Resolution Enhancement Technology Research Articles

SCAPSM: attenuated phase-shift mask structure for EUV lithography.

The attenuated phase-shift mask (Att. PSM) is proven to be a promising resolution enhancement technology (RET) to improve the imaging performance in extreme ultraviolet (EUV) lithography. However, due to the reflective nature of the mask structure, the serious shadowing effect can affect the diffraction near field of the mask intensely and further impact the lithography imaging. With the purpose of improving the contrast of lithography imaging, a novel structure of the Att. PSM, to the best of our knowledge, is proposed in this paper. By introducing an absorbent sidewall along the edge of the mask absorber, the diffraction and shadowing effects can be mitigated. By applying the Kirchhoff approximation of mask diffraction, the ability of the novel structure to improve imaging performance is theoretically analyzed. Additionally, these analyses are confirmed by rigorous lithography simulations. The simulation results demonstrate that the proposed mask structure can improve the imaging contrast of EUV lithography, which has potential usage in advanced integrated circuit (IC) manufacturing.

DevelSet: Deep Neural Level Set for Instant Mask Optimization

As one of the key techniques for resolution enhancement technologies (RETs), optical proximity correction (OPC) suffers from prohibitive computational costs as feature sizes continue to shrink. Inverse lithography techniques (ILT) treat the mask optimization process as an inverse imaging problem, yielding high-quality curvilinear masks. However, ILT methods often fall short of printability and manufacturability due to their time-consuming procedures and excessive computational overhead. In this paper, we propose DevelSet, a potent metal layer OPC engine that replaces discrete pixel-based masks with implicit level set-based representations. With a GPU-accelerated lithography simulator, DevelSet achieves end-to-end mask optimization using a neural network to provide quasi-optimized level set initialization and further evolution with a CUDA-based mask optimizer for fast convergence. The backbone of DevelSet-Net is a transformer-based multi-branch neural network that offers a parameter selector to eliminate the need for manual parameter initialization. Experimental results demonstrate that the DevelSet framework outperforms state-of-the-art approaches in terms of printability while achieving fast runtime performance (around 1 second). We expect this enhanced level set technique, coupled with a CUDA/DNN accelerated joint optimization paradigm, to have a substantial impact on industrial mask optimization solutions.

Inverse lithography physics-informed deep neural level set for mask optimization.

As the feature size of integrated circuits continues to decrease, optical proximity correction (OPC) has emerged as a crucial resolution enhancement technology for ensuring high printability in the lithography process. Recently, level set-based inverse lithography technology (ILT) has drawn considerable attention as a promising OPC solution, showcasing its powerful pattern fidelity, especially in advanced processing. However, the massive computational time consumption of ILT limits its applicability to mainly correcting partial layers and hotspot regions. Deep learning (DL) methods have shown great potential in accelerating ILT. However, the lack of domain knowledge of inverse lithography limits the ability of DL-based algorithms in process window (PW) enhancement, etc. In this paper, we propose an inverse lithography physics-informed deep neural level set (ILDLS) approach for mask optimization. This approach utilizes level set-based ILT as a layer within the DL framework and iteratively conducts mask prediction and correction to significantly enhance printability and PW in comparison with results from pure DL and ILT. With this approach, the computational efficiency is significantly improved compared with ILT. By gearing up DL with the knowledge of inverse lithography physics, ILDLS provides a new and efficient mask optimization solution.

Critical Pattern Selection Method Based on CNN Embeddings for Full-Chip Optimization

Source mask optimization (SMO), a primary resolution enhancement technology, is one of the most pivotal technologies for enhancing lithography imaging quality. Due to the high computation complexity of SMO, patterns should be selected by a selection algorithm before optimization. However, the limitations of existing selection methods are twofold: they are computationally intensive and they produce biased selection results. The representative method having the former limitation is the diffraction signature method. And IBM’s method utilizing the rigid transfer function tends to cause biased selection results. To address this problem, this study proposes a novel pattern cluster and selection algorithm architecture based on a convolutional neural network (CNN). The proposed method provides a paradigm for solving the critical pattern selection problem by CNN to transfer patterns from the source image domain to unified embeddings in a K-dimensional feature space, exhibiting higher efficiency and maintaining high accuracy.

Parameter Estimation in Spectral Resolution Enhancement Based on Forward-Backward Linear Prediction Total Least Square Method.

