Ag. Dirks et al., AL-SI-V AND AL-SI-V-PD FILMS AS ALTERNATIVES FOR AL-SI-CU INTERCONNECT - MICROSTRUCTURE AND ITS IMPACT ON RELIABILITY, Thin solid films, 246(1-2), 1994, pp. 164-171
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.