Nebulous hotspot and algorithm variability in computation lithography

Computation lithography relies on algorithms. However, these algorithms exhibit variability that can be as much as 5% (one standard deviation) of the critical dimension for the 65-nm technology. Using hotspot analysis and fixing as an example, we argue that such variability can be addressed on the algorithm level via controlling and eliminating its root causes, and on the application level by setting specifications that are commensurate with both the limitations of the algorithms and the goals of the application. © 2010 Society of Photo-Optical Instrumentation Engineers.published_or_final_versio

Regularization of inverse photomask synthesis to enhance manufacturability

Mask manufacturability has been considered as a major issue in the adoption of inverse lithography (IL) in practice. With smaller technology nodes, IL distorts the mask pattern more aggressively. The distorted mask often contains curvilinear contour and irregular shapes, which cast a heavy computation burden on segmentation and data preparation. Total variation (TV) has been used for regularization in previous work, but it is not very effective in regulating the mask shape to be rectangular. In this paper, we apply TV regularization not only on the mask image but also on the mask edges, which forces the curves of edges to be more vertical or horizontal, because they give smaller TV values. Except for rectilinearity, a group of geometrical specifications of the mask pattern set by mask manufacture rule control (MRC) is also important for mask manufacturability. To prevent these characteristics from appearing, we also propose an intervention scheme into the optimization framework. © 2009 Copyright SPIE - The International Society for Optical Engineering.published_or_final_versionThe SPIE Lithography Asia 2009, Taipei, Taiwan, 18 November 2009. in Proceedings of SPIE, 2009, v. 7520, p. 1-11, article no. 75200

Alternating phase-shifting mask design for low aberration sensitivity

Theories are developed to optimize the mask structure of alternating phase-shifting masks (PSMs) to minimize the average image placement error towards aberration under coherent imaging. The constraint of the optimization is a given mean value of RMS aberration, which corresponds to infinitely many sets of random Zernike coefficients. To begin the analysis, the image placement error is expressed as a function of the mask spectrum and the wave aberration. Monte Carlo analysis on the Zernike coefficients is then performed, which assures us that a global minimum of average image placement error is likely to occur at low phase widths. This result is confirmed by analytically considering the expected value of the square of the image placement error. By Golden Section Search, the optimal phase width is found to be 0.3707(λ/NA) at 0.07λ RMS aberration. This methodology of finding the optimal phase width is applicable to the design of all alternating PSMs.published_or_final_versio

Standard cell layout with regular contact placement

The practicability and methodology of applying regularly placed contacts on layout design of standard cells are studied. The regular placement enables more effective use of resolution enhancement technologies, which in turn allows for a reduction of critical dimensions. Although placing contacts on a grid adds restrictions during cell layout, overall circuit area can be made smaller by a careful selection of the grid pitch, allowing slight contact offset, applying double exposure, and shrinking the minimum size and pitch. The contact level of 250 nm standard cells was shrunk by 10%, resulting in an area change ranging from -20% to +25% with an average decrease of 5% for the 84 cells studied. The areas of two circuits, a finite-impulse-response (FIR) filter and an add-compare-select (ACS) unit in the Viterbi decoder, decrease by 4% and 2%, respectively.published_or_final_versio

Performance optimization for gridded-layout standard cells

The grid placement of contacts and gates enables more effective use of resolution enhancement techniques, which in turn allow a reduction of critical dimensions. Although the regular placement adds restrictions during cell layout, the overall circuit area can be made smaller and the extra manufacturing cost can be kept to the lowest by a careful selection of the grid pitch, using template-trim lithography method, allowing random contact placement in the vertical direction, and using rectangular rather than square contacts. The purpose of this work is to optimize the gridded-layout-based process. The trade-off between the layout area and manufacturing cost, and the determination of the minimum grid pitch are discussed in this paper. We demonstrate that it is a 1-D scaling instead of the conventional 2-D scaling for standard cells and the narrow MOSFETs inside after the application of the gridded layout on the contact and gate levels. The corresponding effects on circuit performances, including the leakage current, are also explored.published_or_final_versio

Standard cell design with resolution-enhancement-technique-driven regularly placed contacts and gates

