Abstract. Background: Extreme ultraviolet (EUV) lithography was introduced for the high-volume manufacturing of state-of-the-art semiconductor devices in 2019. One of the issues for the CD metrology of an EUV resist pattern is the resist shrinkage since the ratio of the shrinkage to the CD increases in EUV lithography compared with that in immersion argon fluoride lithography. Aim: A CD-SEM metrology for an EUV resist that was compatible with low shrinkage and high spatial resolution was investigated by using primary electrons (PEs) with high energy. Approach: The shrinkage, image sharpness, repeatability, and line edge roughness (LER) were evaluated for the EUV resist using PEs with energies of 200, 800, and 4000 eV. Results: The smallest shrinkage was obtained under the conditions of the repeatability from 0.15 to 0.22 nm by using PEs with an energy of 4000 eV. Moreover, the LERs obtained for 200, 800, and 4000 eV were almost the same. Conclusions: While the electron irradiation damage for an under layer and the amount of shrinkage depending on pattern size could cause issues, the high voltage CD-SEM provides a solution to CD monitoring in high-volume manufacturing using EUV lithography.

Abstract. Background: Design of microelectromechanical system based Bennet’s doubler kinetic energy harvester (KEH) is tricky as it has to satisfy the operating criteria of doubler circuit along with the harvester’s design constraints for its operation. Aim: Design guidelines for an electrostatic KEH using Bennet’s doubler circuit along with its experimental validation are presented. Approach: Bennet’s doubler circuit can work as a KEH only for a specific range of capacitance ratio across interdigitated electrodes of the harvester. The constraints on the resonant frequency of Bennet’s doubler harvester have been deduced to achieve operational capacitance ratio at both low and high vibrational frequencies. Finally, a test structure is fabricated, using silicon-on-insulator multiuser MEMS processes, and tested for capacitance ratio η greater than 1.366, a prerequisite for the operation of Bennet’s doubler circuit. Results: Resonant operation of the test structure achieves capacitance ratio of 1.39 with a capability of harvesting energy density of 4.63  μJ/cm3. Further, an improved harvester design is also presented for η  =  1.5, based on the discussed guidelines that increase the energy density to 19.6  μJ/cm3. Conclusions: We will present an insight into the design of Bennet’s doubler harvester for different vibrational frequencies, which is being widely explored for electrostatic energy harvesting.

Abstract. Background: To reduce defocus from leveling errors at the wafer edge, modern exposure tools offer a broad range of advanced leveling controls. These additional degrees of freedom offer better leveling performance, but users hesitate to spend the tool time, wafers, and engineering hours necessary to find and maintain the optimal settings experimentally. Aim: In order to fully explore the potential of advanced leveling controls, an automated, fast simulation method should be introduced. Approach: Alternative set-point curves and resulting focus residuals are simulated from existing wafer height maps. Optimizations are carried out to obtain the best edge exclusion settings for several dynamic random access memory and NAND flash memory products, across different layers and exposure tools. The simulated focus errors are compared to the POR settings and verified with electrical results. Results: An efficient optimization algorithm was demonstrated and significant leveling improvements found for a number of use cases. The resulting settings vary substantially between different products, layers, and exposure tools. The impact of the improved leveling performance is verified using electrical data. Conclusions: The speed of the presented method proves crucial to help lithographers dial in and maintain numerous settings at optimal values across a typical production line.

Abstract. Dip-pen nanolithography (DPN) is a low-cost, versatile, bench-top technology for direct patterning of materials over surfaces. Our study reports on the production of two-dimensional optical grating nanostructures based on polymers, using DPN. The influence of both the ink composition and the dwell time were investigated. Prototypes of phase masks were manufactured, and their main characteristics were analyzed. The results in our work may contribute to improving the fabrication process of optical structures, including the production of microlenses with controlled focal length.

