Gate electrode having a work-function layer including materials with different average grain sizes

A device comprising:

• a semiconductor fin;
• a gate dielectric on sidewalls and a top surface of the semiconductor fin;
• a work-function layer over and contacting the gate dielectric, wherein the work-function layer has a U-shaped cross-sectional view shape, and wherein the work-function layer comprises a first bottom portion and first sidewall portions over and connecting to opposing ends of the first bottom portion, and wherein the work-function layer comprises:
• a lower layer having a first average grain size;
• and
• an upper layer over the lower layer, wherein the lower layer and the upper layer comprise a same material, and the upper layer has a second average grain size greater than the first average grain size;
• a glue layer over the first bottom portion of the work-function layer, wherein the glue layer comprises a second bottom portion and second sidewall portions over and connecting to the second bottom portion;
• and
• a metal layer having a polycrystalline structure over the second bottom portion of the glue layer.

A device comprising:

• a semiconductor fin;
• a gate dielectric on sidewalls and a top surface of the semiconductor fin;
• a work-function layer over and contacting the gate dielectric, wherein the work-function layer has a polycrystalline structure, and the work-function layer comprises:
• a first sub layer of the work-function layer;
• and
• a second sub layer over the first sub layer, wherein the first sub layer and the second sub layer comprise same first elements, and the second sub layer has a different average grain size than the first sub layer;
• and
• a metal layer over the work-function layer, wherein the metal layer comprises:
• a third sub layer;
• and
• a fourth sub layer, wherein the third sub layer and the fourth sub layer comprise same second elements, and wherein the fourth sub layer has a different average grain size than the third sub layer.