241 research outputs found
Soaring like eagles: ASM's high-tech journey in Asia
No full textSoaring Like Eagles: ASM's High-Tech Journey in Asia is an inspiring tale of the phenomenal accomplishment of this company from the perspective of Patrick Lam, ASM's co-founder and CEO of 30 years. The book first traces its growth in three decade-long periods, along with an insider's look at the development of the semiconductor industry. It then examines ASM's success from several angles: its differentiated strategies, its leadership and culture, its innovative practices, its technologies and products, and its preparations from the future
Aberration sensitivity reduction of alternating phase-shifting mask inphotolithography
No full textpublished_or_final_versionabstracttocElectrical and Electronic EngineeringMasterMaster of Philosoph
Computational surface profilometry and its applications in semiconductor inspection
No full textNon-contact surface profilometry techniques, especially the phase-measuring profilometry, have been evolved dramatically over recent years. Besides the simple triangulation configuration with a fringe pattern projection system and digital imaging system, efficient computational surface profilometry techniques have also drawn tremendous attention from both academia and a wide range of applications. In the semiconductor industry, high-precision and high-speed, automated optical inspection systems are urgently needed to ensure high quality of semiconductor devices and yield improvement on the production and assembly line. However, by assuming the measured object to be stationary, conventional approaches are not suitable for surface profilometry of moving objects. Moreover, different sources of error such as the low contrast fringe patterns on the measured object, the unevenness in the illumination and the perspective projection effect from the optics will decrease the performance of surface profilometry.
To meet these challenges, we have built fringe pattern projection prototypes with projector and camera arrays for surface profilometry of moving objects along the conveyor belt. This design helps to enlarge the field of view with parallel processing. In addition, we have presented an optimization framework to investigate the sources of the error for surface profilometry and generalize various computational surface profilometry approaches under different scenarios.
Under this framework, first, we investigate two important factors determining the precision of surface profilometry, namely, the condition number of the phaseshift matrix and the fringe contrast within the images of the projected fringe patterns. Then, a regularized phase-shift algorithm has been proposed to improve the reconstruction results at the low contrast regions such as on the substrate of the semiconductor devices. Second, we study the intensity fluctuation caused by the uneven illumination for surface profilometry of moving objects. After that, an illumination-reflectivity-focus model has been suggested to describe the unevenness and an illumination-invariant phase-shift algorithm has been developed to handle this uneven illumination effect. Third, the perspective projection effect from the optics also affects the accurate phase-shift estimation for a moving object. Therefore, we propose a general polynomial phase-measuring profilometry model to establish the relationship between the phase-shift and height variation for each measured point. Accordingly, a polynomial phase-shift algorithm with error compensation technique has been put forward to improve the performance of the surface profilometry for moving objects.
Both simulation and real experiments from the prototype have been conducted to verify the improvement on the performance of the proposed methodologies. Furthermore, these research results have demonstrated the effectiveness and efficiency of the presented optimization framework for investigating the sources of error for surface profilometry. Moreover, the proposed computational surface profilometry techniques and the corresponding fringe pattern projection systems have been used in automated optical inspection systems for yield improvement on the production line in the semiconductor industry.published_or_final_versionElectrical and Electronic EngineeringDoctoralDoctor of Philosoph
Computational imaging technologies for optical lithography extension
No full textWith the development and production of integrated circuits at the 22nm node, optical lithography faces increasing challenges to keep up with the specifications on its performance along various metrics, such as pattern fidelity and process window. The past few years saw the emergence of source mask optimization (SMO) as an important technique in computational lithography, which allows lithographers to rise to the challenges by exploiting a larger design space on both mask and illumination configuration, and integrates with methods such as inverse imaging. Yet, many methods that are used to tackle SMO problem arising in the inverse imaging involve heavy computation and slow convergence, making the technique unappealing for full-chip simulations or large circuits. Therefore, the purpose of this research is to take advantage of computational imaging technologies to solve source and mask design problems, extending the lifetime of optical lithography.
The computational burden results in part from identical optimization over the whole mask pattern, consequently, we propose a weighted SMO scheme which applies different degrees of correction in the corresponding regions so that the optimal solutions are reached with fewer iterations. Additionally, undesirably long time is also attributed to the algorithm adopted to solve SMO problem. A fast algorithm based on augmented Lagrangian methods is therefore developed, which use the quasi-Newton method to accelerate convergence, thereby shortening the overall execution time. However, as semiconductor lithography is pushed to even smaller dimensions, mask topography effects have to be taken into account for a more accurate solution of SMO. At this stage, intensive computation is spent mainly in rigorous 3D mask modeling and simulations. To address this issue, we devise an optimization framework incorporating pupil aberrations into SMO procedure, which is performed based on the thin mask model so as to ensure a faster speed.
