In order to achieve an economical design-to-mask (DTM) development cycle in the low k1 domain, designers, lithographers, and mask makers needed to move away from many sequentially isolated developmental activities onto one collaborative environment managed by a computational lithography platform that integrates their respective ecosystems. 1,2 A successful development cycle used to be achievable by designers providing designs to lithographers, who then provided RET/OPC solutions to realize designs, but once k1 fell below a certain level, the lithographers could not provide solutions to realize some critical designs, which then required feedback to designers for further redesigns requiring further lithographic evaluation cycles. So collaboration and automations between lithographers and designers became necessary to reduce feedback loops and development cycle time. RET and design solutions also were impacted by mask making, and so mask maker's feedback on MRC and other constraints needed to be integrated for all three groups to achieve an economical DTM. As many lithographers attempted to print sub-80 nm pitches with 193 nm wavelength, it became necessary to use double patterning to achieve feature resolution. With the effective pitch doubling on each split layer, there could be significant increased design rule freedom for certain complex design situations. Using an integrated computational lithographic platform, one could find design space sweet spots that could further achieve optimal lithographic performance. In this paper, the optimization of design rules (DRD) for double pattern designs (~60 nm pitch) was explored with the mask maker's perspective. The experiment to be presented started with a 2x nm design set of clips. Each set of clips underwent size/width/space/pitch variations to generate a design space, and then each design space underwent SMO with an inverse lithography technology (ILT) engine using various mask MRC's and manhattan segmentations. The lithographic results were analyzed with respect to MRC and manhattan segmentation to show their impact on design space and mask solutions.

Clear-field photo-masks offer significant advantages over dark-field photo-masks for some important classes of target patterns, including small isolated features and dense arrays of contacts. This work compares lithographic performance of clear-field and dark-field images when mask patterns are optimized for respective mask tones. Since the purpose is to study optical behavior, computed images without resist models were compared. In order to explore performance limits, optimized masks were not constrained to limit their complexity. Calculated images were compared for clear-field and dark-field masks, with either opaque or 6% transmission, 180-degree phase-shifted absorbers. In each case, mask patterns were independently optimized to print the targets, which were a set of square and rectangular arrays of contact holes with various dimensions and pitches. The range of the target patterns extended to the limits of ArF resolution with water immersion. Because the intent was to compare inherent optical performance of positive and negative-tone imaging, the study did not use resist models that would combine materials properties or behaviors into the results, but simply applied a constant threshold to calculated intensities to obtain images. Contrast, MEEF, and deviation of images with defocus were the basis of optimizing the mask patterns, and were compared for the four combinations of mask tones and absorbers. Best contrast and MEEF were obtained with bright-field masks that had attenuated, phase-shifting absorbers. The amount of improvement depended on the size of the mask patterns relative to that of their corresponding targets, set here by varying the intensity threshold for the images during mask optimization. Differences in how the images of the four types of masks changed with defocus were statistically insignificant.

The ITRS roadmap(1) lists double patterning 193 nm immersion exposure with inverse lithography as the likely solution through the 22 nm half pitch generation. Three different patterns, scaled to 56 nm pitch, were explored using inverse lithography.(2,3) The patterns are a trim mask design adapted from Schenker, et al.(4), a bit line design published by Pyo, et al.(5) and a metal layer design published by Lucas, et al.(6). A free form gray scale illuminator was determined for each pattern. Good results were obtained for the trim mask design with a process variation of less than 8 nm for 50 nm of defocus and MEEF less than 6. The bit line design had to be modified from the published version which increased the pattern area by 18.8%. For this pattern there was a maximum process variation of 11 nm for 50 nm of defocus and MEEF less than 14. The metal layer design had to be modified which increased the pattern area by 2.6%. With these changes there was a maximum process variation of 8.4 nm for 50 nm of defocus and MEEF less than 7.

An illuminator and mask patterns were optimized (SMO) to minimize CD variation of a set of contact patterns selected from logic layouts and an array of SRAM cells. MEEF and defocus characteristics of the target patterns were modeled as functions of constraints on minimum mask features and spaces (MRC). This process was then repeated after linearly shrinking the input patterns by 10%. Common statistical measures of CD control worsen as MRC becomes more restrictive, but these are weak indicators compared to behavior at points in the image that exhibit high MEEF or low depth of focus. SMO solutions for minimum MEEF and maximum depth of focus are different, so some compromise is necessary. By including exposure time among the variables to be optimized, some control over local mask bias is made available to minimize MEEF and loss of litho quality due to MRC.

Masks computed by use of Inverse Lithography Technology (ILT) are being increasingly used in 32nm and below nodes for their significantly better litho performance outperforming model-based OPC [1,2]. This technique poses the design of photomasks as an inverse problem and then solves for the optimal photomask using rigorous mathematical approach [3,4]. One such approach is the level set based method [5] wherein a level set function φ(x,y) is made to represent the contour of the mask. The zero level set φ(x,y)=0 then represents the actual mask at a given instance. The same level-set technique has now been extended to determine the most optimized source φ(p,q) for a given target or mask. Cooptimization of both the source and mask is a natural extension of optimizing the mask alone in ILT. The same cost function, say maximizing DOF, which is used to compute the ILT mask can be used for the source optimization as well. This approach enables accurate and fast computation of the optimized source and mask for given set of patterns and also utilizes running on a distributed computing environment. In this paper, the level set based SMO approach will be first validated on simple contact array patterns and then extended to the optimization of sample 22nm logic contact design patterns, including array, SRAM and random logic. The effect of using different emphasis in defining the cost function will also be studied.

