Development Of Lithography Research Articles

Current Progress of EUV Spectral Responsivity Calibration for EUV Lithography at CMS/ITRI

Abstract To support the development of advanced EUV lithography for the semiconductor industry in Taiwan, a calibration system for photodiodes’ spectral responsivity was established. The current system utilizes the synchrotron radiation light source and the method is traceable to PTB, Germany. The wavelength range is from 10 nm to 15 nm, including the most often used 13.5 nm. Several techniques were studied to compensate for light source fluctuation and to reduce the measurement uncertainty. The relative expanded uncertainty of the spectral responsivity calibration at 13.5 nm is 4.6 % (k=2). A wafer-type EUV radiant power meter designed to be used in EUV lithography chambers is being developed. Our goal is to develop simple and reliable methods for on-site EUV optical power measurement and dose estimation.

Improving the working distance for near-field lithography with supercell photonic crystal

Near-field lithography technology plays a vital role in chip manufacturing. However, near-field lithography devices with acceptable working distance (WD) have become a long-term pursuit for researchers. Here, a one-dimensional supercell photonic crystal (SPC) is proposed for near-field lithography. The simulation results show that the PCs could provide an air WD of over 100 nm in interference lithography and produce patterns with a resolution reach ∼67 nm (∼λ/6). The analyses indicate that using SPCs in interference lithography can make it more suitable for practical manufacturing. Furthermore, this type of PC can also be used in direct writing lithography. The simulation results show that the direct writing lithography could be realized with a WD of 100 nm, and the full width at half maximum of the focal spot is ∼137 nm. The principle presents a new method for controlling the evanescent waves, and the method would greatly promote the development and application of near field lithography.

Accurate and efficient evaluation of the ionization potentials of extreme ultraviolet photoresists using density functionals and semi-empirical methods

Extreme ultraviolet (EUV) photoresists have become the core materials in lithography with nanometer-sized patterns and are actively explored on the path to realizing smaller critical dimensions. These photoresists can be small molecule-, polymer-, or organic–inorganic hybrid-based, with the full molecular working mechanism under investigation. For the rational design of EUV photoresists, theoretical guidance using tools like first-principle calculations and multi-scale simulations can be of great help. Considering the extremely high standard of accuracy in EUV lithography, it is critical to ensure the adoption of the appropriate methodologies in the theoretical evaluation of EUV photoresists. However, it is known that density functionals and semi-empirical methods differ in accuracy and efficiency, without a universal rule across materials. This poses a challenge in developing a reliable theoretical framework for calculating EUV photoresists. Here, we present a benchmark investigation of density functionals and semi-empirical methods on the three main types of EUV photoresists, focusing on the ionization potential, a key parameter in their microscopic molecular reactions. The vertical detachment energies (VDE) and adiabatic detachment energies (ADE) were calculated using 12 functionals, including pure functionals, hybrid functionals, Minnesota functionals, and the recently developed optimally tuned range-separated (OTRS) functionals. Several efficient semi-empirical methods were also chosen, including AM1, PM6, PM7, and GFN1-xTB in the extended tight-binding theoretical framework. These results guide the accurate and efficient calculation of EUV photoresists and are valuable for the development of multi-scale lithography protocols.Graphical

Evaluation of the X-ray/EUV Nanolithography Facility at AS through wavefront propagation simulations.

Synchrotron light sources can provide the required spatial coherence, stability and control to support the development of advanced lithography at the extreme ultraviolet and soft X-ray wavelengths that are relevant to current and future fabricating technologies. Here an evaluation of the optical performance of thesoft X-ray (SXR) beamline of the Australian Synchrotron (AS) and its suitability for developing interference lithography using radiation in the 91.8 eV (13.5 nm) to 300 eV (4.13 nm) range are presented. A comprehensive physical optics model of the APPLE-II undulator source and SXR beamline was constructed to simulate the properties of the illumination at the proposed location of a photomask, as a function of photon energy, collimation and monochromator parameters. The model is validated using a combination of experimental measurements of the photon intensity distribution of the undulator harmonics. It is shown that the undulator harmonics intensity ratio can be accurately measured using an imaging detector and controlled using beamline optics. Finally, the photomask geometric constraints and achievable performance for the limiting case of fully spatially coherent illumination are evaluated.

