AES and SIMS investigation of diffusion barriers for copper metallization in power-SAW devices

摘要

Barrier layers for Cu-metallization in surface acoustic wave (SAW) devices were investigated by AES and SIMS depth profiles. Two layered systems on LiNbO_3 substrate have been analyzed after annealing in air up to 400 ℃. The investigated systems were (A) Ta(20nm)/Cu(150nm)/Ti(30 nm), deposited by electron beam evaporation, and (B) Ta_(30)Si_(18)N_(52)(50 nm/Cu(150 nm)/Ta_(30)Si_(18)N_(52) (50 nm) deposited by magnetron sputtering. In system A the Ta layer shows oxidation in air for T ≥ 300 ℃. Ti from the buffer layer diffuses into the Cu at about 100 ℃, and segregates at the Ta/Cu interface for T ≥ 200 ℃. Oxidation of the Ti layer starts at 300 ℃. But no remarkable amounts of oxygen could be found in the Cu film. The depth profiles show that the TaSiN layer in system B operates as a more effective barrier for the Cu-SAW technology up to more than 300 ℃.