Method of manufacturing semiconductor devices and semiconductor devices

A semiconductor device, comprising:

• a first field effect transistor (FET) including a first gate structure disposed over a first channel region;
• and
• a second FET including a second gate structure disposed over a second channel region, wherein:
• the first FET is an n-type FET, and second FET is a p-type FET,
• the first gate structure includes:
• a first gate dielectric layer;
• a first work function adjustment material layer over the first gate dielectric layer;
• a second work function adjustment material layer over the first work function adjustment material layer;
• and
• a first metal gate electrode layer over the second work function adjustment material layer,
• the second gate structure includes:
• a second gate dielectric layer;
• a third work function adjustment material layer over the second gate dielectric layer;
• a fourth work function adjustment material layer over the third work function adjustment material layer;
• and
• a second metal gate electrode layer over the fourth work function adjustment material layer,
• the second and fourth work function adjustment material layers include TiAl or TiAlC, and include a diffusion barrier layer containing Al and Ti at a bottom portion of the second and fourth work function adjustment material layers, respectively,
• the diffusion barrier layer is a Ti-rich layer having a higher Ti concentration than a center portion of the second and fourth work function adjustment material layers, and
• a Ti concentration in the diffusion barrier layer increases from a side on the center portion to a surface of the second and fourth work function adjustment material layers.

A method of manufacturing a semiconductor device, comprising:

• forming a gate dielectric layer over a channel region made of a semiconductor material;
• forming a first work function adjustment layer over the gate dielectric layer;
• and
• forming a metal gate electrode layer over the first work function adjustment layer, wherein:
• the first work function adjustment layer includes aluminum and titanium,
• the forming the first work function adjustment layer comprises forming a Ti-rich diffusion barrier layer at at least one of a bottom portion and a top portion of the first work function adjustment layer, and
• a Ti concentration in the diffusion barrier layer increases from a side on the center portion to a surface of the first work function adjustment material layer.