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Electromigration (EM) studies revealed a strong correlation between observed failure scenario and local microstructural properties at the via-to-line-transition, in particular that of the liner. "Early" failure modes were found to have not only smaller failure times but also a lower current density exponent. The influence of specific processes on the occurrence ofcertain failure modes will he discussed. IntroductionThe EM resistivity of bulk copper is known to be larger compared to AI(Cu) [I]. However, failure times measured on integrated Cu interconnects strongly depend on the used integration scheme and the degree of process control. The presence of "early" failure modes can result in a reduction of EM lifetimes to a level similar to AI(Cu) or even below. Ofien, two or more different physical failure mechanisms act in parallel within a test sample or a single interconnect.

Electromigration results for a 264 sample electromigration study performed on dual damascene copper interconnects are presented and reviewed. The stress results show multi-modal failure distributions and extensive failure analysis provides possible explanations as to the failure modes. Monte-carlo 'ype simulations are used to investigate the statistical implications of using hi-modal fitting to predict reliability performance.

The influence of the SIN cap-layer deposition process including different pre-clean treatments on the electromigration (EM) and stressvoiding (SV) behavior of copper dual damascene metalli:rations has been studied. A rcmarkable trade-off between the EM and SV performance was revealed depcnding primarily on the pre-treatment beforc cap-layer deposition rather than the deposition process itself On the one hand an "aggressive" pre-treatment yields improved CdSiN-interface properties with higher electromigration failure times and activation energies (1.22 ... 1.26eV). On the other hand these pre-cleans were found to provoke stressvoiding failures because of the recovery of crystal defects induced in the hulk copper during the plasma treatment. The degree of microstructural damage and hence thc SV susceptibility was found to increase with the preclean intensity. In contrast, no SV risk is related to "less aggressive" pre-clean treatments since they are influencing only the copper surface. The crystal structure of the bulk remains unaffected and hence -in absence of any crystal recovery -no vacancies will be generated. However, these pre-cleans result in significantly lower EM performance with smaller failure times and activation energies (1.03 ... 1.06eV).The results illustrate the need to adjust the SIN cap-layer process parameters with respect to both EM & SV performance to meet the overall reliability requirements for these wear-out mechanisms: at the same time.

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