Simulation aspects of patterning polymer films via evaporative lithography and composite substrates

The continuing development of evaporative lithography is important for many areas such as the creation of photonic crystals for optronics and microelectronics, the development of biosensors for medical applications and biotechnology, and for the formation of functional coatings for nanotechnology, including the application of thin, protective polymer coatings. The article proposes a mathematical model that allows us to explain the basic mechanisms of the formation of thin polymer films (less than 50 μm thick) during their deposition onto a composite substrate by methanol evaporation from a solution. If the thermal conductivity of the substrate is spatially non-uniform, this results in inhomogeneous evaporation along the free film surface. Therefore, as the film dries, a patterned polymer coating is left behind on the substrate. The mathematical model described here is based on the lubrication approximation and takes into account the dependence of the solution density on the concentration. The numerical computation results are in qualitative agreement with the experimental data of other authors. The article shows that solutal Marangoni flow plays a primary role in the process under consideration. This study allows us to better understand the mechanisms that can be used in evaporative lithography.

Three-dimensional plasmonic lithography imaging modeling based on the RCWA algorithm for computational lithography.

This paper reminds the principle and characteristics of plasmonic lithography, and points out the importance of establishing a fast and high precision plasmonic lithography imaging model and developing computational lithography. According to the characteristics of plasmonic lithography, the rigorous coupled-wave analysis (RCWA) algorithm is a very suitable alternative algorithm. In this paper, a three-dimensional plasmonic lithography model based on RCWA algorithm is established for computational lithography requirements. This model improves the existing RCWA algorithm, that is, deduces the formula for calculating the light field inside the structure and proposes the integration, storage and invocation of the scattering matrix to improve the computation speed. Finally, the results are compared with commercial software for the two typical patterns. The results show that the two calculation results are very close, with the root mean square error (RMSE) less than 0.04 (V/m)2. In addition, the calculation speed can be increased by more than 2 times in the first calculation, and by about 8 times by integrating, storing and invoking the scattering matrix, which creates conditions for the development of plasmonic computational lithography.

Research progress of laser lithography

Lithography is one of the key technologies that restrict the development of the semiconductor industry and its important role continues to be highlighted. This paper will review laser projection lithography and laser maskless lithography based on the theoretical knowledge of laser lithography, present the advantages of laser maskless lithography, discuss the latest progress of laser lithography in application fields, explore its development prospects and trends, and provide some ideas and inspiration for the further development of human laser lithography. The result shows that laser lithography can be used in the field of material processing, and lithography is one of the key technologies to fabricate semiconductor devices. The world’s most advanced lithography machine is the EUV lithography machine of the Dutch ASML. This EUV lithography machine can be used for the production of 5nm chips, so 5nm is the most advanced chip manufacturing process that EUV lithography machine can achieve. Since lithography is a high degree of composite technology, each component plays an irreplaceable role. Therefore, if further improvements are to be made to the chip process, researchers should look at all parts of the exposure system, photoresist and process technology to make them work together in harmony.

Direct etching of nano/microscale patterns with both few-layer graphene and high-depth graphite structures by the raster STM electric lithography in the ambient conditions.

The development of raster STM electric lithography has enabled the etching of nano/microscale patterns on both few-layer graphene (FLG) and high-depth graphite structures on the bulk HOPG substrates under ambient conditions. This approach utilises a nanoscale probe tip as a machining tool to directly fabricate conductive sample surfaces without the need for resists or masks. Compared to conventional nano/micro machining methods, the capability of ultraaccurate fabrication of nanoscale patterns using this technique is unmatched. The resulting FLG structures exhibit ultrasmooth flat bottoms and uniformly controlled depths ranging from 0.34 to 3.0nm (less than 10 layers). This work represents a significant advancement as it demonstrates the perfect etching of FLG structures in designated nano/microscale regions using raster STM electric lithography in the constant current mode, which reaches the limitation of top-down manufacturing techniques. Additionally, raster STM electric lithography in the constant height mode can directly etch high-depth structures (up to ∼100nm). The geometric shape and number of layers of the etched graphene structures determined by either local anodic oxidation (LAO) or the electric discharge (ED) mechanism. The LAO mechanism results in less debris and smoother edges compared to the ED mechanism, which is caused by the random electrical discharge between the tip and the sample. The well-controlled raster STM electric lithography technique is believed to be a promising and facile approach for constructing nano/microscale graphene-based devices.

