The actinic patterned mask inspection tool "ACTIS" has become essential for EUV photomask qualification in mask shops and semiconductor fabs. It provides high-resolution, high-throughput inspection that can detect all types of mask defects with lithographic implications because it uses the 13.5nm EUV light. ACTIS is equipped with a high-brightness EUV light source with an optimally sized etendue. It minimizes the heat load on the pellicles while increasing the number of photons on the detector to improve inspection sensitivity and throughput. High NA EUV lithography is scheduled to be introduced for the angstrom-generation technology node. Lasertec has developed a new model of ACTIS, the ACTIS A300, to meet the requirements of high-NA mask inspection. In high-NA EUV imaging, the effect of pattern edge roughness on inspection becomes more significant because the image resolution is higher than that of the current NA imaging. This paper discusses how Die-to-Database inspection using a machine learning-based reference image generation model minimizes the effects of edge roughness and further improves the sensitivity of A300.
High-NA extreme ultraviolet lithography (EUVL) at 0.55 NA provides the resolution for single-exposure patterning of devices at 2-nm technology node and beyond. In a single exposure, the feature sizes in the 4× direction on the high-NA masks are tighter than the minimum dimensions imageable at 0.33 NA. We present a general discussion of the need for actinic inspections and then a detailed description of actinic pattern mask inspection (APMI) and actinic blank inspection (ABI), two critical capabilities for the EUV mask infrastructure. The advantages of actinic inspection are to detect all types of defects on blanks and masks with and without a pellicle. The recently developed APMI capabilities for high-NA EUV mask inspections offer higher resolution, image contrast, and defect sensitivity. The high-NA APMI is significantly upgraded from the platform with optics, EUV light source, and detector. The high-NA APMI has been released in 2023, and we presented the inspection results. Equally important is the ABI capability for high-NA mask blanks. The upgrade from the current platform includes a Schwarzschild objective with higher magnification that enhances defect signals in the dark field and improved optics with better imaging in the bright field for defect review. The new ABI provides not only higher sensitivity to multilayer phase defects but also an improved defect location accuracy, both are required for blank inspection in high-NA EUVL applications.
The successful development of Actinic Pattern Mask Inspection (APMI) has enabled the high-volume manufacturing of advanced chips, such as N5 and N3, due to the production of defect-free masks by tsmc's mask shop. This accomplishment can be attributed to the utilization of an innovative Extreme Ultraviolet (EUV) inspector and Graphics Processing Unit (GPU)-based defect detection with Artificial Intelligence (AI) assistance. The application of EUV inspector unleashed pellicle inspection to prolong mask operation periods in wafer foundries. Besides, the improving in the manufacturing efficiency via automation also boost the productivity in the mask shop. According to our previous report in BACUS 2023, the improvement by performing various approaches in the novel Laser-Produced Plasma (LPP) system enabled tsmc to capture EUV image with high stability. The continual improving in the system in later keep reducing the vibration of the crucible and hence improve the tin stability. Furthermore, tsmc developed a GPU-based inspection system, which allowed for flexible algorithm development compared to FPGA. The ML-based rendering model aligned features with tool images and reduced image residue. Therefore, the final inspected image could be possessed with high SNR in advanced node and aggressive OPC compared to DUV inspector. Additionally, the final inspection results will be processed via a Deep Learning (DL) based model, reducing false positives, and implementing auto-defect classification. By combining these contributions, the actinic tools were able to streamline the manufacturing flow and fulfill the requirements for massive production significantly.
As the design rule continues to shrink towards the EUV lithography and beyond, the EUV mask inspection is one of the most important technologies for HVM lithography. Until now, most of the EUV mask inspection was performed by the DUV inspection tools. However, due to the nature of 193nm source, the DUV inspection has resolution limit and is unable to perform through-pellicle inspection. To overcome these limitations, the actinic tool was proposed to achieve high-resolution pattern imaging performance and inspection sensitivity. As a result, the EUV imaging resolution of tested pattern such as DRAM and Logic design was improved by 4.7 times compared to DUV resolution and it can achieve the high-resolution inspection for the extreme OPC type pattern and SRAF pattern. While studies on EUV inspection algorithm was mainly focused on masks for logic devices, we developed the EUV mask inspection technology for DRAM and LOGIC devices with Lasertec ACTIS 150 tool. By using the 13.5nm EUV wavelength the APMI can selectively detect printable defects and reduce the detection of nuisance and false defects. Overall, the defect classification of APMI inspection can be easily done hence the higher-resolution imaging performance. We also applied machine-learning based DB inspection algorithm to overcome resolution limit and accuracy of conventional DB modeling based DUV mask inspection. Finally, by using the 13.5nm actinic source, we acquired the technology to detect phase defect and perform through-pellicle inspection.
