Optical wafer defect inspection at the 10 nm technology node and beyond

The growing demand for electronic devices, smart devices, and the Internet of Things constitutes the primary driving force for marching down the path of decreased critical dimension and increased circuit intricacy of integrated circuits. However, as sub-10 nm high-volume manufacturing is becoming the mainstream, there is greater awareness that defects introduced by original equipment manufacturer components impact yield and manufacturing costs. The identification, positioning, and classification of these defects, including random particles and systematic defects, are becoming more and more challenging at the 10 nm node and beyond.Very recently, the combination of conventional optical defect inspection with emerging techniques such as nanophotonics, optical vortices, computational imaging, quantitative phase imaging, and deep learning is giving the field a new possibility. Hence, it is extremely necessary to make a thorough review for disclosing new perspectives and exciting trends, on the foundation of former great reviews in the field of defect inspection methods. In this article, we give a comprehensive review of the emerging topics in the past decade with a focus on three specific areas:(a) the defect detectability evaluation,(b) the diverse optical inspection systems,and(c) the post-processing algorithms. We hope, this work can be of importance to both new entrants in the field and people who are seeking to use it in interdisciplinary work.

Layer-dependent photoexcited carrier dynamics of WS_(2) observed using single pulse pump probe method

Understanding the ultrafast carrier dynamics and the mechanism of two-dimensional(2D)transition metal dichalcogenides(TMDs)is key to their applications in the field of optoelectronic devices.In this work,a single pulse pump probe method is introduced to detect the layer-dependent ultrafast carrier dynamics of monolayer and few-layer WS_(2) excited by a femtosecond pulse.Results show that the ultrafast carrier dynamics of the layered WS_(2) films can be divided into three stages:the fast photoexcitation phase with the characteristic time of 2–4 ps,the fast decay phase with the characteristic time of 4–20 ps,and the slow decay phase lasting several hundred picoseconds.Moreover,the layer dependency of the characteristic time of each stage has been observed,and the corresponding mechanism of free carrier dynamics has been discussed.It has been observed as well that the monolayer WS_(2) exhibits a unique rising time of carriers after photoexcitation.The proposed method can be expected to be an effective approach for studying the dynamics of the photoexcited carriers in 2D TMDs.Our results provide a comprehensive understanding of the photoexcited carrier dynamics of layered WS_(2),which is essential for its application in optoelectronics and photovoltaic devices.

Wide-spectrum polarization-sensitive and fast-response photodetector based on 2D group Ⅳ-Ⅵ semiconductor tin selenide

Tin selenide(SnSe)has attracted considerable interest recently on account of its low-symmetry lattice structure,great compatibility with key semiconductor technology,and remarkable electrical and optical performance.SnSe-based polarization-sensitive photodetectors show promising application prospects because of their fast response and excellent photoelectric performance.Here,an in-plane anisotropic SnSe nanosheet was synthesized and reported in detail by applying angle-resolved polarized Raman spectroscopy(ARPRS),polarization-resolved optical microscopy(PROM),angle-resolved optical absorption spectroscopy(AROAS),and other crystal structure characterization methods.Moreover,SnSe crystals exhibit superior polarization detection performance with a high anisotropic photocurrent ratio(2.31 at 1064 nm)due to the structure formed by the Van der Waals superposition of covalently bonded atomic layers.Furthermore,SnSe-based photodetectors have high responsivity(9.27 A/W),high detectivity(4.08×10^(10)Jones),and fast response(in the order of nanoseconds).These results suggest a new method for fabricating 2D fast-response polarization-sensitive photodetectors in the future.