Development of EUV interference lithography for 25 nm line/space patterns

In this study, we present the performance of an extreme ultraviolet interference lithography (EUV-IL) setup that was reconstructed at Taiwan Light Source 21B2 EUV beamline in the National Synchrotron Radiation Research Center (NSRRC), Taiwan. An easy-to-perform fabrication method to produce a high-quality transmission grating mask and a simple design of experimental setup for EUV-IL were developed. The current EUV-IL setup is capable of fabricating line/space patterns down to 25 nm half-pitch in hydrogen silsesquioxane (HSQ) resist. Preliminary exposure results revealed that optimized slit width and exposure time significantly improved line/space pattern quality. The current EUV-IL tool at NSRRC can be used for nano-patterning and resist screening to advance the next generation of semiconductor devices.

Highly tunable and ultrasensitive hybrid plasmonic platform for multi-spectral sensing: Non-invasive diabetes surveillance and global warming directives

The development of tunable and extremely sensitive devices, as well as the emergence of metamaterials, has tremendously aided the evolution of plasmonic sensing technologies. However, the natural property of metamaterials severely restricts the scalability and application potential of mono-functional sensor systems. To address this shortcoming, we have investigated an ultranarrow five-band plasmonic sensor with structural tunability and high sensing behaviors in compatibility with multi-purpose application scenarios, using the finite-difference time-domain approach rigorously. Meanwhile, we theoretically formulated a hybridization model for the mutual induction of Fabry–Pérot resonances and localized surface plasmon polariton resonance, providing a theoretical basis for the utilization and conception of the highly-sensitive tunable plasmonic sensor. Most notably, we discovered and interpreted far-field phase extinction inducing separation of polarization resonance peaks in physical mechanisms. The tunability of its mutual inductance effect at the intersection distances from two-intersecting silver nanogroove was adequately exploited to further validate and effectively attain five ultra-narrow absorptivities of 96.70%, 93.93%, 99.73%, 100.00%, and 89.72% by top-level optimization. In addition, the redundant proximity between nearby peaks is compensated, extending the operating band and enhancing the practicability in multi-purpose scenarios. As a reliable source for future optical sensing, it performs well in the visible to near-infrared region, enabling detection response to non-invasive diabetes mellitus, global climate warming, and unrestricted temperature and pressure measurement. Meanwhile, minimum FWHM = 4.806 nm and maximum FOM = 115.13 RIU−1 are obtained at 293.15 K, with an associated highest sensitivity of 557.93 nm/RIU. Moreover, the fabrication technologies development of electron beam lithography and focused ion beam etching technologies enables large-scale mass production at low cost and long-term stability.

Advancements, Versatility, and Flexibility of Dual-Layer Material System for Advanced Packaging Applications

Integrated circuits (IC) have seen a major shift in development within the past 10-20 years with traditional lithography methods showing a drastic increase in development time for more advanced nodes, as well as an exponential increase in cost to achieve the same performance gains as before. The increase in cost and the decline in development in lithography have resulted in looking at advanced packaging technologies to achieve the same performance gains by changing the way IC design is approached. The look towards advanced packaging technologies for the future in terms of increasing performance for a substantially lower cost has resulted in considering the IC as a system of components working intertwined with each other rather than as individual components. This shift in mindset has resulted in technologies such as system in package (SiP), package on package (PoP), and fan-out wafer-level packaging (FOWLP). One advanced packaging technology that plays a critical role enabling these aforementioned technologies is temporary bond and debond (TB/DB). TB/DB’s crucial role in advanced packaging is due to the enablement of backside processing such as wafer thinning, bumping of the wafer, die stacking, and chemical vapor deposition/physical vapor deposition (CVD/PVD)–type processes by the use of a support carrier wafer. The support carrier wafer also allows for the use of highly warp-prone materials such as epoxy mold compound (EMC), which are critical in FOWLP applications, by reducing the overall warpage of the entire wafer stack. To utilize the support carrier wafer, a robust material solution is required to allow for the wafers to be bonded together and subsequently released after backside processing by one of the primary separation methods of thermal slide, mechanical, or laser debond. Brewer Science has designed and developed a dual-layer temporary bonding system. This system consists of two materials, a thermoplastic layer that is typically coated on the device, and a thermoset layer which is typically coated on the carrier. The materials developed for the dual-layer system demonstrate very good performance in very high temperature applications, EMC wafer handling, and device thinning to sub-20 µm. In this paper, we will summarize their capabilities and introduce how adhesion between the two temporary layers can be adjusted by material design. We will also cover a new feature of the thermoset layer that can be patterned to allow for the use of a patterned bonding material for TB/DB-type applications.