In a Fourier transform infrared (IR) spectrometer, the Michelson interference signal extrapolation method based on linear prediction is often used to improve spectral resolution. In this method, an autoregressive (AR) model is established for the Michelson interference signal in the spectrometer. Once the AR model parameters are determined, the AR process is predictable. The interference signal can be used to figure out the AR model's parameters. Based on this, the AR model can be used to extrapolate the interference signal to improve the spectral resolution. In this paper, the forward-backward linear prediction total least squares (FB-TLS) method is proposed to estimate the parameters of the AR model. The parameters that are estimated are used to improve the IR spectral resolution. By simulating different order and signal-to-noise ratio situations, the effects of the Burg, the least square, and the FB-TLS parameter estimation methods on spectral resolution enhancement are studied. The simulation results demonstrate that the FB-TLS parameter estimation method can effectively suppress noise and avoid spurious peaks. The experimental results demonstrate that the FB-TLS parameter estimation method is effective for spectral resolution enhancement technology based on linear prediction. When the FB-TLS method is used to enhance NH3 IR spectral resolution from 2 cm-1 to 1 cm-1, the spectral prediction error in the NH3 characteristic band is only 0.21% compared with the measured NH3 spectrum, whose spectral resolution is 1 cm-1.

The Inverse Optimization of an Optical Lithographic Source with a Hybrid Genetic Algorithm

As an effective resolution enhancement technology, source optimization (SO) is considered key for significantly improving the image quality of optical lithography at advanced nodes. To solve the problem of unsatisfactory SO performance, it is necessary to combine it with optimization algorithms. In this study, an SO method based on a hybrid genetic algorithm is proposed to achieve an acceptable source shape in the imaging process for optical lithography. To overcome the problems of local optima and the small search scope, an update strategy that uses particle swarm optimization and the tabu list method from the tabu search algorithm are utilized to enhance the optimization performance. Meanwhile, different feature patterns were employed as the input of the optimization model. These simulation results show that the proposed SO method exhibits dominant optimization performance for SO in optical lithography.

Endoscopic Surveillance and Treatment of Upper GI Tract Lesions in Patients with Familial Adenomatous Polyposis—A New Perspective on an Old Disease

Familial adenomatous polyposis (FAP) is an autosomal dominant disease caused by a germline mutation in the adenomatous polyposis coli (APC) gene. Patients with FAP develop up to thousands of colorectal adenomas as well as lesions in the upper GI tract. In FAP, the upper digestive lesions include gastric fundic gland polyps (FGPs), antrum adenomas, duodenal or small intestinal adenomas, and carcinoma. Patients, after colectomy, are still at significant risk for extracolonic malignancies. Advances in endoscope resolution and optical enhancement technologies allow endoscopists to provide assessments of benign and malignant polyps. For this reason, in the past decades, endoscopic resection techniques have become the first line of treatment in patients with polyps in the upper GI, whereby polyps and even early cancers can be successfully cured. In FAP patients, endoscopic ampullectomy appears to be a safe and effective way of treating patients with ampullary tumors. According to current indications, endoscopic retrograde cholangiopancreatography (ERCP) and stenting of the main pancreatic duct follow ampullectomy.

Global optimisation of source and mask in inverse lithography via tabu search combined with genetic algorithm.

Source mask optimisation (SMO) is a resolution enhancement technology that is utilised in the advanced process node of optical lithography to achieve acceptable imaging quality and fidelity. It is crucial in enhancing the convergence performance and optimisation capability of pixel-based SMO. In this study, an SMO approach that employs a genetic algorithm (GA), combined with the tabu search method (TS), is proposed. GA-TS, a hybrid-type global optimisation algorithm, has an outperforming capacity to avoid local optima owing to the excellent local searching function of TS. Furthermore, an edge-optimisation strategy was implemented to optimise the mask for a low-complexity mask layout. The simulation results confirm that the proposed approach exhibits exceptional optimisation capability and convergence performance.

Postoperative Examination of Laryngeal Malignant Tumor Based on Narrowband Imaging Resolution Enhancement Technology.

