Simulation of the effect of microstructure on electromigration induced failure of interconnects

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1997.Includes bibliographical references (leaves 85-87).by Walid R. Fayad.M.S

Microstructure evolution and interconnect realiability

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2000.Includes bibliographical references (leaves 207-213).In the context of predicting the effects of geometry, microstructure, and processing conditions on electromigration (EM) induced interconnect failure, normal grain growth in thin films was studied, analytic models were built for the grain structure statistics in 2D and 3D interconnects, and simulation programs were developed for generation of process and complex-geometry-sensitive interconnect structures. The models were validated through simulations and experiments and were integrated into tools for circuit-design level interconnect reliability predictions. The universal scaling behavior of 2D normal grain growth was demonstrated and characterized using a simulation of 2D grain growth (GGSim). We showed that the constant rate of change of the average grain area is equal to the grain boundary mobility constant pt. We also found that the steady state grain size distribution obtained using our simulation technique, as well as those reported in experiments on simple model systems and those reported for very different simulation techniques, are all very well fit by a Weibull distribution function with the dimensionless parameter p = 5/2, and are better fit by this function than the log normal, Gamma or Rayleigh functions. The 2D simulation was used to simulate the development of film structures with drag induced lognormal grain size distributions from which interconnect strips were etched and then annealed, in order to analyze the statistics of as-patterned, as well as post-pattern annealed, interconnect grain structures. These statistics were characterized as a function of the ratios of the line-widths to the initial-grain-sizes. Among the important findings is that polygranular cluster and bamboo segment length distributions for as-patterned lines are best fit by Weibull distribution functions. Analytic formulae describing grain structure statistics were reported, for usage in EM simulations and reliability predictions. A differential model predicting the evolution of the polygranular cluster length distribution during post-patterning annealing was developed. It was shown that the rate of bamboo-segment nucleation per unit time and unit of untransformed length is proportional to [mu]/w 3 , and is negligible in the growth-dominated steady-state. The cluster shrinkage velocity was demonstrated to reach a constant steady-state value proportional to [mu]/w (assuming constant and uniform [mu]). This was shown to lead to a time-invariant, steady-state exponential cluster length distribution with an average cluster length proportional to the strip width, and a cluster length fraction decaying exponentially with U=[mu]/w2 . The distribution of grain lengths in the resulting final bamboo grain structure is well fit by a log normal distribution, with a median grain length scaling with the line width, and a line-width-independent normalized deviation in the grain length. This result was used to show, using an EM simulation, that grain-orientation-dependent variations in surface diffusivities constitute a likely cause for the variabilities in lifetimes observed experimentally. The 2D simulation GGSim was also substantially modified to simulate the patterning of interconnect features of general shapes from polygranular thin film structures, as well as to simulate further grain structure evolution due to post-patterning annealing in these complex shapes. A grain structure extraction tool, PolySeg, was developed to allow extraction of the atomic transport details in the case of complex interconnect trees for EM reliability predictions using EM simulations. To assess the 3D effects on grain structure evolution, and therefore on interconnect reliability, a soap froth experiment was used to study 3D normal grain growth in long rectangular prisms. The kinetics were found to scale with the normalized time [mu]/w 2 (with w being the largest of the two prism cross-sectional dimensions). It was found that the normalized duration of the conversion from 3D (non-columnar) to 2D (columnar) structures and the normalized duration of the initial phase during which the structure was polygranular became longer as w/h approached 1. The same results obtained in the 2D case for the scaling behaviors of the bamboo nucleation rate and the polygranular cluster shrinkage rate were demonstrated. Based on a 2D approach, a prism-geometry-sensitive analytic model was developed for the transformation to fully-bamboo structures. These results were compared with preliminary results obtained using a 3D grain growth simulation and qualitative agreement was demonstrated. We have successfully captured with simple analytic models as well as elaborate simulations the physics of microstructure evolution in complex patterned thin-film structures. In particular, we have developed an array of models and simulations that can be used to investigate the impact of geometry and process history on microstructure evolution, and ultimately on EM-induced failure statistics.by Walid R. Fayad.Ph.D