Abstract. Microsystem technology is well suited to batch fabricate microhemispherical resonator gyroscopes (HRG) to reduce cost and volume. In the processing of micro-HRG, a crucial step is to get a 3-D hemispherical mold with the large-scale, high-symmetry, and smooth surface. Compared with the hemispherical resonator, the toroidal resonator has the smaller frequency split and larger effective resonance mass under the same processing accuracy. A wafer-scale etching method for the toroidal resonator mold was presented, which is based on the deep reactive ion etching and improved HNA isotropic etching. The advantages of this method include low cost, time savings, and easy operation. With this method, toroidal molds with an average diameter over 1900  μm, asymmetry <0.2  %  , and roughness <10  nm were successfully fabricated. The uniformity and surface smoothness of the molds are mainly determined by the parameters of HNA etching. A series of controlled experiments were conducted to optimize isotropic etching parameters that include mask design, bath agitation, HNA composition, and temperature. The influence of these parameters on etching rate and uniformity was discussed. The result shows that the composition of 2.5:7:1 (HF  :  HNO3  :  CH3COOH), temperature of 30°C, and bath agitation of 20 revolutions per minute are optimal etching conditions to achieve high-performance molds.

With the introduction of the NXE:3400B scanner, ASML has brought extreme ultraviolet lithography (EUV) to high-volume manufacturing (HVM). The high-EUV power of >200 W being realized with this system satisfies the throughput requirements of HVM, but also requires reconsideration of the imaging aspects of spectral purity, both from the details of the EUV emission spectrum and from the deep-ultraviolet (DUV) emission. We present simulation and experimental results for the spectral purity of high-power EUV systems and the imaging impact of this, both for the case of with and without a pellicle. Also, possible controls for spectral purity will be discussed, and an innovative method will be described to measure imaging impact of varying conversion efficiency (CE) and DUV. It will be shown that CE optimization toward higher source power leads to reduction in relative DUV content, and the small deltas in EUV source spectrum for higher power do not influence imaging. It will also be shown that resulting variations in DUV do not affect imaging performance significantly, provided that a suitable reticle black border is used. In summary, spectral purity performance is found to enable current and upcoming nodes of EUV lithography and to not be a bottleneck for further increasing power of EUV systems to well above 250 W.

Abstract. Directed self-assembly (DSA) of block copolymers (BCPs) is one of the most promising techniques to tackle the ever-increasing demand for sublithographic features in semiconductor industries. BCPs with high Flory–Huggins parameter (χ) are of particular interest due to their ability to self-assemble at the length scale of sub-10 nm. However, such high-χ BCPs typically have imbalanced surface energies between respective blocks, making it a challenge to achieve desired perpendicular orientation. To address this challenge, we mixed a fluorine-containing polymeric additive with poly(2-vinylpyridine)-block-polystyrene-block-poly(2-vinylpyridine) (P2VP-b-PS-b-P2VP) and successfully controlled the orientation of the high-χ triblock copolymer. The additive selectively mixes with P2VP block through hydrogen bonding and can reduce the dissimilarity of surface energies between PS and P2VP blocks. After optimizing additive dose and annealing conditions, desired perpendicular orientation formed upon simple thermal annealing. We further demonstrated DSA of this material system with five times density multiplication and a half-pitch as small as 8.5 nm. This material system is also amenable to sequential infiltration synthesis treatment to selectively grow metal oxide in P2VP domains, which can facilitate the subsequent pattern transfer. We believe that this integration-friendly DSA platform using simple thermal annealing holds the great potential for sub-10 nm nanopatterning applications.

Next-generation extreme ultraviolet (EUV) systems with numerical apertures of 0.55 have the potential to provide sub-8-nm half-pitch resolution. The increased importance of stochastic effects at smaller feature sizes places further demands on scanner and mask to provide high contrast images. We use rigorous mask diffraction and imaging simulation to understand the impact of the EUV mask absorber and to identify the most appropriate optical parameters for high NA EUV imaging. Simulations of various use cases and material options indicate two main types of solutions: high extinction materials, especially for lines spaces, and low refractive index materials that can provide phase shift mask solutions. EUV phase masks behave very different from phase shift masks for DUV. Carefully designed low refractive index materials and masks can open up a new path toward high contrast edge printing.

Background: With continuous decrease in the technology node of dynamic random access memories (DRAMs) down to sub-20 nm, the self-aligned double patterning (SADP) is an effective approach to generate two-dimensional (2-D) patterns, particularly contact arrays. Aim: We demonstrate a patterning scheme using the SADP technique to produce active trim contacts with anisotropic pattern pitches. Approach: The proposed scheme uses two consecutive spacer-formation processes. Results: By making the ellipsoidal core pillars and minimizing the spacer thickness, 2-D critical dimensions (CDs) for self-generated contacts match well with those for core contacts. In addition, an interesting cross-dependence of X -CD and Y -CD variations for the core and self-generated contacts is observed. Conclusion: This patterning approach is useful for forming active trim contacts in sub-20 nm DRAMs using fewer numbers of ArF immersion photolithography steps.

