This is a list of reviewers who served JM3 in 2018.

The traditional state-of-the-art miniature directional microphones suffer from a higher noise level mainly due to size constraints. Herein, a miniature directional microphone mimicking the fly Ormia ochracea’s ear anatomy is presented with the prime focus on achieving higher signal-to-noise ratio at reduced size. The microphone has circular shape with aluminum nitride (AlN)-based piezoelectric readout scheme deposited at the center of the diaphragm. The 3-3 transduction mode is adopted for sensitivity enhancement. The microphone testing is performed in an anechoic chamber. Besides the bidirectional response, the A-weighted noise under broadband excitation is ∼29  dBA, which is lower than the optical directional microphone of Miles et al., which is the most prominent noise analysis work in the area of fly inspired MEMS directional microphone.

This guest editorial summarizes the Special Section on Challenges and Approaches to EUV-Based Patterning for High-Volume Manufacturing Applications

We report a sub-30-nm pitch self-aligned double patterning (SADP) integration scheme with EUV lithography coupled with self-aligned block technology targeting the back end of line metal line patterning applications for logic nodes beyond 5 nm. The integration demonstration is a validation of the scalability of a previously reported flow, which used 193-nm immersion SADP targeting a 40-nm pitch with the same material sets (Si₃N₄ mandrel, SiO₂ spacer, spin on carbon, spin on glass). The multicolor integration approach is successfully demonstrated and provides a valuable method to address overlay concerns and, more generally, edge placement error as a whole for advanced process nodes. Unbiased line edge roughness (LER)/line width roughness (LWR) analysis comparison between EUV SADP and 193-nm immersion SADP shows that both integrations follow the same trend throughout the process steps. While EUV SADP shows increased LER after mandrel pull, metal hardmask open, and dielectric etch compared to 193-nm immersion SADP, the final process performance is matched in terms of LWR (1.08-nm 3 sigma unbiased) and is 6% higher than 193-nm immersion SADP for average unbiased LER. Using EUV, SADP enables almost doubling the line density while keeping most of the remaining processes and films unchanged and provides a compelling alternative to other multipatterning integrations, which present their own sets of challenges.

The next-generation beyond 7-nm node potentially requires the implementation of subresolution assist features (SRAF) with extreme ultraviolet (EUV) lithography. This paper aims at providing a clear SRAF strategy for the next-generation beyond 7-nm node designs through a series of experiments. Various factors are considered, including stochastic effects, three-dimensional (3-D) mask effects, through-slit effects, aberrations, and pixelated source mask optimization (SMO) sources. We consider process variability bands with a variety of process conditions, including focus/dose/mask bias changes and also the normalized image log-slope/image log-slope as our objective functions, to determine what the best SRAF solution is for a set of test patterns. Inverse lithography technology is implemented to optimize both the main feature (MF) mask and SRAF placement, in particular, asymmetric SRAF placement to balance the 3-D mask effects. SRAF can potentially mitigate image shift through-focus, i.e., nontelecentricity, caused by EUV 3-D shadowing effect. This shadowing effect is pattern-dependent and contributes to the overlay variation. As we approach the next-generation beyond 7-nm node, this image shift can be more significant relative to the overlay budget, hence, we further investigate the impact of SRAF placement to the image shift. Moreover, the center of focus shift due to the large 3-D mask absorber thickness can be potentially mitigated by SRAF implementation. The common process window is significantly impacted by both the center of focus shift and the individual depth of focus and is evaluated using both metal and contact layer test cases. We study the source impact to SRAF insertion by experimenting with both a symmetric source (standard source) and an asymmetric source (SMO source). Finally, we understand the importance of using full flare map and full through-slit model (including aberration variation through-slit) in the MF correction. Furthermore, we evaluate the need of using full models in SRAF insertion. This is a necessary step to determine the strategy of SRAF implementation for the next-generation beyond 7-nm node.