Lasertec released an actinic patterned mask inspection (APMI) system named ACTIS in 2019 and has since been providing it as an EUV mask inspection solution for use at mask shops and semiconductor fabs in high-volume manufacturing. Actinic inspection is a type of inspection that utilizes 13.5nm EUV, the wavelength of light used in EUV lithography. ACTIS performs high-resolution, high-throughput inspection of EUV masks and detects mask defects that print on wafers in the lithography process (printable defects). One of the key advantages offered by APMI is its ability to perform highresolution through-pellicle inspection. EUV pellicles are expected to be used in semiconductor fabs, and ACTIS can detect printable defects on EUV masks even when a pellicle is attached to them. High-NA EUV lithography will be used at the technology nodes of N2 and beyond. The projection optics of high-NA EUV lithography are anamorphic optics, which have different scales of magnification for the horizontal and vertical axes. Lasertec has developed a next-generation model of ACTIS for high-NA mask inspection. It uses higher NA objective optics to meet the requirements of high-NA EUV mask inspection. This paper discusses the next-generation ACTIS for high-NA EUV lithography and its inspection performance on programmed defect masks that are similar to actual production masks. The paper also discusses the characteristics of a light source and illumination optics required for APMI.
Lasertec released the actinic patterned mask inspection (APMI) system ACTIS in 2019 and has since been providing it as an actinic inspection solution for EUV mask inspection. ACTIS performs high-resolution, high-throughput inspection of EUV photomasks. It detects all types of mask defects making lithographic impact because it uses the wavelength of light used in EUV lithography as its light source. While actinic inspection is typically known for its capability to detect phase defects, it is also indispensable for detecting phase shift defects on EUV PSM. ACTIS performs both die-to-die (D2D) and die-to-database (DDB) inspections and can inspect all types of EUV masks including multi-die masks and single-die masks. High-NA lithography is expected to be used for the EUV process at the technology nodes of N2 and beyond. The nextgeneration ACTIS has an objective mirror with a higher NA. This makes it possible to have different resolution characteristics in the X and Y directions, enabling it to meet the sensitivity required to detect defects in the anamorphic patterns used for high-NA EUV lithography. In addition, as design nodes become smaller, curvilinear masks will be adopted to improve resolution characteristics on wafers, which will require handling a large amount of design data per mask. For DDB inspection, which generates reference images using sophisticated, high-speed computer processing, the inspection of curvilinear masks is a major challenge. In DDB inspection, curve masks generate large amounts of data because complex curve shapes are approximated using polygons with a large number of vertices. It needs more computing resources and leads to a longer processing time. The reference images generated for inspection must be more intricate. APMI is necessary for pattern mask qualification of EUV masks with pellicles. However, the high sensitivity inspection of masks with EUV pellicles was prevented by the incident power limitation by heat load on the pellicle. Therefore, we have developed a new EUV light source that can minimize the thermal load. This paper describes the development results of the next-generation ACTIS for high-NA EUV lithography, the DDB inspection capability of ACTIS for curvilinear masks, as well as the requirements for APMI light sources, which differ from those of EUV scanner light sources, and the development result of Lasertec's EUV light source "URASHIMA".
Given the successful development in actinic pattern mask inspection (APMI), high-volume manufacturing of advanced chips including N5 and N3 was realized due to the defect-free masks provided by the TSMC mask shop. This achievement was attributed to the newly developed EUV source and GPU-based defect detection with machine learning (ML) assistance. Unlike conventional approaches which sustain less than two weeks, the rotated crucible fed by Sn fuel in the LPP (Laser-produced plasma) system provided one month of operating stability with ultra-low tin consumption. The newly developed LPP EUV light source has been moved towards double IR power to produce higher EUV photon counts, resulting in better throughput and inspection sensitivity. It enables captured images to possess an effective signalto-noise ratio (SNR) and reasonable inspection nuisance counts. The common technique challenges, Sn auto-refuel and debris mitigation, were overcome by auto-refuel and reuse, debris mitigation, and plasma position control. Moreover, the LPP system also showed its capability in performing pellicle inspection to prolong mask operation periods in wafer foundries. For the GPU-based inspection system, it provided the feasibility and flexibility in algorithm development compared to the FPGA approach. The TSMC developed machine-learning (ML) based rendering model played a key role in aligning features with tool images in D2D mode, as well as residue reduction of D2DB mode. All rendering models were implemented by CUDA coding and running on TSMC-customized GPU architecture to fulfill the goal of high-speed computation and defect capture rate that met production specifications. Combining with the ML model, proper detectors were designed for each specific feature, such as SRAF and curvy OPC design, and the performance of auto defect classification (ADC) with the model has been proven. By integrating all the work, it enabled the actinic tools to fulfill the requirement of massive production significantly.
