An approach to forming a semiconductor structure with improved negative bias temperature instability includes forming an interfacial layer on a semiconductor substrate with an nFET and a pFET. The semiconductor structure includes a gate dielectric layer on the interfacial layer and a pFET work function metal layer on a portion of the gate dielectric layer over an area above the pFET. The semiconductor structure includes a nFET work function metal layer on a portion of the gate dielectric layer over an area above the nFET and on the pFET work function metal layer in the area above the pFET. The semiconductor structure includes a gate electrode metal on the nFET work function metal layer where a plurality of fluorine atoms and a plurality of reducing gas atoms are incorporated into at least a portion of the interfacial layer, the gate layer, and a portion of the nFET work function metal.