Generation of Ultrafast Extreme Ultraviolet Light Source and its Applications in Semiconductor Detection(Invited)
Significance Currently,the rapid development of artificial intelligence(AI),cloud computing,mobile communications,the Internet of Things,and other fields has created a significant demand for advanced chips.Lithography is a core step in the manufacture of these chips,as its level directly determines the process and performance of the chip.The most advanced extreme ultraviolet(EUV)lithography machines currently use 13.5 nm light and are employed in high-volume manufacturing(HVM)of chips at 5 nm node and below.Throughout the production process,each step must be quantitatively measured to ensure that key parameters meet the process targets.While optical technology is predominant in semiconductor inspection and metrology,the sensitivity of traditional optical methods is gradually diminishing.Due to the substantial wavelength shift from 193 nm to 13.5 nm,EUV lithography necessitates new components and materials.Consequently,the detection of these components and research into material interactions need to be conducted anew under EUV light sources.Presently,EUV optical equipment mainly uses discharged produced plasma(DPP)and laser produced plasma(LPP)light sources.However,these plasma light sources have several drawbacks.They produce significant contamination,as plasma fragments can affect devices from the collection mirror to the sample,impacting their lifespan and operating environment.In addition,although plasma EUV light sources offer high power,its radiation of 4π solid angle leads to its low brightness,which will affect its application in high-resolution detection.Therefore,exploring new EUV light sources for quantitative detection is crucial.Since the first discovery of high-order harmonics(HHG)in 1987,extreme ultraviolet high-order harmonics(HHG-EUV)have been widely used in electron dynamics research and various spectroscopy and imaging studies due to its high coherence,short pulses,and high photon energy.High-order harmonics exhibit unique properties,such as good directionality,excellent temporal and spatial coherence,and a broadband spectrum ranging from extreme ultraviolet(XUV)to soft X-ray bands.This makes it feasible to use Table-top-terawatt(T3)lasers to obtain tunable coherent XUV and soft X-ray sources,which have become an important research tool in EUV lithography technology.Concurrently,research on the application of these ultrafast EUV light sources in lithography and semiconductor metrology is advancing rapidly.Progress Our study reviews the development of high-repetition-rate and high-brightness ultrafast EUV light sources in recent years and their applications in semiconductor metrology.The high-order harmonic method can generate a single harmonic with a power of up to 12.9 mW in the EUV region,significantly expanding its application range.In the lithography process,the exposure step transfers patterns from the mask to the photoresist.During exposure,tiny mask defects can cause substantial changes in the critical dimension(CD)on the wafer.Defects above a certain size on the mask must be detected and repaired.Due to the high brightness,broad spectrum,and broad coherence of high-order harmonics,they currently have prospects in coherent diffraction imaging and coherent scattering imaging.Samsung has developed an EMDRS(extreme ultraviolet lithography mask defect review system)device to meet the review needs of EUV mask defects.Hyogo and RIKEN have jointly developed the HHG-CSM(HHG-coherent scatterometry microscope)device based on coherent scattering microscopy,which can observe line defects as small as 2 nm in mask inspection.Huazhong University of Science and Technology has proposed a new high-resolution mask defect detection method that can detect defects with high sensitivity and accurately inspect defects with higher resolution.In wafer inspection and metrology,inspection refers to detecting heterogeneities on the wafer surface or within the circuit structure,while metrology involves the quantitative description of structural dimensions and material properties on the observed wafer.KMlabs can perform interface detection within a certain depth range beneath the surface using coherent diffraction imaging.Researchers from ASML and Intel use 10‒20 nm wavelength EUV scattering measurements to offer a promising next-generation metrology technology,expected to enable 3D nanometer-size measurements of transistors.Conclusions and Prospects The application of high-repetition-rate and high-brightness high-harmonic EUV light sources in semiconductor nanostructure detection has gradually emerged,with significant research results obtained in the actinic detection of mask defects and wafer metrology.The EUV light source generated by the high-harmonic process features a wide spectrum and high brightness,providing unique advantages in inspection and metrology.High-brightness EUV light sources enhance the detection resolution of EUV masks and wafer patterns,while multi-wavelength broadband spectra improve the accuracy of critical dimension measurement,overlay measurements,and complex three-dimensional transistor structures.This advancement is crucial for the development of future semiconductor processes.
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