Innovative Gap-Fill Strategy for 28 nm Shallow Trench Isolation

Abstract

At the 28 nm technology node, the conventional Shallow Trench Isolation (STI) gap-fill process shows some filling limitations due to voids formation in the oxide layer (SiO2), leading to electrical isolation trouble. In this paper, a new gap-fill strategy called L-E-G (for Liner - Etch-back - Gap-fill) is presented. This strategy is based on an innovative etch-back step, using downstream plasma, which allows liner profile reshaping and improves the slope in trenches. First, the etch-back process on blanket wafers is studied. A slowdown phenomenon of the etch rate with plasma exposure time is observed. Then, the relation between plasma conditions and liner profile reshaping is established. Finally, the L-E-G strategy is applied on 28 nm technology wafers. Successful STI void-free is obtained.