Accelerated Electromigration Tests Research Articles

Θ CuAl2 Precipitate Coarsening in Al-2% Cu Thin Films

AbstractΘ phase CuAl2 precipitate size evolution during coarsening at 310°C in 0.5 μm thick Al-2% (wt) Cu thin films was characterized by transmission electron microscopy. Films were sputter deposited onto oxidized Si substrates by standard techniques. The coarsening process preferred the growth of blocky Θ morphologies at Al triple points. Coarsening was via solute Cu diffusion along Al grain boundaries during annealing. The average Θ size dependence on annealing time (t) is approximately (t)1/4 in general agreement with models for particle coarsening along grain boundaries. Concurrent Al grain growth was shown to initially enhance the Θ coarsening rate above (t)1/4 behavior. This boundary coarsening process leads to a grain size dependence of the coarsening rate which has been observed in related and other previous work in thin films. These results are shown to be relevant for effects produced during accelerated electromigration testing, such as previous ‘curious’ 0 morphologies at triple points observed by others, the enhanced flux of Cu during testing, and possible mechanisms affecting electromigration failure processes.

Microstructural Analysis of Electromigration-Induced Voids and Hillocks

ABSTRACTInterconnect reliability is of continuing concern in modem VLSI circuits. This work presents analyses of the microstructural detail in electromigration-induced damage in Al and Al-Cu unpassivated interconnects. Such failure analysis is crucial for the characterization of the fundamental processes responsible for failure. Results, via TEM, SEM and focussed-ion beam techniques, suggest possible second phase precipitate-void growth interactions, show slit-like open circuit failures in narrow interconnects, and illustrate the microstructures of hillocks and whiskers formed during accelerated electromigration testing. These results are discussed in terms of existing models for electromigration failure processes and lifetimes. The results are further intended to suggest mechanisms for future modelling and to direct the design of more reliable interconnect material systems.

Microstructural effects on the 1/f α noise of thin aluminum based films

The 1 /fα noise was measured on a variety of Al-based thin metal films with widely varying microstructure using an ac bridge technique. The magnitude of the current noise in response to a small, non-destructive ac signal was found to vary several orders of magnitude between 0.01 and 10 Hz and was correlated to the microstructural differ-ences of the films. These differences have a strong affect on film lifetimes as measured in an accelerated electromigration test. Variation in microstructure was accomplished by different deposition temperatures and annealing parameters, and verified using TEM micrographs. Following fabrication, the current noise magnitude was measured and found to be sensitive to film width and grain size. The use of this technique to discriminate differences in film microstructure is discussed along with the correlations between ex-cess noise and the quality of the thin film as a metallic interconnection.