The application of endoscopic imaging in the biopsy of malignant laryngeal lesions is one of the current research hotspots in the medical field. Based on the narrowband imaging resolution enhancement technology, a model for postoperative examination of laryngeal malignant tumor was constructed in this paper. The article calculated the biopsy detection rate of malignant lesions and the correct biopsy detection rate of the two groups and made a statistical comparison. In the NBI mode group, the mucosal morphology and superficial mucosal microvascular morphology of the same lesion under two different modes of white light and NBI were compared, which solved the problem of data processing of cases. During the case comparison process, patients who needed biopsies to be sent for pathology were selected for inclusion in the study and were randomly divided into two groups. The coincidence rate of EUS combined with NBI diagnosis was significantly higher than that of ordinary white light gastroscopy (47.92%), and the difference was statistically significant (P=0.000 < 0.05). The experimental results compared the accuracy of the normal white light mode and the NBI mode to diagnose the nature of the lesions: according to the Kudo classification criteria, 23 cases of tumor lesions were to be diagnosed in the normal white light mode, with an accuracy rate of 69.70%, and the NBI mode was to be used to diagnose tumors. There were 81 cases of sexual lesions, with an accuracy rate of 93.94%. The NBI mode was more accurate in diagnosing the nature of the lesions under the Kudo classification standard (P < 0.05). In 64 cases, the accuracy rate was 63.63%. Under the NBI mode, 29 cases of tumor lesions were proposed to be diagnosed, and the accuracy rate was 87.88% to promote the application of NBI endoscopy in the biopsy of malignant laryngeal lesions.

Research on Resolution Enhancement Technology of Orthogonal Multimode Fiber Imaging

This paper presents a new scheme to improve the imaging resolution of optical fiber endoscope. Multimode fiber imaging is combined with correlation imaging experimental architecture, and Schmidt orthogonalization algorithm is used to reduce the correlation of light field. The simulation and experimental results show that this scheme can greatly improve the imaging quality and resolution, especially in the case of under sampling. In addition, the scheme can also resist the low resolution problem caused by the light field divergence of multimode fiber correlation imaging, and when the light field divergence reaches a certain extent, the resolution of the orthogonalized multimode fiber light field will no longer be affected. The feasibility of orthogonal multimode fiber imaging scheme in large depth of field is verified.

Inverse lithography technology: 30 years from concept to practical, full-chip reality

In lithography, optical proximity and process bias/effects need to be corrected to achieve the best wafer print. Efforts to correct for these effects started with a simple bias, adding a hammer head in line-ends to prevent line-end shortening. This first-generation correction was called rule-based optical proximity correction (OPC). Then, as chip feature sizes continued to shrink, OPC became more complicated and evolved to a model-based approach. Some extra patterns were added to masks, to improve the wafer process window, a measure of resilience to manufacturing variation. Around this time, the concept of inverse lithography technology (ILT), a mathematically rigorous inverse approach that determines the mask shapes that will produce the desired on-wafer results, was introduced. ILT has been explored and developed over the last three decades as the next generation of OPC, promising a solution to several challenges of advanced-node lithography, whether optical or extreme ultraviolet (EUV). Today, both OPC and ILT are part of an arsenal of lithography technologies called resolution enhancement technologies. Since OPC and ILT both involve computation, they are also considered as part of computational lithography. We explore the background and history of ILT and detail the significant milestones that have taken full-chip ILT from an academic concept to a practical production reality.

(Invited) History of Micro-/Nano-Electronics Development; Breakthroughs and Innovations

