Continuous progression of Moore’s law brings new challenges in metrology and defect inspection. As the semiconductor industry embraces High-Numerical Aperture Extreme Ultraviolet Lithography (High-NA EUVL), there is a current industry-wide evaluation of this technology for potential pitch reduction in future nodes. One of the primary hurdles in implementing High-NA EUVL in High Volume Manufacturing (HVM) is its low depth of focus. Consequently, suppliers of resist materials are compelled to opt for thin resist and/or new underlayers/hardmask’s. Experimental combinations of thin resist materials with novel underlayers and hardmask’s seem to pose signal detection challenges due to poor Signal-to-Noise Ratio (SNR). In such a scenario, manual classification of these nano-scale defects faces limitations in terms of required time and workforce, and the robustness and generalizability of outcomes are also questionable. In recent years, vision-based machine learning (ML) algorithms have emerged as an effective solution for image-based semiconductor defect inspection applications. However, developing a robust ML model across various image resolutions without explicit training remains a challenge for nano-scale defect inspection. The goal of this research is to propose a scale-invariant Automated Defect Classification and Detection (ADCD) framework capable to upscale images, addressing this issue. We propose an improvised ADCD framework as SEMI-SuperYOLO-NAS, which builds upon the baseline YOLO-NAS architecture. This framework integrates a Super-Resolution (SR) assisted branch to aid in learning high-resolution (HR) features by the defect detection backbone, particularly for detecting nano-scale defect instances from low-resolution (LR) images. Additionally, the SR-assisted branch can recursively generate or reconstruct upscaled images (∼ ×2/×4/×8...) from their corresponding downscaled counterparts, enabling defect detection inference across various image resolutions without requiring explicit training. Moreover, we investigate improved data augmentation strategy aimed at generating diverse and realistic training datasets to enhance model performance. We have evaluated our proposed approach using two original FAB datasets obtained from two distinct processes and captured using two different imaging tools. Finally, we demonstrate zero-shot inference for our model on a new, originating from a process condition distinct from the training dataset and possessing different CD/Pitch characteristics. Our experimental validation demonstrates that our proposed ADCD framework aids in increasing the throughput of imaging tools (∼ ×8) for defect inspection by reducing the required image pixel resolutions.
With the introduction of high-numerical aperture extreme ultraviolet lithography, the thickness of layers in the lithographic stack will scale owing to reduced depth of focus and etch budget. While several studies have explored the impact of thickness scaling on photoresists, the consequence of thinning down underlayers for extreme ultraviolet (EUV) lithography has been scarcely investigated. In this work we assessed the readiness of nine state-of-the-art underlayers, spin-on and dry deposited, scaled in thickness series down to 4 nm nominal (~3 nm actual). Dose-to-size and exposure latitude changed by less than 5 % when thickness of underlayer was decreased. In summary, most of EUV underlayers investigated in this work showed minimal impact on the physical and chemical properties as well as the patterning performance when scaling in view of high numerical aperture extreme ultraviolet lithography.
With the introduction of high-numerical aperture (NA) extreme ultraviolet (EUV) lithography, the thickness of layers in the lithographic stack will scale owing to reduced depth of focus and etch budget. The consequence of thinning down underlayers for EUV lithography has been scarcely investigated. In here, we assessed the readiness of nine state-of-the-art underlayers, spin-on and dry deposited, in thickness series down to 4 nm nominal. Preliminarily, the coating quality of these underlayers was evaluated. Thickness uniformity across 300 mm wafer ranged from about ±0.5 nm to < ± 0.05 nm depending on the coating technique employed. Surface roughness of the underlayers varied from as much as 0.63 nm to as low as 0.062 nm but was not impacted by thickness scaling. Film density and total surface energy varied by <10 % with thickness. EUV lithography of dense lines/spaces arrays of pitch 28 nm was carried out using a positive tone chemically amplified photoresist. Dose-to-size and exposure latitude changed by < ± 5 % when thickness of underlayer was decreased. Failure free process was at most 1 nm smaller for thinner underlayer than it was for the thinnest version of each type. The unbiased linewidth roughness increased consistently but limitedly (<5 % ) when thinner underlayers were used, mainly due to a reduction in the correlation length. By calculating the power spectral density of the blanket underlayer we can pinpoint this effect to a reduction of correlation length of the underlayer own surface roughness. Finally, Z-factor calculations demonstrated that overall photoresist performance depended more significantly on the specific underlayer type (±12.6 % ) than it did on underlayer thickness (±8 % ). All these results indicate that most of underlayers investigated had limited impact on the properties as well as the patterning performance when scaling in view of high NA EUV.
Pattern collapse and photoresist scumming are major limiting factors to achieve a failure-free process window in extreme ultraviolet lithography. Previous works on this topic have empirically proven the importance of matching photoresist and underlayer surface energy, and the role played by developer liquid in wet development. In this work, we extend those concepts and formulate a figure of merit for the free energy at the exposed and unexposed photoresist-underlayer-developer interfaces. This figure of merit provides a tool to optimize the underlayer surface energy components that best match a given photoresist and developer process. The model is tested against experimental patterning of a chemically amplified resist at pitch 32 nm and pitch 80-nm line spaces, successfully predicting the likelihood of pattern collapse and photoresist scumming. Moreover, we write a quantitative expression for the peeling force acting on photoresist lines owing to unbalanced capillary forces and the threshold energy at which film delamination onsets. It is shown that adhesion and scumming are two manifestations of the same phenomenon at these interfaces.
Pattern collapse and photoresist scumming reduce lithographic quality with detrimental consequence on the process window, etching and pattern transfer. As extreme ultraviolet (EUV) lithography patterning moves to smaller and smaller technology nodes, these phenomena become increasingly dominant. In this work, we propose a three-interface model that accounts for the collapse and wiggling during development (due to developer infiltration) and rinse and drying (due to capillary force). We introduce a metric W3 (dependant on photoresist thickness, pitch, CD, and linewidth roughness) and demonstrate experimentally that W3 of exposed materials predicts scumming while the W3 of unexposed materials predicts collapse and wiggling.
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