The practicability and methodology of applying resolution-enhancement- technique-driven regularly placed contacts and gates on standard cell layout design are studied. The regular placement enables more effective use of resolution enhancement techniques (RETs), which in turn enables a reduction of critical dimensions. Although regular placement of contacts and gates adds restrictions during cell layout, the over-all circuit area can be made smaller and the number of extra masks and exposures can be kept to the lowest by careful selection of the grid pitch, using template-trim chromeless phase-shifting lithography approaches, enabling unrestricted contact placement in one direction, and using rectangular rather than square contacts. Four different fabrication-friendly layouts are compared. The average area change of 64 standard cells in a 130-nm library range from -4.2 to -15.8% with the four fabricationfriendly layout approaches. The area change of five test circuits using the four approaches range from -16.2 to +2.6%. Dynamic power consumption and intrinsic delay also improve with the decrease in circuits area, which is verified with the examination results. © 2005 Society of Pnoto-Optical Instrumentation Engineers.published_or_final_versio

Activation of autophagy by FOXO3 regulates redox homeostasis during osteogenic differentiation

Bone remodeling is a continuous physiological process that requires constant generation of new osteoblasts from mesenchymal stem cells (MSCs). Differentiation of MSCs to osteoblast requires a metabolic switch from glycolysis to increased mitochondrial respiration to ensure the sufficient energy supply to complete this process. As a consequence of this increased mitochondrial metabolism, the levels of endogenous reactive oxygen species (ROS) rise. In the current study we analyzed the role of forkhead box O3 (FOXO3) in the control of ROS levels in human MSCs (hMSCs) during osteogenic differentiation. Treatment of hMSCs with H2O2 induced FOXO3 phosphorylation at Ser294 and nuclear translocation. This ROS-mediated activation of FOXO3 was dependent on mitogen-activated protein kinase 8 (MAPK8/JNK) activity. Upon FOXO3 downregulation, osteoblastic differentiation was impaired and hMSCs lost their ability to control elevated ROS levels. Our results also demonstrate that in response to elevated ROS levels, FOXO3 induces autophagy in hMSCs. In line with this, impairment of autophagy by autophagy-related 7 (ATG7) knockdown resulted in a reduced capacity of hMSCs to regulate elevated ROS levels, together with a reduced osteoblast differentiation. Taken together our findings are consistent with a model where in hMSCs, FOXO3 is required to induce autophagy and thereby reduce elevated ROS levels resulting from the increased mitochondrial respiration during osteoblast differentiation. These new molecular insights provide an important contribution to our better understanding of bone physiology

Assessment and Localization of Active Discontinuities Using Energy Distribution Between Intrinsic Modes

A method for localization and severity assessment of structural damages is proposed. The algorithm works based on nonlinear behavior of certain type of damages such as breathing cracks which are called active discontinuities in this paper. Generally, nonlinear features are more sensitive to such damages although their extraction is sometimes controversial. A major controversy is the imposition of spurious modes on the expansion of the signal which needs to be addressed for an effective application and robustness of the method. The energy content of Intrinsic Mode Functions (IMFs), which are the resultants of Empirical Mode Decomposition (EMD), and also the shape of energy distribution between these modes before and after damage, are used for localization and severity assessment of the damages. By using EMD, we preserve the nonlinear aspects of the signal while avoiding imposition of spurious harmonics on its expansion without any assumption of stationarity. The developed algorithms are used to localize and assess the damage in a steel cantilever beam. The results show that the method can be used effectively for detecting active structural discontinuities due to damage

A Versatile Orthotopic Nude Mouse Model for Study of Esophageal Squamous Cell Carcinoma

Increasing evidence indicates tumor-stromal interactions play a crucial role in cancer. An in vivo esophageal squamous cell carcinoma (ESCC) orthotopic animal model was developed with bioluminescence imaging established with a real-time monitoring platform for functional and signaling investigation of tumor-stromal interactions. The model was produced by injection of luciferase-labelled ESCC cells into the intraesophageal wall of nude mice. Histological examination indicates this orthotopic model is highly reproducible with 100% tumorigenesis among the four ESCC cell lines tested. This new model recapitulates many clinical and pathological properties of human ESCC, including esophageal luminal stricture by squamous cell carcinoma with nodular tumor growth, adventitia invasion, lymphovascular invasion, and perineural infiltration. It was tested using an AKT shRNA knockdown of ESCC cell lines and the in vivo tumor suppressive effects of AKT knockdown were observed. In conclusion, this ESCC orthotopic mouse model allows investigation of gene functions of cancer cells in a more natural tumor microenvironment and has advantages over previous established models. It provides a versatile platform with potential application for metastasis and therapeutic regimen testing.published_or_final_versio

Pulmonary artery sarcoma diagnosed by endobronchial ultrasound-guided transbronchial needle aspiration

published_or_final_versio