The EUV reticle masking process has enabled the creation of smaller and more intricate integrated circuits, which are essential components of modern electronic devices. However, ensuring defect-free control and evaluation in the cutting-edge EUV reticle masking process is a challenging task. Currently, every potential defect must be judged by wafer printing assessment for almost 3 days, which can be both time-consuming and expensive, and even commercial approaches are incapable of meeting the demands of high-volume manufacturing. In this paper, we successfully developed the EUV Actinic Mask Review System (AMRS) to emulate wafer printability behaviors, utilizing a stable LPP EUV source with over 95% available time and a specialized TSMC-made SMO to achieve high throughput for more than 80 sites/hr. In addition, various EUV resist models have been developed to emulate the risk defect printing assessment with good matching results, and an in-house automation EUV defect analysis platform was developed to achieve fast and accurate areal image measurement. With this solution, all EUV repaired and potential defects, including 18nm HP L/S, ML defects, and even through EUV pellicle defects, can be addressed in technology nodes N5, N3, and beyond N3, on the brand-new actinic review platform. The development of the EUV Actinic Mask Review System represents a significant advancement in ensuring the quality and reliability of semiconductor devices. It provides a practical solution to the challenges posed by the EUV reticle masking process and enables the production of defect-free integrated circuits, paving the way for the continued innovation and progress of the semiconductor industry.
In 2019, Lasertec successfully developed ACTIS™, the world’s first actinic patterned mask inspection (APMI) system, and has since been providing it as a solution to customers for use in EUV lithography production processes. APMI, is a type of inspection that utilizes the same 13.5nm EUV light used in EUV lithography. ACTIS can perform high-resolution, high-throughput inspection of EUV photomasks and detect all types of printable defects, the mask defects that would be printed on wafers in the EUV lithography process. DUV inspection can detect some of the printable defects. However, DUV inspection cannot detect phase defects, whereas APMI can. A comparison between the inspection performance of DUV and APMI for several defects, including phase defects, is provided in this paper. High-NA lithography is expected to be used for the EUV process at the technology nodes of N3 and beyond. High-NA lithography will be achieved by utilizing anamorphic optics, where magnification scales of projection differ along the horizontal and vertical axes. ACTIS has the extendibility to meet the requirements of high-NA lithography as it can be modified to have the NA on the mask extended along a single axis. Lasertec is developing a new generation ACTIS for use in high NA EUV lithography with higher NA projection optics. In this paper, we present the progress of ACTIS inspection technology, suitable characteristics of the Light Source Required for APMI, and simulation results generated by a rigorous optical simulator using electromagnetic calculations which shows performance improvement of new generation ACTIS with higher NA projection optics.
The demand for EUV mask qualification by inspection and metrology techniques continues with the technology node shrink. Smaller node products contain a higher number of masks that require EUV exposure. Semiconductor industries have developed a variety of inspection and metrology tools to accommodate these needs. The progress of these techniques provides well-qualified semiconductor devices. Blank manufacturing is the initial step of the mask-making process. Nanometer-scale bumps and pits on the substrate, uniformity of multilayer stack, and particle-induced wafer printing defects must be controlled during the blank-making process. Both optical mask inspection and actinic blank inspection (ABI) are widely used as effective qualification methods to detect a defect of interest. Patterned mask inspection is an essential process step for mask making. The optical pattern inspection operating at DUV wavelengths near 193nm, Actinic Patterned Mask Inspection (APMI) that uses EUV 13.5nm wavelength, and EB inspection are the presently used patterned mask inspection technologies. APMI plays a key role in EUV mask inspection due to its high-resolution imaging. The introduction of reliable database mode inspection capability added more usability for the latest single die configuration masks. To manage all the printing defects, actinic solutions have the capability to realize fast and reliable results. EUV pellicles are already in use with EUV masks. Thus, the actinic solution is considered a required inspection method for patterned mask qualification for pellicle mounted mask too. Multiple APMI systems have already been installed in mask industries for through-pellicle inspection purposes. We will report the current progress of patterned mask inspection technologies, applications, and the future roadmap for high NA EUV.