Extreme ultraviolet (EUV) patterning offers an opportunity to explore hardmask materials and patterning approaches. Traditional patterning stacks for deep ultraviolet patterning have been based on optimizing multilayer schemes for reflectivity control and pattern transfer. At the EUV wavelength, the patterning challenges are dominated by stochastics and aspect ratio control. This offers an opportunity to think differently about underlayer design for sub-36-nm pitch patterning. The choice of hardmask can be used to modulate postlitho defectivity to mitigate the stochastics effects and enable more efficient pattern transfer. Through different case studies this paper will explore a range of silicon-based inorganic hardmasks for sub-36-nm EUV patterning. How film properties dominate patterning performance will be studied systematically. The relative merits of patterning a chemically amplified organic resist directly on an inorganic hardmask or having different types of organic adhesion promoters as an intermediate layer will also be presented.

The understanding, characterization, and mitigation of three-dimensional (3-D) mask effects including telecentricity errors, contrast fading, and best focus shifts become increasingly important for the performance optimization of future extreme ultraviolet (EUV) projection systems and mask designs. We explore the potential of attenuated phase shift mask (attPSM) to mitigate 3-D mask effects and exploit them for future EUV imaging. The scattering of light at the absorber edges results in significant phase deformations, which impact the effective phase and the lithographic performance of attPSM for EUV. Rigorous mask and imaging simulations in combination with multiobjective optimization techniques are employed to identify the most appropriate material properties, mask, and source geometries. The resulting imaging performance is compared to the achievable performance of binary EUV masks.

The key challenge for enablement of a second node of single-expose EUV patterning is understanding and mitigating the patterning-related defects that narrow the process window. Typical in-line inspection techniques, such as broadband plasma and e-beam systems, find it difficult to detect the main yield-detracting defects postdevelop, and thus understanding the effects of process improvement strategies has become more challenging. New techniques and methodologies for detection of EUV lithography defects, along with judicious process partitioning, are required to develop process solutions that improve yield. This paper will first discuss alternative techniques and methodologies for detection of lithography-related defects, such as scumming and microbridging. These strategies will then be used to gain a better understanding of the effects of material property changes, process partitioning, and hardware improvements, ultimately correlating them directly with electrical yield detractors.

With the rapid development of semiconductors, today’s optical lithography is approaching its physical limits, and thus alternative patterning technology is urgently needed. Extreme ultraviolet (EUV) lithography, using a wavelength of 13.5 nm, is considered one of the most prominent candidates for next-generation lithography. The main challenge for EUV resists is to simultaneously satisfy resolution, line-width roughness, and sensitivity requirements following the ITRS roadmap. Though polymer-based chemically amplified resist is the current standard photoresist, entirely new resist platforms are required due to the performance targets of future process nodes. Our recent progress in metal oxide nanoparticle photoresist research will be discussed with a focus on zirconium and hafnium oxides. A brief discussion of a number of important structural and material properties pertaining to key characteristics affecting resist performance is also included.

Extreme ultraviolet interference lithography (EUV-IL) is a 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 is rather complicated. The beam polarization and relative phases of the individual beams play a significant role in the aerial image formation in four-beam interference lithography. In particular, controlling the relative phase of the beams is very difficult to achieve due to short wavelength. To circumvent this problem, we propose an effective double exposure four-beam interference lithography method, 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 numerically prove the effective double exposure four-beam interference is not sensitive to the phases difference and verify our analytical model by printing both positive tone chemically amplified resist and a negative tone inorganic resist.

In optical lithography, aberrations induced by lens heating effects of a projection lens lead to degradation of imaging quality. In order to compensate for thermal aberrations, it is crucial to apply an accurate method for thermal aberration prediction. An effective and accurate method for thermal aberration prediction is proposed. A double exponential model is modified in respect of the timing of exposure tools, and a particle filter is used to adjust the double exponential model. Parameters of the model are updated recursively pursuant to the aberration data measured during the exchange of wafers. The updated model is used to predict thermal aberrations during the following exposure of wafers. The performance of the algorithm is evaluated by the simulation of a projection lens for argon fluoride lithography. Simulation results show that predictive errors of primary defocus and astigmatism are significantly reduced, and the mean value of wavefront error in the whole field of view is reduced by about 30% in a vertical line/space pattern. The proposed method is easily adaptable to different types of aberration measurement error.