Abstract. Background: Switchable glasses allow the control of light transmission—an attractive property for applications such as car sunroofs, aircraft windows, building windows, augmented reality, imaging, and displays. Commercialized switchable glasses have severe limitations, such as speed, cost, and operating conditions, among others. Microshutters, a type of switchable glass with very distinctive properties, are reviewed, as they are a technology that could significantly improve some or all of the shortcomings mentioned above. Aim: We will summarize the various types of microshutters and tentatively identify various critical designs, fabrication schemes, and performance criteria by the many research groups implementing them and investigating their properties. Approach: We will describe the various approaches used to control light transmission through microelectromechanical systems. It will compare their performances and comment on fabrication and implementation challenges. Conclusions: Microshutters have performance levels that could make them good candidates for switchable glasses. Many research groups have investigated various approaches to fabricate microshutters and have shown that they can be implemented reliably on a small scale, with fast actuation, low power, and high contrast and are relatively easy to manufacture. Work is needed to demonstrate that they can be scaled-up and still be economical to produce.

Abstract Background: Microfluidics has been widely used in the biological and medical fields, and polymers are the most widely used materials in microfluidics at present due to their low cost and ease of processing. Both thermoplastics and thermosets were used as the bulk materials in microfluidics. The third option of a material with both advantages from thermoplastics and thermosets will be of great significance. Aim: We try to establish a low cost and rapid fabrication approach for thermoplastic polyurethane (TPU)-based microfluidics. Several demonstrations were also provided with the proposed fabrication method for TPU-based microfluidics. Approach: A CO2 laser ablation instrument was used for the fabrication of the TPU-based microfluidic devices. The width and depth of microchannels fabricated with various laser scan speeds and energies were studied in detail. For sealing the fabricated channels, a thermal fusion bonding method was also proposed with the bonding strength testing. Several types of the most commonly used microfluidic chips were fabricated for demonstration of the proposed fabrication method. Results: A comprehensive fabrication approach for TPU-based microfluidic devices was achieved. A series of microfluidic chips were designed, fabricated, and tested. Conclusions: TPU-based microfluidics is achievable and could be used as an alternative material for polydimethylsiloxane or thermoplastics for the fabrication of microfluidic devices. The proposed method could have broad potential applications in biological and chemical fields.

Abstract. An optimized source has the ability to improve the process window during lithography in semiconductor manufacturing. Source optimization is always a key technique to improve printing performance. Conventionally, source optimization relies on mathematical–physical model calibration, which is computationally expensive and extremely time-consuming. Machine learning could learn from existing data, construct a prediction model, and speed up the whole process. We propose the first source optimization process based on autoencoder neural networks. The goal of this autoencoder-based process is to increase the speed of the source optimization process with high-quality imaging results. We also make additional technical efforts to improve the performance of our work, including data augmentation and batch normalization. Experimental results demonstrate that our autoencoder-based source optimization achieves about 105  ×   speed up with 4.67% compromise on depth of focus (DOF), when compared to conventional model-based source optimization method.

Abstract. Background: Modern one-digit technological nodes demand strict reproduction of the optical proximity corrections for repeatable congruent patterns. To ensure this property, the optical and process simulations must be invariant to the geometrical transformations of the translation, rotation, and reflection. Simulators must support invariance both in theory, mathematically, and in practice, numerically. The invariance of compact modeling operators has never been scrutinized before. Aim: We aim to examine manner and conditions under which optical simulations preserve or violate intrinsic invariances of exact imaging. We analyze invariances of Volterra operators, which are widely used in compact process modeling. Our goal is to determine necessary and sufficient conditions under which such operators become fully invariant Approach: We use theoretical analysis to deduce full invariance conditions and numerical simulations to illustrate the results. Results: The linear fully invariant operators are convolutions with rotationally symmetrical kernels. The fully invariant quadratic operators have special functional form with two radial and one polar argument and are not necessarily rotationally symmetrical. We deduced invariance conditions for the kernels of high-order Volterra operators. Conclusions: We suggest to use fully invariant nonlinear Volterra operators as atomic construction blocks in machine learning and neural networks for compact process modeling.

