Author: Peng Cheng
When discussing EUV (Extreme Ultraviolet), most people first think of lithography scanners. However, in the field of metrology and inspection, EUV is also gradually being introduced. The drastic shift in lithography wavelength from 193 nm to 13.5 nm requires entirely new components and materials for the EUV lithography process, which means that component inspection and material interaction studies must be re-conducted at the operating wavelength (i.e., 13.5 nm).
01. Why is EUV Metrology and Inspection Needed?
Every process step in semiconductor manufacturing requires quantitative measurement to ensure that critical physical parameters meet the standards, with optical inspection equipment dominating the market. However, as chip process nodes continue to advance and device physical dimensions keep shrinking, transistors are evolving from FinFET to 3D structures such as Gate-All-Around (GAA). Inspection requirements have extended from 2D planes to 3D volumes, making the identification of buried interfaces and the detection of nanoscale defects significantly more challenging. The sensitivity of traditional optical inspection can no longer meet the precision requirements.
Although electron beam inspection offers higher precision, it suffers from slow scanning speed and low throughput, and may even cause damage to wafer materials. In contrast, inspection technologies based on EUV light sources combine high resolution and high inspection speed, while being non-contact and non-destructive. According to the empirical formula for scattering signals, signal intensity is proportional to the sixth power of particle size and inversely proportional to the fourth power of the illumination wavelength. Shortening the wavelength to 13.5 nm can significantly improve the detection sensitivity for nanoscale defects, showing particularly prominent advantages in scenarios such as overlay metrology.
Currently, non-destructive measurement has become the mainstream development direction in semiconductor metrology and inspection, but high-end EUV light sources have long been monopolized by overseas manufacturers.
02. What are the Types of EUV Light Sources?
Whether for lithography or metrology and inspection, the issue of EUV light sources must be resolved first. Currently, there are three main technical routes for EUV light sources.
The first type is traditional plasma sources (the mainstream for lithography), including Laser-Produced Plasma (LPP) and Discharge-Produced Plasma (DPP). LPP sources typically use high-power lasers (usually CO₂ lasers with a wavelength of 10.6 μm) to bombard molten tin droplets, heating them to millions of degrees Celsius to form plasma. The transition of highly charged tin ions then radiates 13.5 nm EUV light. The Lawrence Livermore National Laboratory in the US is developing a petawatt-class thulium laser, which is reported to be 10 times more efficient than the CO₂ lasers used in EUV tools and could replace CO₂ lasers in lithography systems for many years to come. DPP sources generate EUV radiation by exciting Sn plasma through high-voltage discharge. They offer the advantages of compact size and controllable costs, enabling high-speed and highly stable in-line characterization. However, when characterizing internal defects in multilayer films, DPP sources can cause a series of specific issues, and their non-tunable wavelengths cannot adapt to the next-generation 6.7 nm BEUV (Beyond EUV) lithography, resulting in a slight lack of long-term research capability. Although both routes offer high power, their systems are complex, contamination control is difficult, and they are expensive.
The second type is accelerator-based sources, including Free Electron Lasers (FEL), Synchrotron Radiation (SR), and Steady-State Microbunching (SSMB) sources. The principle of FEL is to accelerate an electron beam to near the speed of light and then guide it into a periodic magnetic field (undulator), where the electrons are forced to oscillate and emit coherent EUV light. Synchrotron radiation is based on an electron storage ring, where electrons radiate a continuous spectrum in a deflection magnetic field. The SSMB source combines the characteristics of synchrotron radiation and FEL, forming microbunches in an electron storage ring to generate high-power coherent radiation. This is led by a team at Tsinghua University, and its principle was experimentally verified in 2021, being regarded as a potential new path for high-power EUV light sources.
