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.
Life time characterization for a highly robust metallization
For mixed signal applications it is necessary to have metallization which are able to carry high currents. Also the on chip integration leads to special requirements on the metallization concerning their robustness. A common method for the determination of interconnect lifetime is described in JP001A and based on Black's law and the measurement of time to failure, medium stress current density and medium stress temperature. The highly robust metallization presented here, which was developed for higher current and temperature applications shows more complicated shapes than presently used metallization systems with metal line tracks and via. To determine a realistic life time of highly robust metallization the used method is not applicable anymore. A more suitable determination of the variables current density and temperature for AlCu metallization with W-plug can be achieved by simulations. In the metal line layout the most critical locations regarding mass flux are chosen. The results are validated by measurements.
Laser probing of thermal behaviour of electronic components and its application in quality and reliability testing
Abstract We have developed two optical laser probes for the contactless characterisation of microelectronic components and ICs. The first is a high resolution interferometer for the measurement of dilatations, absolute values over 11 decades are obtained ranging from 10 -3 to 10 -14 m. The second is a reflectance probe for the absolute measurement of surface temperature variations upon ICs. The instrument is a thermometer for surface micrometric analysis able to measure temperature variation in the 10 -3 to 500 °K range. The outstanding performances of these probes have been the starting point of the development of new investigation methods in the field of quality and reliability measurements. We show results of hot points detection upon integrated circuits with micrometric lateral resolution. We also present a method for homogeneity analysis of current density inside power MOS transistors. Finally we present a method for absolute temperature mapping upon metallic lines used in accelerated tests of current stress to study their reliability with regard to electromigration.