Development of controlled nanosphere lithography technology

This work is devoted to the development of nanosphere lithography (NSL) technology, which is a low-cost and efficient method to form nanostructures for nanoelectronics, as well as optoelectronic, plasmonic and photovoltaic applications. Creating a nanosphere mask by spin-coating is a promising, but not sufficiently studied method, requiring a large experimental base for different sizes of nanospheres. So, in this work, we investigated the influence of the technological parameters of NSL by spin-coating on the substrate coverage area by a monolayer of nanospheres with a diameter of 300 nm. It was found that the coverage area increases with decreasing spin speed and time, isopropyl and propylene glycol content, and with increasing the content of nanospheres in solution. Moreover, the process of controllably reducing the size of nanospheres in inductively coupled oxygen plasma was studied in detail. It was determined that increasing the oxygen flow rate from 9 to 15 sccm does not change the polystyrene etching rate, whereas changing the high-frequency power from 250 to 500 W increases the etching rate and allows us to control the decreasing diameter with high accuracy. Based on the experimental data, the optimal technological parameters of NSL were selected and the nanosphere mask on Si substrate was created with coverage area of 97.8% and process reproducibility of 98.6%. Subsequently reducing the nanosphere diameter lets us obtain nanoneedles of various sizes, which can be used in field emission cathodes. In this work, the reduction of nanosphere size, silicon etching, and removal of polystyrene residues occurred in unified continuous process of plasma etching without sample unloading to atmosphere.

Two-photon shape-modulated maskless lithography of positive photoresist of S1813

The authors systematically investigated influence factors for two-photon maskless lithography of S1813 photoresist. A trench with a width of 155 nm, about 1/5 of the laser wavelength, was fabricated by accurate tuning the scanning speed. Two-photon shape-modulated maskless lithography, a method which employs different combined scanning and exposing approaches was proposed and studied. The patterns of rectangle, parallelogram, rice grain, arc, and “x” letter, and the quatrefoil hole patterns with different shape hearts, were all fabricated by using this method. This work is a protocol for lithography of S1813 photoresist with a high spatial resolution and flexibility. The fabricated trenches and diverse micro/nano patterns can be applied in the fabrication of integrated circuits, metamaterials structures, and SERS and biosensor substrates. This work will be conducive to the development and application of the two-photon maskless lithography of S1813.

Current State and Prospects for the Development of X-Ray Lithography

Current State and Prospects for the Development of X-Ray Lithography

Enhanced extreme ultraviolet lighting using carbon nanotube-based cold cathode electron beam irradiation

Laser-produced tin (Sn) plasma (LPP) is used to produce high-performance semiconductors using extreme ultraviolet (EUV), but LPP generates debris that limits the lifespan of the optical system, so research on debris mitigation is being conducted. When electrons are directly irradiated to a solid target, occurrence of debris can be minimized, and compact and low-cost EUV lighting can be manufactured. Here, we demonstrated enhanced EUV generation by optimizing the irradiation of Sn with electrons emitted from carbon nanotube-based cold cathode electron beam (C-beam). To minimize debris, a usable zone in which Sn does not melt was identified. It was demonstrated that using two C-beams in the usable zone increased the EUV intensity by about two times compared to using one C-beam. The multiple C-beam irradiation technique enables high-output EUV lighting by overlapping EUV light, which should be led by the development of advanced lithography and inspection technology.