Introduction Although the first MOSFET-like device ideas were proposed about 90 years ago by J. E. Lilienfeld [1], it took 30 years for the first operational MOSFET to have been successfully fabricated by selecting Al/SiO2/Si as the MOS materials by D. Kahng and M. Attalla [2]. Then, another 10 years were necessary until it had evolved to Large Scale Integrated circuits (LSIs). Indeed ‘microelectronics’ started in early 1970’s with microprocessors fabricated on the LSI chips. At that time, the technology was 10 μm PMOS LSIs. Now, it has evolved to 10 nm-range CMOS LSIs. In the past 50 years, we have experienced 23 generations (each about 2.5 years) of the shrinkage, and the MOSFETs size has decreased by 1,000 times, resulting in an increase in integration density with 1 million times. The continuous increase with the constant rate is the Moore’s law [3], but no one including me could imagine its continuation of over 50 years. The downsizing of MOSFETs has been accomplished based on the scaling scheme proposed by R. Dennard [4], but we have encountered very serious problems at every new generation. Fortunately, however, we have so far succeeded in finding the solutions. This presentation explains some of the history of micro-/nano-electronics technology developments in the past 50 years based on my experience and memory. Technology development for the past 50 years In order to shrink the size, removing the misalignment space margin between the layers is effective, and 2 self-align techniques, Si-gate (between gate and source/drain) and LOCOS (between filed diffusion and oxide) were developed at the end of 1960’s. Then, at the beginning of 1970’s, the fabrication process was simple, with 5 masks for the lithography; field isolation, gate electrode, contact hole, Al interconnects, and bonding pad, with options of a few more masks; channel ion-implantation, or direct-contact between poly-Si lines and source/drain layers, etc.Another factor to reduce the size is to minimize the side-etching and side-diffusion, and anisotropic technologies (or 'dry-process'), such as reactive ion etching and heavy source/drain implantation, were developed at the beginning of 1980’s for the VLSI era. At the same time, stepper (step-and-repeat reduction-projection system) was introduced for higher-resolution lithography. The resolution of the lithography has been improved continuously by introducing a shorter optical wavelength and also by developing various resolution enhancement technologies. Recent introduction of the EUV is a big leap for the wavelength.Since the early 1970’s, short-channel effects (threshold voltage decrease and off-leakage current increase) have been the hurdle for the gate length reduction. The solution was to decrease source/drain junction depth and gate oxide thickness. In order to realize shallow source/drain diffused layers with low resistance, the diffusion element changed from P to As, and new technologies such as low-energy implantation, rapid thermal annealing, and silicided-source/drain were developed. For the thin gate oxide, rapid thermal oxidation, oxynitride gate insulator and finally high-k metal gate technologies were developed. In the early stage of the LSI in 1970s, the semiconductor chips were composed of only 3 major elements, i.e., Si, O, Al with 3 other ones, P, B and H, as additives, but now so many new elements are used for the gate, source, and drain of the MOSFETs, memory cells, and interconnects.Other problems were the degradations of yield and reliability. The mechanisms of the degradations were investigated and many new process/structure/material technologies have been developed as the solutions.In order to suppress the short-channel effects and also to increase the integration density, the structures of the MOSFETs and DRAM/flash memory cells have changed from flat to 3D. Conclusions So huge resources have been invested for the development of micro/nano-electronics in the past 50 years because of its impact to and demands from our modern society, and unbelievably huge progress in engineering and science has been achieved. Indeed, the scales of investment and impact were much bigger than those of the Apollo moon project. The dedication of so many people during the past 50 years has opened up a new smart society in the 21st century with AI, big data, internet and so on. Past 50 years have been really an exciting period. However, the next 50 years will be a more exciting period with a great leap on the base of the micro/nano-electronics.[1] J. Lilienfeld, US1900018A, filed March 28, 1928[2] M. Atalla, and D. Kahng, IRE-AIEE Solid State Device Research Conference, 1960[3] G. Moore, Electronics, Vol. 38, No. 8, April 19, 1965[4] R. Dennard et al., IEEE JSSC, Vol.SC-9, No.5, October, 1974

Gradient-based source mask and polarization optimization with the hybrid Hopkins–Abbe model

Source mask and polarization optimization (SMPO) is a promising extension of the widely used resolution enhancement technology, source mask optimization (SMO), to further enhance chip manufacturability beyond 28-nm node. Our work is aimed to develop an efficient gradient-based SMPO method by employing the hybrid Hopkins–Abbe imaging model to fulfill the goal. In addition to source and mask variables, the model is adapted to also include polarization variables to realize the optimization. Compact formulas for forward and backward model application are derived. The computation benefits from precomputed transmission cross coefficients and features high efficiency. Validity of the method is confirmed by case studies. For dense array pattern case, the optimal source and polarization can be found analytically. SMPO optimized results match well with the theoretical expectations. In addition, process window, mask error enhancement factor, and normalized image log-slope for the studied cases all get improved over the counterpart SMO results, which employ commonly used polarization. Runtime analysis shows the method is computationally efficient. Our work provides a valid way to optimize polarization together with source and mask.

Programmable pupil correction method for photolithography illumination system

The off-axis illumination (OAI) technology is one of the resolution enhancement technologies, and it used to reduce critical dimension (CD) and increase depth of focus (DOF) which are the important performance parameters of photolithography machine. The performance of illumination modes has great effect on critical dimension uniformity (CDU), H–V bias and overlay accuracy. In order that the pupil characteristic parameters can always meet the requirements for a long time using, it is necessary to adopt the pupil correction technology for photolithography illumination system. Using experiments and photolithography performance simulation, a programmable pupil correction method based on correction fingers is studied. The correction algorithm and its operation process are analyzed in detail. The experimental results show that the energy distribution of corrected pupils is more balanced than the uncorrected ones. Furthermore, the simulation results indicate that the corrected pupil could improve the exposure patterns in different aspects. The proposed method could determine the fingers’ position easily, and could directly reflect the pupil performance requirements.

