A Comprehensive Evaluation of Time-Dependent Dielectric Breakdown of CuAl₂ on SiO₂ for Advanced Interconnect Application

The intermetallic compound CuAl2 is a promising alternative to advanced Cu interconnections because of low electrical resistivity, short electron mean free path, good electromigration reliability, and good gap-filling property. In this study, to further examine the feasibility of CuAl2 interconnects for future technology node, a comprehensive study of the time-dependent dielectric breakdown (TDDB) was conducted on CuAl2 and compared with NiAl and Cu/TaN. The self-formation of a proper thickness of an AlOx interface layer by reaction with SiO2 brought about excellent TDDB reliability in CuAl2/SiO2. Voltage ramp test was also carried out to understand the electron transport mechanism in CuAl2 stressed under the same condition as that of the TDDB test. Leakage current versus voltage relation revealed the Cu ion drift into SiO2, which gave rise to Schottky emission as an electron transport mechanism across SiO2 and the accumulation of Cu ions eventually led to TDDB failure.