Impact of patterning and ashing on electrical properties and reliability of interconnects in a porous SiOCH ultra low-k dielectric material

In this study, a PECVD porous SiOCH dielectric with k = 2.4 is integrated in a Cu single damascene architecture. The main issue investigated is the low k compatibility with different photo-resist ash chemistries as well as their effects on the properties of the dielectric after integration. Metal 1 test structures are characterized by TEM, EFTEM and by electrical measurements. Conduction mechanisms are studied from I(V) measurements for different strip conditions. Impacts of ash processes on leakage, integrated k value and TDDB are discussed. Oxygen-based ash chemistries were found to damage the physical and electrical properties of the material (lower barrier integrity, lower dielectric breakdown field, higher leakage) as well as the reliability of interconnect test structures (lower lifetimes) whereas nitrogen-based chemistries enhance these properties.