Projection lithography using extreme ultraviolet (EUV) light at 13-nm wavelength is expected to achieve production of integrated circuits below 10 nm design-rules. In pursuit of further miniaturization, however, stochastic pattern defect problems have arisen. Here, we discuss the possible impact of spatially inhomogeneous secondary electron (SE) generation on stochastic defects. Two mechanisms are investigated: (1) accidental connections of photon shot noises enhanced by densely localized SE generation and (2) cascading SE generation along photoelectron trajectory traveling from pattern edge into a dark region. Since such defect probabilities are extremely low (typically 10^−  4 to ∼10^−  12), results of Monte Carlo simulation based on classical optical image and electron scattering simulations are converted into probability functions for densities of physical/chemical events such as photon absorption, SE generation, and elementary reaction in chemically amplified resists. Probabilities of pattern formation and of defect generation are modeled using these functions. Results of performance optimization using a multiobjective genetic algorithm show higher stochastic defects probability in EUV than in conventional deep-UV exposure due to larger spatial inhomogeneity in reaction density and existence of SE generation strings. Defect probabilities are strongly dependent on absolute pattern sizes in the two mechanisms, regardless of the resolution capability of imaging systems. Guidelines for suppressing stochastic defects are suggested, such as homogenization of reaction density, material composition for increasing scattering cross-section, and suppression of pattern edge fluctuation.

Background: Inorganic resists show promising performances in extreme ultraviolet (EUV) lithography. Yet, there is a need for understanding the exact chemical mechanisms induced by EUV light on these materials.

Aim: To gain knowledge on the EUV chemistry of inorganic resists, we investigate hybrid inorganic–organic molecular compounds, metal oxoclusters (MOCs). Their molecular nature allows for the monitoring of specific structural changes by means of spectroscopy and thus for the elucidation of the mechanisms behind pattern formation.

Approach: We compare the sensitivity of MOCs based on Zr and Hf, and methacrylate ligands as EUV resists. The chemical and structural changes causing the solubility switch were investigated by ex situ x-ray spectroscopy, infrared spectroscopy, ultraviolet–visible spectroscopy, and grazing incidence x-ray scattering.

Results: Higher sensitivity was detected for the Hf-based material, in line with its higher absorptivity. A small fraction of the carboxylate ligands is lost at doses that yield solubility contrast, whereas aggregation of the inorganic clusters was not observed.

Conclusions: These results provide evidence that, although the mechanism of solubility switch in these materials starts with decarboxylation reactions, it mainly proceeds through cross linking of the organic shells instead of aggregation of the inorganic clusters.

Background: Resolution enhancement combined with multiple patterning enables photolithography to write patterns with both feature size and spacing below the diffraction limit. Continued resolution enhancement at i-line will enable an older generation of lithographic tools to reach resolutions typically achieved using deep UV (DUV).

Aim: A demonstration and deterministic model of large critical dimension enhancement at i-line. In addition to enhanced resolution, the technique must also achieve high repeatability and low line edge roughness (LER), while using commercial resists.

Approach: Overexposing photoresist with high-contrast interference nulls leads to subwavelength critical dimensions. Starting with a theoretical analysis of the technique, we consider limits imposed by optics, linewidth scaling rates, and LER. This analysis shows that low LER and deterministic linewidth control are both readily achievable.

Results: We demonstrate large area, i-line patterning of features with 50-nm linewidth, without the aid of subsequent trim or etch and with LER of 5 nm. Linewidth is shown to scale with dose as predicted from the optical model, independent of photoresist.

