features, which are very challenging to realize with traditional planar microfabrication techniques, are fabricated in a single patterning step. The usability of these FP cavities as thermal radiation sensors with excellent linear response and sensitivity over a broad range of temperature is reported. The 3D structuring capability the 2PP process has enabled the creation of a suspended FP heat sensor that exhibited linear response over the temperature range of 20 ºC –120 ºC; temperature sensitivity of ∼50 pm ºC−1 at around 1550 nm wavelength; and sensitivity improvement of better than 9x of the solidly-mounted sensors.

Variability-Aware Predictive Modeling of Line-to-Line Dielectric Reliability

We present a predictive model for line-to-line dielectric reliability that takes variability into account. The lifetime distribution is obtained by performing series-parallel reliability computations, starting from the failure distributions of single dielectric unit cells, assumed to be Weibull. The electric field in between the lines is estimated point-by-point, and the power law is applied to account for the related impact on the Weibull scale parameter of every single cell. Finally, the model is calibrated to actual reliability measurements to fix the reference parameters of the Weibull distribution and power law. We employ our model to predict the impact of line-edge roughness (LER), and die-to-die spacing variations on the reliability of scaled interconnects and derive specs from meeting ten years lifetime at operating conditions. We show that specs can be expressed in terms of a single combined-metric, that is, the line-spacing roughness over the wafer (WLSR). Consequently, tradeoffs can be made between specs on LER and die-to-die spacing variations to achieve the same reliability margin. We calibrate our model to Time-Dependent Dielectric Breakdown (TDDB) data from low- ${k}$ planar capacitors (p-caps) and generate WLSR specs for dimensions ranging from 16- to 8-nm spacing. We predict a significant drop in the reliability margin when scaling down the spacing or the dielectric ${k}$ -value. As an example, we observe more than 50% reduction in the allowed $\sigma _{{\text {WLSR}}}$ from 16- to 10-nm spacing. We also compare single with multipatterned interconnects. For spacer-assisted multipatterning, spacing edges are cross-correlated, and we predict that for the same die-to-die spacing variations more than two times higher LER is allowed with respect to single patterning to meet the same reliability requirements.

Enhanced Reliability of 7-nm Process Technology Featuring EUV

In this article, we report the reliability characterization of 7-nm technology, in which the highly scaled sixth generation of FinFETs and 256-Mb static random access memory (SRAM) cells were newly developed by featuring extreme ultraviolet (EUV). The intrinsic reliability mechanisms of 7-nm FinFET including hot carrier injection (HCI), bias temperature instability (BTI), and time-dependent dielectric-breakdown (TDDB) are similar to that of the previous nodes, and would not be degraded by introducing the scaled FinFET. Moreover, we found that the use of EUV single patterning of middle of line (MOL) and back end of line (BEOL) improves reliability distribution remarkably as compared to the previous nodes using argon fluoride (ArF) multiple patterning techniques. We successfully demonstrated SRAM and logic high-temperature operating life (HTOL) up to 500 h, indicating the robustness of product-level reliability. These findings strongly suggest that the 7-nm technology featuring EUV is fully ready for high-volume manufacturing as well as providing a near future logic production with high-quality reliability.

The Line Roughness Improvement in Self-aligned Multiple Patterning

Multi-patterning has been widely used in the semiconductor industry to enable the continued scaling requirement such as Fin, Gate, and critical Metal lines. Either Self-aligned Multiple Patterning (SaMP) or Litho-Etch/Litho-Etch (LELE) shows plasma etch become more dominant for the line edge and width roughness (LER/LWR) than single patterning technology [1]. To mitigate the strict line roughness requirements for advanced technology nodes (14nm and below), we proposed and demonstrated a novel nitrogen-based Inductively Coupled Plasma (ICP) treatment and an argon-based Capacitively Coupled Plasma (CCP) treatment on LER/LWR improvement, separately. Both recipes are optimized with an optimal design experiment (ODE) statistical method. The optimal organic mandrel etch recipe can improve the LER of the final pattern to 1.2nm. Furthermore, two effective Si mandrel post etch treatment (PET) methods are investigated: special surface plasma treatment and H2 anneal. The H2 anneal effect was found related to the capping layer, different from former published paper. We also found out the different chemistry in Spacer etch can impact line roughness but trade-off with defect performance. Finally, we achieved a 20% LWR improvement of final pattern in a self-aligned quadruple patterning (SAQP) without any side effect.

The Line Roughness Improvement in Self-Aligned Multiple Patterning

Multi-patterning has been widely adopted in the semiconductor manufacturing industry to enable the continued scaling requirement such as fin, gate, and critical metal lines. Either Self-aligned Multiple Patterning (SaMP) or Litho-Etch-Litho-Etch (LELE) shows plasma etch becomes more dominant for the line roughness than single patterning technology (1). To mitigate the strict line roughness requirements for advanced technology nodes, we demonstrated a novel nitrogen-based inductively coupled plasma (ICP) treatment. The recipe was optimized with an optimal design experiment (ODE). The optimal mandrel etch recipe coupled with HBr plasma curing can improve 60% line edge roughness (LER) of the final pattern. Furthermore, two post etch treatment (PET) methods were investigated on Si mandrel: special argon-based plasma treatment and hydrogen annealing. The hydrogen annealing effect was found related to the capping layer, different from previously published paper. Finally, we achieved a 20% line width roughness (LWR) improvement of final pattern in a self-aligned quadruple patterning (SaQP) without any side effect.

Photoresist Challenges for Logic and Memory using 0.33NA EUV Lithography

With the scaling evolution of logic and memory technologies the extreme ultraviolet lithography (EUVL) technology is becoming part of the high-volume manufacturing device landscape. Currently, the single patterning of both logic metal layer and DRAM storage layer are approaching the resolution limit on the 0.33NA full field exposure scanner. Furthermore, because the logic technology nodes are scaling at a faster pace than memory nodes, the development of leading-edge logic node (N5) will move first the EUVL insertion from a single patterning to a double patterning technology with relaxed pitches to overcome the current 0.33NA EUVL limits. In this paper, the EUV photoresist challenges are discussed on the horizon of up-coming industry technology nodes.

Cell Printing in Complex Hydrogel Scaffolds.

Advancements in the microfabrication of soft materials have enabled the creation of increasingly sophisticated functional synthetic tissue structures for a myriad of tissue engineering applications. A challenge facing the field is mimicking the complex microarchitecture necessary to recapitulate proper morphology and function of many endogenous tissue constructs. This paper describes the creation of PEGDA hydrogel microenvironments (microgels) that maintain a high level of viability at single cell patterning scales and can be integrated into composite scaffolds with tunable modulus. PEGDA was stereolithographically patterned using a digital micromirror device to print single cell microgels at progressively decreasing length scales. The effect of feature size on cell viability was assessed and inert gas purging was introduced to preserve viability. A composite PEGDA scaffold created by this technique was mechanically tested and found to enable dynamic adjustability of the modulus. Together this approach advances the ability to microfabricate tissues that better mimic native constructs on cellular and subcellular length scales.