Recent Status of the Stochastic Issues of Photoresist Materials in EUV Lithography

In 2019, finally, extreme ultraviolet (EUV) lithography has been applied to high volume manufacturing (HVM) for preparing advanced semiconductor devices. That was very important year for EUV enthusiasts and semiconductor industry. Because it takes for a long time, more than 30 years, to study EUV lithography for realizing HVM. With recent rapid progress on the source power improvement, EUV lithography development including photoresist materials has been achieved HVM requirements. However, the performance of EUV resist materials are still not enough for the expected HVM requirements, even by using the latest qualifying EUV resist materials. One of the critical issues is the stochastic issues, which will be become ‘defectivity’, like a nano-bridge or a nano-pinching. The analyzing summary of the stochastic factors in EUV lithography, and their improvement status are described in this paper. 2 (two) major stochastic issues, which are photon stochastic and chemical stochastic, were observed in the lithography steps. And the improvement status of each stochastic issues including lithographic results are also described.

Label-free neural networks-based inverse lithography technology.

Neural network-based inverse lithography technology (NNILT) has been used to improve the computational efficiency of large-scale mask optimization for advanced photolithography. NNILT is now mostly based on labels, and its performance is affected by the quality of labels. It is difficult for NNILT to achieve high performance and extrapolation ability for mask optimization without using labels. Here, we propose a label-free NNILT (LF-NNILT), which is implemented completely without labels and greatly improves the printability of the target layouts and the manufacturability of the synthesized masks compared to the traditional ILT. More importantly, the optimization speed of LF-NNILT is two orders of magnitude faster than the traditional ILT. Furthermore, LF-NNILT is simpler to implement and can achieve better solvers to support the development of advanced lithography.

Study on deprotonation from radiation-induced ionized acrylate polymers including acid-generation promoters for improving chemically amplified resists

The demand for improved performance of chemically amplified resists (CARs) is continually increasing with the development of extreme ultraviolet lithography. Acid-generation promoters (AGPs) increase the sensitivity of CARs by increasing the initial acid yield immediately after the exposure process. However, the detailed mechanism of acid-yield enhancement has not been clarified yet. Deprotonation from the ionized polymer (i.e. radical cations) is an important reaction to assess acid generation. In this study, we investigated the dynamics of the radical cations of methacrylate polymers and the effect of an AGP on deprotonation from the radical cations formed by ionizing radiation. We clarified that the promotion of deprotonation by the AGP is more effective for the polymer with lower deprotonation efficiency. In addition, a molecular-level approach using density functional theory and molecular dynamics calculations were carried out.

80 K cryogenic stage for ice lithography

We present a cryogenic system design and development for ice lithography. The cryo-stage is designed with embedded channels to allow direct liquid nitrogen flow, enabling fast cryogenic cooling, and low sample temperature. The stage cools down to 78.8 K in 20 min and heats up to room temperature in 15 min, which increases throughput significantly. Compared to the previous designs, the new system reduces cooling time by 85%, and it is 50 K colder. The cryo-stage is fabricated using copper, aluminum, and polyether ether ketone (PEEK) polymer. Numerical simulations show that the thermal stress on the cryo-stage during the cooling process remains well below stage materials' mechanical yield limits. Finally, the lower stage temperature enables us to explore new precursors, materials, and applications, which we demonstrate by combining ice lithography with printed flexible electronics technology.

Predictive Biophysical Cue Mapping for Direct Cell Reprogramming Using Combinatorial Nanoarrays.

Biophysical cues, such as nanotopographies of extracellular matrix (ECM), are key cell regulators for direct cell reprogramming. Therefore, high-throughput methods capable of systematically screening a wide range of biophysical cue-regulated cell reprogramming are increasingly needed for tissue engineering and regenerative medicine. Here, we report the development of a dynamic laser interference lithography (DIL) to generate large-scale combinatorial biophysical cue (CBC) arrays with diverse micro/nanostructures at higher complexities than most current arrays. Using CBC arrays, a high-throughput cell mapping method is further demonstrated for the systematic investigation of biophysical cue-mediated direct cell reprogramming. This CBC array-based high-throughput cell screening approach facilitates the rapid identification of unconventional hierarchical nanopatterns that induce the direct reprogramming of human fibroblasts into neurons through epigenetic modulation mechanisms. In this way, we successfully demonstrate DIL for generating highly complex CBC arrays and establish CBC array-based cell screening as a valuable strategy for systematically investigating the role of biophysical cues in cell reprogramming.