Semiconductor device and manufacturing method thereof

A method of manufacturing a semiconductor device, comprising:

• forming a stack of nanostructures on a substrate, the nanostructures comprising a plurality of first semiconductor layers, a plurality of diffusion barrier layers and a plurality of second semiconductor layers that are alternately stacked, wherein each of the diffusion barrier layers is disposed between the first and second semiconductor layers;
• forming a sacrificial gate structure over a portion of the nanostructures;
• removing the first semiconductor layers, the diffusion barrier layers and the second semiconductor layers exposed through the sacrificial gate structure in a source/drain region of the nanostructures;
• forming an epitaxial source/drain feature in the source/drain region;
• removing the sacrificial gate structure to expose the first semiconductor layers, the diffusion barrier layers and the second semiconductor layers;
• removing the second semiconductor layers to form a plurality of openings between the diffusion barrier layers;
• forming a gate dielectric layer into the openings to surround exposed surfaces of each of the first semiconductor layers and the diffusion barrier layers;
• and
• forming a gate electrode layer on the gate dielectric layer.

A semiconductor device, comprising:

• a substrate;
• a first source/drain epitaxial feature disposed in a first source/drain region;
• a second source/drain epitaxial feature disposed in a second source/drain region;
• two or more semiconductor layers disposed between the first source/drain epitaxial feature and the second source/drain epitaxial feature;
• and
• a plurality of diffusion barrier layers disposed between the two or more semiconductor layers adjacent to each other.