The third type is High-Harmonic Generation (HHG) sources. HHG technology generates high harmonics through the interaction of femtosecond lasers with rare gases in a nonlinear response, thereby outputting EUV light in the 10–50 nm wavelength band. This type of light source has several notable features: First, it is compact in size and low in cost. The entire system can be deployed on a desktop, which is much smaller than traditional EUV light sources. Second, it features high coherence and tunable wavelengths. The beam has high coherence, can cover multiple bands, and has quasi-continuous ultra-broadband spectral output. Third, it has strong engineering feasibility. It does not require complex EUV multilayer mirrors or metal target contamination control, resulting in a stable system with low maintenance costs. The drawback is its relatively low power, and it is currently mainly used in scientific research and metrology fields such as mask defect inspection, attosecond physics, and ultrafast spectroscopy. Currently, international companies such as ASML, Intel, Samsung, and TSMC (Taiwan Semiconductor Manufacturing Company) have begun to use HHG technology in metrology and inspection to verify its industrialization potential. The US NIST (National Institute of Standards and Technology) has also defined HHG as the "optimal route integrating broadband, ultrafast, and coherent properties," and the IRDS 2024 International Roadmap for Devices and Systems explicitly points out that HHG is the core technology for next-generation EUV metrology.
03. Where is EUV Metrology and Inspection Applied?
EUV metrology and inspection mainly cover scenarios such as mask defect inspection, wafer metrology and inspection, and material analysis. The underlying principles mainly include Coherent Diffractive Imaging (CDI), Coherent Scatterometry Metrology (CSM), and Transient Grating (TG).
First is EUV mask inspection. EUV lithography uses a reflective optical path, and the mask consists of a substrate, Mo/Si multilayer films, and an absorber layer. Even tiny defects can lead to significant deviations in the critical dimensions of the wafer, making defect-free masks a core prerequisite for mass production. EUV mask defects can be divided into amplitude defects and phase defects. Traditional DUV light sources and electron beam inspection struggle to penetrate the Mo/Si multilayer films, making it difficult to detect phase defects within the multilayers. Moreover, the imaging results differ greatly from the actual aerial images of lithography exposure, making it impossible to verify the reliability of the exposure results.
CDI is a lensless imaging technology that collects the diffraction pattern of a sample in the Fourier domain (reciprocal space) and uses phase retrieval algorithms to reconstruct the sample structure, avoiding the stringent requirements for optical element aberrations at short wavelengths. Ptychography combines scanning technology with CDI, scanning the sample point by point and collecting diffraction patterns from adjacent overlapping areas, using redundant information to robustly reconstruct the amplitude and phase of the sample. The RESCAN tool developed by PSI (Paul Scherrer Institute) in Switzerland aims to complete a full inspection of EUV masks within 7 hours, detecting defects smaller than 10nm×10nm. The EMCI cross-scale inspection strategy proposed by Huazhong University of Science and Technology combines reflective fly-scan scatterometry with CDI, enabling rapid screening and high-resolution re-inspection of actinic defects. The HHG-CSM system, a collaboration between Hyogo and RIKEN in Japan, has improved the line defect detection limit from10nm with synchrotron radiation sources to 2nm.
Coherent Scatterometry Microscopy (HHG-CSM) based on HHG-EUV light sources can directly use a CCD to record the diffraction of mask patterns without the need for complex imaging systems. Based on this, Samsung developed the EMDRS (EUV Mask Defect Review System) to verify the effects of mask repair and defect mitigation avoidance (MDA).
Second is wafer metrology and inspection. Wafer metrology and inspection are generally divided into metrology and inspection. Inspection refers to detecting whether heterogeneous conditions occur on the wafer surface or in circuit structures, such as characteristic structural defects that adversely affect chip process performance, including particle contamination, surface scratches, and open/short circuits. As FinFET evolves into nanowire and GAA structures, the difficulty of 3D measurement continues to increase. The stacking of multiple patterning processes also sharply increases the complexity of overlay accuracy and periodic structure characterization, while the shrinking of feature sizes brings about the problem of decreased signal-to-noise ratio.
Scatterometry is a commonly used fast, precise, and low-cost metrology and inspection technology in the semiconductor field. Researchers at ASML and Intel have utilized HHG-EUV broadband light sources with wavelengths of 10–20 nm to conduct scatterometry, which is suitable for 3D profile measurement and overlay applications. Compared to traditional visible light, short wavelengths can provide higher resolution. Scattering in the EUV band is dominated by single scattering, with low correlation between parameters, facilitating physical interpretation. Moreover, the penetration depth can reach 400 nm, supporting the metrology of complex 3D structures such as GAA.