We apply the above approaches to various mask geometries with different critical dimensions. Compared to conventional SMO, simulation results show that the proposed methods lead to better pattern fidelity and larger process window, especially in rigorous calculations. This demonstrates that the source and mask design generated through our algorithms are more practical. More importantly, the improved performance is not at the cost of speed. Instead, our methods take the least time to achieve it. This allows the advantages of computational imaging technologies to be worth exploring for further applications in optical lithography.published_or_final_versionElectrical and Electronic EngineeringDoctoralDoctor of Philosoph
Optimization schemes for process robustness enhancement in optical lithography
No full textpublished_or_final_versionElectrical and Electronic EngineeringDoctoralDoctor of Philosoph
Mask-based coded imaging systems and image reconstruction algorithms
No full textComputational imaging is an emerging field. Its rapid development has drawn tremendous attention from both research and commercial points of view. Unlike traditional imaging, which separately considers the optical imaging and computational processing, computational imaging combines the power of the optical elements and signal processing techniques to achieve augmented capabilities.
Previous work on various aspects of computational imaging has shown the powerful abilities that computations can bring into the imaging systems. However, the research is still in an early stage. Some drawbacks need to be conquered. For example, in compressed sensing (CS) related systems, the reconstruction quality cannot be satisfactory due to the ill-posed nature of the problem. Likely, in computational photography, the systems share a major defect. That is, as four-dimensional radiance information is recorded by a regular two-dimensional sensor, an unavoidable sacrifice of the spatial resolution has to be made to resolve angular differences. This eventually causes the low spatial resolution output.
To meet these challenges, more efforts have to be made in both imaging part and computational part. In this dissertation, we concentrate ourselves on a more specific form of computational imaging, i.e., mask-based coded imaging systems. In particular, the first part of the dissertation focuses on a mask-based terahertz (THz) CS imaging system. There we focus on the computational part and explore the reconstruction algorithms that can estimate the underlying scene as accurately as possible. After that, we discuss the lightfield photography and show that by combining the system modification and proper postprocessing algorithms, we can achieve a high-resolution lightfield. The corresponding simulation demonstrates the performance of our methods.published_or_final_versionElectrical and Electronic EngineeringDoctoralDoctor of Philosoph
Curvature domain stitching of digital photographs
No full textpublished_or_final_versionabstractElectrical and Electronic EngineeringMasterMaster of Philosoph
Out-of-focus 3D alignment for digital holography
No full textImage alignment plays a crucial role in the semiconductor industry. However, achieving high alignment accuracy with fine image resolution while maintaining the depth of field of optics can be challenging. A novel method utilizing digital holography is proposed to address this issue. This method allows for object retrieval without the need to adjust the focus of the optics, specifically targeting out-of-focus targets.
The research builds upon the original phase correlation method applied to the extracted hologram and introduces a phase unwrapping algorithm on the phase difference buffer for curve fitting. This enhancement significantly improves accuracy in the axial direction while preserving lateral accuracy. Through simulation cases, the algorithm demonstrates subpixel accuracy in translation, rotation, and tilt measurements, showcasing its robustness against various sources of error.
In the experimental phase, the algorithm’s accuracy is evaluated using a carefully designed setup and real samples. By aligning holograms with different x and z positions, a total of 1110 cases are processed. Results indicate an overall alignment accuracy of 0.1μm in x and y translation and 2μm in the z-axis.
The experimental results demonstrate that hologram alignment can achieve higher accuracy than is currently demanded by the industry, highlighting promising applications. Although certain sources of error, such as distortion, need to be addressed, the study suggests satisfactory performance of the algorithm. By tackling these factors, further improvements can be made to enhance the alignment algorithm and broaden its potential applications in various industries.published_or_final_versionElectrical and Electronic EngineeringMasterMaster of Philosoph
Characterizations and applications of carbon nanotubes contrast agentsin magnetic resonance molecular imaging
No full textpublished_or_final_versionElectrical and Electronic EngineeringDoctoralDoctor of Philosoph
Efficient finite-difference schemes in thermal analysis and inverse lithography for integrated circuit manufacturing
No full textpublished_or_final_versionElectrical and Electronic EngineeringDoctoralDoctor of Philosoph
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