In 2019, Lasertec successfully developed ACTISTM, the world’s first actinic patterned mask inspection (APMI) system, and has since been providing it as a solution to customers for use in EUV lithography production processes. APMI, is a type of inspection that utilizes the same 13.5nm EUV light used in EUV lithography. ACTIS can perform high-resolution, high-throughput inspection of EUV photomasks and detect all types of printable defects, the mask defects that would be printed on wafers in the EUV lithography process. DUV inspection can detect some of the printable defects. However, DUV inspection cannot detect phase defects, whereas APMI can. A comparison between the inspection performance of DUV and APMI for several defects, including phase defects, is provided in this paper. High-NA lithography is expected to be used for the EUV process at the technology nodes of N3 and beyond. High-NA lithography will be achieved by utilizing anamorphic optics, where magnification scales of projection differ along the horizontal and vertical axes. ACTIS has the extendibility to meet the requirements of high-NA lithography as it can be modified to have the NA on the mask extended along a single axis. Lasertec will develop a new generation ACTIS for use in high NA EUV lithography with higher NA projection optics. Discussions on increasing the NA of projection optics give rise to questions about inspection resolution due to light being blocked by the absorber on the EUV photomask. This paper will discuss this question using the results of simulations at varying absorber heights and NA values.
EUV lithography enters the high-volume manufacturing stage, and the semiconductor industry considers a lithography-wavelength- matched actinic patterned mask inspection (APMI) tool to be a crucial infrastructure for EUV mask qualification. ACTISTM, the world’s first high-sensitivity actinic patterned mask inspection system, was released in 2019. ACTIS detects lithographic impact defects that cannot be seen with the existing DUV inspection tools. The actual results of production mask inspection show that only an actinic EUV inspection system can visualize small surface topography and phase changes that propagate through multilayer stacks. In this paper, we present the progress of ACTIS inspection technology, defect sensitivity, die-to-database inspection and through pellicle inspection. For technology nodes beyond N3, a high-NA EUV anamorphic lithography system will be used. The mask structure in the high-NA era will be different from the current configuration. For inspection tool design, it is necessary to adopt a different magnification of mask-to-wafer projection in the vertical and horizontal directions. ACTIS has the extendibility to a high-NA system since its projection NA area has room for extension in one direction. The high-NA EUV inspection tool will be discussed in this paper as well.
As extreme ultraviolet lithography (EUVL) enters high volume manufacturing (HVM), the integrated circuit (IC) industry considers actinic patterned mask inspection (APMI) to be the last major EUV mask infrastructure gap. For over 20 years, there have been calls for an APMI tool for both the final qualification of EUV masks in the mask shop and for the requalification of EUV masks in the wafer fab1. Actinic, in this context, is matching the 13.5 nm scanner wavelength to that of the inspection tool so that all types of EUV mask defects can be detected. In order to enable EUVL HVM, we have developed and introduced the world’s first commercially available APMI tool. Actinic inspection enables HVM EUVL by ensuring that the EUV mask going to the EUV scanner is free from EUVprintable defects that may have been overlooked during EUV blank manufacturing or occurred during EUV mask manufacturing, cleaning and use. In this paper we will review EUV mask defect requirements from the maskshop and fab perspective, as well as capabilities of different inspection methods available for HVM. Further, we will provide an overview of the history of APMI tool development and highlight challenges and successes made when designing major components for the tool. APMI enables reliable detection of all classes of EUV-printable mask defects: small absorber defects, phase and amplitude defects in the multi-layer, In this paper, inspection performance of the APMI tool will be reviewed using representative cases from programmed defect masks with designs resembling real production cases. Finally, we will provide an outlook for the next steps in tool development including Die-to-Database inspection, throughpellicle inspection and platform extendibility to high NA EUVL.
As extreme ultraviolet (EUV) lithography enters high volume manufacturing, the semiconductor industry has considered a lithography-wavelength-matched actinic patterned mask inspection (APMI) tool to be a major remaining EUV mask infrastructure gap. Now, an actinic patterned mask inspection system has been developed to fill this gap. Combining experience gained from developing and commercializing the 13.5nm wavelength actinic blank inspection (ABI) system with decades of deep ultraviolet (DUV) patterned mask defect inspection system manufacturing, we have introduced the world’s first high-sensitivity actinic patterned mask inspection and review system, the ACTIS A150 (ACTinic Inspection System). Producing this APMI system required developing and implementing new technologies including a high-intensity EUV source and high-numerical aperture EUV optics. The APMI system achieves extremely high sensitivity to defects because of its high-resolution, low noise imaging. It has demonstrated a capability to detect mask defects having an estimated lithographic impact of 10% CD deviation on the printed wafer.