Finally, there is material analysis, with the main application being the in-situ characterization of photoresist exposure performance. In the EUV lithography process, the performance of the photoresist directly affects the quality and critical dimensions of the manufactured structures. During EUV exposure, the molecular structure and material composition of the exposed areas of the photoresist will undergo certain changes, and the decomposition of polymers during the Post-Exposure Bake (PEB) process can be captured through changes in optical constants. EUV reflectometry, as a non-destructive metrology technique, can measure the broadband reflectivity of samples in the EUV spectral range. Combined with the high sensitivity to periodic nanostructures and high sensitivity to material composition under grazing incidence angle conditions, it enables the characterization of latent images in periodic structures. Furthermore, comparing the reflectivity measurement results of exposed and unexposed photoresists can reveal changes in the optical constants and thickness shrinkage of the photoresist after exposure and baking treatments, thereby extracting structural parameter information including the latent image profile and surface morphology. Additionally, EUV scatterometry also has important applications in the roughness characterization of nanoscale patterns/lines.
EUV Transient Grating utilizes two beams of EUV light to interfere on a sample to form a spatially periodic grating, exciting the phonons or thermal response of the sample, and then uses a third probe beam for time-resolved measurement. This technology can directly measure the quasi-ballistic heat transport effect from nanoscale heat sources to the surrounding environment, study the phonon dynamics and thermoelastic properties of thin films such as SiC and Si₃N₄, and measure the variation of elastic modulus with temperature. This is critical for thermal management at advanced process nodes and for understanding nanoscale heat transport dynamics.
04. Domestic EUV Metrology and Inspection Layout
Currently, domestic manufacturers have made multi-faceted layouts in EUV light sources applied to metrology and inspection. Start-ups and university technology transfer teams have jointly built a preliminary matrix for domestic substitution.
Huaxin Jiguang is a technology company founded in Shanghai in August 2025, mainly engaged in the R&D of Extreme Ultraviolet (EUV) light source technology and semiconductor equipment. Professor Lin Nan, the founder of Huaxin Jiguang, is a national leading talent, a doctoral supervisor, and a Marie Skłodowska-Curie Fellow. He studied under Academician Anne L'Huillier, the winner of the 2023 Nobel Prize in Physics, and worked in the R&D department of ASML in the Netherlands for many years. He has been engaged in the R&D of advanced light sources for a long time, with a total of more than 120 international patents published and authorized. However, Huaxin Jiguang mainly faces the market demand for advanced light sources, focusing on commercialized innovative EUV light source solutions, and the industrialization implementation is mainly completed by Huaxin Quanzhu. Huaxin Quanzhu is a joint venture established by Quanzhu Shares and Huaxin Jiguang, dedicated to the R&D and manufacturing of core precision measurement equipment for EUV light sources.
Landao Technology is an R&D enterprise for specialized equipment in semiconductor manufacturing founded in 2024. The company's core business focuses on the R&D of LPP-EUV light sources. Dr. Wang Hao, the founder, and his team, based on the R&D achievements of the Gas Discharge Plasma Laboratory at Tsinghua University, are committed to providing high-power and highly stable EUV light sources for China's chip manufacturing industry. Landao Technology currently has three core business segments: providing integrated inspection/lithography-grade EUV light source systems to offer reliable EUV light source solutions for semiconductor manufacturers; focusing on high-power CO₂ axial fast-flow laser amplifiers used for EUV light sources in lasers, catering to various industrial application scenarios; and focusing on the R&D and services of plasma simulation software, developing electromagnetic fluid multi-physics simulation programs, molecular dynamics multi-scale numerical simulation programs, etc., which have been successfully embedded in industrial scenarios in the semiconductor, aerospace, and other industries.