Resilient cooling strategies – A critical review and qualitative assessment

The global effects of climate change will increase the frequency and intensity of extreme events such as heatwaves and power outages, which have consequences for buildings and their cooling systems. Buildings and their cooling systems should be designed and operated to be resilient under such events to protect occupants from potentially dangerous indoor thermal conditions. This study performed a critical review on the state-of-the-art of cooling strategies, with special attention to their performance under heatwaves and power outages. We proposed a definition of resilient cooling and described four criteria for resilience—absorptive capacity, adaptive capacity, restorative capacity, and recovery speed —and used them to qualitatively evaluate the resilience of each strategy. The literature review and qualitative analyses show that to attain resilient cooling, the four resilience criteria should be considered in the design phase of a building or during the planning of retrofits. The building and relevant cooling system characteristics should be considered simultaneously to withstand extreme events. A combination of strategies with different resilience capacities, such as a passive envelope strategy coupled with a low-energy space-cooling solution, may be needed to obtain resilient cooling. Finally, a further direction for a quantitative assessment approach has been pointed out

Biological Characterstics Of Buffaloes Hydatid Cysts

Hydatid cysts infection rate was 13.56% in buffaloes, slaughtered at Al-Diwania abbatoir, Al-Qaddisia province,Iraq, during the time period from July,2000 to June, 2001.The only infected animals were the females, and the higher rateof infection was found in those aged buffaloes. Lungs,livers, livers and lungs wereinfected with 50%, 37.5% and 12.5%, respectively. The total rate of hydatid cystsfertility was 53.85%, and the sterile, caseated and calcified cysts were 23.08%, 11,54% and 11.5%, respectively. The mean total rate of viability of protoscoleces was73.91%, and that of livers and lungs protoscoleces were 82.62% and 70.60%.Results denoted that the numbers of protoscoleces was increased proportionallywith size of their cysts, and in contrary to that the viability of protoscolecesdiminished with the increase size of cysts. The study concluded that buffaloes havean important role in maintaining the life cycle and epidemiology of Echinococcusgranuolosus in dogs in those areas where buffaloes are raised, and this is incontroversy with the claims of previous authors.</jats:p

PREVALENCE OF CRYPTOSPORIDIUM OOCYSTS IN THE WATER OF AL-DEHAB AL-ABYAD VILLAGE IN BAGHDAD- IRAO

Detection of oocysts of Cryptosporidium in water of Al-Dehab AL-Abyad village was carried, from January to December 2001, through examination of 240 different water samples, using millipore cartridge filter and an alternative Iraqi filters. The oocysts were revealed in 73 samples in rate of 30.41%, all water samples collected from ponds revealed oocysts, in 29.16 % of water tanks and 22.91% of sewage samples. Oocysts were not found in the water samples from municipal water supply. Statistical differences (P&lt;0.05) in the presence of oocysts in the different samples were revealed. The alternative tissue filter was efficient for isolation of oocysts in comparison with the imported filters. Differences were found in the measurement and shape of isolated Cryptosporidium oocysts, and they were ranged from round (4.3 * 3.9 - 5 x 4.2 Mm) to oval (7.4 *5.5-8 x 6 mm) and they were also varied in the number according to the samples. </jats:p

Overheating calculation methods, criteria, and indicators in European regulation for residential buildings

With the ongoing significance of overheating calculations in the residential building sector, building codes such as the European Energy Performance of Building Directive (EPBD) are essential for harmonizing the indicators and performance thresholds. This paper investigates Europe's overheating calculation methods, indicators, and thresholds and evaluates their ability to address climate change and heat events. e study aims to identify the suitability of existing overheating calculation methods and propose recommendations for the EPBD. The study results provide a cross-sectional overview of twenty-six European countries. The most influential overheating calculation criteria are listed the best approaches are ranked. The paper provides a thorough comparative assessment and recommendations to align current calculations with climate-sensitive metrics. The results suggest a framework and key performance indicators that are comfort-based, multi-zonal, and time-integrated to calculate overheating and modify the EU's next building energy efficiency regulations. The results can help policymakers and building professionals to develop the next overheating calculation framework and approach for the future development of climate-proof and resilient residential buildings