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Thermal hillocks in sputter-deposited Al films have been studied as a part of a broad study of stress-induced diffusional processes in Al. Trace amounts of the impurities Ti, W, and O were incorporated into the films during deposition, causing them to be much stronger than most sputter deposited Al films. Stress measurement during thermal cycling, using the wafer curvature method, showed that these Al films are very strong; this finding was corroborated by hardness measurements. Microstructural studies using TEM and FIB showed that the hillocks start to form at the Al/SiO2 interface and grow under the original Al film, with its columnar grain structure. In some cases, the film fails as hillocks grow completely through the original film. The Al film on top of the hillocks appears to inhibit hillock growth by creating a back pressure associated with power law creep of the film. We modeled this form of hillock formation by modifying the boundary conditions in Chaudhari's hillock model . Our model describes hillock formation by diffusion of Al atoms from the surrounding area into isolated hillocks, assuming that the original Al film on top of hillocks deforms following power law creep. Our model can be applied to many different situations by using different creep laws for the top Al film.
Knowledge of the mechanical properties of interlevel dielectric films and their impact on sub-micron interconnect reliability is becoming more and more important as critical dimensions in ULSI circuits are scaled down. For example, lateral aluminum (Al) extrusions into spaces between metal lines, which become a more of a concern as the pitches shrink, appear to depend partially on properties of SiO2 underlayers. In this paper, the mechanical properties of several common interlevel dielectric SiO2 films such as undoped silica glass using a silane (SiH4) precursor, undoped silica glass using a tetraethylorthosilicate (TEOS) precursor, phosphosilicate glass (PSG) deposited by plasma-enhanced chemical vapor deposition (PECVD) and borophosphosilicate glass (BPSG) deposited by sub-atmosphere chemical vapor deposition (SACVD) were studied. Among the four common interlevel layers, BPSG exhibits the smallest modulus (E), hardness (H) and the highest the coefficients of thermal expansion (CTE). BPSG again has the lowest as-deposited compressive stress and the lowest local Si-O-Si strain before annealing. Stress interactions between the various SiO2 underlayers and the Al metal film are further investigated. The impact of dielectric elastic properties on interconnect reliability during thermal cycles is proposed.
This paper describes our current work on electrical percolation in carbon nanotubes filled thermoplastic polymer fibers. The objective of this work is to develop an understanding of how the electrical properties of the nanotube/polymer composites are affected by processing conditions, orientation of nanotubes, and their loading fraction. In the first part of the work, mesoscale modelling of nanotubes was carried out using a dissipative particle dynamics method. The percolation threshold required to achieve an electrically conductive network of nanotubes within in a polymer fibre was predicted as a function of orientation and aspect ratio of nanotubes using a Monte Carlo method to measure the network impedance. In the second part of this work, X-ray diffraction analyses were carried out to find the degree of alignment of nanotubes in polyamide 12 fibers.
Industrialization of the food and agricultural sectors changes the pattern of external effects. Participants helped or harmed in the process attempt to influence outcomes through markets and politics. Decisions about property rights and boundaries determine benefits and burdens and the relative cost of animal agriculture in different jurisdictions. Prescriptions to redefine property rights are influenced by selective perception of rights to share in the benefits and be protected from costs. Political choices about the appropriate jurisdiction (state versus local) for addressing environmental and nuisance effects of animal agriculture affect whose preferences count and will influence the development of these sectors.
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