An optimized W process for metal gate electrode gap filling application

As IC technology advances to 16/14 nm and beyond, W film will not only be used to fill contact plug, but also act as electrode layer of replacement metal gate. High resistivity and W seam are two major concerns. W gap-fill capability is very good due to its conformal growth characteristic and easy transportation of reactive gases. However, the remaining opening of 16/14 nm FinFET replacement metal gate before W gap-fill is very narrow and sometimes has a re-entrant profile, which makes it very easy to form seams or voids. This paper reports an optimized W gap-fill process, which can fill in trenches of the aspect ratio > 30:1, with CD opening shrinking to less than 4nm. A NF3 etching back process is introduced, which can help to modulate the re-entrant profile and enlarge the gap-fill window. This D-E-D process can be easily extended to 10 nm technology node. Meanwhile, B2H6 post nucleation treatment is applied to lower W resistivity, down to 9.3 μΩ-cm at a thickness of 200 nm.