Temperature-dependent stress-induced voiding in dual-damascene Cu interconnects

Temperature-dependent stress-induced voiding (SIV) of Cu dual-damascene interconnects in via-line structures has been studied by stress modeling and focused-ion-beam (FIB) cross-section analysis. The via-line structures have been studied at temperatures ranging from 100 to 250 °C, with highest voiding rate being detected at 200 °C. The hydrostatic stress and stress gradient reach each peak values and lead to void nucleation symmetrically underneath the edge of the via. Stress gradient instead of stress shows crucial effect on the SIV process. Voids tend to grow horizontally along the Cu/SiN interface under larger stress gradient in the line length direction as compared to the line height direction.A voiding model based on Nabarro–Herring equations has been proposed and the relation between the voiding rate and stress gradient has been built. The voiding model shows that the stress-induced voiding is a process by which vacancies diffuse and concentrate to form voids under the force of stress gradient. The stress and the diffusional factors grow oppositely with temperature and the maximum voiding rate is reached at a medium temperature.