Simulation of mass flux divergence distributions for an evaluation of commercial test structures with tungsten-plugs
The evaluation of via structures, metallisations as well as a miniaturisation of the layout dimensions lead to the determination of new test structures. The time for prediction of the reliability of such structures should be very short but also effective. For instance for fast reliability prediction, constant power or constant current tests can be used. Due to a change in fault mechanisms an extrapolation to working conditions is sometimes difficult. Simulations can help in prediction of the failure mechanism as well as the determination of the weakest link in the structures. In this study the void location as well as the mass flux divergence distribution of a conventional tungsten-plugged metallisation structure was investigated by finite element simulation (using ANSYS/spl reg/). A calculation routine is used for the determination of the mass flux divergences and the void formation in the model. The suitability of the simulation in test structure design will be shown. Based on the default models the overlap of the metallisation, the metallisation length, and width and the applied current density was varied. The stress free temperature was set to 450/spl deg/C. This temperature was taken from the last process step. The substrate temperature was set to 150/spl deg/C like the temperature in the reliability stress test. The mechanical stress and temperature and current density distribution as well as the influence of the different migration mechanism was determined. Using these results the void formation and its localisation was calculated and compared with the measurement.
Simulation of Electromigration Test Structures with and without Extrusion Monitors
The thermal-electrical behavior of metallization structures with and without extrusion monitors has been investigated by finite element method (FEM) simulations. The explanation of changes in stress conditions (line temperature, spatial temperature distributions) has been proven to be helpful for the interpretation of electromigration test results. The simulation results of metallization structures with and without extrusion monitors are then compared to corresponding results from standard wafer-level electromigration accelerated test (SWEAT) and isothermal electromigration tests. The detected failure mode has been verified by optical observation of the metallization structures during and after electromigration stress. The investigations performed on a 0.35 um metallization process suggest that it is necessary to use optimized test structure layouts featuring extrusion monitors to obtain accurate electromigration results.
Impacts of climate and land use changes on flood risk management for the Schijn River, Belgium
Abstract Flooding is the most common natural disaster in Europe. Modern flood risk management relies not only infrastructure development but also on governmental and non-governmental actors applying legal, economic and communicative water management instruments. Within the European Union (EU), flood management closely relies on policy set at the EU and national levels. It is now recognized that a sound understanding of climate change is required in addition to current management by taking into account land use change and socio-political context, as climate and land use changes have major impacts on hydrological responses. This paper investigates the hydrological behavior due to urbanization under current and future climate scenarios of high summer and high winter rainfall for 20 sub-catchments of the Schijn River, located in the Flanders region near Antwerp, Belgium. As urbanization increases and existing rainfall-runoff models neglecting the specific behavior of urban runoff, a hydrological model was developed based on a basic reservoir concept and applied to the existing rainfall-runoff model (PDM) flow to examine the specific urban contribution. Results revealed that peak flow for urban runoff and the total peak flow (i.e. rural and urban runoff) were significantly higher (i.e. ranges from 200% to 500%) than the existing rainfall-runoff model (PDM) flows, because of faster and more peaked urban runoff response. The impact of climate change on current and future conditions was also assessed by estimating peak flows with respect to return periods from the flood frequency curve. The predicted peak flow of high summer future climate scenario was significantly higher (i.e. ranges from 200% to 250%) than that of the current climatic condition for this region. Furthermore, hourly peak flow and daily volume ratios of 100-year return period for the highest, lowest and average impervious area were projected for the time horizon of the year 2100. It is concluded that climate change impacts contribute the most in producing peak flow in coming years, while increased urbanization takes the second place for both hourly and daily values. Results on urbanization effect and climate change impact assessment are useful to the water managers for spatial planning, emergency planning and insurance industry.