AL-SI-V AND AL-SI-V-PD FILMS AS ALTERNATIVES FOR AL-SI-CU INTERCONNECT - MICROSTRUCTURE AND ITS IMPACT ON RELIABILITY

In this paper new data on highly reliable interconnect materials based on aluminium will be presented. Compared with Al-Si-Cu alloy films, a lternative alloys such as Al-Si-V and Al-Si-V-Pd combine excellent pla sma etchability with good corrosion resistance. Addition of V to Al-Si increases the electrical resistivity, but if the concentration of V d oes not exceed 0.2-0.3 at.%, the increase is not a problem for most pr actical applications in ultralarge-scale integration. Al-Si-V and Al-S i-V-Pd films have been subjected to electromigration stress (180-degre es-C, 2 x 10(6) A cm-2). Al-Si-V-Pd films showed surprisingly high res istance to damage. Understanding the microstructure becomes increasing ly important as integrated circuit feature sizes become smaller than t he average grain size of the aluminium alloy films used for interconne ct. Therefore the microstructural details of the above alloys have bee n studied using transmission electron microscopy. Based on the results , a model has been developed which explains the action of V and Pd in the aluminium lattice. According to this model, both V and Pd are need ed concurrently to obtain a high reliability Al-based interconnect. Fu rthermore, recent findings suggest that electromigration failure of na rrow lines may be dominated by diffusion along the Al/Al-oxide interfa ce, such that lines fail by thinning. The above model and the reliabil ity results presented here are consistent with an interface diffusion mechanism. Finally, the (Al, Pd) precipitates observed have been chara cterized and identified as the decagonal ''Al75Pd25''-type phase.