Metal gate structure and method of formation
Embodiments of the present invention provide a metal gate structure and method of formation. In the replacement metal gate (RMG) process flow, the gate cut process is performed after the metal gate is formed. This allows for a reduced margin between the end of the gate and an adjacent fin. It enables a thinner sacrificial layer on top of the dummy gate, since the gate cut step is deferred. The thinner sacrificial layer improves device quality by reducing the adverse effect of shadowing during implantation. Furthermore, in this process flow, the work function metal layer is terminated along the semiconductor substrate by a capping layer, which reduces undesirable shifts in threshold voltage that occurred in prior methods and structures.
1. A method of forming a semiconductor structure, comprising:
forming a dummy gate on a semiconductor substrate;
depositing a sacrificial layer on the dummy gate;
forming spacers adjacent to the dummy gate;
removing the dummy gate and sacrificial layer;
depositing a work function metal layer;
depositing a fill metal layer;
performing a gate cut through the fill metal layer and the work function metal layer, whereby an upper surface of the semiconductor substrate is exposed; and
depositing a gate capping layer.
2. The method of claim 1 , wherein depositing a gate capping layer comprises depositing a silicon nitride layer.
3. The method of claim 2 , wherein depositing a gate capping layer is performed using an atomic layer deposition process.
4. The method of claim 1 , wherein depositing a fill metal layer comprises depositing tungsten.
5. The method of claim 1 , wherein depositing a work function metal layer comprises depositing titanium.
6. The method of claim 1 , wherein depositing a work function metal layer comprises depositing aluminum.
7. The method of claim 1 , wherein forming a dummy gate on a semiconductor substrate comprises depositing polysilicon.
8. The method of claim 1 , wherein depositing a sacrificial layer on the dummy gate comprises depositing a silicon nitride layer.
9. The method of claim 8 , wherein depositing a silicon nitride layer comprises depositing a silicon nitride layer having a thickness ranging from about 25 nanometers to about 35 nanometers.