Conclusions: These dimensions are similar to what may be achieved using scanning near-field, DUV, or e-beam lithography, yet achieved with far-field near UV exposures over a large area. Deterministic linewidth control and low LER make this process viable for fabrication at length scales well below those typically achieved with i-line tools.

Background: One of the challenges for extreme ultraviolet (EUV) lithography is the mitigation of mask three-dimensional effects arising from the oblique incident angle and the mask topography. As the scanners’ numerical aperture and the pattern aspect ratio increase, these effects become more prominent. A potential solution to reduce them consists in replacing the current TaBN absorber for a higher-k material. Aim: We demonstrate the potential of a mask inspection platform to evaluate the impact of different absorber materials on actinic defect inspection. Approach: We evaluate the performance of a reflective-mode EUV mask scanning microscope (RESCAN), our actinic lensless inspection tool, with three different absorber materials (hydrogen silsesquioxane, TaBN, and Ni). We study the effect of these materials on the image formation and compare the defect maps. Results: The Ni absorber mask exhibits a better contrast compared to the TaBN one, even though the thickness of the layers differs only by 10 nm. Programmed defects are localized and detected with a high signal-to-noise ratio (SNR). Conclusions: The gain in contrast for the Ni absorber being significant, the SNR is higher for a smaller defect in a TaBN absorber photomask. RESCAN allows the evaluation of the performance of absorber materials in defectivity and image formation on small samples.

With the shrinking feature sizes of semiconductor devices, manufacturing challenges increase dramatically. Among these challenges, lithography hotspot stands out as a prominent ramification of the growing gap between design and manufacturing. Practically, a hotspot refers to the failure in printing desired patterns in lithography. As lithography hotspots have significant impacts on manufacturing yield, the detection of hotspots in the early design stage is desired to achieve fast design closure. We propose a lithography hotspot detection framework using a double inception module structure. This structure performs better in both accuracy and false alarms by widening the conventional stacked structure to benefit feature extraction and using global average pooling to keep the spatial information. Experimental results show that the proposed structure achieves better performance than existing methods.

Sampling-limited inline defect inspections may fall short in the timely detection of new defects or small baseline populations, especially when the defects have unique spatial orientations. In such cases, it may be beneficial to also consider fault detection and classification signals from unit process modules. Lithography scanners determine the optimal focus position for a wafer by a process called leveling. This work uses a defect analysis approach to examine focus spot data, a litho tool level signal extracted from wafer leveling, and to isolate the sources of inline defectivity from four consecutive front-end-of-line litho steps in a high-volume manufacturing fab. The scope is broadened to examine all litho layers from the same technology node that process on the same tool platform. This work highlights the immense potential of mining focus spot data as a powerful complement to inline defect monitoring.

Background: The purpose of EUV pellicles is to protect the surface of EUV lithography masks from particle contamination. It is important to ensure that the optical characteristics of the pellicle membrane do not critically affect the reticle image quality. Aim: We want to verify the possibility to integrate pellicle inspection and characterization capabilities in reflective-mode EUV mask scanning microscope (RESCAN), our actinic mask inspection platform based on coherent diffraction imaging. Approach: We studied the impact of a few selected EUV pellicle prototypes on the quality and the contrast of the reticle image obtained with RESCAN. Results: We measured the scattering distribution of the pellicles, and we correlated it with the mask image contrast and fidelity. We also detected the presence of a 6.5-μm-diameter fiber on the pellicle surface. Conclusions: We demonstrated that RESCAN is suitable for through-pellicle actinic mask inspection and can be also used to characterize and monitor the pellicle quality.

A low-power three-degree-of-freedom scanning micromirror is presented. The 2-  ×  2-mm mirror is a gimbaless structure, directly supported by single-crystal microsprings. It is actuated by Lorentz force and is able to tilt about two axes and has linear motion in a third-axis. The transient and frequency responses of the micromirror are analyzed. The Lagrange’s equations of motions describing the dynamic behavior of the system are presented and show a good agreement with the experimental results. The fabricated microelectromechanical system mirror demonstrates a tilt angle of 22.8 deg at 247.5 Hz about y-axis, and 13.3 deg at 292.7 Hz about x-axis, in a 0.1 T magnetic field and 20-mA current on the mirror. Power consumption is 2.6 mW of power in tilting motions in resonant operation. With a total DC-drive current of 110 mA, 232-μm linear motion is achieved.