Improvements in the detection capability of a high-volume-manufacturing (HVM) actinic blank inspection (ABI) prototype for native defects caused by illumination numerical aperture (NA) enlargement were evaluated. A mask blank was inspected by varying the illumination NA. The defect signal intensity increased with illumination NA enlargement as predicted from simulation. The mask blank was also inspected with optical tools, and no additional phase defect was detected. All of the printable phase defects were verified to have been detected by the HVM ABI prototype.
A high-volume manufacturing (HVM) actinic blank inspection (ABI) prototype could detect a printable phase defect for 16 nm node at almost 100 % of the capture rate. However, although a printable phase defect where the aspect ratio was lower than 0.01 was hardly existed, it was not detected by the HVM ABI prototype. For the purpose that could detect the low-aspect phase defects, scattered light angle from the defect was analyzed. As the result of analysis, an enlargement of the illumination NA was found to enhance the signal intensity of a low-aspect phase defect without any significant influence to the noise signal. The illumination optics of the HVM ABI prototype was improved and the illumination NA was enlarged from 0.07 to nearly 0.1. It was demonstrated that the low-aspect phase defect became to be detectable by the HVM ABI prototype, and no negative influence to other defects was found.
A high volume manufacturing (HVM) model of EUV Actinic Blank Inspection (ABI) tool has been developed for the purpose of detecting phase defects on EUV masks. Simulation has been carried out as to how defect aspect ratio (height/width) and illumination numerical aperture (NA) affect defect signal intensity (DSI). It shows that a higher illumination NA leads to a higher DSI for defects with low-aspect ratios. For example, if the illumination NA is changed from 0.07 to 0.1, DSI is expected to increase 20% or more for defects with an aspect ratio lower than 0.015. The ABI tool has shown an enhanced sensitivity, especially for low-aspect ratio defects, after its NA illumination is raised from its original 0.07 NA to 0.1 NA. Actual inspection results using programmed-defect masks show that DSI has increased significantly for defects with low aspect ratios while the signal intensities for defects with high aspect ratios remain the same.
While extreme ultraviolet lithography (EUVL) is the leading candidate of the next generation lithography, the challenge of managing blank defects must be overcome before EUVL being put to practical use. Besides the efforts of manufacturing defect free blanks, the use of mitigation technique called “pattern shift” is now considered to be a more feasible solution. Whether we aim for defect free blanks or use pattern shift, however, it is quite important to understand the properties of the defects on EUV masks. Of particular interest is to distinguish phase defects from amplitude defects, and pits from bumps. To address the need to understand defect properties, the Actinic Blank Inspection (ABI) high volume manufacturing (HVM) model has acquired a review function using a 1200x magnification optics capable of accurately measuring the size and shape of defects. In this paper, we will discuss how the ABI HVM model classifies defects into pits and bumps.
A high-volume manufacturing (HVM) actinic blank inspection (ABI) prototype has been developed, of which the inspection capability for a native defect was evaluated. An analysis of defect signal intensity (DSI) analysis showed that the DSI varied as a result of mask surface roughness. Operating the ABI under a review mode reduced that variation by 71 %, and therefore this operation was made available for precise DSI evaluation. The result also indicated that the defect capture rate was influenced by the DSI variation caused by mask surface roughness. A mask blank was inspected three times by the HVM ABI prototype, and impact of the detected native defects on wafer CD was evaluated. There was observed a pronounced relationship between the DSI and wafer CD; and this means that the ABI tool could detect wafer printable defects. Using the total DSI variation, the capture rate of the smallest defect critical for 16 nm node was estimated to be 93.2 %. This means that most of the critical defects for 16 nm node can be detected with the HVM ABI prototype.
