THE MICROSTRUCTURE, MECHANICAL-STRESS, TEXTURE, AND ELECTROMIGRATION BEHAVIOR OF AL-PD ALLOYS

As the minimum feature size of interconnect lines decreases below 0.5 mum, the need to control the line microstructure becomes increasingly important. The alloy content, deposition process, fabrication method, and thermal history all determine the microstructure of an interconnec t, which, in turn, affects its performance and reliability. The motiva tion for this work was to characterize the microstructure of various s puttered Al-Pd alloys (Al-0.3wt.%Pd, Al-2Cu-0.3Pd, and Al-0.3Nb-0.3Pd) vs sputtered Al-Cu control samples (Al-0.5Cu and Al-2Cu) and to asses s the role of grain size, mechanical stress, and crystallographic text ure on the electromigration behavior of submicrometer wide lines. The grain size, mechanical stress, and texture of blanket films were measu red as a function of annealing. The as-deposited film stress was tensi le and followed a similar stress history on heating for all of the fil ms; on cooling, however, significant differences were observed between the Al-Pd and Al-Cu films in the shape of their stress-temperature-cu rves. A strong (111) crystallographic texture was typically found for Al-Cu films deposited on SiO2. A stronger (111) texture resulted when Al-Cu was deposited on 25 nm titanium. Al-0.3Pd films, however, exhibi ted either a weak (111) or (220) texture when deposited on SiO2, which reverted to a strong (111) texture when deposited on 25 nm titanium. The electromigration lifetimes of passivated, approximately 0.7 mum wi de lines at 250-degrees-C and 2.5 x 10(6) A/cm2 for both single and mu lti-level samples (separated with W studs) are reported. The electromi gration behavior of Al-0.3Pd was found to be less dependent on film mi crostructure than on the annealing atmosphere used, i.e. forming gas ( 90% N2-10%H-2) annealed Al-0.3Pd films were superior to all of the all oys investigated, while annealing in only N2 resulted in poor lifetime s.