Experiments and results of Raman and FTIR complementary vibrational spectroscopy for IC reliability failure analysis

Time-dependent dielectric breakdown (TDDB) of ultra-low-k materials is one of the most critical reliability issues in leading edge Cu/low-k technology due to the weak intrinsic breakdown strength of ultra-low-k materials as compared to that of SiO₂ dielectrics. With continuous device dimension scaling, this problem is further exacerbated for Cu/ultra-low-k interconnects. There are different TDDB models proposed to address this issue, however, there is no direct evidence to get into the failure mechanism. The key technical reason is that the damage to the dielectric material properties is not able to be monitored during the TDDB test. In this paper, we will describe the experiments and the setup used to capture the dielectric bonding damage during the reliability test. Raman and FTIR complimentary vibrational spectroscopy were used to detect the dielectric bonding on the pattern wafer, which has historically been a challenge for current leading edge Cu/low k or ultra-low-k technologies due to the influence of the metal interconnects and the thin dielectric layer. From our experiments, we successfully detected the TDDB degradation behavior of ultra-low-k dielectric in Cu/ultra-low-k interconnects and found the intrinsic degradation of the ultra-low-k dielectric. Further study on the damaged structures with TEM analysis revealed that the Ta ions migrated from the Ta/TaN barrier bi-layer into the ultra-low-k dielectrics. In addition, no out-diffusion of Cu ions was observed in our TEM investigation on Cu/Ta/TaN/SiCOH structures.