Thermal stress and relaxation behaviour of Al(Cu) submicron interconnects

This paper addresses the reliability problem of stress-induced void formation in submicron Al(Cu) interconnect metallization. The discussion is focused on the driving force for void formation which is investigated by examining the nature of the thermal stress and its relaxation characteristics of submicron interconnect structures. The recent experimental results obtained by bending beam and X-ray diffraction techniques on the thermal stress and stress relaxation in Al(Cu) interconnect metallization are reviewed. The results reveal that as passivated Al(Cu) lines become narrower, the metal exhibits increasingly elastic behaviour with higher stress levels, a combination of stress characteristics which favour void formation. Stress relaxation behaviour has been investigated in Al(Cu) line structures with line widths of 3, 1 and 0.5 microns at 150, 200 and 250°C. Results are consistent with a thermally activated dislocation glide mechanism and the kinetics is controlled by a combined effects of mass transport (diffusion) and shear stress (driving force). Results of these studies and their impact on stress voiding are discussed