Optical and electronic anisotropy of a 2D semiconductor SiP

Two-dimensional anisotropic materials have been widely concerned by researchers because of their great application potential in the field of polarized detector devices and optical elements,which is a very important and popular research direction at present.As a IV-V two-dimensional material,silicon phosphide(SiP)has obvious in-plane anisotropy and exhibits excellent optical and electrical anisotropy properties.Herein,the optical anisotropy of SiP is studied by spectrometric ellipsometry measurements and polarization-resolved optical microscopy,and its electrical anisotropy is tested by SiP-based field-effect transistor.In addition,the normal and anisotropic photoelectric performance of SiP is shown by fabricating a photodetector and measuring it.In various measurements,SiP exhibits obvious anisotropy and good photoelectric performance.This work provides basic optical,electrical,and photoelectric performance information of SiP,and lays a foundation for further study of SiP and applications of SiP-based devices.

Dynamic modulation performance of ferroelectric liquid crystal polarization rotators and Mueller matrix polarimeter optimization

A ferroelectric liquid crystal polarization rotator(FLCPR)has been widely used in polarization measurement due to its fast and stable modulation characteristics.The accurate characterization of the modulation performance of FLCPR directly affects the measurement accuracy of the instrument based on liquid crystal modulation.In this study,FLCPR is accurately characterized using a self-developed high-speed Stokes polarimeter.Strong linear and weak circular birefringence are observed during modulation processes,and all the optical parameters of FLCPR are dependent on driving voltage.A dual FLCPR-based Mueller matrix polarimeter is designed on the basis of the Stokes polarimeter.The designed polarimeter combines the advantages of the high modulation frequency of FLCPR and the ultrahigh temporal resolution of the fast polarization measurement system in the Stokes polarimeter.The optimal configuration of the designed polarizer is predicted in accordance with singular value decomposition.A simulated thickness measurement of a 24 nm standard SiO2 thin film is performed using the optimal configuration.Results show that the relative error in thickness measurement caused by using the unsatisfactory modulation characteristics of FLCPR reaches up to−4.34%.This finding demonstrates the importance of the accurate characterization of FLCPR in developing a Mueller matrix polarizer.

Remote Absolute Roll-Angle Measurement in Range of 180°Based on Polarization Modulation

Remote measurement of object orientation is often required in many applications.Out of the six degrees of freedom(DoF)that determine object orientation in space,the roll angle is the most difficult to measure using optical methods.In this letter,we propose a remote Stokes roll-angle sensor that measures roll angles from the detected Stokes vectors of modulated polarized light retroreflected from a sensing unit comprised simply of a retarder and a planar reflection mirror.Experimental results have shown that the proposed sensor can realize absolute roll angle measurement in an unprecedented range of 180°with a maximum absolute error of less than 0.25°and a measurement resolution of better than 0.01°.The proposed sensor adopts a coaxial design and takes the advantages of compactness,simplicity and low cost,and moreover,can be further expanded to a three-DoF angle sensor due to the sensitivity of the sensing unit to other two kinds of angles(pitch and yaw).

Ultra-simplified diffraction-based computational spectrometer

Miniaturizing spectrometers for compact and cost-effective mobile platforms is a major challenge in current spectroscopy research,where conventional spectrometers are impractical due to their bulky footprint.Existing miniaturized designs primarily rely on precalibrated response functions of nanophotonic structures to encode spectral information captured in a snapshot by detector arrays.Accurate spectrum reconstruction is achieved through computational techniques,but this requires precise component design,high-precision fabrication,and calibration.We propose an ultra-simplified computational spectrometer that employs a one-to-broadband diffraction decomposition strategy facilitated by a numerical regularized transform that depends only on the spectrum of the diffracted radiation.The key feature of our design is the use of a simple,arbitrarily shaped pinhole as the partial disperser,eliminating the need for complex encoding designs and full spectrum calibration.Our spectrometer achieves a reconstructed spectral peak location accuracy of better than 1 nm over a 200 nm bandwidth and excellent resolution for peaks separated by 3 nm in a bimodal spectrum,all within a compact footprint of under half an inch.Notably,our approach also reveals a breakthrough in broadband coherent diffractive imaging without requiring any prior knowledge of the broadband illumination spectrum,assumptions of non-dispersive specimens,or correction for detector quantum efficiency.