As technology nodes shrink, EUV photoresists are critical for high-resolution nanopatterning. However, slow electrons (below 20 eV) generated during EUV exposure can cause electron blur and defect formation through unintended chemical reactions. Understanding the behavior of these electrons is crucial for improving resist performance. This work aims to study how different resist materials, particularly photoacid generators (PAGs) and quenchers, influence electron-induced chemistry under EUV exposure. Additionally, the goal is to develop high-throughput methods to screen hundreds of samples efficiently. Simultaneous total electron yield (TEY) and residual gas analysis (RGA) were used to investigate electron behavior in various polymers and model resists during EUV exposure. TEY measured electron generation and capture, while outgassing experiments explored molecular bond scission. The methods are designed for high-throughput analysis, allowing rapid sample evaluation. TEY measurements showed that PAGs and quenchers significantly affect electron generation and capture. Combined TEY and outgassing results revealed insights into EUV-induced molecular bond scission and the correlation to the resist sensitivity. This study highlights the importance of optimizing resist composition to control slow-electron behavior and outgassing. The developed high-throughput screening methods can accelerate the evaluation and development of next-generation EUV photoresists.
Metrology plays a crucial role in semiconductor manufacturing by providing accurate and precise measurement and characterization of critical parameters. With the development of high-resolution extreme ultraviolet lithography (EUVL) processes, critical dimensions are shrinking to sub-10 nm. Resist materials encounter the challenge of providing heightened sensitivity and a handle on exacerbating stochastic variations. A comprehensive understanding of the chemical profile of the latent image is pivotal for mitigating stochastic effects and optimizing pattern quality. However, the subtle differences in chemistry between the exposed and unexposed regions of the resists make it extremely challenging to characterize the latent images with sub-nanometer precision. Here, we develop the metrology with critical-dimension resonant soft X-ray scattering (CD-RSoXS) to probe the chemical profiles of latent images stored in resist after exposure. The combination of absorption spectroscopy and enhanced scattering contrast makes it possible to characterize the subtle structural and chemical variations in the latent image. Moreover, the results of the measurements are compared with the simulations with a finite element method–based Maxwell solver to extract a detailed profile of the latent and developed images. We demonstrate that the CD-RSoXS technique can provide valuable insights into the high spatial resolution and local chemical sensitivity simultaneously, which is crucial to understanding the resolution limits and stochastic effects in EUVL processes.
The adoption of EUV lithography has enabled the reduction of device dimensions; however, the commensurate scaling of variability, such as line edge and width roughness (LER/LWR), has remained elusive. Understanding the origins of these effects has proven challenging, as they cannot be detected until after the final dissolution step. In this study, we present our recent findings using critical-dimension resonant soft X-ray scattering (CD-RSoXS) to investigate the scattering behavior of photoresist materials. Our primary objective is to gain insights into the contributions of each process step to the generation of LER/LWR as well as footing/scumming. RSoXS capitalizes on tunable soft X-ray sources to significantly enhance the scattering cross-sections from heterogeneous materials. This enhancement provides valuable insights into sub-nanometer spatial resolution and local chemical sensitivity concurrently. To extract a comprehensive profile of the latent image, we employ simulations involving the form factor and subsequent reconstruction of line shapes.
Metrology plays a crucial role in semiconductor manufacturing by providing accurate and precise measurement and characterization of critical parameters. With the development of high-resolution extreme ultraviolet (EUV) lithography processes, critical dimensions are shrinking to sub-10 nanometer. The small differences in chemistry between the exposed and unexposed regions of the resists make it extremely challenging to characterize the latent images with sub-nanometer precision. Here we report on our recent results using critical-dimension resonant soft x-ray scattering (CD-RSoXS) to probe the scattering behavior of latent images at specific energy levels. RSoXS leverages tunable soft x-ray sources in order to dramatically enhance the scattering cross sections from heterogeneous materials, which can provide valuable insights into the sub-nm spatial resolution and local chemical sensitivity simultaneously. Moreover, to extract a detailed profile of the latent image, the simulations of the form factor and subsequent reconstruction of the line shapes are performed under DWBA and RCWA.
The newly formed Center for High Precision Patterning Science (CHiPPS) pursues a holistic approach to patterning science by studying the fundamentals of relevant interactions of light and matter and proposing co-designed materials and processes for precision patterning such as sequence defined and/or structured hybrid photoresists, molecular-level control of solvation steps, self-assembling materials for low-impact stochastics and molecularly precise and selective pattern transfer. The center leverages a world class EUV patterning research facility together with unique X-ray characterization built at the Advanced Light Source (ALS).
In this presentation we will introduce the center’s overall efforts in high precision patterning science and, in particular, we will put emphasis on an approach that employs novel self-assembling, hierarchical materials to heal the adverse stochastic effects on EUV photoresists and to enable pattern transfer methods with atomic or molecular precision.