Three-dimensional resolution enhancement in confocal microscopy with radially polarized illumination using subtractive imaging

A method based on the subtraction of images taken under radially polarized illumination is provided to improve the three-dimensional resolution in confocal microscopy. Radially polarized light and vortex phase modulated radially polarized light are used as confocal microscopy illumination light. Our numerical simulations predict that lateral resolutions close to 0.218λ is possible for practical confocal laser scanning microscopy with visible light. Theoretically, by applying radially polarized light and image subtraction method, we can enhance lateral resolution 47.3% higher than that in confocal microscopy with a pinhole of 0.3AU, and improve the axial resolving ability by 20.9% simultaneously. Simulation results of both 3D array model and cell microtubules are presented to verify the applicability and effectiveness of our method. In conclusion, the resolution of confocal microscopy using radially polarized light illumination and image subtraction could be improved. Compared with other resolution enhancement technologies, this method can offer significant spatial resolution improvements for fluorescence imaging at lower cost.

55‐2: Essential Mask Quality for High‐End Resolution Displays

This paper proposes a best practice to produce the photomasks with the state‐of‐the‐art quality, suitable for high resolution panel patterning. In order to extend the panel patterning process capability, high CD performance (Resolution, CD MTT and CD Uniformity) of photomask is essential and RET(Resolution Enhancement Technology) such as PSM, OPC and OAI will be prominent technology for mask business. PSM and OPC technology on RET will be new challenges for future high resolution panel. These challenges require new generation photomask writer, PSM manufacturing capability.

定量相位显微中分辨率增强技术综述

定量相位显微中分辨率增强技术综述

Improving confocal microscopy resolution by tangentially polarized illumination and image subtraction

Abstract Confocal microscopy is widely used, but its resolution is limited. To improve confocal microscopy resolution, tangentially polarized illumination light and image subtraction are studied. Tangentially polarized light or vortex phase modulated tangentially polarized light are used as confocal microscopy illumination light. The effective point spread function difference of the confocal microscopy using tangentially polarized light and using vortex phase modulated tangentially polarized light is got first. The full width at half maximum of the point spread function difference is smaller. Simulation shows that the resolution of the confocal microscopy using tangentially polarized light illumination and image subtraction is increased by 19.9% compared with ordinary circularly polarized light. When compared with confocal microscopy using vortex phase modulated tangentially polarized light, simulation and fluorescence beads imaging experiment show that the resolution of the aforementioned confocal microscopy is improved by 13.6% and 11.2%. In conclusion, the resolution of confocal microscopy using tangentially polarized light illumination and image subtraction could be improved. Compared with other resolution enhancement technologies, this method is much simpler and does not need strong lasers.

A nonlinear measurement method of polarization aberration in immersion projection optics by spectrum analysis of aerial image.

Polarization aberrations (PA) can be presented by Jones pupil and can also impact the imaging performance of immersion projection optics significantly. Precise PA measurement is most important for resolution enhancement technology and holistic lithography at 7nm node and below, in order to improve the pattern fidelity and processing stability. However, the current imaging-based measurement method of PA by linear approximation has not taken the coupling effect of the PA coefficients into account. This paper proposes a nonlinear measurement method of PA based on a rigorous nonlinear model to improve the measurement accuracy significantly. In this invention, the new spectrum modulation theory is developed to establish a rigorous quadratic form of PA and aerial image spectrum. A hybrid genetic algorithm is developed to solve the quadratic form inversely to obtain the PA accurately. An overall simulation validates that this method provides a superior quality of PA measurement with very high precision of 10-4λ.

Active lens for thermal aberration compensation in lithography lens.

High laser absorption and strong resolution enhancement technology make thermal aberration control of lithography lenses more challenging. We present an active lens that uses four bellows actuators to generate astigmatism (Z5) on the lens surface. The apparatus utilizes optical path difference to compensate the system wavefront. In order to assess the specifications of the compensator, the finite element method and experimental analyses are carried out to obtain and validate the general properties of the apparatus. The results show that the Z5 deformation quantity of lens's upper surface exceeds 600nm; further, Z5 coefficient accuracy is better than ±1 nm. The apparatus can be an efficient compensator for thermal aberration compensation, especially aberration caused by the dipole illumination.