A study on the effect of nitrogen in FSG film on Cu VFDD integration

Via electric characteristic is very important to achieve high yield and reliable device performance in Cu VFDD(Via First Dual Damascene). In this paper, the effect of FSG film as intermetallic dielectric on via module process is studied. Nitrogen in FSG film makes hard polymer with C-N bond inside of via during via etching and contributes to induce PR poisoning in small overlap contact between metal and via after trench photolithography. After trench etching, the PR poisoning is developed to fence around via contact. Such hard polymer and fence make via Rc degraded and Rc failed up to 50% in via chain pattern with small overlap between metal and via. Therefore, in order to solve these problems, low-nitrogen PEFSG has been adopted, which is originated from He-ambient process. Finally, robust via module process with 20% lower Rc value and competitive pass-rate became to be obtained.