As high-resolution lithography processes edge past the 7 nm node, resist thicknesses continue to shrink and interfacial effects start to dominate performance. This is a challenging metrology problem, as it requires tools that can be used deconstruct the complex interplay of physicochemical nanoscale parameters. This requires the development of multimodal operando characterization capabilities and dedicated analytical techniques to study buried chemical profile and line edge/width roughness in the latent image; to understand the effect of EUV exposure, electron induced chemical reaction in the in situ process; and to reveal how the interfacial chemistry and structure affect the area selective deposition and etching process. We report on our recent results using resonant soft x-ray scattering (RSoXS), whose contrast is enhanced by tuning the incident x-ray energy in order to coincide with chemical inhomogeneities in a sample’s near-edge x-ray absorption fine structure (NEXAFS), which uniquely suited to extract critical information from thin interfacial areas for both top down and bottom up patterning approaches. We will describe how sensitivity can also be extended to study interfacial processes on nanostructured surfaces where the nano patterns can be tailored to enhance the sensitivity of the interfacial region where the we can achieve sub-nm spatial resolution and local chemical sensitivity at the same time. We will present the various experimental configurations and in-situ capabilities being developed to accelerate advances in both general RSoXS metrology and its application to understanding each stage of patterning process.
With the adoption of extreme ultraviolet (EUV) lithography across the semiconductor industry, there comes a need to develop new resist materials that will become the mainstay enabling technology. This development places pressure on the metrology community to develop adequate non-destructive techniques capable of measuring the sub-10 nm patterns that such resists are meant to produce. Recent progress in grazing incidence and resonant x-ray scattering techniques [1-3] have shown particular promise at being able to address part of these characterization challenges.
In this paper, we highlight the potential for various techniques which use energy-tunable x-rays to probe buried structures critical to progress in EUVL. We show how resonant contrast can harness spatially distributed chemical heterogeneities within a resist in order to probe buried structures in a variety of photoresists containing key inorganic components. Specifically, by focusing on inorganic/organic hybrid resists, we demonstrate the potential insights from and correlation between contrast acquired at different elemental absorption edges and chemistries from a given resist.
As the lithographically manufactured nanostructures are shrinking in size, conventional techniques, such as microscopies (SEM, AFM) reach their resolution limits. We have developed a high-performance Grazing Incidence SAXS simulation tool to reconstruct the in-depth profile highly ordered material such as line gratings [1, 2].
Here, we will present the latest development and applications of the technique using x-rays to characterize line gratings and contact holes. Specifically, we will show how the CD-GISAXS approach has been extended to extract the in-depth profile dispersion of the lines, leading to a quantification of the line edge roughness. Finally, by introducing a recent study which harnessed the chemical sensitivity provided by soft x-ray scattering to extract latent image profiles from resists [3], we highlight new applications for this technique with high potential.
The development of novel resists that can match the challenges posed by the next generation of lithography partly hinges on our ability to develop new methods for extracting spatial information with sub-nm precision at each step of the lithographic process. This is particularly important for EUV resists, which tend to suffer from the seemingly inescapable trade-off between improving photon sensitivity and resolution, while reducing line edge roughness (LER). The strategies used to optimize this trade-off rely on tailoring the physicochemical mechanisms that take place before the final development of the resists, thus finding a way to characterize the structure of their latent image is critical to future progress.
To meet some of these challenges, resonant x-ray scattering (ReXS) has emerged as a powerful technique which leverages the chemical contrast that exists between exposed and unexposed regions before the final development step in order to produce the average cross-sectional profile of the latent image with sub-nm precision. Most recently, the ReXS technique was demonstrated in a grazing incidence configuration by leveraging contrast in the carbon element’s local chemistry in order to extract the latent image of a patterned chemically amplified resist (CARs) directly on a silicon substrate[1]. In this work, we show how this capability may be extended to extract chemical contrast from other active elements in a given resist and expand on the potential benefits and drawbacks (i.e. beam damage, experimental configurations, and LER sensitivity) of performing such measurements both before and after the post-exposure baking step has taken place. Finally, we will present comparisons between the latent image profile collected at various resonant x-ray energies and the final developed structure corresponding to a variety of modern commercial resists used both for e-beam and EUV lithography. Such unique spatiochemical information should provide useful guidelines for both the synthesis and processing of the next generations of resist materials.
[1] G. Freychet, I.A. Cordova, T. McAfee, D. Kumar, R.J. Pandolfi, C. Anderson, P. Naulleau, C. Wang, A. Hexemer, Using resonant soft x-ray scattering to image patterns on undeveloped resists, SPIE2018.
