Effect of chemical mechanical polishing scratch on TDDB reliability and its reduction in 45nm BEOL process

The correlation of time-dependent dielectric breakdown (TDDB) reliability failure with scratches generated from chemical mechanical polishing (CMP) in 45 nm backend-ofline (BEOL) process is investigated and established. The wafer map of early TDDB failure samples matches well with the defect wafer map from bright field scans. Electrical fault isolation using thermally induced voltage alteration (TIVA) analysis is employed to locate the hot spot where TDDB leakage occurs. Polish scratch induced metal damage at the hot spot is further analyzed by top down scanning electron microscopy (SEM) after de-processing. Also, the depth of the polish scratch is confirmed by using transmission electron microscopy (TEM) analysis. It clearly shows that the embedded particle on copper (Cu) surface and the liner damage resulted from polish scratch severely affect the TDDB reliability. In-situ CMP platen3 (P3) pad chemical preclean is found to reduce the polish scratch density effectively and significantly improve the V-ramp/TDDB reliability performance. However, inappropriate usage of chemical pre-clean would cause Cu corrosion and lead to EM degradation. Hence, a balance between polish scratch reduction and Cu corrosion associated with P3 pad pre-clean needs to be achieved.