The present disclosure relates to a method for fabricating a semiconductor structure. The method includes providing a substrate with a gate structure, an insulating structure over the gate structure, and a S/D region; depositing a titanium silicide layer over the S/D region with a first chemical vapor deposition (CVD) process. The first CVD process includes a first hydrogen gas flow. The method also includes depositing a titanium nitride layer over the insulating structure with a second CVD process. The second CVD process includes a second hydrogen gas flow. The first and second CVD processes are performed in a single reaction chamber and a flow rate of the first hydrogen gas flow is higher than a flow rate of the second hydrogen gas flow.

The present disclosure describes a semiconductor device that includes a substrate and a first transistor on the substrate. The first transistor includes a first gate structure and the first gate structure includes a gate dielectric layer and a first work function layer on the gate dielectric layer. The first gate structure also includes a capping layer on the first work function layer. The semiconductor device also includes a second transistor on the substrate, in which the second transistor includes a second gate structure. The second gate structure includes the gate dielectric layer and a second work function layer on the gate dielectric layer. The second gate structure also includes the first work function layer on the second work function layer and the silicon capping layer on the first work function layer.

A semiconductor device is provided and includes a substrate, a gate structure and a conductive plug. The gate structure is formed in the substrate and includes a conductive layer and an insulating capping layer. The conductive layer has a first portion and a second portion extending in a vertical direction from the upper surface of the first portion, so that a step height is formed between the upper surface of the first portion and the upper surface of the second portion. The insulating capping layer covers the upper surfaces of the first portion and the second portion.