A major challenge for extreme ultraviolet lithography (EUVL) is avoiding defects in the fabrication of multilayered (ML) mask blanks. Substrate defects and adders during ML coating are responsible for ML defects which causes changes on phase and amplitude of EUV light. ML defects must be identified by inspection prior to absorber patterning in order to reduce the effects of ML defects via covering them with patterns to permit the use of fewer ML defect blanks. Fiducial marks (FMs) on ML blanks can
be used for mask alignment and to accurately and precisely determine the locations of ML defects. In this study, we fabricated an FM mask by resist exposure using an e-beam writer and etching. Then, we inspected FMs and ML defects with an EUV actinic full-field mask blank inspection tool developed by EIDEC-LaserTec (LT ABI). Next, we evaluated the ML defect location accuracy on the mask based on FMs of several line depths by deriving center position of FMs and defects with Lorentz, Gaussian fitting and center-of-mass calculation. Here, we explain the estimation of defect location accuracy using FMs and the LT ABI, and discuss the defect numbers which can be covered by absorber patterns. Fewer than 19 defects per blank should be required for EUV blanks to cover ML defects with patterns.
A major challenge for extreme ultraviolet (EUV) lithography is avoiding defects in the fabrication of multilayered (ML) mask blanks. Substrate defects and adders during ML coating are responsible for ML defects, which cause changes on phase and amplitude of EUV light. The ML defects must be identified by inspection prior to absorber patterning in order to reduce the effects of ML defects via covering them with patterns to permit the use of fewer ML defect blanks. Fiducial marks (FMs) on ML blanks can be used for mask alignment and to accurately and precisely determine the locations of ML defects. In this study, we fabricated an FM mask by resist exposure using an e-beam writer and etching. Then, we inspected FMs and ML defects with an EUV actinic full-field mask blank inspection tool developed by EIDEC-LaserTec (LT ABI; EIDEC, Tsukuba, Japan and LaserTec, Yokohama, Japan). Next, we evaluated the ML defect location accuracy on the mask based on FMs of several line depths. Here, we explain the estimation of defect location accuracy using FMs and the LT ABI and discuss the defect numbers which can be covered by absorber patterns. Fewer than 19 defects per blank should be required for EUV blanks to cover the ML defects with patterns.
One of the most challenging tasks to make EUVL (Extreme Ultra Violet Lithography) a reality is to achieve zero
defects for mask blanks. However, since it is uncertain whether mask blanks can be made completely defect-free, defect
mitigation schemes are considered crucial for realization of EUVL. One of the mitigation schemes, pattern shift, covers
ML defects under absorber patterns by device pattern adjustment and prevents the defects from being printed onto wafers.
This scheme, however, requires accurate defect locations, and blank inspection tools must be able to provide the
locations within a margin of the error of tens of nanometers. In this paper we describe a high accuracy defect locating
function of the EUV Actinic Blank Inspection (ABI) tool being developed for HVM hp16 nm and 11 nm nodes.
The availability of actinic blank inspection is one of the key milestones for EUV lithography on the way to high volume
manufacturing. Placed at the very beginning of the mask manufacturing flow, blank inspection delivers the most critical data set for the judgment of the initial blank quality and final mask performance. From all actinic metrology tools proposed and discussed over the last years, actinic blank inspection (ABI) tool is the first one to reach the pre-production status. In this paper we give an overview of EIDEC-Lasertec ABI program, provide a description of the system and share the most recent performance test results of the tool for 16 nm technology node.
Because the realization of defect-free Extreme Ultra-violet Lithography (EUVL) mask blanks is uncertain, the defect
mitigation techniques are becoming quite important. One mitigation technique, "Pattern shift", is a technique that places a
device pattern to cover multilayer (ML) defects underneath the absorber pattern in such a way that the ML defects are not
printed onto wafers. This mitigation method requires the defect coordinate accuracy of down to tens of nanometers.
Consequently, there is a strong demand for a Blank Inspection tool that is capable of providing such defect coordinate
accuracy.
To meet such requirement, we have started to develop a high accuracy defect locating function as an optional feature to
our EUV Actinic Blank Inspection (ABI) system which is currently being developed aiming at HVM hp16 nm-11 nm node.
Since a 26x Schwarzschild optics is used in this inspection tool, it is quite difficult to pinpoint defect location with high
accuracy. Therefore we have decided to realize a high magnification review optics of 600x or higher by adding two mirrors
to the Schwarzschild optics. One of the additional two mirrors is retractable so that the magnification can be switched
according to the purpose of inspections. The high magnification review mode locates defect coordinates accurately with
respect to the fiducial position. We set the accuracy target at 20 nm so that the mitigation technique can be implemented
successfully. The optical configuration proposed in this paper allows both a high speed inspection for HVM and a high
accuracy defect locating function to be achieved on one inspection system.
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