Nanoscale wear affects the performance of atomic force microscopy (AFM)-based measurements for all applications including process control measurements and nanoelectronics characterization. As such, methods to prevent or reduce AFM tip wear is an area of active research. However, most prior work has been on conventional AFMs rather than critical dimension AFM (CD-AFM). Hence, less is known about CD-AFM tip-wear. Given that tip-wear directly affects the accuracy of dimensional measurements, a basic understanding of CD-AFM tip wear is needed. Toward this goal, we evaluated the wear performance of electron beam deposited CD-AFM tips. Using a continuous scanning strategy, we evaluated the overall wear rate and tip lifetime and compared these with those of silicon-based CD-AFM tips. Our data show improved tip lifetime of as much as a factor of five and reduced wear rates of more than 17 times. Such improvements in wear rate means less measurement variability and lower cost.

Abstract. 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.

We compare the speed and effectiveness of two genetic optimization algorithms to the results of statistical sampling via a Markov chain Monte Carlo algorithm to find which is the most robust method for determining real space structure in periodic gratings measured using critical dimension small angle X-ray scattering. Both a covariance matrix adaptation evolutionary strategy and differential evolution algorithm are implemented and compared using various objective functions. The algorithms and objective functions are used to minimize differences between diffraction simulations and measured diffraction data. These simulations are parameterized with an electron density model known to roughly correspond to the real space structure of our nanogratings. The study shows that for X-ray scattering data, the covariance matrix adaptation coupled with a mean-absolute error log objective function is the most efficient combination of algorithm and goodness of fit criterion for finding structures with little foreknowledge about the underlying fine scale structure features of the nanograting.

Methods exist for the creation of antireflective thin film layers; however, many of these methods depend on the use of high temperatures, harsh chemical etches, or are made with difficult pattern materials, rendering them unusable for many applications. In addition, most methods of light blocking are specifically designed to increase light coupling and absorption in the substrate, making them incompatible with some appli-cations that also require blocking transmission of light. A method of forming a simple, patternable light-blocking layer that drastically reduces both transmission and reflection of light without dependence on processes that could damage underlying structures using a light scattering matte coating over a partially antireflective thin film light-blocking layer is presented.

Abstract. A single-chip microelectromechanical system (MEMS) capacitive microphone is designed and modeled. The mechanical model of the structure is extracted and the mathematical equations for a description of the microphone behavior are obtained. Then the proposed microphone characteristics are considered. In this structure, by adding Z-shape arms around the diaphragm, diaphragm hardness is decreased and diaphragm displacement becomes uniform. The sensitivity and the pull-in voltage are improved despite the decreasing size. The perforated diaphragm of this microphone is supported by Z-shape arms at its four corners. These arms around the diaphragm decrease the stiffness and air damping of the microphone. The behavior of this microphone is also analyzed by the finite element method. The structure has a diaphragm thickness of 2  μm, a diaphragm size of 0.32  ×  0.32  mm2, an air gap of 2  μm, and a highly doped monocrystalline silicon wafer as a backplate. The proposed microphone is simulated with IntelliSuite software. According to the results, the new microphone has a sensitivity of 14.245  mV  /  Pa and a pull-in voltage of 5.83 V. The results show that the proposed MEMS capacitive microphone is one of the best structures in performance. The obtained mathematical equations for description of the microphone’s behavior have good agreement with the simulation results.

Abstract. Background: Continued shrinkage of pattern size has caused difficulties in detecting small defects. Multibeam scanning electron microscopy (SEM) is a potential method for pattern inspection below 7-nm node. Performance of the tool depends on charge control, resolution, and defect detection capability. Aim: The goal of this study is to develop a method for evaluating the performance of multibeam SEM for 7-nm nodes. Approach: By developing various standard samples with programmed defects (PDs) on 12 in. Si wafer, we evaluate the performance of multibeam SEM. Results: The first wafer had line and space (LS) patterns and PDs with varying contrast. A second wafer had various shaped small PDs, ∼5  nm in size in 16- to 12-nm half-pitch LS patterns. A third wafer with extremely small PDs of around 1 nm was fabricated in LS patterns with ultralow line-edge roughness (LER) of less than 1 nm. The first wafer was effective for charge control, whereas second and third wafer confirms resolution and defect detection capability. Conclusions: A set of minimum three standard wafer samples is effective to confirm the performance of multibeam SEM for below 7-nm nodes. Besides, we proposed a method to verify the LER values measured by a critical-dimension SEM.