Extreme ultraviolet (EUV) lithography is one of the most promising printing techniques for high-volume semiconductor manufacturing at the 14-nm half-pitch device node and beyond. However, key challenges around EUV photoresist materials, such as the exposure-dose sensitivity or the line-width roughness, continue to impede its full adoption into industrial nanofab facilities. Metrology tools are required to address these challenges by helping to assess the impact of the EUV materials’ properties and processing conditions along different steps of the nanofabrication process. We apply the resonant soft x-ray scattering (RSoXS) technique to gain insights into the structure of patterned EUV resists before the development step takes place. By using energies around the carbon K-edge to take advantage of small differences in chemistry, the electronic density contrast between the exposed and unexposed regions of the resists could be enhanced in order to image the patterns with subnanometer precision. Critical-dimension grazing-incidence small-angle x-ray scattering is then performed at energies where the contrast is maximized, enabling the reconstruction of the three-dimensional shape of the latent image. We demonstrate the potential of RSoXS to provide a high-resolution height-sensitive profile of patterned EUV resists, which will help in quantifying the evolution of critical features, such as the line-edge roughness, at a key step of the nanofabrication process.
Even though instrumentation for electron beam lithography (EBL) has progressed immensely since it was first introduced almost 50 years ago[1], enabling beam spot sizes below 5 nm for certain systems, its lithographic resolution limits are still bound by the primary and secondary electron scattering processes that occur when a specific resist is exposed. As the feature sizes become smaller and resists designed with higher sensitivities, these stochastic processes play an increasing role in the resulting line edge roughness (LER) thus leading to an effect known as shot noise. Unfortunately, unraveling the impact of these processes from the impact of the development step is partly hindered by our inability to measure the 3D profile of the latent image from resists directly after exposure. Furthermore, given the recent rise of chemically-amplified resists (CARs) used for the next generation extreme ultraviolet lithography (EUV), it has become even more critical to find ways to characterize and investigate the shot noise effect.
In this work, we tackle this challenge by applying the resonant soft x-ray scattering (RSoXS) technique in a grazing incidence configuration to extract the cross-sectional profile of resists that have already been patterned, but have yet to be developed (i.e., latent image). We find that the difference in chemistry induced by the chain scission process in exposed PMMA and CAR resists is enough to produce enough scattering contrast at certain X-ray energies near the absorption edge of carbon in order to provide a latent image profile of the pattern with sub-nanometer resolution. In this paper, we will compare the latent image profiles extracted from this RSoXS data to the profiles obtained after development, as well as expand on the nature of this chemical contrast mechanism. We will show how this scattering data may be interpreted and the information used to shed light on the nature of the resolution limit of a specific combination of resist and exposure plus development conditions. Finally, we will elaborate on the impact of the measurement itself on the resulting pattern morphology as well as how similar insights might be gained across other types of resists.
1. Hans C. Pfeiffer, } "Direct write electron beam lithography: a historical overview", Proc. SPIE 7823, Photomask Technology 2010, 782316 (24 September 2010); doi: 10.1117/12.868477
Extreme ultraviolet lithography is one of the most promising printing techniques for high volume semiconductor manufacturing at the 14 nm half-pitch device node and beyond. However, key challenges around EUV photoresist materials such as the exposure-dose sensitivity or the line-width roughness continue to impede the full adoption into industrial nanofab facilities. New metrology tools are required to address these challenges by helping to determine the impact of the EUV materials’ properties and processing conditions on the roughness through the different step of the process. Here, we apply the resonant soft x-ray scattering (RSOXS) technique to gain insights into the structure of patterned EUV resists before the development step takes place. By using energies around the carbon absorption edge to take advantage of small differences in chemistry, the electronic density contrast between the exposed and unexposed regions of the resists could be enhanced in order to image the patterns with sub-nm precision. Critical-dimension grazing incidence small-angle X-ray scattering (CDGISAXS) was then performed at energies where the contrast was maximized, enabling the reconstruction of the 3D shape of the latent image. This demonstrates the potential of RSOXS to provide a high-resolution heightsensitive profile of patterned EUV resists, which will help to quantify the evolution of critical features, such as the line edge roughness, at each step of the nanofabrication process.
Ternary blend solar cells are considered presents one route to construct the devices with a broad absorption of the solar spectrum. However, the morphological studies on such mixtures have been limited. Here, the morphology of P3HT/PCPDTBT/PC61BM ternary blend thin films were studied. By adjusting the blending ratio of two polymers, P3HT molecular weight, thermal annealing time and spin-coating solvents, the crystallinity of both polymers and phase separation among each component were controlled. It was found that a high crystallinity of the polymers is important for good device performance. Due to the crystallization of the polymers and the immiscibility between P3HT and PCPDTBT, a hierarchical morphology was generated that mimicked a tandem cell connected in parallel and extended the absorption. In addition, the amorphous PCPDTBT was found to guide the orientation of P3HT nanocrystals before they merged into fibrils, and it also served as a photosensitizer to form a cascade energy level alignment. Therefore, the two polymers worked synergistically to achieve the improved device performance relative to the binary reference.
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