Diffusion ability of Stress Induced Voiding in advanced BEOL copper process

Stress Induced Voiding is strongly influenced by test key structure. Wider and longer interconnect will have larger total supply of vacancies for voiding than a narrower one (reservoir effect). The critical diffusion volume which could cause RC open failure of advanced node Cu process is about 100um². The vacancy diffusion length is about ~250um, that means a vacancy that is incredibly far away could participate in the via voiding process through random diffusion, and the diffusion coefficient would be about 0.34cm²/sec. As was determined using Creep rate equation, the diffusion activation energy would be about 0.83eV, which might be consistent with an interface diffusion problem.