Yunqi Jiyao is a developer of compact plasma light sources, established on February 7, 2025, mainly engaged in the R&D of compact plasma light source technology. The company is committed to improving the performance and integration of precision optical and microelectronic equipment through technological innovation to meet the demand for light source technology in the high-end manufacturing field. On February 9, 2026, Yunqi Jiyao announced the completion of its angel round of financing, jointly invested by five institutions: SMIC Juyuan, Junlan Capital, Qiling Enterprise Management, Puhua Capital, and Jin Jieji. Yunqi Jiyao stated that it will rely on the new funds to accelerate product implementation and promote the application of plasma light source technology in fields such as semiconductors and optical instruments.
Huarui Laser is also laying out EUV coherent light sources. Huarui Laser is the technology transfer vehicle for the Hubei Optics Valley Laboratory and the team of Lu Peixiang at Huazhong University of Science and Technology, promoting the transition of EUV coherent light sources from the laboratory to industrialization. Professor Lu Peixiang from Huazhong University of Science and Technology has led his team in researching EUV coherent light source technology for over a decade, achieving key technological breakthroughs. However, to truly apply the technology to the industry, the laboratory setup must be further developed to create an industrialized prototype of the laser to further test its stability. Therefore, Lu Peixiang and Wuhan Huarui Precision Laser Co., Ltd. are carrying out the industrialization of related technologies together. In the proposed project list for the 2021 Hubei Province "Double Innovation Strategic Team," the Huarui Laser "R&D and Industrialization Project Team of High-Brightness EUV Lasers Applied to Online Defect Inspection in IC (Integrated Circuit) Manufacturing" was shortlisted for the 2021 "Hubei Province Double Innovation Science and Technology Innovation Strategic Team."
Haoyu Xinguang is a high-tech enterprise focusing on advanced laser applications and the development of semiconductor metrology and inspection equipment. It was jointly founded by well-known experts in the EUV laser field, national overseas high-level experts, and talents with many years of industry experience. Established in November 2023, its technical route is HHG EUV light sources. The team comes from frontier fields such as EUV lasers, attosecond physics, and semiconductor metrology. The core members include both national-level overseas high-level talents and engineering experts who have long been active on the front lines of the international industry. Currently, its technical capabilities cover the entire spectral range from soft X-ray (SXR) to EUV and then to vacuum ultraviolet (VUV).
05. Opportunities and Challenges for Domestic EUV Metrology and Inspection
Given the expansion of advanced process nodes, the demand for EUV metrology and inspection equipment will surge directly. At the same time, top overseas talents returning to China to start businesses, along with the long-term technological accumulation of universities and research institutes such as Tsinghua University, Huazhong University of Science and Technology, and the Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences, have also provided a talent and technology foundation for industrial development.
However, challenges still remain. First, the bottleneck in light source performance has not yet been broken through. LPP light sources have extremely high requirements for the generation accuracy of droplet tin targets (diameter standard deviation < 0.5μm, position stability < 1μm), and power, lifespan, and stability still need to be improved. The debris control and discharge stability issues of DPP light sources have not been completely resolved. The power of HHG light sources is still at the milliwatt to watt level, requiring further improvement in repetition rate and average power to adapt to large-scale production lines. Accelerator light sources such as synchrotron radiation are limited by size and cost, and compact new light sources are still in the principle verification stage. Second, the industrialization cycle is long. Currently, domestic entities related to EUV metrology and inspection are mostly start-ups or university transfer teams, generally in the early stage of industrialization. From laboratory prototypes to mass production implementation, substantial capital investment and long-term process iteration are still required. Third, the requirements for supply chain collaboration are high. The performance verification and implementation of metrology and inspection equipment require deep adaptation across the entire chain of lithography scanners, photoresists, and wafer manufacturing processes, relying on the collaborative progress of the entire semiconductor supply chain.
Domestic enterprises, from light source R&D and equipment manufacturing to system integration, have initially formed a domestic substitution matrix for EUV metrology and inspection. Given the steady advancement of high-brightness coherent EUV light source technology, and the deep integration of technologies such as CDI, scatterometry, and transient grating, domestic EUV metrology and inspection tools are expected to achieve breakthroughs in key links such as mask defect inspection, wafer 3D metrology, and photoresist characterization.