When completed in 2009, Trump International Hotel and Tower, Chicago will rise to a height of 1134 ft (345.6 m) (1362 ft [415.1 m] including the spire). Designed by Skidmore, Owings & Merrill LLP (SOM) the 92 story Trump Tower will be the tallest concrete building in the United States, and the tallest building built in North America since the completion of Sears Tower in 1974. New ground is being broken through a series of high performance concrete mixes designed by Prairie Material Sales, Inc. and employed by SOM on the project. It is believed to be the first application of 16,000 psi (110 MPa) self-consolidating concrete pumped and placed to an elevation up to 650' (200 metres) above grade. Dense limestone ½" (12 mm) topsize aggregate from the Material Service Corporation. Thornton quarry in northern Illinois has been specified for the high strength concrete on the project. The paper presents detailed structural engineering aspects of the tower design including a description of the reinforced concrete systems chosen for the project, design for occupant perception of motion due to wind, design challenges and the creative use of high strength concrete for this landmark tower.

The structural engineering design and constructive aspects of a unique stainless steel-clad pedestrian crossing at the Millennium Park in Chicago are presented. The overall bridge form is characteristic of architect Frank O. Gehry.s work: metallic surfaces freely flowing in profile and serpentine in plan. Details of the computer aided steelwork detailing, fabrication, and erection are presented. Substantive engineering analysis and design details including the issue of pedestrian walking vibrations are summarized.

While high-rise construction serves as one of the most challenging projects undertaken by society each year, tall buildings are one of the few constructed facilities whose design relies solely upon analytical and scaled models, which, though based upon fundamental mechanics and years of research and experience, have yet to be systematically validated in full-scale. In response to this deficiency, a full-scale monitoring project was initiated through the combined efforts of members of academe (University of Notre Dame), practicing design firms (Skidmore, Owings & Merrill LLP, Chicago) and commercial testing laboratories (Boundary Layer Wind Tunnel Laboratory, University of Western Ontario, Canada). The objective of this program is to monitor the full-scale response of some representative tall building structures and compare their actual performance to the predictions from wind tunnel testing and finite element computer models used in their design. As such, this program offers the opportunity to refine the design state-of-the-art based on any discrepancies revealed. As part of this full-scale evaluation, in-situ periods and damping ratios over a range of response amplitudes are being ascertained, which will prove vital for expanding the existing databases of full-scale dynamic properties. This paper presents a brief overview of the program.

Post-modern architecture has moved significantly from directly expressing the structural systems of tall buildings, which symbolized their strength and stability. Tall buildings have become more slender, require large open views along their perimeter, include multiple setbacks, and have been proposed for regions with potentially large wind forces and seismic events. These factors have influenced structural system selection significantly. In an effort to reduce the structural cost, and to resist overturning forces, several structural systems have been proposed that are nearly determinate and thus have relatively little redundancy. These structures are highly efficient, from a material expenditure standpoint. The issue of redundancy as it relates to the underlying robustness of the structural system has traditionally been left to the discretion of the individual engineer. Unlike highly redundant framed tube structures such as the Sears Tower, Chicago, and the World Trade Center Towers, New York, unpredictable events and design forces, including acts of terrorism, could have a large impact on these nearly determinate systems. Research is needed to study the approach and philosophy that engineers should adopt to evaluate the redundancy and robustness of these systems and to establish design criteria.

The design of tall buildings is predominantly governed by the need to provide adequate strength and stiffness against lateral dynamic forces induced by wind, and to satisfy stability and serviceability conditions. While serviceability requirements are fulfilled by limiting lateral displacements (drifts) to maintain the integrity of architectural elements such as cladding and partitions; the minimization of perceptible accelerations assures occupant comfort. These conditions are directly affected by the dynamic and aerodynamic characteristics of the building and the severity of the local wind climate. The design process involves the selection of an appropriate structural system, and the evaluation of that system under design wind environments utilizing code, analytical methods, and wind tunnel testing. This may be an iterative process for exceptionally tall, slender, or unusual building forms. Interestingly enough, while tall building structures serve as one of our most vital constructed facilities, the design process is based almost solely on the information provided by analytical and scaled models. Understandably, while full scale models are not feasible, considering their sheer size and cost, monitoring the performance of actual structures is paramount and must be undertaken following construction as a means of verification and improvement of current design practices and analytical models.

One of the most visually unique building designs of the twentieth century, the Guggenheim Museum project in Bilbao, Spain, required an innovative structural engineering solution and pioneering use and sharing of computer generated information between architects, engineers, steel detailers, and fabricators. The design for the building form is highly stylized, geometric, and characteristic of architect Frank O. Gehry's work: an interplay of compound curvilinear forms in concert with fractured and acute planar surfaces symbolizes the abstract artwork to be displayed within the building. The structural system for the curved exterior surfaces can best be described as a three-dimensional equivalent of a traditional concrete bearing wall framed entirely in structural steel. The system was conceived based upon a universal system that could be applied to any geometric arrangement. To fit the geometric contour of the exterior envelope, a discretized structural fabric grid was developed. The segmented steel lattice frame system allowed for prefabrication in a shop environment using computer-controlled techniques to achieve a high degree of accuracy for assembly in the field.

The Guggenheim Museum Bilbao is the first step in a planned redevelopment of the former trade and warehouse district in Bilbao, Spain. Directly accessible from the historic and business districts of the city, the museum is at the center of a cultural triangle formed by the Museo de Bellas Artes, the University, and the old Town Hall. The overall program for the museum involves approximately 12,000 m² of exhibition space, a 300-seat auditorium, a restaurant, a cafe, shops, offices and parking. The museum design is geometrically complex, consisting of a series of interconnected building masses.