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Ma X.,Key Laboratory of Photoelectronic Imaging Technology and System | Arce G.R.,University of Delaware | Li Y.,Key Laboratory of Photoelectronic Imaging Technology and System
Applied Optics | Year: 2011

Gradient-based phase-shifting mask (PSM) optimization methods have emerged as an important tool in computational lithography to solve for the inverse lithography problem under the thin-mask assumption, where the mask is considered a thin two-dimensional object. As the critical dimension printed on the wafer shrinks into the subwavelength regime, thick-mask effects become prevalent and thus these effects must be taken into account in PSM optimization methods. Thick-mask effects are particularly aggravated and pronounced in etching profiles with abrupt discontinuities and trench depths. PSM methods derived under the thin-mask assumption have inherent limitations and perform poorly in the subwavelength scenario. This paper focuses on developing three-dimensional PSM optimization methods that can overcome the thick-mask effects in lithography systems with partially coherent illumination. The boundary layer model is exploited to simplify and characterize the thick-mask effects, leading to a gradientbased PSM optimization method. Several illustrative simulations are presented. © 2011 Optical Society of America. Source


Wei L.,Key Laboratory of Photoelectronic Imaging Technology and System | Li Y.,Key Laboratory of Photoelectronic Imaging Technology and System
Optik | Year: 2014

Source and mask optimization (SMO) has emerged as a key resolution enhancement technique (RET) for 45 nm technology node and below in lithography. The design method of freeform illumination sources predicted by SMO is significant for the scanner development. We present a hybrid approach combining simultaneous and sequential approaches to optimize the tilt angles of the mirrors to produce multi target freeform illumination sources accurately and quickly. The size of spot reflect by plane mirror can be easily controlled by changing different microlens arrays with appropriate focal length, which reduce the complexity of the system and makes it more flexible to produce the specific freeform sources compared to curving the mirrors used in previous work. The relationship between the tilt angles of plane mirrors and the positions of the spots in the pupil is obtained by chief ray tracing. Using the hybrid approach the freeform illumination sources required by SMO can be designed by merely adjusting the tilt angles of mirrors without changing other parameters of optical elements, which is most effective for both lithography tool manufacture and its applications. The real ray tracing results demonstrate that our design method is capable of creating multi freeform illumination sources with high transmittance, and confirm that the effectiveness of the hybrid approach for optimized design and control of mirror array in immersion lithography system. © 2014 Elsevier GmbH. All rights reserved. Source


Lv Y.,Key Laboratory of Photoelectronic Imaging Technology and System | Lv Y.,Lotus Hill Research Institute | Yao B.,University of California at Los Angeles | Yao B.,Lotus Hill Research Institute | And 3 more authors.
Proceedings of IEEE Workshop on Applications of Computer Vision | Year: 2012

In this paper, we learn a reconfigurable template for detecting vehicles and classifying their types. We adopt a popular design for the part based model that has one coarse template covering entire object window and several small high-resolution templates representing parts. The reconfigurable template can learn part configurations that capture the spatial correlation of features for a deformable part based model. The features of templates are Histograms of Gradients (HoG). In order to better describe the actual dimensions and locations of "parts" (i.e. features with strong spatial correlations), we design a dictionary of rectangular primitives of various sizes, aspect-ratios and positions. A configuration is defined as a subset of non-overlapping primitives from this dictionary. To learn the optimal configuration using SVM amounts, we need to find the subset of parts that minimize the regularized hinge loss, which leads to a non-convex optimization problem. We solve this problem by replacing the hinge loss with a negative sigmoid loss that can be approximately decomposed into losses (or negative sigmoid scores) of individual parts. In the experiment, we compare our method empirically with group lasso and a state of the art method [7] and demonstrate that models learned with our method outperform others on two computer vision applications: vehicle localization and vehicle model recognition. © 2012 IEEE. Source


Wang F.,Key Laboratory of Photoelectronic Imaging Technology and System | Cao F.,Key Laboratory of Photoelectronic Imaging Technology and System | Bai T.,Key Laboratory of Photoelectronic Imaging Technology and System
Optik | Year: 2013

Space-variant sensors are of great importance in both machine and biological vision, and they have superior imaging property than the rectilinear sensors during high-speed forward motion. We focus on the modulation transfer function (MTF) of a particular spatially variant sampling retina-like sensor, pixels of which are arranged in a log-polar fashion. The 3D MTF of the sensor has been built using Hankel Transformation (HT) based on sampling and imaging property of the sensor. Moreover, the output image is simulated in the light of MTF. This research helps to model the imaging process of an imaging system containing retina-like sensor. © 2012 Elsevier GmbH. Source


Liu K.,Key Laboratory of Photoelectronic Imaging Technology and System | Li Y.,Key Laboratory of Photoelectronic Imaging Technology and System | Wang H.,Key Laboratory of Photoelectronic Imaging Technology and System
Review of Scientific Instruments | Year: 2011

Characterization of measurement accuracy of the phase-shifting point diffraction interferometer (PSPDI) is usually performed by two-pinhole null test. In this procedure, the geometrical coma and detector tilt astigmatism systematic errors are almost one or two magnitude higher than the desired accuracy of PSPDI. These errors must be accurately removed from the null test result to achieve high accuracy. Published calibration methods, which can remove the geometrical coma error successfully, have some limitations in calibrating the astigmatism error. In this paper, we propose a method to simultaneously calibrate the geometrical coma and detector tilt astigmatism errors in PSPDI null test. Based on the measurement results obtained from two pinhole pairs in orthogonal directions, the method utilizes the orthogonal and rotational symmetry properties of Zernike polynomials over unit circle to calculate the systematic errors introduced in null test of PSPDI. The experiment using PSPDI operated at visible light is performed to verify the method. The results show that the method is effective in isolating the systematic errors of PSPDI and the measurement accuracy of the calibrated PSPDI is 0.0088λ rms (λ = 632.8 nm). © 2011 American Institute of Physics. Source

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