Investigation of the thermal stress field in a multilevel aluminium metallisation in VLSI systems

A residual thermal stress field in a multilevel aluminium metallisation in VLSI systems is investigated in this paper. Using finite element technique different structures (interconnecting stud, and metallisation systems containing two, three and six aluminium lines) were modelled. It is confirmed that residual stress in these more complex structures significantly differs from the one that residues in single metal line. Finally, it is shown that in a multilayer metallisation, the upper aluminium layer relieves stress in the lower metal lines (and vice versa), adding an extra compressive stress term to the final tensile stress field.