Replacement Metal Gate

Replacement metal gate process flow integration has to coordinate several sequential steps precisely: forming and later removing a sacrificial gate, depositing the high-k dielectric, depositing separate work-function-tuning layers for NMOS and PMOS, and finally filling with bulk gate metal, commonly via atomic layer deposition for its conformal coverage. Each of these steps has to be executed in the correct order and with tight dimensional control, since an error at any one step, incomplete sacrificial gate removal, uneven high-k deposition, incorrect work-function layer thickness, directly propagates into a finished transistor with incorrect threshold voltage or elevated leakage.