Using microelectromechanical systems technology, a high-performance extended-gate field-effect transistor (EGFET)-based pesticide microsensor for organophosphorus and carbamate (CM) detection is developed. To minimize the whole pesticide-sensing system, we also integrated a planar Ti/Ag/AgCl/KCl-gel microreference electrode into the same silicon chip. The total dimensions of the proposed pesticide-sensing system are only 0.92  ×  0.95  ×  0.1  cm³. This EGFET-based microsensor for organophosphorus and CMs demonstrates extremely high sensitivity (194 and 268.1 mV/dec, respectively) and sensing linearity (0.993 and 0.974, respectively) and extremely low response time (120 and 300 s, respectively). The microsensor detection limit for both pesticides is 0.001 ppm.

Background: Many MEMS and optical sensor devices can benefit from layers that block transmission and suppress reflection of light across the visible spectrum. Because these devices can include complicated topography, many existing methods for depositing antireflective layers are difficult, impractical, or unusable.

Aim: To create a light-blocking antireflective layer that works well with complicated MEMS and sensor devices, a layer should be made that is cheap, simple, and can be deposited and patterned with high resolution at low temperatures.

Approach: Light blocking is achieved using an aluminum layer. Suppressing reflection is achieved by mixing aluminum oxide nanoparticles in photoresist to create a layer that partially absorbs and partially scatters light.

Results: The combination of a layer of metal and a layer of nanoparticles and photoresist completely blocks transmission of light and significantly reduces reflections across the visible spectrum, particularly for shorter wavelengths. The layer is also patternable to sizes as small as a few microns with high resolution.

Conclusion: By combining a metal layer and a layer of nanoparticles in photoresist, a simple, cheap, and effective light-blocking antireflective layer can be created that is compatible with planar devices with complex topography.

Background: Optical stimulation of the brain is based on optrodes with integrated optical splitters to excite multiple neurons simultaneously. This requires efficient light delivery systems.

Aim: In order to satisfy optical requirements, to reduce the fabrication costs, and to obtain less invasive implantation into the brain, we assess a polymer-based microdevice both in theory and experiments.

Approach: In addition to design and evaluation of the device using Multiphysics software, to achieve a feasible implementation, we base our fabrication process on off-the-shelf ultraviolet adhesives as the functional material with fascinating optical and mechanical characteristics all together, easy photolithographic-only curing, and no more steps required for common soft lithographic-based materials.

Results: Wideband transmission of optical signals over the visible/near-infrared together with uniform splitting of the input power from different light sources has been observed and recorded using an optical setup with acceptable agreement with the simulation outcomes.

Conclusions: Our research proposes a flexible and biocompatible optical splitter to be used as a light delivery system for a wide variety of optical stimulation methods in neuroscience studies with fewer or no changes in the design, dimensions, and even exploited materials. So it is a multipurpose device.

An electrostatically actuated MEMS cantilever beam-based waveguide Bragg grating tunable optical filter has been designed and simulated. The tunable filter is obtained by shifting the reflected wavelength of the waveguide Bragg grating located on the electrostatically actuated cantilever beam. An approach to increasing the electrostatic actuation of the beam by having an electrode underneath the beam is used and a large wavelength tuning range for the optical filter is achieved. Dimensions of the device are chosen such that full-width-half-maximum is 0.75 nm, thus capable of filtering adjacent channels of the dense wavelength division multiplexing (DWDM) network. The filter has a tuning range of 10.65 nm (1552.52 to 1563.17 nm) providing add/drop functionality for 14 adjacent DWDM channels.

This erratum corrects mistakes in the original paper.