Gate stack of fin field effect transistor

A Fin field effect transistor (FinFET) comprising:

• a substrate comprising a first surface;
• an insulation region covering a portion of the first surface, wherein a top of the insulation region defines a second surface;
• a fin disposed through an opening in the insulation region to a first height above the second surface, wherein a base of an upper portion of the fin is broader than a top of the upper portion, wherein the upper portion has first tapered sidewalls and a third surface;
• a gate dielectric covering the first tapered sidewalls and the third surface;
• and
• a conductive gate strip traversing over the gate dielectric, wherein the conductive gate strip has second tapered sidewalls along a longitudinal direction of the fin perpendicular to the first height, and the conductive gate strip is broader in the longitudinal direction of the fin at a base of the second tapered sidewalls than at a top of the second tapered sidewalls.