Thèse de doctorat : Informatique : Nice : 2004. / Bibliogr. p. 145-151. Résumés en français et en anglais.

With 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_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

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In recent years rapid prototyping technology has been implemented in many spheres of industry, particularly the field of product development. Existing process provide the capability to rapidly produce a tangible solid part, directly from three dimensional CAD data, from a range of nonmetallic materials. In many situations the desired end product of a development cycle is a metallic object, whether a component or a tool. The development of a system capable of the direct manufacture of fully dense, metal parts is therefore seen as an important landmark in the evolution of rapid prototyping technology. A unique experimental project has been carried out to investigate the potential of laser surface cladding by pneumatic powder delivery to form the basis for such a process. A layered manufacturing part building strategy is proposed, in which laser cladding is used to deposit the near net shape of each layer. Conventional machining techniques are then used to trim each layer to the exact dimensions specified by the CAD data. A multi-kilowatt carbon dioxide laser was integrated with a four axis machine tool to create an opto-mechanical workstation on which to perform the process. A detailed study of the effects of cladding process parameters on the geometry of the deposited metal was carried out and quantitative relationships derived. These relationships are used to select process parameters appropriate to the geometry of the deposition required. A numerical method to fully describe the deposited clad geometry was developed in order that efficient cutter paths could be generated for the back machining cycle. These relationships are also used to determine the minimum size of deposited bead from which the required layer section may be machined, in order to optimise process efficiency. The application of the technique to the generation of a variety of simple geometries was investigated and the potential problems identified. A preliminary investigation into the process accuracy is made, relating specifically to the predictability of the geometry of multiple layer depositions and the distortion of parts as subsequent layers are deposited. The limits of geometrical complexity possible with the current apparatus, and the unsatisfactory build times involved, suggest that the most attractive application of this technique is as part of a hybrid process, adding a novel additive dimension to existing automated fabrication techniques.

published_or_final_version / Computer Science / Doctoral / Doctor of Philosophy

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

No description available.

The research problem to be explored in this study is to what extent colonial ideologies continue to influence museum society and contemporary museum practices. The museological display of non-Western, and specifically African material cultures will be investigated. This study will enter into a dialogue with the construction of the ‘Other’, both in a colonial context and within museological paradigms. The evolutionary nature of culture and heritage will be emphasized, with particular prominence given to the dangers of exhibiting cultures as static and objectified. The Exhibitions Congo. The Colonial Era (Royal Museum of Central Africa, Tervuren) and Zulu heritage: the history and culture of the Zulu people (Msunduzi Museum, Pietermaritzburg) are used as case studies, as both displays raise questions of appropriation and the display of ‘Other’. These exhibitions are analysed and then contextualized within existing museological research. Current debates located in post-colonial discourse, notably those of Edward Said, are discussed in relation to the display of African material culture. In discussing museum exhibitions and readership, the writings of Hooper-Greenhill and Kaplan are considered. An understanding of heritage is generated in relation to the theories of Lowenthal. The paper concludes that by combining a ‘contrapuntal’ (Said) view of the histories surrounding an artefact, with the acknowledgment of the viewer’s lived experience in accordance with Reader-Response criticism, one would create a basis from which the viewer could begin to question and engage with cultural representations of the ‘Other’. / Thesis (M.A.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

No description available.

No description available.