Many challenges exist as semiconductor structures scale smaller and smaller. For example, complementary metal oxide semiconductors (CMOS) in the 7 nm node require small Lgate. Small Lgate, though, poses challenges in replacement high-k metal gate processes.
For example, with a gate length (Lg) less than 20 nm, a workfunction metal is deposited within a small opening formed by removal of a dummy gate structure. The deposition of the workfunction metal in such a small opening forms a seam due to a pinch-off effect. The deposition process is then followed by a recessing (chamfering) which removes workfunction metal in the upper portion of the gate before tungsten deposition, in order to improve gate resistance. However, it is very difficult to recess the workfunction metal without undesirably removing some of workfunction metal at a bottom of the seam and then etching the gate dielectric material and exposing the underlying fin structure, once the seam is open. Also, the formation of the self-aligned contact exposes the metal material of the replacement gate due to erosion of the sidewall spacer material, e.g., SiO2, resulting in potential contact to gate shorting or other reliability issues.